{"paper_id":"017edbad-c26a-4a54-ae68-2aff226edbe2","body_text":"Relationship of the largest GIC during geomagnetic storms with solar wind-IMF parameters | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Relationship of the largest GIC during geomagnetic storms with solar wind-IMF parameters Nanan Balan, Wen-Bin Li, Zan-Yang XING, R. Skoug, V. Manu, Li-Kai Liang, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1980192/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The association of GIC (geomagnetically induced current) with various solar and geophysical conditions has been known. However, what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms, which during extreme storms can cause sudden damage of vulnerable utility systems, is not yet known. We address this important question by analyzing the GIC data measured in Finland for 21 years (1999–2019) during 106 geomagnetic activities (DstMin ≤-50 nT) at low, mid and high latitudes and the corresponding solar wind velocity V, dynamic pressure P, north-south component of interplanetary magnetic field (IMF Bz), and the products V×Bz and P×Bz. The results show for the first time that the largest GIC (≥ 10 A) occurs at the time of the largest -(V×Bz) in all seasons and solar activity levels with its time determined by the time of the largest -Bz and magnitude determined by both V and -Bz, except in one case. The two power outages happened in the 21-year period (06 November 2001 and 30 October 2003) also occurred at the UT time of the largest GICmax. The correlation of largest GICmax is also highest (0.92) with the largest -(V×Bz) at September equinox. The results highlight the importance of the single station GIC measurements and possibility of improving the forecasting of the rate of change of the local horizontal geomagnetic field (dH/dt) directly related to GIC. Space weather geomagnetically induced current (GIC) geomagnetic storms solar wind and IMF Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Background The geomagnetically induced current (GIC) was noticed nearly two centuries ago by Barlow ( 1849 ) from his observation of the deflection of the telegraph magnetic needles of the Midland Railroad station coinciding with auroral activity. Later, the GIC induced during geomagnetic activities was found flowing through the earthed utility systems such as oil and gas metal pipe lines, electric power grids, tele-communication networks, etc. (e.g., Campbell 1980 ; Pirjola and Lehtinen 1985 ; Pirjola 2000 ). The GIC is large at high latitudes (e.g., Campbell 1980 ; Pulkkinen et al. 2001 ; Vladimir et al. 2019 ) and smaller at lower latitudes (e.g., Watari et al. 2009 ; Liu et al. 2009 , 2014 ; Barbosa et al. 2015 ; Carter et al. 2015 ) probably basically due to the orientation of the geomagnetic field changing from vertical and open at high latitudes to closed and horizontal at low latitudes. The large geomagnetic field fluctuations produced by the large electric currents flowing in the magnetosphere and ionosphere during space weather events are referred as geomagnetic storms at low and mid latitudes and geomagnetic activities or storm-time substorms at high latitudes (e.g., Gonzalez et al. 1994 ). The GIC during extreme geomagnetic activities produced by fast solar storms such as ICMEs (interplanetary coronal mass ejections with frozen-in solar magnetic field or interplanetary magnetic field IMF) can exceed the tolerance limit of the systems and cause system damages as has happened during a number of such events (e.g., Albertson and Thorson 1974 ; Bolduc 2002 ; Kappenman 2005 ; Pulkkinen et al. 2005 ; Wik et al. 2009 ; Marshall et al. 2012 ; Balan et al. 2019a ). The extreme event on 13 March 1989 caused electric power outage in Quebec for nine hours costing hundreds of millions of US $ (Medford et al. 1989 ; Boteler 2001 , 2019 ). An event similar to the famous Carrington event of September 1859 (Carrington 1859 ) occurring at the present time could cause damages costing up to (estimated) 1–2 trillion US $ (e.g., Baker 2002 ; Pulkkinen et al. 2017 ; Hapgood et al. 2021 ). On the other hand, low-to-medium level GIC flowing for long periods can cause cumulative impacts such as reactive power loss in transformers and corrosion in metal pipe lines, which can pose significant risk especially when there are defects in the systems (Gaunt 2014 ; Dimmock et al. 2019 ; Khanal et al. 2019 ; Ingham and Rodger 2018 ; Clilverd et al. 2018 , 2020 ]. Therefore, for forecasting the devastating effects of GIC, it is important to understand the relationship between the GIC during geomagnetic activities and solar wind-IMF parameters. The GIC has been measured routinely in the Finnish natural gas pipeline station Mäntsälä (MAN) since 1999 (Pulkkinen et al. 2001 ; Viljanen et al. 2006 ). Using the Finland data, several scientific groups studied the association of GIC with local time and season, solar and geomagnetic activities, substorms and electrojets, and solar wind and IMF (e.g., Viljanen et al. 2010 ; Borovsky and Denton 2006 ; Huttunen at al. 2008; Dimmock et al. 2019 ; Tsurutani and Hajra 2021 ; Hajra 2022a , b ). Viljanen et al. ( 2010 ) conducted an 11-year study of GIC > 5A. Using the data during 1999–2005, Borovsky and Denton ( 2006 ) and Kataoka and Pulkkinen ( 2008 ) showed that the GIC due to CME-driven storms pose most of the problems for ground-based conductor systems, whereas the effect of CIR-driven storms is minor. Huttunen at al. (2008) examined the relative effects of the ejecta, sheath and boundary regions of ICMEs on GIC ≥ 10A. According to them (Huttunen at al. 2008) the most intense GIC activity (> 10A) is likely to take place during the passage of the turbulent sheath region of ICMEs possibly due to their capacity to drive substorms. Dimmock et al. ( 2019 ) showed that the unusually large GIC (up to 28A) occurred during the 7–8 September 2017 storm could be associated with westward and eastward electrojets. Recently, Tsurutani and Hajra ( 2021 ) surveyed the GIC > 10A and > 30A in 21 years (1999–2019) of the GIC data. They suggested that the shocks and substorms are probably the predominant causes of the intense GICs, and super-substorm and intense substorm auroral electrojet intensifications are the most frequent (76%) cause of GIC > 30A. Following this, Hajra ( 2022a ) reported the correlations between the occurrence rate of 48 GIC clusters and solar activity (0.68), integrated intensity of the GIC clusters and SymHMin (0.73), and peak intensity of the GIC clusters and integrated intensity of substorm clusters (0.85). In another paper, Hajra ( 2022b ) showed the occurrence rate of GIC > 10A is high in solar cycle 23 and at September equinox, low at March equinox and lowest around summer solstice; and the occurrence rate is 67%, 31% and 2%, respectively, during super storms, intense storms and moderate storms. However, what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms/activities, which during extreme storms can cause sudden damage of vulnerable utility systems, is not yet known. We address this important question using the 21-year (1999–2019) GIC data measured at MAN in Finland (Pulkkinen et al. 2001 ). We investigate the relationship of the largest GIC event (defined in section 2 ) observed during the geomagnetic activities at high, mid and low latitudes with the corresponding ICME front velocity ΔV (defined in section 2 ), solar wind velocity V, dynamic pressure P and IMF Bz, and the products V×Bz and P×Bz. The results reveal for the first time that the largest GIC during all geomagnetic activities occurs at around the time of the largest negative value of the product V×Bz in all seasons and solar activity levels, except in one case. The geomagnetic activity data are from the Kyoto University websites and solar wind and IMF data are from the ACE (advanced composition explorer) satellite at the L1 point (McComas et al. 1998 ; Skoug et al. 2004 ) for the same 21 years as the GIC data. The data and analysis are described in section 2 . The results are presented and discussed in sections 3 and 4 . 2. Data And Analysis We use the 10-second resolution GIC data measured (Pulkkinen et al. 2001 ; Viljanen et al. 2010 ) in the Finnish natural gas pipeline compressor station at Mäntsälä (MAN, 60.6ºN, 25.2ºE; 57.9ᵒN geomagnetic latitude) for 21 years (1999–2019). The data are available at http://space.fmi.fi/gic/man_ascii/ . Pulkkinen et al. ( 2001 ) estimated the GIC from the geomagnetic field measured at MAN and a reference magnetometer at Nurmijärvi (NUR, 24.7°E, 60.5°N) 30 km away. The estimated GIC agrees well with model GIC (Viljanen et al. 2006 ). However, the estimated GIC has some uncertainty due to various reasons such as spatial inhomogeneity of the geomagnetic field or separation (30 km) between the GIC station and reference magnetometer, cathodic corrosion protection system used in the pipeline, instrumental problems causing electromagnetic noise, hard weather conditions, etc. As an overall estimate, the noise contribution is less than 0.1A (occasionally > 1A) and uncertainty due to various reasons is 10–15% (Pulkkinen et al. 2001 ; Viljanen et al. 2006 , 2010 , 2015 ). The GIC data have a gap for 16 months during April 2014-August 2015 and other small gaps. Since the GIC direction (eastward or westward) is unimportant in our study, we use its magnitude and refer it as GIC. As illustrated by an example in Fig. 1 , the GIC during geomagnetic activities undergoes large and rapid fluctuations that we call GIC events. We define a large GIC event as the one having amplitude GICmax ≥ 5A and duration at the 2A level ≥ 1 minute. The 2A level used for fixing the duration and 5A level used for the lower amplitude limit are well above the noise contribution and uncertainty (Pulkkinen et al. 2001 ; Viljanen et al. 2015 ). The first time GIC exceeds the 2A level is considered as the start of GIC activity. The largest GIC event of amplitude largest GICmax illustrated in Fig. 1 b is important because it during extreme geomagnetic activity can cause sudden damage of vulnerable utility systems (e.g., Marshall et al. 2012 ; Pulkkinen et al. 2005 ). 2.1. Geomagnetic activities The geomagnetic storms/activities at high, mid and low latitudes are identified in the high latitude auroral electrojet index (AE) of 1-minute resolution available at http://wdc.kugi.kyoto-u.ac.jp/aedir/ , mid latitude Kp index of 3-hour resolution available at http://wdc.kugi.kyoto-u.ac.jp/kp/index.html ) , and low latitude SymH index of 1-minute resolution available at http://wdc.kugi.kyoto-u.ac.jp/aeasy/index.html . First, the low latitude Dst data of 1-hour resolution ( http://wdc.kugi.kyoto-u.ac.jp/dstdir/ ) are used to identify 226 clear geomagnetic storms of intensity DstMin ≤-50 nT (Gonzalez et al. 1994 ) during 1999–2019 using four selection criteria that minimize non-storm like fluctuations in Dst (Balan et al. 1917a). DstMin is the minimum Dst during the main phase (MP) of a storm. The corresponding 226 geomagnetic storms/activities in SymH, Kp and AE indices are identified, and their intensities SymHMin (minimum value of SymH during the MP) and Kpmax and AEmax (maximum values of Kp and AE) are obtained. Using a computer algorithm, we identified 1848 large GIC events occurred during the 106 geomagnetic storms (DstMin ≤-50 nT) in 21 years (1999–2019). GIC is found < 5A for 68 storms and 52 storms have no GIC data. The largest GICmax ≥ 5A corresponding to the 106 storms are obtained. 2.2. Solar wind and IMF The solar wind and IMF data have been provided continuously since 1998 by the ACE (Advanced Composition Explorer) satellite at the L1 point. The solar wind velocity V and density N (and dynamic pressure P) are measured by the SWEPAM (Solar Wind Electron Proton Alpha Monitor) instrument in the SWI (Solar Wind Ion) mode at 64-second resolution (e.g., McComas et al. 1998 ; Skoug et al. 2004 ). These data are available at Caltech ( http://www.srl.caltech.edu/ACE/ASC/ ). During high energy particle events, the SWI mode often does not cover the full solar wind flux spectrum. Under such conditions, the 64-second data collected in the SSTI (Search/Supra Thermal Ion) mode once every ~ 32 minutes are used. The data (time) is shifted for the ACE-Earth distance. The values of V, P, IMF Bz and the products (V×Bz) and (P×Bz) during the 106 geomagnetic activities in 1999–2019 are obtained. The product (V×Bz) was used before for modeling the geomagnetic storms (e.g., Burton et al. 1975 ; Zhu et al. 2007 ) and for addressing what determines the severity of space weather (Balan et al. 2014 ) and developing a scheme for forecasting severe space weather (SvSW, Balan et al. 2017b ). The peak values of -Bz, -(V×Bz) and -(P×Bz) and the values of V and P at the peaks of -(V×Bz) are obtained. The ICME front velocity ΔV is the difference between the peak ICME velocity at its front and the upstream solar wind velocity V. However, the high velocity of 32-minute resolution is found to take up to two hours to reach its peak (Skoug et al. 2004 ). Therefore, ΔV is generally taken as the difference between the mean velocity for 2 hours after and 2 hours before the start of the velocity increase (Balan et al. 2014 ). 3. Results First, we briefly discuss the important aspects in the distribution of the 106 largest GIC events (or largest GICmax) that are relevant to the present study. Then we will present the detailed relationship of the time of occurrence and amplitude of the largest GIC events with the geomagnetic activities and solar wind-IMF parameters through case studies and correlations. We will also briefly describe the advantages of using the product (V×Bz) for forecasting the rate-of-change of the local horizontal geomagnetic field (dH/dt) directly related to GIC. 3.1. Distribution of largest GIC The largest GIC events during all 106 geomagnetic storms are found to occur during the SSC-MP (storm sudden commencement-main phase) of the storms. Figure 2 shows the distribution of the largest GICmax and intensity (DstMin) of the storms during 1999–2019. There is a striking September equinox preference for the largest GICmax (and storms) to occur especially during the declining phase of solar cycle 23 (1999–2009). Of the 106 largest GICmax, 38 occurred at September equinox and only 68 occurred in all other seasons together (34 at March equinox and 17 each in June and December solstices). The largest GICmax is also generally much larger at September equinox than in other seasons. Figure 2 also shows a preference for the largest GIC events to occur during super double-storms (DstMin ≤-250 nT) at September equinox (29–31 October 2003 and 07–10 November 2004). However, in other seasons, the largest GICmax occur even during comparatively weak storms. For example, the weak storm on 21 January 2005 (DstMin − 89 nT) has the largest GICmax ~ 28A in December solstice; and the weak storm on 15–16 March 2012 (DstMin − 88 nT) has the largest GICmax ~ 39A at March equinox. At the same time, the largest super storm at March equinox (31 March 2001, DstMin − 387 nT) corresponds to the largest GICmax of only 15.8A. The double-storm on 07–10 September 2017, though comparatively weak (DstMin − 124 nT, -109 nT), also produced very large GICmax (~ 30A). Earlier, Dimmock et al. ( 2019 ) studied the GIC activity (up to 28A) during the storm on 07–08 September 2017. Tsurutani and Hajra ( 2021 ) reported the occurrence of a large number of GIC > 10A at September equinox with 168 of them occurring during the MP of the super double-storm on 29–31 October 2003. 3.2. Case studies Here, we present the 14 cases of largest GICmax > 25A including the two power outages occurred in the 21 years of this study. Table 1 lists the date and storm intensity (SymHMin) of the 14 cases and magnitude of the largest GICmax (with the number of GICmax > 25A in brackets) and their time of occurrence. The magnitude of the corresponding largest -(V×Bz) and their time of occurrence, and time of start of GIC activity (≥ 2A) and time of impact of the ICME front are also listed. The important results are (1) the largest GICmax (> 25A) and corresponding largest -(V×Bz) occur at around the same UT time in all cases within the time resolution of up to ± 32 minutes, except on 06 November 2001 (discussed below). (2) The start of GIC activity and impact of ICME front occur at around the same time in all cases within the time resolution. (3) The power outage in New Zealand on 06 November 2001 (Marshall et al. 2012 ) and Sweden on 30 October2003 (Pulkkinen et al. 2005 ) happened at the UT time of the respective largest GICmax. Table 1 also shows that out of the 37 GICmax > 25A, 32 occurred at September equinox, which also shows the preference for the large GIC events to occur at September equinox. 3.2.1. Largest GIC in seasons Here we discuss the largest GIC events in 4 seasons. Figure 3 shows the GIC (3a) data at September equinox (29–30 October 2003) when the largest GICmax (57.05A) and largest number (11) of GICmax > 25A occurred in the 21 years of this study (Table 1). This case is associated with the first of a super double geomagnetic storm (SymHMin − 391 nT, Kpmax 9 and AEmax 4056 nT; 3b-3c), fastest solar wind velocity (2242 km/s; 3d) (e.g., Skoug et al. 2004 ) and largest negative V×Bz (-97.23x10 3 km/s nT; 3f) in 21 years with -Bz up to -45.05 nT (3e). Most importantly, the largest GICmax (57.05A, 06:57:40 UT) occurred at the time (06:57:40 UT) of the largest negative value of the product V×Bz (Table 1). Though this time is determined by the time of the largest -Bz, its magnitude depends on both -Bz and V (section 3.2.3 ). Also, the GIC activity started at 06:11:50 UT with a GIC pulse (25.1A) at the impact (06:15:28 UT) of the fastest ICME (ΔV ~ 1145 km/s) in the 21 years of this study (e.g., Skoug et al. 2004 ). Figure 4 is similar to Fig. 3 but for the largest GICmax (39.14A, 4a) at March equinox (15–16 March 2012). This case is associated with a moderate geomagnetic storm (SymHMin − 79 nT, Kpmax 6 and AEmax 2210 nT, 4b-c), fast solar wind up 801 km/s (4d) and comparatively weak -Bz (-13.62 nT, 4e). In this case, there are only 2 GICmax > 25A (4a, Table 1). Most importantly, as in the previous case, the largest GICmax occurred (17:03:50 UT) at around the time (17:05:20 UT) of the largest negative value of V×Bz (-10.06×10 3 km/s nT; 4f), and GIC activity started (13:03:40 UT) with a small GIC pulse at the impact (13:06:20 UT) of a comparatively slow ICME front of ΔV ~ 100 km/s. Figure 5 is for the largest GICmax (30.34A) in June solstice (15–16 July 2000). This case is associated with a super storm (SymHMin − 343 nT, Kpmax 9 and AEmax 3330 nT; 5b-5c), fast solar wind of velocity up to 1110 km/s (5d) and large Bz negative (-57.02 nT; 5e). As in the previous cases, the largest GICmax occurred (20:01:50 UT) at the time (20:01:00 UT) of the largest negative value of V×Bz (-59.86x10 3 km/s nT; 3f), and GIC activity started (14:39:40 UT) with the impact (14:40:15 UT) of a fast ICME front of ΔV 230 km/s with IMF Bz positive. There is also a large solar wind pressure pulse (~ 60 nPa, 5d) at the ICME front; but after the large pulse, the pressure is small. The case of the largest GICmax (27.44A) in December solstice occurred on 21–22 January 2005 (figure not shown). This case is associated with a moderate geomagnetic storm (SymHMin − 101 nT, Kpmax 8 and AEmax 3449 nT), fast solar wind of velocity up to 1090 km/s and very large dynamic pressure up to 600 nPa and large Bz negative of -27.02 nT. As in the previous 3 cases, the GIC activity started (17:12:30 UT) with the impact (17:08:30 UT) of a fast ICME front of ΔV ~ 345 km/s with Bz positive and the largest GICmax occurred (19:10:00 UT) at around the time (18:48:33 UT) of the largest negative value of V×Bz (-24.78x10 3 km/s nT), which in this case is also around the largest negative of P×Bz (-10x10 3 nPa nT). However, the solar wind density (and pressure) is not available in most cases of GICmax > 25A. For this reason, the dynamic pressure will not be considered further in the study. 3.2.2. Cases of power outage Two power outages happened in the 21 years of this study. Figure 6 shows the data for the power outage happened in Sweden during the super storm on 30 October 2003 (Pulkkinen et al. 2005 ). The power outage occurred at 20:07 UT at around the time 20:08:40 UT of the largest GICmax (48.57A) measured in Finland, which is also around the time 20:09:40 UT of the largest negative value of V×Bz (-45.25 units) measured by the ACE satellite (Table 1). The GIC activity started at 16:56:40 UT at around the impact (16:52:20 UT) of a fast ICME front of ΔV ~ 650 km/s when IMF Bz turned largely southward. Only in this case of the second of a super double-storm did a few GICmax > 25A occur during the RP of the storm. Figure 7 is similar to Fig. 6 but for the power outage happened in New Zealand during the super storm on 06 November 2001 (Marshall et al. 2012 ). In this case also, the power outage occurred (01:52 UT) at around the time (01:53:30 UT) of the largest GICmax (31.63A), which is at the time (01:53:30 UT) of start of GIC activity and time of impact of the ICME front with IMF Bz largely negative. However, (V×Bz) attained its largest negative value (-55.28 units) about 1.3 hours later (03:14:55 UT) when -Bz reached its maximum value (-77.28 nT). In this case, the first large GIC event became the largest GIC event most probably because IMF Bz was largely negative at the ICME front of high ΔV ~ 285 km/s, so that the high impulsive power of the ICME became most effective right at its impact (Balan et al. 2019a ). 3.2.3. Time of occurrence and amplitude The relationship of the time of occurrence and amplitude of the largest GIC event with those of the largest -(V×Bz) is discussed further here. As shown in Fig. 8 a, the time of all largest GICmax (> 10A) occurs at or around the time of the largest -(V×Bz) with a maximum time difference less than the resolution (up to 32 minutes), except in one case (06 November 2001, discussed in Fig. 7 ). The correlation between the two times is high (0.986) and highly significant (0 p-value). The corresponding GIC activity begins at or around the time of impact of the ICME front as shown in Fig. 8 b; the two times are highly correlated (0.998) with 0 p-value. The largest GICmax > ~ 10A are considered for Fig. 8 as there are significant differences in the times for smaller GICmax. While the time of the largest -(V×Bz) is determined by the time of the largest -Bz, its magnitude depends on both -Bz and V. This observation is understood from Figs. 3 – 7 showing the variations of -(V×Bz), V and -Bz. For example, -(V×Bz) has the largest value (-97.23 units) on 29–30 October 2003 (Fig. 3 ) mainly due to the highest value of V (1650 km/s) though the corresponding -Bz (-49 nT) is much below its largest value. For the case of the largest -Bz (-77.28 nT, 06 November 2001, Fig. 7 ), the largest -(V×Bz) is comparatively small (-55.28 units) mainly due to the small V (710 km/s). The relationship is illustrated further in Fig. 9 showing the correlations of the largest GICmax at September equinox with the largest -(V×Bz), V and -Bz. The correlation is highest (0.92, 9a) with the largest -(V×Bz), lowest (0.69, 9c) with the largest -Bz and in between (0.85, 9b) with the V at largest -Bz. The 0 p-values indicate the correlations are highly significant. The correlations of the largest GICmax at September equinox with the intensity of the corresponding geomagnetic activities at high, mid and low latitudes are shown in Fig. 10 . The correlation is highest (0.81, 10a) with AEmax and slightly smaller with Kpmax (0.73, 10b) and SymHMin (0.72, 10c). Forecasting Several physics-based and empirical models including machine learning techniques and driven by solar wind data have been developed for 10–30 minutes forecasting of local dH/dt (rate of change of horizontal geomagnetic field) during geomagnetic storms (e.g., Gleisner and Lundstedt, 2001 ; Pulkkinen et al. 2011 ; Wintoft et al. 2015 ; Zhang et al. 2019 ; Camporeale et al. 2020 ; Grawe et al. 2021). The models have been developed for forecasting dH/dt than GIC for the linear relationship observed between dH/dt and GIC (Viljanen et al. 2001 , Wintoft 2005 ), abundance of accurate H data and uncertainties involved in GIC. All models perform well through the progress of the storms though they do not fully capture the response around SSC (e.g., Pulkkinen et al. 2013 ; Smith et al. 2021 ). The present study has revealed that the largest GICmax measured at a single station, largest -(V×Bz) measured using the ACE satellite at the L1 point giving ~ 60 − 15 minutes forecast time for the solar wind speed of 400–1600 km/s, and power outages happened at widely separated places all occurred at the same UT time. This result indicates that the capability of the models for forecasting dH/dt directly related to GIC will be improved when the combination V×Bz is used together with V and Bz in the model. 4. Discussion As introduced in section 1 , the association of GIC with local time and season, solar and geomagnetic activities, substorms and electrojets, and solar wind and IMF have been known thanks to the works of several scientific groups (e.g., Viljanen et al. 2010 ; Borovsky and Denton, 2006 ; Huttunen at al. 2008; Dimmock et al. 2019 ; Tsurutani and Hajra 2021 ; Hajra, 2022a ). However, what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms, which during extreme storms can cause sudden damage of vulnerable utility systems, was not known. In this paper, we have addressed this important question using 21 years (1999–2019) of the GIC data measured in Finland (Pulkkinen et al. 2001 ; Viljanen et al. 2006 ). We have investigated the relationship of the largest GIC events (largest GICmax ≥ 5A and duration ≥ 1 minute at the 2A level) occurred during 106 geomagnetic storms (DstMin ≤-50 nT) in the 21-year period (1999–2019) with the intensity of the geomagnetic activities at low, mid and high latitudes (SymHMin, Kpmax and AEmax) and solar wind velocity V, dynamic pressure P and IMF Bz, and the product V×Bz. Unlike earlier studies, (1) the present study has identified a specific solar wind-IMF combination -(V×Bz) which should have the best relationship with the largest GIC during the geomagnetic storms in all seasons and solar activity levels. (2) The largest GIC (> 10A) occurs at the time of the largest negative value of (V×Bz) with its time determined by the time of largest -Bz and magnitude determined by both -Bz and V, except in one case; in this case the largest GICmax occurred at the impact of the ICME front when IMF Bz was largely negative and largest -(V×Bz) occurred about 1.3 hours later when -Bz became largest. (3) The two power outages happened in the 21-year period of the study (Marshall et al. 2012 ; Pulkkinen et al. 2005 ) also occurred at the time of the respective largest GICmax. (4) The largest GICmax also has the highest correlation (0.92) with the combination -(V×Bz). (5) The GIC activity corresponding to the largest GICmax (> 10A) begins with the impact of the ICME front. The physical mechanism of the largest GIC activity occurring at the time of the largest -(V×Bz) probably begins with continuous and rapid magnetic reconnection between the large Bz southward immersed in a fast ICME (large V) and Earth’s northward magnetic field (e.g., Dungey, 1961 ; Akasofu, 1981; Borovsky et al. 2008 ). The Bz southward opens the dayside magnetopause and the high V provides the force for the entry of a large number of high-energy charged particles into the magnetosphere and ring current. This causes large magnetospheric currents and auroral electrojet currents (Boteler and Beek, 1999 ) producing large geomagnetic field fluctuations leading to geomagnetic activities (e.g., Gonzalez et al. 1994 ), and the large field fluctuations reaching down the Earth inducing large GIC (Viljanen et al. 2010 ). The processes seem to become most impulsive when the ICME has large front velocity ΔV (and large V) and large IMF Bz southward at the front (Balan et al. 2014 , 2017b ). The most impulsive action generates the largest GIC at the locations and times of large ionospheric and ground conductivities. Under such conditions, the vulnerable utility systems such as electric power grids, telecommunication networks, etc. get damaged (Albertson and Thorson, 1974 ; Kappenman, 2005 ; Pulkkinen et al. 2005 ; Wik et al. 2009 ; Marshall et al. 2012 ; Boteler, 2001 , 2019 ; Balan et al. 2019a , b ). The results have also shown a striking preference for the large GIC activity to occur most frequent during the SSC-MP of the geomagnetic storms at September equinox especially during the declining phase of solar cycle 23 (Fig. 2 ) as reported before (e.g., Tsurutani et al. 2021). The preference during the SSC-MP of the storms was shown related to the passage of the turbulent sheath region of ICMEs possibly due to their capacity to drive substorms and electrojets (Huttunen at al. 2008; Dimmock et al. 2019 ; Tsurutani et al. 2021). This preference at September equinox especially during the declining phase of large solar cycles could, for some reason, be due to the frequent occurrence of fast ICMEs with large IMF Bz negative during this season at this phase of solar cycles (e.g., Gopalswamy et al. 2005 ). It seems interesting to refer earlier related studies. In a study of the annual variation of the geomagnetic activity during 1995–2017 (SC23-24), Lockwood et al. ( 2020 ) found a much stronger activity peak at September equinox than March equinox. The ionosphere and thermosphere during the solar cycle prior to 1995 also showed large asymmetry between the two equinoxes (Aruliah at al. 1996; Balan et al. 1998 ). Conclusions In this paper, we have addressed what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms, which during extreme storms can cause sudden damage of vulnerable utility systems. We have used the GIC data measured for 21 years (1999–2019) in Finland, solar wind and IMF data measured by the ACE satellite and geomagnetic activity data from Kyoto University websites. The results reveal that the GIC activity (> 2A) corresponding to the largest GIC greater than about 10A during all geomagnetic storms begins with the impact of the ICME front and attains largest amplitude at the time of the largest combination of the solar wind velocity V and IMF Bz southward (or at the time of largest -(V×Bz)) in all seasons and solar activity levels except during one storm. The two power outages happened on 06 November 2001 in New Zealand and 30 October 2003 in Sweden also occurred at the UT time of the respective largest GICmax highlighting the importance of the single station GIC measurements. The results also indicate the possibility of improving the forecasting of dH/dt directly related to GIC by including the combination V×Bz in the forecast models together with V and Bz. Declarations Authors’ contributions : NB initiated the study and prepared the paper. WBL developed the computer program and did the data analysis. RS provided the 32-minute resolution ACE data. RS, MV, ZYX, LKL and QHZ are involved in the discussions and preparation of the paper. All authors read and approved the final manuscript. Acknowledgements We thank Professor Ari Viljanenfor the helpful discussions. This study is supported by the National Natural Science Foundation (Grants 42120104003,41904169 and 41874170) and the Stable-Support Scientific Project of China Research Institute of Radiowave Propagation (Grant No. A132101W02). Work at Los Alamos was performed under the auspices of the U.S. Department of Energy with support from the NASA-ACE program. The GIC recordings are maintained by the Finnish Meteorological Institute in collaboration with Gasum Oy. Competing interests: The authors declare that they have no competing interests. Funding: N Balan thanks ISS of Shandong University (China) for a distinguished professor position. Publisher’s Note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Open Research & Data Availability Statement We thank the IMAGE (International Monitor for Auroral Geomagnetic Effects) team for the GIC data available at http://space.fmi.fi/gic/man_ascii/, magnetic field data available at https://space.fmi.fi/image/www/index.php?page=monthly, ACE team for the solar wind and IMF data available at http://www.srl.caltech.edu/ACE/ASC/, and Kyoto University team for the Dst, SymH, Kp, and AE indices available at http://wdc.kugi.kyoto-u.ac.jp/dstdir/, http://wdc.kugi.kyoto-u.ac.jp/aeasy/index.html, http://wdc.kugi.kyoto-u.ac.jp/kp/index.html and http://wdc.kugi.kyoto-u.ac.jp/aedir/, respectively. References Albertson VD, Thorson JM (1974) Power system disturbances during a K-8 geomagnetic storm. August 4, 1972, IEEE Trans. Power App. & Sys. PAS-93: 1025 Akasofu S.-I Aspnes JD (1982) Auroral effects on power transmission line systems. 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Res., 112: A06205, doi:10.1029/2006JA012079, 2007 Tables Table 1: Lists the dates and storm intensity (SymHMin) of the 14 cases of largest GICmax >25A (with the number of GICmax >25A in brackets), their time of occurrence (with the time of the power outages on 06 November 2001 and 30 October 2003 in brackets), and the corresponding largest -(V×Bz) in units of 10 3 km/s nT and their time of occurrence. Time of start of GIC activity and time of impact of ICME front are also listed. No. Date SymHMin (-nT) Largest GICmax (A) Time of largest GICmax (UT) Largest -(V×Bz) (km/s nT) Time of largest -(V×Bz) (UT) Time of start of GIC (UT) Time of impact of ICME (UT) 1 15-07-2000 347 30.34 (1) 20:01:50 -59.86 20:01:00 14:39:40 14:40:15 2 06-11-2001 320 31.63 (2) 01.53:30 (01:52) 55.28 03:14:55 01:53:30 01:58:08 3 24-11-2001 234 31.97 (2) 07:14:30 -31.26 07:18:13 06:14:20 06:08:44 4 07-09-2002 166 26.51 (1) 18:38:40 -14.82 18:13:33 17:09:00 17:09:29 5 01-10-2002 150 28.15 (2) 16:29:40 -30.30 16:31:40 13:23:00 13:23:00 6 14-10-2003 88 28.76 (1) 18:28:20 -8.28 18:24:46 18:18:20 18:18:20 7 29-10-2003 390 57.04 (11) 06:57:40 -97.23 06:57:40 06:11:50 06:15:28 8 30-10-2003 432 48.57 (6) 20:08:40 (20:07) -45.25 20:09:40 16:56:40 16:52:20 9 07-11-2004 394 35.36 (2) 23:31:20 -34.30 23:24:40 18:29:10 18:24:00 10 09-11-2004 282 42.82 (2) 19:50:50 -32.23 19:49:44 13:49:50 13:45:40 11 21-01-2005 101 27.44 (1) 19:10:00 -24.78 18:38:33 17:12:30 17:08:30 12 15-03-2012 79 39.14 (2) 17:03:50 -10.06 17:05:20 13:03:40 13:06:20 13 17-03-2013 131 31.65 (1) 18:04:50 -7.15 18:02:48 06:03:30 06:07:20 14 07-09-2017 146 28.18 (1) 00:31:30 -31.47 23:33:03 22:50:40 22:48:00 Supplementary Files Slide1.png Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-1980192\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":true,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":135455627,\"identity\":\"150246ff-5fc7-484f-a83b-b0f733f9d56c\",\"order_by\":0,\"name\":\"Nanan Balan\",\"email\":\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA5UlEQVRIiWNgGAWjYBACAwbmBhib8QEDwwFitDDCtTAbkKyFTYIoLebsBxs/FzDckTdnP3usmqfmjhw/A/PDRzfwaLHsSWyWnsHwzHBnT17abZ5jz4wlG9iMjXPwOexAYoM0D8Nhxg0Hcsxu87AdTtxwgIdNGq+W8w+bfwO12G84/8asmOcfMVpuJLaBbEnccCPHjJm3jQgtljMetlnzGBxO3nDjjbHk3L7DxpLNBPxizp98+DZPxWHbDedzDD+8+XZYjp+9+eFjfFqgzoNQTDwgkpmgciTA+IMU1aNgFIyCUTBiAAAuDE8xVW2J8AAAAABJRU5ErkJggg==\",\"orcid\":\"https://orcid.org/0000-0001-7079-887X\",\"institution\":\"Shandong University - Weihai Branch: Shandong University at Weihai\",\"correspondingAuthor\":true,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Nanan\",\"middleName\":\"\",\"lastName\":\"Balan\",\"suffix\":\"\"},{\"id\":135455628,\"identity\":\"1421890a-bc0f-419a-874a-395ed2fcb7a0\",\"order_by\":1,\"name\":\"Wen-Bin Li\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shandong University - Weihai Branch: Shandong University at Weihai\",\"correspondingAuthor\":false,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Wen-Bin\",\"middleName\":\"\",\"lastName\":\"Li\",\"suffix\":\"\"},{\"id\":135455629,\"identity\":\"aaaeb4b6-7c88-4976-8104-2cc0b4f2a21e\",\"order_by\":2,\"name\":\"Zan-Yang XING\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shandong University - Weihai Branch: Shandong University at Weihai\",\"correspondingAuthor\":false,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Zan-Yang\",\"middleName\":\"\",\"lastName\":\"XING\",\"suffix\":\"\"},{\"id\":135455630,\"identity\":\"ef27fded-0623-42c2-941d-a883f9a38397\",\"order_by\":3,\"name\":\"R. Skoug\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Los Alamos National Laboratory\",\"correspondingAuthor\":false,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"R.\",\"middleName\":\"\",\"lastName\":\"Skoug\",\"suffix\":\"\"},{\"id\":135455631,\"identity\":\"99996467-1fe3-46da-aba6-ccf0e373dbc2\",\"order_by\":4,\"name\":\"V. Manu\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shandong University - Weihai Branch: Shandong University at Weihai\",\"correspondingAuthor\":false,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"V.\",\"middleName\":\"\",\"lastName\":\"Manu\",\"suffix\":\"\"},{\"id\":135455632,\"identity\":\"c9d38b8d-aedc-45a3-a607-8177e1d73c66\",\"order_by\":5,\"name\":\"Li-Kai Liang\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shandong University - Weihai Branch: Shandong University at Weihai\",\"correspondingAuthor\":false,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Li-Kai\",\"middleName\":\"\",\"lastName\":\"Liang\",\"suffix\":\"\"},{\"id\":135455633,\"identity\":\"3f7b7844-6594-4c20-be93-4e3c9135ee60\",\"order_by\":6,\"name\":\"Qing-He Zhang\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Shandong University - Weihai Branch: Shandong University at Weihai\",\"correspondingAuthor\":false,\"submittingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Qing-He\",\"middleName\":\"\",\"lastName\":\"Zhang\",\"suffix\":\"\"}],\"badges\":[],\"createdAt\":\"2022-08-20 06:16:44\",\"currentVersionCode\":1,\"declarations\":\"\",\"doi\":\"10.21203/rs.3.rs-1980192/v1\",\"doiUrl\":\"https://doi.org/10.21203/rs.3.rs-1980192/v1\",\"draftVersion\":[],\"editorialEvents\":[],\"editorialNote\":\"\",\"failedWorkflow\":false,\"files\":[{\"id\":26781025,\"identity\":\"0dbfd966-ebb5-4595-a3b7-84d23ed12e6a\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:02\",\"extension\":\"png\",\"order_by\":1,\"title\":\"Figure 1\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":147994,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eExample of the largest GIC event (a) and N large GIC events (b) occurred during the geomagnetic activity on 06 November 2001, see text.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/64f23f8676d1a35fdb6a4446.png\"},{\"id\":26781017,\"identity\":\"49fadf3a-cb8b-4da6-9a20-6a0e9e94ee3f\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:16:56\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":202724,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eDistribution of the (a) intensity DstMin of the 106 geomagnetic storms in 1999-2019 and (b) corresponding largest GICmax. The colors correspond to the seasons (red - September equinox, blue - March equinox, green - December solstice, yellow - June solstice).; The gray curve in (b) shows monthly mean F10.7.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/2417f6e9422c23fa12b11006.png\"},{\"id\":26781014,\"identity\":\"68c7ec40-4676-49e8-b013-461fc58f6081\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:16:53\",\"extension\":\"png\",\"order_by\":3,\"title\":\"Figure 3\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":240923,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eShows the data during the first of a super double geomagnetic storm on 29-30 October 2003 (September equinox) when the largest GICmax (57.05A) occurred in the 21 years (1999-2019). The geomagnetic activities in the SymH and Dst and Kp and AE indices, and corresponding solar wind velocity V, IMF Bz and (V×Bz) are displayed in panels (b), (c), (d), (e) and (f). V is of 32 minutes resolution. Bz of 4 minutes resolution at the 32 minutes intervals of V are used. Solar wind density data are not available.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure32930Oct2003.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/4a43e550eb281ed1bd33db88.png\"},{\"id\":26781028,\"identity\":\"a9102206-3cfa-4031-93b7-0678703ef855\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:02\",\"extension\":\"png\",\"order_by\":4,\"title\":\"Figure 4\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":257156,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eThis figure is similar to Figure 3 but for the largest GICmax (39.14A) at March equinox (15-16 March 2012). V and Bz are of 64 seconds resolution. Solar wind density is not available.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure41516March2012.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/f472260542a2ba3ef9c3aae1.png\"},{\"id\":26781023,\"identity\":\"1ec31f57-5a79-4110-a0ac-45fa044a3698\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:01\",\"extension\":\"png\",\"order_by\":5,\"title\":\"Figure 5\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":270790,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eThis figure is similar to Figure 3 but for the largest GICmax (30.34A) in June solstice (15-16 July 2000). V and P are of 32 minutes resolution. Bz of 4 minutes resolution are used at the 32 minutes intervals of V.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"FIG51516July2000.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/4135fe4833f946315b43812e.png\"},{\"id\":26781015,\"identity\":\"472a5f4a-57da-4466-96e6-dd29f74e2634\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:16:53\",\"extension\":\"png\",\"order_by\":6,\"title\":\"Figure 6\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":257342,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eThis figure is similar to Figure 3 but for the power outage happened in Sweden during the super storm on 30 October 2003. V is of 32 minutes resolution. Bz of 4 minutes resolution at the times of V are used. Solar wind density is not available.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"FIG63031October2003.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/5c95af69f1027851d7e37776.png\"},{\"id\":26781021,\"identity\":\"a1056da8-376d-41f5-ab0a-a897b299f64e\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:00\",\"extension\":\"png\",\"order_by\":7,\"title\":\"Figure 7\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":239701,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eThis figure is similar to Figure 3 but for the power outage happened in New Zealand during the super storm on 06 November 2001. Bz of 4 minutes resolution at the times of V are used for (V×Bz). Solar wind density is not available.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"FIG70506November2001.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/722dda7f903176fe2343f636.png\"},{\"id\":26781019,\"identity\":\"e05cd7cd-2cd2-4a02-97f9-9f41819f8d35\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:00\",\"extension\":\"png\",\"order_by\":8,\"title\":\"Figure 8\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":95078,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eRelationship between the (a) time of occurrence of largest GICmax (\\u0026gt;10A) and time of occurrence of the corresponding largest -(V×Bz) and (b) time of start of GIC activity (GIC \\u0026gt;2A) and time of impact of ICME front.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure8TimeLGICmaxLVxBz.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/c7d7b47997f97e3f9cf2722d.png\"},{\"id\":26781034,\"identity\":\"e761b6e3-d006-48ab-b01b-c9d3b9bab6bd\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:03\",\"extension\":\"png\",\"order_by\":9,\"title\":\"Figure 9\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":120096,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eCorrelations of the largest GICmax at September equinox during 1999-2019 with the corresponding (a) largest -(V×Bz), (b) largest -Bz, and (c) velocity V at largest -Bz.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure9LCmaxLVxBzVBz.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/66855f3b3a9e7d4c61e2d968.png\"},{\"id\":26781016,\"identity\":\"447582de-d24e-459a-8502-1a7018053452\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:16:53\",\"extension\":\"png\",\"order_by\":10,\"title\":\"Figure 10\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":93438,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eCorrelations of the largest GICmax with the intensities (AEmax Kpmax and SymHMin) of the geomagnetic activities at high (a), mid (c) and low (d) latitudes at\\u003c/p\\u003e\\n\\u003cp\\u003eSeptember equinox in 1999-2019.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"Figure10LCmaxAEKPSymH.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/62eb2f01f2aba42ff64345f0.png\"},{\"id\":28202859,\"identity\":\"2e7aa209-e7a6-42d0-b90f-5cdf6cfed9f7\",\"added_by\":\"auto\",\"created_at\":\"2022-10-24 22:20:24\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":2205130,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/99912fb8-f704-47bd-b627-0485b4d5fb0d.pdf\"},{\"id\":26781020,\"identity\":\"92c50e94-731e-45fe-adad-b9c4dbb512d1\",\"added_by\":\"auto\",\"created_at\":\"2022-09-21 18:17:00\",\"extension\":\"png\",\"order_by\":15,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":1334859,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Slide1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-1980192/v1/f956b0fcaa3ef271dd2e2a51.png\"}],\"financialInterests\":\"\",\"formattedTitle\":\"Relationship of the largest GIC during geomagnetic storms with solar wind-IMF parameters\",\"fulltext\":[{\"header\":\"1. Background\",\"content\":\"\\u003cp\\u003eThe geomagnetically induced current (GIC) was noticed nearly two centuries ago by Barlow (\\u003cspan citationid=\\\"CR14\\\" class=\\\"CitationRef\\\"\\u003e1849\\u003c/span\\u003e) from his observation of the deflection of the telegraph magnetic needles of the Midland Railroad station coinciding with auroral activity. Later, the GIC induced during geomagnetic activities was found flowing through the earthed utility systems such as oil and gas metal pipe lines, electric power grids, tele-communication networks, etc. (e.g., Campbell \\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e1980\\u003c/span\\u003e; Pirjola and Lehtinen \\u003cspan citationid=\\\"CR50\\\" class=\\\"CitationRef\\\"\\u003e1985\\u003c/span\\u003e; Pirjola \\u003cspan citationid=\\\"CR51\\\" class=\\\"CitationRef\\\"\\u003e2000\\u003c/span\\u003e). The GIC is large at high latitudes (e.g., Campbell \\u003cspan citationid=\\\"CR23\\\" class=\\\"CitationRef\\\"\\u003e1980\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Vladimir et al. \\u003cspan citationid=\\\"CR15\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e) and smaller at lower latitudes (e.g., Watari et al. \\u003cspan citationid=\\\"CR65\\\" class=\\\"CitationRef\\\"\\u003e2009\\u003c/span\\u003e; Liu et al. \\u003cspan citationid=\\\"CR44\\\" class=\\\"CitationRef\\\"\\u003e2009\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR45\\\" class=\\\"CitationRef\\\"\\u003e2014\\u003c/span\\u003e; Barbosa et al. \\u003cspan citationid=\\\"CR13\\\" class=\\\"CitationRef\\\"\\u003e2015\\u003c/span\\u003e; Carter et al. \\u003cspan citationid=\\\"CR25\\\" class=\\\"CitationRef\\\"\\u003e2015\\u003c/span\\u003e) probably basically due to the orientation of the geomagnetic field changing from vertical and open at high latitudes to closed and horizontal at low latitudes. The large geomagnetic field fluctuations produced by the large electric currents flowing in the magnetosphere and ionosphere during space weather events are referred as geomagnetic storms at low and mid latitudes and geomagnetic activities or storm-time substorms at high latitudes (e.g., Gonzalez et al. \\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e1994\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003eThe GIC during extreme geomagnetic activities produced by fast solar storms such as ICMEs (interplanetary coronal mass ejections with frozen-in solar magnetic field or interplanetary magnetic field IMF) can exceed the tolerance limit of the systems and cause system damages as has happened during a number of such events (e.g., Albertson and Thorson \\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1974\\u003c/span\\u003e; Bolduc \\u003cspan citationid=\\\"CR16\\\" class=\\\"CitationRef\\\"\\u003e2002\\u003c/span\\u003e; Kappenman \\u003cspan citationid=\\\"CR41\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan citationid=\\\"CR53\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e; Wik et al. \\u003cspan citationid=\\\"CR68\\\" class=\\\"CitationRef\\\"\\u003e2009\\u003c/span\\u003e; Marshall et al. \\u003cspan citationid=\\\"CR47\\\" class=\\\"CitationRef\\\"\\u003e2012\\u003c/span\\u003e; Balan et al. \\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e2019a\\u003c/span\\u003e). The extreme event on 13 March 1989 caused electric power outage in Quebec for nine hours costing hundreds of millions of US\\u003cspan\\u003e$\\u003c/span\\u003e (Medford et al. \\u003cspan citationid=\\\"CR49\\\" class=\\\"CitationRef\\\"\\u003e1989\\u003c/span\\u003e; Boteler \\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e). An event similar to the famous Carrington event of September 1859 (Carrington \\u003cspan citationid=\\\"CR26\\\" class=\\\"CitationRef\\\"\\u003e1859\\u003c/span\\u003e) occurring at the present time could cause damages costing up to (estimated) 1\\u0026ndash;2 trillion US\\u003cspan\\u003e$\\u003c/span\\u003e (e.g., Baker \\u003cspan citationid=\\\"CR5\\\" class=\\\"CitationRef\\\"\\u003e2002\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan citationid=\\\"CR56\\\" class=\\\"CitationRef\\\"\\u003e2017\\u003c/span\\u003e; Hapgood et al. \\u003cspan citationid=\\\"CR38\\\" class=\\\"CitationRef\\\"\\u003e2021\\u003c/span\\u003e). On the other hand, low-to-medium level GIC flowing for long periods can cause cumulative impacts such as reactive power loss in transformers and corrosion in metal pipe lines, which can pose significant risk especially when there are defects in the systems (Gaunt \\u003cspan citationid=\\\"CR31\\\" class=\\\"CitationRef\\\"\\u003e2014\\u003c/span\\u003e; Dimmock et al. \\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Khanal et al. \\u003cspan citationid=\\\"CR43\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Ingham and Rodger \\u003cspan citationid=\\\"CR40\\\" class=\\\"CitationRef\\\"\\u003e2018\\u003c/span\\u003e; Clilverd et al. \\u003cspan citationid=\\\"CR27\\\" class=\\\"CitationRef\\\"\\u003e2018\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR28\\\" class=\\\"CitationRef\\\"\\u003e2020\\u003c/span\\u003e]. Therefore, for forecasting the devastating effects of GIC, it is important to understand the relationship between the GIC during geomagnetic activities and solar wind-IMF parameters.\\u003c/p\\u003e \\u003cp\\u003eThe GIC has been measured routinely in the Finnish natural gas pipeline station M\\u0026auml;nts\\u0026auml;l\\u0026auml; (MAN) since 1999 (Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Viljanen et al. \\u003cspan citationid=\\\"CR61\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e). Using the Finland data, several scientific groups studied the association of GIC with local time and season, solar and geomagnetic activities, substorms and electrojets, and solar wind and IMF (e.g., Viljanen et al. \\u003cspan citationid=\\\"CR62\\\" class=\\\"CitationRef\\\"\\u003e2010\\u003c/span\\u003e; Borovsky and Denton \\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e; Huttunen at al. 2008; Dimmock et al. \\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Tsurutani and Hajra \\u003cspan citationid=\\\"CR59\\\" class=\\\"CitationRef\\\"\\u003e2021\\u003c/span\\u003e; Hajra \\u003cspan citationid=\\\"CR36\\\" class=\\\"CitationRef\\\"\\u003e2022a\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR37\\\" class=\\\"CitationRef\\\"\\u003eb\\u003c/span\\u003e). Viljanen et al. (\\u003cspan citationid=\\\"CR62\\\" class=\\\"CitationRef\\\"\\u003e2010\\u003c/span\\u003e) conducted an 11-year study of GIC\\u0026thinsp;\\u0026gt;\\u0026thinsp;5A. Using the data during 1999\\u0026ndash;2005, Borovsky and Denton (\\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e) and Kataoka and Pulkkinen (\\u003cspan citationid=\\\"CR42\\\" class=\\\"CitationRef\\\"\\u003e2008\\u003c/span\\u003e) showed that the GIC due to CME-driven storms pose most of the problems for ground-based conductor systems, whereas the effect of CIR-driven storms is minor. Huttunen at al. (2008) examined the relative effects of the ejecta, sheath and boundary regions of ICMEs on GIC\\u0026thinsp;\\u0026ge;\\u0026thinsp;10A. According to them (Huttunen at al. 2008) the most intense GIC activity (\\u0026gt;\\u0026thinsp;10A) is likely to take place during the passage of the turbulent sheath region of ICMEs possibly due to their capacity to drive substorms. Dimmock et al. (\\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e) showed that the unusually large GIC (up to 28A) occurred during the 7\\u0026ndash;8 September 2017 storm could be associated with westward and eastward electrojets. Recently, Tsurutani and Hajra (\\u003cspan citationid=\\\"CR59\\\" class=\\\"CitationRef\\\"\\u003e2021\\u003c/span\\u003e) surveyed the GIC\\u0026thinsp;\\u0026gt;\\u0026thinsp;10A and \\u0026gt;\\u0026thinsp;30A in 21 years (1999\\u0026ndash;2019) of the GIC data. They suggested that the shocks and substorms are probably the predominant causes of the intense GICs, and super-substorm and intense substorm auroral electrojet intensifications are the most frequent (76%) cause of GIC\\u0026thinsp;\\u0026gt;\\u0026thinsp;30A. Following this, Hajra (\\u003cspan citationid=\\\"CR36\\\" class=\\\"CitationRef\\\"\\u003e2022a\\u003c/span\\u003e) reported the correlations between the occurrence rate of 48 GIC clusters and solar activity (0.68), integrated intensity of the GIC clusters and SymHMin (0.73), and peak intensity of the GIC clusters and integrated intensity of substorm clusters (0.85). In another paper, Hajra (\\u003cspan citationid=\\\"CR37\\\" class=\\\"CitationRef\\\"\\u003e2022b\\u003c/span\\u003e) showed the occurrence rate of GIC\\u0026thinsp;\\u0026gt;\\u0026thinsp;10A is high in solar cycle 23 and at September equinox, low at March equinox and lowest around summer solstice; and the occurrence rate is 67%, 31% and 2%, respectively, during super storms, intense storms and moderate storms.\\u003c/p\\u003e \\u003cp\\u003eHowever, what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms/activities, which during extreme storms can cause sudden damage of vulnerable utility systems, is not yet known. We address this important question using the 21-year (1999\\u0026ndash;2019) GIC data measured at MAN in Finland (Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e). We investigate the relationship of the largest GIC event (defined in section \\u003cspan refid=\\\"Sec2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e) observed during the geomagnetic activities at high, mid and low latitudes with the corresponding ICME front velocity ΔV (defined in section \\u003cspan refid=\\\"Sec2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e), solar wind velocity V, dynamic pressure P and IMF Bz, and the products V\\u0026times;Bz and P\\u0026times;Bz. The results reveal for the first time that the largest GIC during all geomagnetic activities occurs at around the time of the largest negative value of the product V\\u0026times;Bz in all seasons and solar activity levels, except in one case. The geomagnetic activity data are from the Kyoto University websites and solar wind and IMF data are from the ACE (advanced composition explorer) satellite at the L1 point (McComas et al. \\u003cspan citationid=\\\"CR48\\\" class=\\\"CitationRef\\\"\\u003e1998\\u003c/span\\u003e; Skoug et al. \\u003cspan citationid=\\\"CR57\\\" class=\\\"CitationRef\\\"\\u003e2004\\u003c/span\\u003e) for the same 21 years as the GIC data. The data and analysis are described in section \\u003cspan refid=\\\"Sec2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e. The results are presented and discussed in sections \\u003cspan refid=\\\"Sec5\\\" class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e and \\u003cspan refid=\\\"Sec11\\\" class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e.\\u003c/p\\u003e\"},{\"header\":\"2. Data And Analysis\",\"content\":\"\\u003cp\\u003eWe use the 10-second resolution GIC data measured (Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Viljanen et al. \\u003cspan citationid=\\\"CR62\\\" class=\\\"CitationRef\\\"\\u003e2010\\u003c/span\\u003e) in the Finnish natural gas pipeline compressor station at M\\u0026auml;nts\\u0026auml;l\\u0026auml; (MAN, 60.6\\u0026ordm;N, 25.2\\u0026ordm;E; 57.9ᵒN geomagnetic latitude) for 21 years (1999\\u0026ndash;2019). The data are available at \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttp://space.fmi.fi/gic/man_ascii/\\u003c/span\\u003e\\u003cspan address=\\\"http://space.fmi.fi/gic/man_ascii/\\\" targettype=\\\"URL\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e. Pulkkinen et al. (\\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e) estimated the GIC from the geomagnetic field measured at MAN and a reference magnetometer at Nurmij\\u0026auml;rvi (NUR, 24.7\\u0026deg;E, 60.5\\u0026deg;N) 30 km away. The estimated GIC agrees well with model GIC (Viljanen et al. \\u003cspan citationid=\\\"CR61\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e). However, the estimated GIC has some uncertainty due to various reasons such as spatial inhomogeneity of the geomagnetic field or separation (30 km) between the GIC station and reference magnetometer, cathodic corrosion protection system used in the pipeline, instrumental problems causing electromagnetic noise, hard weather conditions, etc. As an overall estimate, the noise contribution is less than 0.1A (occasionally\\u0026thinsp;\\u0026gt;\\u0026thinsp;1A) and uncertainty due to various reasons is 10\\u0026ndash;15% (Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Viljanen et al. \\u003cspan citationid=\\\"CR61\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR62\\\" class=\\\"CitationRef\\\"\\u003e2010\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR63\\\" class=\\\"CitationRef\\\"\\u003e2015\\u003c/span\\u003e). The GIC data have a gap for 16 months during April 2014-August 2015 and other small gaps.\\u003c/p\\u003e \\u003cp\\u003eSince the GIC direction (eastward or westward) is unimportant in our study, we use its magnitude and refer it as GIC. As illustrated by an example in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e, the GIC during geomagnetic activities undergoes large and rapid fluctuations that we call GIC events. We define a large GIC event as the one having amplitude GICmax\\u0026thinsp;\\u0026ge;\\u0026thinsp;5A and duration at the 2A level\\u0026thinsp;\\u0026ge;\\u0026thinsp;1 minute. The 2A level used for fixing the duration and 5A level used for the lower amplitude limit are well above the noise contribution and uncertainty (Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Viljanen et al. \\u003cspan citationid=\\\"CR63\\\" class=\\\"CitationRef\\\"\\u003e2015\\u003c/span\\u003e). The first time GIC exceeds the 2A level is considered as the start of GIC activity. The largest GIC event of amplitude largest GICmax illustrated in Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003eb is important because it during extreme geomagnetic activity can cause sudden damage of vulnerable utility systems (e.g., Marshall et al. \\u003cspan citationid=\\\"CR47\\\" class=\\\"CitationRef\\\"\\u003e2012\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan citationid=\\\"CR53\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.1. Geomagnetic activities\\u003c/h2\\u003e \\u003cp\\u003eThe geomagnetic storms/activities at high, mid and low latitudes are identified in the high latitude auroral electrojet index (AE) of 1-minute resolution available at \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttp://wdc.kugi.kyoto-u.ac.jp/aedir/\\u003c/span\\u003e\\u003cspan address=\\\"http://wdc.kugi.kyoto-u.ac.jp/aedir/\\\" targettype=\\\"URL\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e, mid latitude Kp index of 3-hour resolution available at \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttp://wdc.kugi.kyoto-u.ac.jp/kp/index.html\\u003c/span\\u003e\\u003cspan address=\\\"http://wdc.kugi.kyoto-u.ac.jp/kp/index.html\\\" targettype=\\\"URL\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003cspan type=\\\"Underline\\\" class=\\\"Underline\\\" name=\\\"Emphasis\\\"\\u003e)\\u003c/span\\u003e, and low latitude SymH index of 1-minute resolution available at \\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttp://wdc.kugi.kyoto-u.ac.jp/aeasy/index.html\\u003c/span\\u003e\\u003cspan address=\\\"http://wdc.kugi.kyoto-u.ac.jp/aeasy/index.html\\\" targettype=\\\"URL\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e. First, the low latitude Dst data of 1-hour resolution (\\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttp://wdc.kugi.kyoto-u.ac.jp/dstdir/\\u003c/span\\u003e\\u003cspan address=\\\"http://wdc.kugi.kyoto-u.ac.jp/dstdir/\\\" targettype=\\\"URL\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003cspan type=\\\"Underline\\\" class=\\\"Underline\\\" name=\\\"Emphasis\\\"\\u003e)\\u003c/span\\u003e are used to identify 226 clear geomagnetic storms of intensity DstMin \\u0026le;-50 nT (Gonzalez et al. \\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e1994\\u003c/span\\u003e) during 1999\\u0026ndash;2019 using four selection criteria that minimize non-storm like fluctuations in Dst (Balan et al. 1917a). DstMin is the minimum Dst during the main phase (MP) of a storm. The corresponding 226 geomagnetic storms/activities in SymH, Kp and AE indices are identified, and their intensities SymHMin (minimum value of SymH during the MP) and Kpmax and AEmax (maximum values of Kp and AE) are obtained. Using a computer algorithm, we identified 1848 large GIC events occurred during the 106 geomagnetic storms (DstMin \\u0026le;-50 nT) in 21 years (1999\\u0026ndash;2019). GIC is found\\u0026thinsp;\\u0026lt;\\u0026thinsp;5A for 68 storms and 52 storms have no GIC data. The largest GICmax\\u0026thinsp;\\u0026ge;\\u0026thinsp;5A corresponding to the 106 storms are obtained.\\u003c/p\\u003e \\u003c/div\\u003e \\u003cdiv id=\\\"Sec4\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003e2.2. Solar wind and IMF\\u003c/h2\\u003e \\u003cp\\u003eThe solar wind and IMF data have been provided continuously since 1998 by the ACE (Advanced Composition Explorer) satellite at the L1 point. The solar wind velocity V and density N (and dynamic pressure P) are measured by the SWEPAM (Solar Wind Electron Proton Alpha Monitor) instrument in the SWI (Solar Wind Ion) mode at 64-second resolution (e.g., McComas et al. \\u003cspan citationid=\\\"CR48\\\" class=\\\"CitationRef\\\"\\u003e1998\\u003c/span\\u003e; Skoug et al. \\u003cspan citationid=\\\"CR57\\\" class=\\\"CitationRef\\\"\\u003e2004\\u003c/span\\u003e). These data are available at Caltech (\\u003cspan class=\\\"ExternalRef\\\"\\u003e\\u003cspan class=\\\"RefSource\\\"\\u003ehttp://www.srl.caltech.edu/ACE/ASC/\\u003c/span\\u003e\\u003cspan address=\\\"http://www.srl.caltech.edu/ACE/ASC/\\\" targettype=\\\"URL\\\" class=\\\"RefTarget\\\"\\u003e\\u003c/span\\u003e\\u003c/span\\u003e\\u003cspan type=\\\"Underline\\\" class=\\\"Underline\\\" name=\\\"Emphasis\\\"\\u003e).\\u003c/span\\u003e During high energy particle events, the SWI mode often does not cover the full solar wind flux spectrum. Under such conditions, the 64-second data collected in the SSTI (Search/Supra Thermal Ion) mode once every\\u0026thinsp;~\\u0026thinsp;32 minutes are used. The data (time) is shifted for the ACE-Earth distance.\\u003c/p\\u003e \\u003cp\\u003eThe values of V, P, IMF Bz and the products (V\\u0026times;Bz) and (P\\u0026times;Bz) during the 106 geomagnetic activities in 1999\\u0026ndash;2019 are obtained. The product (V\\u0026times;Bz) was used before for modeling the geomagnetic storms (e.g., Burton et al. \\u003cspan citationid=\\\"CR22\\\" class=\\\"CitationRef\\\"\\u003e1975\\u003c/span\\u003e; Zhu et al. \\u003cspan citationid=\\\"CR70\\\" class=\\\"CitationRef\\\"\\u003e2007\\u003c/span\\u003e) and for addressing what determines the severity of space weather (Balan et al. \\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e2014\\u003c/span\\u003e) and developing a scheme for forecasting severe space weather (SvSW, Balan et al. \\u003cspan citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e2017b\\u003c/span\\u003e). The peak values of -Bz, -(V\\u0026times;Bz) and -(P\\u0026times;Bz) and the values of V and P at the peaks of -(V\\u0026times;Bz) are obtained. The ICME front velocity ΔV is the difference between the peak ICME velocity at its front and the upstream solar wind velocity V. However, the high velocity of 32-minute resolution is found to take up to two hours to reach its peak (Skoug et al. \\u003cspan citationid=\\\"CR57\\\" class=\\\"CitationRef\\\"\\u003e2004\\u003c/span\\u003e). Therefore, ΔV is generally taken as the difference between the mean velocity for 2 hours after and 2 hours before the start of the velocity increase (Balan et al. \\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e2014\\u003c/span\\u003e).\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"3. Results\",\"content\":\"\\u003cp\\u003eFirst, we briefly discuss the important aspects in the distribution of the 106 largest GIC events (or largest GICmax) that are relevant to the present study. Then we will present the detailed relationship of the time of occurrence and amplitude of the largest GIC events with the geomagnetic activities and solar wind-IMF parameters through case studies and correlations. We will also briefly describe the advantages of using the product (V\\u0026times;Bz) for forecasting the rate-of-change of the local horizontal geomagnetic field (dH/dt) directly related to GIC.\\u003c/p\\u003e\\n\\u003cdiv class=\\\"Section2\\\" id=\\\"Sec6\\\"\\u003e\\n \\u003ch2\\u003e3.1. Distribution of largest GIC\\u003c/h2\\u003e\\n \\u003cp\\u003eThe largest GIC events during all 106 geomagnetic storms are found to occur during the SSC-MP (storm sudden commencement-main phase) of the storms. Figure \\u003cspan class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e shows the distribution of the largest GICmax and intensity (DstMin) of the storms during 1999\\u0026ndash;2019. There is a striking September equinox preference for the largest GICmax (and storms) to occur especially during the declining phase of solar cycle 23 (1999\\u0026ndash;2009). Of the 106 largest GICmax, 38 occurred at September equinox and only 68 occurred in all other seasons together (34 at March equinox and 17 each in June and December solstices). The largest GICmax is also generally much larger at September equinox than in other seasons.\\u003c/p\\u003e\\n \\u003cp\\u003eFigure \\u003cspan class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e also shows a preference for the largest GIC events to occur during super double-storms (DstMin \\u0026le;-250 nT) at September equinox (29\\u0026ndash;31 October 2003 and 07\\u0026ndash;10 November 2004). However, in other seasons, the largest GICmax occur even during comparatively weak storms. For example, the weak storm on 21 January 2005 (DstMin \\u0026minus;\\u0026thinsp;89 nT) has the largest GICmax\\u0026thinsp;~\\u0026thinsp;28A in December solstice; and the weak storm on 15\\u0026ndash;16 March 2012 (DstMin \\u0026minus;\\u0026thinsp;88 nT) has the largest GICmax\\u0026thinsp;~\\u0026thinsp;39A at March equinox. At the same time, the largest super storm at March equinox (31 March 2001, DstMin \\u0026minus;\\u0026thinsp;387 nT) corresponds to the largest GICmax of only 15.8A. The double-storm on 07\\u0026ndash;10 September 2017, though comparatively weak (DstMin \\u0026minus;\\u0026thinsp;124 nT, -109 nT), also produced very large GICmax (~\\u0026thinsp;30A). Earlier, Dimmock et al. (\\u003cspan class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e) studied the GIC activity (up to 28A) during the storm on 07\\u0026ndash;08 September 2017. Tsurutani and Hajra (\\u003cspan class=\\\"CitationRef\\\"\\u003e2021\\u003c/span\\u003e) reported the occurrence of a large number of GIC\\u0026thinsp;\\u0026gt;\\u0026thinsp;10A at September equinox with 168 of them occurring during the MP of the super double-storm on 29\\u0026ndash;31 October 2003.\\u003c/p\\u003e\\n\\u003c/div\\u003e\\n\\u003cdiv class=\\\"Section2\\\" id=\\\"Sec7\\\"\\u003e\\n \\u003ch2\\u003e3.2. Case studies\\u003c/h2\\u003e\\n \\u003cp\\u003eHere, we present the 14 cases of largest GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A including the two power outages occurred in the 21 years of this study. Table\\u0026nbsp;1 lists the date and storm intensity (SymHMin) of the 14 cases and magnitude of the largest GICmax (with the number of GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A in brackets) and their time of occurrence. The magnitude of the corresponding largest -(V\\u0026times;Bz) and their time of occurrence, and time of start of GIC activity (\\u0026ge;\\u0026thinsp;2A) and time of impact of the ICME front are also listed. The important results are (1) the largest GICmax (\\u0026gt;\\u0026thinsp;25A) and corresponding largest -(V\\u0026times;Bz) occur at around the same UT time in all cases within the time resolution of up to \\u0026plusmn;\\u0026thinsp;32 minutes, except on 06 November 2001 (discussed below). (2) The start of GIC activity and impact of ICME front occur at around the same time in all cases within the time resolution. (3) The power outage in New Zealand on 06 November 2001 (Marshall et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2012\\u003c/span\\u003e) and Sweden on 30 October2003 (Pulkkinen et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e) happened at the UT time of the respective largest GICmax. Table\\u0026nbsp;1 also shows that out of the 37 GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A, 32 occurred at September equinox, which also shows the preference for the large GIC events to occur at September equinox.\\u003c/p\\u003e\\n \\u003cdiv class=\\\"Section3\\\" id=\\\"Sec8\\\"\\u003e\\n \\u003ch2\\u003e3.2.1. Largest GIC in seasons\\u003c/h2\\u003e\\n \\u003cp\\u003eHere we discuss the largest GIC events in 4 seasons. Figure \\u003cspan class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e shows the GIC (3a) data at September equinox (29\\u0026ndash;30 October 2003) when the largest GICmax (57.05A) and largest number (11) of GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A occurred in the 21 years of this study (Table 1). This case is associated with the first of a super double geomagnetic storm (SymHMin \\u0026minus;\\u0026thinsp;391 nT, Kpmax 9 and AEmax 4056 nT; 3b-3c), fastest solar wind velocity (2242 km/s; 3d) (e.g., Skoug et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2004\\u003c/span\\u003e) and largest negative V\\u0026times;Bz (-97.23x10\\u003csup\\u003e3\\u003c/sup\\u003e km/s nT; 3f) in 21 years with -Bz up to -45.05 nT (3e). Most importantly, the largest GICmax (57.05A, 06:57:40 UT) occurred at the time (06:57:40 UT) of the largest negative value of the product V\\u0026times;Bz (Table 1). Though this time is determined by the time of the largest -Bz, its magnitude depends on both -Bz and V (section \\u003cspan class=\\\"InternalRef\\\"\\u003e3.2.3\\u003c/span\\u003e). Also, the GIC activity started at 06:11:50 UT with a GIC pulse (25.1A) at the impact (06:15:28 UT) of the fastest ICME (\\u0026Delta;V\\u0026thinsp;~\\u0026thinsp;1145 km/s) in the 21 years of this study (e.g., Skoug et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2004\\u003c/span\\u003e).\\u003c/p\\u003e\\n \\u003cp\\u003eFigure \\u003cspan class=\\\"InternalRef\\\"\\u003e4\\u003c/span\\u003e is similar to Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e but for the largest GICmax (39.14A, 4a) at March equinox (15\\u0026ndash;16 March 2012). This case is associated with a moderate geomagnetic storm (SymHMin \\u0026minus;\\u0026thinsp;79 nT, Kpmax 6 and AEmax 2210 nT, 4b-c), fast solar wind up 801 km/s (4d) and comparatively weak -Bz (-13.62 nT, 4e). In this case, there are only 2 GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A (4a, Table 1). Most importantly, as in the previous case, the largest GICmax occurred (17:03:50 UT) at around the time (17:05:20 UT) of the largest negative value of V\\u0026times;Bz (-10.06\\u0026times;10\\u003csup\\u003e3\\u003c/sup\\u003e km/s nT; 4f), and GIC activity started (13:03:40 UT) with a small GIC pulse at the impact (13:06:20 UT) of a comparatively slow ICME front of \\u0026Delta;V\\u0026thinsp;~\\u0026thinsp;100 km/s. Figure \\u003cspan class=\\\"InternalRef\\\"\\u003e5\\u003c/span\\u003e is for the largest GICmax (30.34A) in June solstice (15\\u0026ndash;16 July 2000). This case is associated with a super storm (SymHMin \\u0026minus;\\u0026thinsp;343 nT, Kpmax 9 and AEmax 3330 nT; 5b-5c), fast solar wind of velocity up to 1110 km/s (5d) and large Bz negative (-57.02 nT; 5e). As in the previous cases, the largest GICmax occurred (20:01:50 UT) at the time (20:01:00 UT) of the largest negative value of V\\u0026times;Bz (-59.86x10\\u003csup\\u003e3\\u003c/sup\\u003e km/s nT; 3f), and GIC activity started (14:39:40 UT) with the impact (14:40:15 UT) of a fast ICME front of \\u0026Delta;V 230 km/s with IMF Bz positive. There is also a large solar wind pressure pulse (~\\u0026thinsp;60 nPa, 5d) at the ICME front; but after the large pulse, the pressure is small.\\u003c/p\\u003e\\n \\u003cp\\u003eThe case of the largest GICmax (27.44A) in December solstice occurred on 21\\u0026ndash;22 January 2005 (figure not shown). This case is associated with a moderate geomagnetic storm (SymHMin \\u0026minus;\\u0026thinsp;101 nT, Kpmax 8 and AEmax 3449 nT), fast solar wind of velocity up to 1090 km/s and very large dynamic pressure up to 600 nPa and large Bz negative of -27.02 nT. As in the previous 3 cases, the GIC activity started (17:12:30 UT) with the impact (17:08:30 UT) of a fast ICME front of \\u0026Delta;V\\u0026thinsp;~\\u0026thinsp;345 km/s with Bz positive and the largest GICmax occurred (19:10:00 UT) at around the time (18:48:33 UT) of the largest negative value of V\\u0026times;Bz (-24.78x10\\u003csup\\u003e3\\u003c/sup\\u003e km/s nT), which in this case is also around the largest negative of P\\u0026times;Bz (-10x10\\u003csup\\u003e3\\u003c/sup\\u003e nPa nT). However, the solar wind density (and pressure) is not available in most cases of GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A. For this reason, the dynamic pressure will not be considered further in the study.\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n \\u003cdiv class=\\\"Section3\\\" id=\\\"Sec9\\\"\\u003e\\n \\u003ch2\\u003e3.2.2. Cases of power outage\\u003c/h2\\u003e\\n \\u003cp\\u003eTwo power outages happened in the 21 years of this study. Figure \\u003cspan class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e shows the data for the power outage happened in Sweden during the super storm on 30 October 2003 (Pulkkinen et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e). The power outage occurred at 20:07 UT at around the time 20:08:40 UT of the largest GICmax (48.57A) measured in Finland, which is also around the time 20:09:40 UT of the largest negative value of V\\u0026times;Bz (-45.25 units) measured by the ACE satellite (Table 1). The GIC activity started at 16:56:40 UT at around the impact (16:52:20 UT) of a fast ICME front of \\u0026Delta;V\\u0026thinsp;~\\u0026thinsp;650 km/s when IMF Bz turned largely southward. Only in this case of the second of a super double-storm did a few GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;25A occur during the RP of the storm. Figure \\u003cspan class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e is similar to Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e6\\u003c/span\\u003e but for the power outage happened in New Zealand during the super storm on 06 November 2001 (Marshall et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2012\\u003c/span\\u003e). In this case also, the power outage occurred (01:52 UT) at around the time (01:53:30 UT) of the largest GICmax (31.63A), which is at the time (01:53:30 UT) of start of GIC activity and time of impact of the ICME front with IMF Bz largely negative. However, (V\\u0026times;Bz) attained its largest negative value (-55.28 units) about 1.3 hours later (03:14:55 UT) when -Bz reached its maximum value (-77.28 nT). In this case, the first large GIC event became the largest GIC event most probably because IMF Bz was largely negative at the ICME front of high \\u0026Delta;V\\u0026thinsp;~\\u0026thinsp;285 km/s, so that the high impulsive power of the ICME became most effective right at its impact (Balan et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2019a\\u003c/span\\u003e).\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n \\u003cdiv class=\\\"Section3\\\" id=\\\"Sec10\\\"\\u003e\\n \\u003ch2\\u003e3.2.3. Time of occurrence and amplitude\\u003c/h2\\u003e\\n \\u003cp\\u003eThe relationship of the time of occurrence and amplitude of the largest GIC event with those of the largest -(V\\u0026times;Bz) is discussed further here. As shown in Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e8\\u003c/span\\u003ea, the time of all largest GICmax (\\u0026gt;\\u0026thinsp;10A) occurs at or around the time of the largest -(V\\u0026times;Bz) with a maximum time difference less than the resolution (up to 32 minutes), except in one case (06 November 2001, discussed in Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e). The correlation between the two times is high (0.986) and highly significant (0 p-value). The corresponding GIC activity begins at or around the time of impact of the ICME front as shown in Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e8\\u003c/span\\u003eb; the two times are highly correlated (0.998) with 0 p-value. The largest GICmax\\u0026thinsp;\\u0026gt;\\u0026thinsp;~\\u0026thinsp;10A are considered for Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e8\\u003c/span\\u003e as there are significant differences in the times for smaller GICmax.\\u003c/p\\u003e\\n \\u003cp\\u003eWhile the time of the largest -(V\\u0026times;Bz) is determined by the time of the largest -Bz, its magnitude depends on both -Bz and V. This observation is understood from Figs. \\u003cspan class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e\\u0026ndash;\\u003cspan class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e showing the variations of -(V\\u0026times;Bz), V and -Bz. For example, -(V\\u0026times;Bz) has the largest value (-97.23 units) on 29\\u0026ndash;30 October 2003 (Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e3\\u003c/span\\u003e) mainly due to the highest value of V (1650 km/s) though the corresponding -Bz (-49 nT) is much below its largest value. For the case of the largest -Bz (-77.28 nT, 06 November 2001, Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e7\\u003c/span\\u003e), the largest -(V\\u0026times;Bz) is comparatively small (-55.28 units) mainly due to the small V (710 km/s). The relationship is illustrated further in Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e9\\u003c/span\\u003e showing the correlations of the largest GICmax at September equinox with the largest -(V\\u0026times;Bz), V and -Bz. The correlation is highest (0.92, 9a) with the largest -(V\\u0026times;Bz), lowest (0.69, 9c) with the largest -Bz and in between (0.85, 9b) with the V at largest -Bz. The 0 p-values indicate the correlations are highly significant. The correlations of the largest GICmax at September equinox with the intensity of the corresponding geomagnetic activities at high, mid and low latitudes are shown in Fig. \\u003cspan class=\\\"InternalRef\\\"\\u003e10\\u003c/span\\u003e. The correlation is highest (0.81, 10a) with AEmax and slightly smaller with Kpmax (0.73, 10b) and SymHMin (0.72, 10c).\\u003c/p\\u003e\\n \\u003ch2\\u003eForecasting\\u003c/h2\\u003e\\n \\u003cp\\u003eSeveral physics-based and empirical models including machine learning techniques and driven by solar wind data have been developed for 10\\u0026ndash;30 minutes forecasting of local dH/dt (rate of change of horizontal geomagnetic field) during geomagnetic storms (e.g., Gleisner and Lundstedt, \\u003cspan class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2011\\u003c/span\\u003e; Wintoft et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2015\\u003c/span\\u003e; Zhang et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Camporeale et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2020\\u003c/span\\u003e; Grawe et al. 2021). The models have been developed for forecasting dH/dt than GIC for the linear relationship observed between dH/dt and GIC (Viljanen et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e, Wintoft \\u003cspan class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e), abundance of accurate H data and uncertainties involved in GIC. All models perform well through the progress of the storms though they do not fully capture the response around SSC (e.g., Pulkkinen et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2013\\u003c/span\\u003e; Smith et al. \\u003cspan class=\\\"CitationRef\\\"\\u003e2021\\u003c/span\\u003e). The present study has revealed that the largest GICmax measured at a single station, largest -(V\\u0026times;Bz) measured using the ACE satellite at the L1 point giving\\u0026thinsp;~\\u0026thinsp;60\\u0026thinsp;\\u0026minus;\\u0026thinsp;15 minutes forecast time for the solar wind speed of 400\\u0026ndash;1600 km/s, and power outages happened at widely separated places all occurred at the same UT time. This result indicates that the capability of the models for forecasting dH/dt directly related to GIC will be improved when the combination V\\u0026times;Bz is used together with V and Bz in the model.\\u003c/p\\u003e\\n \\u003c/div\\u003e\\n\\u003c/div\\u003e\"},{\"header\":\"4. Discussion\",\"content\":\"\\u003cp\\u003eAs introduced in section \\u003cspan refid=\\\"Sec1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e, the association of GIC with local time and season, solar and geomagnetic activities, substorms and electrojets, and solar wind and IMF have been known thanks to the works of several scientific groups (e.g., Viljanen et al. \\u003cspan citationid=\\\"CR62\\\" class=\\\"CitationRef\\\"\\u003e2010\\u003c/span\\u003e; Borovsky and Denton, \\u003cspan citationid=\\\"CR17\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e; Huttunen at al. 2008; Dimmock et al. \\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Tsurutani and Hajra \\u003cspan citationid=\\\"CR59\\\" class=\\\"CitationRef\\\"\\u003e2021\\u003c/span\\u003e; Hajra, \\u003cspan citationid=\\\"CR36\\\" class=\\\"CitationRef\\\"\\u003e2022a\\u003c/span\\u003e). However, what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms, which during extreme storms can cause sudden damage of vulnerable utility systems, was not known. In this paper, we have addressed this important question using 21 years (1999\\u0026ndash;2019) of the GIC data measured in Finland (Pulkkinen et al. \\u003cspan citationid=\\\"CR52\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e; Viljanen et al. \\u003cspan citationid=\\\"CR61\\\" class=\\\"CitationRef\\\"\\u003e2006\\u003c/span\\u003e). We have investigated the relationship of the largest GIC events (largest GICmax\\u0026thinsp;\\u0026ge;\\u0026thinsp;5A and duration\\u0026thinsp;\\u0026ge;\\u0026thinsp;1 minute at the 2A level) occurred during 106 geomagnetic storms (DstMin \\u0026le;-50 nT) in the 21-year period (1999\\u0026ndash;2019) with the intensity of the geomagnetic activities at low, mid and high latitudes (SymHMin, Kpmax and AEmax) and solar wind velocity V, dynamic pressure P and IMF Bz, and the product V\\u0026times;Bz.\\u003c/p\\u003e \\u003cp\\u003eUnlike earlier studies, (1) the present study has identified a specific solar wind-IMF combination -(V\\u0026times;Bz) which should have the best relationship with the largest GIC during the geomagnetic storms in all seasons and solar activity levels. (2) The largest GIC (\\u0026gt;\\u0026thinsp;10A) occurs at the time of the largest negative value of (V\\u0026times;Bz) with its time determined by the time of largest -Bz and magnitude determined by both -Bz and V, except in one case; in this case the largest GICmax occurred at the impact of the ICME front when IMF Bz was largely negative and largest -(V\\u0026times;Bz) occurred about 1.3 hours later when -Bz became largest. (3) The two power outages happened in the 21-year period of the study (Marshall et al. \\u003cspan citationid=\\\"CR47\\\" class=\\\"CitationRef\\\"\\u003e2012\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan citationid=\\\"CR53\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e) also occurred at the time of the respective largest GICmax. (4) The largest GICmax also has the highest correlation (0.92) with the combination -(V\\u0026times;Bz). (5) The GIC activity corresponding to the largest GICmax (\\u0026gt;\\u0026thinsp;10A) begins with the impact of the ICME front.\\u003c/p\\u003e \\u003cp\\u003eThe physical mechanism of the largest GIC activity occurring at the time of the largest -(V\\u0026times;Bz) probably begins with continuous and rapid magnetic reconnection between the large Bz southward immersed in a fast ICME (large V) and Earth\\u0026rsquo;s northward magnetic field (e.g., Dungey, \\u003cspan citationid=\\\"CR30\\\" class=\\\"CitationRef\\\"\\u003e1961\\u003c/span\\u003e; Akasofu, 1981; Borovsky et al. \\u003cspan citationid=\\\"CR18\\\" class=\\\"CitationRef\\\"\\u003e2008\\u003c/span\\u003e). The Bz southward opens the dayside magnetopause and the high V provides the force for the entry of a large number of high-energy charged particles into the magnetosphere and ring current. This causes large magnetospheric currents and auroral electrojet currents (Boteler and Beek, \\u003cspan citationid=\\\"CR19\\\" class=\\\"CitationRef\\\"\\u003e1999\\u003c/span\\u003e) producing large geomagnetic field fluctuations leading to geomagnetic activities (e.g., Gonzalez et al. \\u003cspan citationid=\\\"CR33\\\" class=\\\"CitationRef\\\"\\u003e1994\\u003c/span\\u003e), and the large field fluctuations reaching down the Earth inducing large GIC (Viljanen et al. \\u003cspan citationid=\\\"CR62\\\" class=\\\"CitationRef\\\"\\u003e2010\\u003c/span\\u003e). The processes seem to become most impulsive when the ICME has large front velocity ΔV (and large V) and large IMF Bz southward at the front (Balan et al. \\u003cspan citationid=\\\"CR7\\\" class=\\\"CitationRef\\\"\\u003e2014\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR9\\\" class=\\\"CitationRef\\\"\\u003e2017b\\u003c/span\\u003e). The most impulsive action generates the largest GIC at the locations and times of large ionospheric and ground conductivities. Under such conditions, the vulnerable utility systems such as electric power grids, telecommunication networks, etc. get damaged (Albertson and Thorson, \\u003cspan citationid=\\\"CR1\\\" class=\\\"CitationRef\\\"\\u003e1974\\u003c/span\\u003e; Kappenman, \\u003cspan citationid=\\\"CR41\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e; Pulkkinen et al. \\u003cspan citationid=\\\"CR53\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e; Wik et al. \\u003cspan citationid=\\\"CR68\\\" class=\\\"CitationRef\\\"\\u003e2009\\u003c/span\\u003e; Marshall et al. \\u003cspan citationid=\\\"CR47\\\" class=\\\"CitationRef\\\"\\u003e2012\\u003c/span\\u003e; Boteler, \\u003cspan citationid=\\\"CR20\\\" class=\\\"CitationRef\\\"\\u003e2001\\u003c/span\\u003e, \\u003cspan citationid=\\\"CR21\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Balan et al. \\u003cspan citationid=\\\"CR10\\\" class=\\\"CitationRef\\\"\\u003e2019a\\u003c/span\\u003e,\\u003cspan citationid=\\\"CR11\\\" class=\\\"CitationRef\\\"\\u003eb\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003eThe results have also shown a striking preference for the large GIC activity to occur most frequent during the SSC-MP of the geomagnetic storms at September equinox especially during the declining phase of solar cycle 23 (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e) as reported before (e.g., Tsurutani et al. 2021). The preference during the SSC-MP of the storms was shown related to the passage of the turbulent sheath region of ICMEs possibly due to their capacity to drive substorms and electrojets (Huttunen at al. 2008; Dimmock et al. \\u003cspan citationid=\\\"CR29\\\" class=\\\"CitationRef\\\"\\u003e2019\\u003c/span\\u003e; Tsurutani et al. 2021). This preference at September equinox especially during the declining phase of large solar cycles could, for some reason, be due to the frequent occurrence of fast ICMEs with large IMF Bz negative during this season at this phase of solar cycles (e.g., Gopalswamy et al. \\u003cspan citationid=\\\"CR34\\\" class=\\\"CitationRef\\\"\\u003e2005\\u003c/span\\u003e). It seems interesting to refer earlier related studies. In a study of the annual variation of the geomagnetic activity during 1995\\u0026ndash;2017 (SC23-24), Lockwood et al. (\\u003cspan citationid=\\\"CR46\\\" class=\\\"CitationRef\\\"\\u003e2020\\u003c/span\\u003e) found a much stronger activity peak at September equinox than March equinox. The ionosphere and thermosphere during the solar cycle prior to 1995 also showed large asymmetry between the two equinoxes (Aruliah at al. 1996; Balan et al. \\u003cspan citationid=\\\"CR6\\\" class=\\\"CitationRef\\\"\\u003e1998\\u003c/span\\u003e).\\u003c/p\\u003e\"},{\"header\":\"Conclusions\",\"content\":\"\\u003cp\\u003eIn this paper, we have addressed what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms, which during extreme storms can cause sudden damage of vulnerable utility systems. We have used the GIC data measured for 21 years (1999\\u0026ndash;2019) in Finland, solar wind and IMF data measured by the ACE satellite and geomagnetic activity data from Kyoto University websites. The results reveal that the GIC activity (\\u0026gt;\\u0026thinsp;2A) corresponding to the largest GIC greater than about 10A during all geomagnetic storms begins with the impact of the ICME front and attains largest amplitude at the time of the largest combination of the solar wind velocity V and IMF Bz southward (or at the time of largest -(V\\u0026times;Bz)) in all seasons and solar activity levels except during one storm. The two power outages happened on 06 November 2001 in New Zealand and 30 October 2003 in Sweden also occurred at the UT time of the respective largest GICmax highlighting the importance of the single station GIC measurements. The results also indicate the possibility of improving the forecasting of dH/dt directly related to GIC by including the combination V\\u0026times;Bz in the forecast models together with V and Bz.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eAuthors\\u0026rsquo; contributions\\u003c/strong\\u003e: NB initiated the study and prepared the paper. WBL developed the computer program and did the data analysis. RS provided the 32-minute resolution ACE data. RS, MV, ZYX, LKL and QHZ are involved in the discussions and preparation of the paper. All authors read and approved the final manuscript.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eAcknowledgements\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eWe thank Professor\\u0026nbsp;Ari Viljanenfor the helpful discussions.\\u0026nbsp;This study is supported by the National Natural Science Foundation (Grants 42120104003,41904169 and 41874170) and the Stable-Support Scientific Project of China Research Institute of Radiowave Propagation (Grant No. A132101W02).\\u0026nbsp;Work at Los Alamos was performed under the auspices of the U.S. Department of Energy with support from the NASA-ACE program. The\\u0026nbsp;GIC recordings are maintained by the Finnish Meteorological Institute in collaboration with Gasum Oy.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eCompeting interests:\\u003c/strong\\u003e The authors declare that they have no competing interests.\\u0026nbsp;\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFunding:\\u003c/strong\\u003e N Balan thanks ISS of Shandong University (China) for a distinguished professor position.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003ePublisher\\u0026rsquo;s Note:\\u0026nbsp;\\u003c/strong\\u003eSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eOpen Research \\u0026amp; Data Availability Statement\\u003c/strong\\u003e\\u003c/p\\u003e\\n\\u003cp\\u003eWe thank the IMAGE (International Monitor for Auroral Geomagnetic Effects) team for the GIC data available at http://space.fmi.fi/gic/man_ascii/, magnetic field data available at https://space.fmi.fi/image/www/index.php?page=monthly, ACE team for the solar wind and IMF data available at http://www.srl.caltech.edu/ACE/ASC/, and Kyoto University team for the Dst, SymH, Kp, and AE indices available at http://wdc.kugi.kyoto-u.ac.jp/dstdir/, http://wdc.kugi.kyoto-u.ac.jp/aeasy/index.html, http://wdc.kugi.kyoto-u.ac.jp/kp/index.html and http://wdc.kugi.kyoto-u.ac.jp/aedir/, respectively.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003eAlbertson VD, Thorson JM (1974) Power system disturbances during a K-8 geomagnetic storm. August 4, 1972, \\u003cem\\u003eIEEE Trans. Power App. \\u0026amp; Sys.\\u003c/em\\u003ePAS-93: 1025\\u003c/li\\u003e\\n\\u003cli\\u003eAkasofu S.-I Aspnes JD (1982) Auroral effects on power transmission line systems. Nature 295: 136. https://doi.org/10.1038/295136a0\\u003c/li\\u003e\\n\\u003cli\\u003eAruliah AL, Farmer AD, Fuller-Rowell TJ, Wild MN, Hapgood M, Rees D (1996) An equinoctial asymmerry in the high-latitude thermosphere and ionosphere. J. Geophys. Res 101: 15,713\\u003c/li\\u003e\\n\\u003cli\\u003eBaker DN (2002) How to cope with space weather. Science 297: 1486, doi:10.1126/science.1074956\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, Otsuka Y, Bailey, GJ, Fukao S (1998) Equinoctial asymmetries in the ionosphere and thermosphere observed by the MU radar. J. Geophys. Res. 103:NO. A5, 9481\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, Skoug R, TulasiRam S, Rajesh P, Shiokawa K, Otsuka Y, Batista IS, Ebihara Y, Nakamura T (2014) CME front and severe space weather. J. Geophys. Res.Space Physics 119:\\u003cem\\u003e doi:10.1002/2014\\u003c/em\\u003eJA020151\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, TulasiRam S, Kamide Y, Batista IS, Souza JR, Shiokawa K, Rajesh PK, Victor NJ (2017a) Automatic selection of Dst storms and their seasonal variations in two versions of Dst in 50 years. Earth, Planet and Space 69: 59, doi10.1186/s40623-017-0642-2\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, Ebihara Y, Skoug R, Shiokawa K, Batista IS, TulasiRam S, Omura Y, Nakamura T, Fok M-C (2017b) A scheme for forecasting severe space weather. J. Geophys. Res. 122: doi:10.1002/2016JA023853\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, Zhang Q-H., Xing Z-Y, Skoug R, Shiokawa K, Lühr H, Tulasi Ram S, Otsuka Y (2019a) Capability of Geomagnetic Storm Parameters to Identify Severe Space Weather. Astrophysical Journal 887:51, doi.org/10.3847/1538-4357/ab5113, 2019\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, Zhang, Q-H, Shiokawa K, Skoug R, Xing Z, Tulasi Ram S, Otsuka Y (2019b) IpsDst of Dst storms applied to ionosphere‐thermosphere storms and low latitude aurora. J. Geophys. Res. 124:doi.org/10.1029/2019JA027080\\u003c/li\\u003e\\n\\u003cli\\u003eBalan N, Tulasi Ram S, Manu V, Lingxin Zhao, Zan-Yang Xing Qing-He Zhang (2021) Diurnal UT Variation of low Latitude Geomagnetic Storms Using six Indices. J. Geophys. Res. Space Physics 126: DOI: 10.1029/2020JA028854\\u003c/li\\u003e\\n\\u003cli\\u003eBarbosa C, Alves L, Caraballo R, Hartmann GA, Papa ARR, Pirjola RJ (2015) Analysis of geomagnetically induced currents at a low-latitude region over the solar cycles 23 and 24: comparison between measurements and calculations. J. 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Res., 112: A06205, doi:10.1029/2006JA012079, 2007\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"},{\"header\":\"Tables\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eTable 1:\\u003c/strong\\u003e Lists the dates and storm intensity (SymHMin) of the 14 cases of largest GICmax \\u0026gt;25A (with the number of GICmax \\u0026gt;25A in brackets), their time of occurrence (with the time of the power outages on 06 November 2001 and 30 October 2003 in brackets), and the corresponding largest -(V\\u0026times;Bz) in units of 10\\u003csup\\u003e3\\u0026nbsp;\\u003c/sup\\u003ekm/s nT and their time of occurrence. Time of start of GIC activity and time of impact of ICME front are also listed.\\u003c/p\\u003e\\n\\u003ctable border=\\\"1\\\" cellpadding=\\\"0\\\" cellspacing=\\\"0\\\" width=\\\"0\\\"\\u003e\\n \\u003ctbody\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"5.872756933115824%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003eNo.\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"13.866231647634583%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003eDate\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003eSymHMin\\u003c/p\\u003e\\n \\u003cp\\u003e(-nT)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003eLargest\\u003c/p\\u003e\\n \\u003cp\\u003eGICmax (A)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003eTime of largest GICmax\\u003c/p\\u003e\\n \\u003cp\\u003e(UT)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003eLargest \\u0026nbsp; \\u0026nbsp; \\u0026nbsp; -(V\\u0026times;Bz) (km/s nT)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003eTime of largest\\u003c/p\\u003e\\n \\u003cp\\u003e-(V\\u0026times;Bz)\\u003c/p\\u003e\\n \\u003cp\\u003e(UT)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003eTime of start of GIC\\u003c/p\\u003e\\n \\u003cp\\u003e(UT)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003eTime of impact of ICME\\u003c/p\\u003e\\n \\u003cp\\u003e(UT)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"5.872756933115824%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e1\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"13.866231647634583%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e15-07-2000\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e347\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e30.34 (1)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e20:01:50\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e-59.86\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e20:01:00\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e14:39:40\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e14:40:15\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"5.872756933115824%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e2\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"13.866231647634583%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e06-11-2001\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e320\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e31.63 (2)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e01.53:30\\u003c/p\\u003e\\n \\u003cp\\u003e(01:52)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e55.28\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e\\u003cem\\u003e03:14:55\\u003c/em\\u003e\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e01:53:30\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e01:58:08\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003c/tr\\u003e\\n \\u003ctr\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"5.872756933115824%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e3\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"13.866231647634583%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e24-11-2001\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e234\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e31.97 (2)\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e07:14:30\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"12.398042414355627%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e-31.26\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e07:18:13\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd valign=\\\"top\\\" width=\\\"10.766721044045678%\\\"\\u003e\\n \\u003cp\\u003e\\u0026nbsp;\\u003c/p\\u003e\\n \\u003cp\\u003e06:14:20\\u003c/p\\u003e\\n \\u003c/td\\u003e\\n \\u003ctd 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Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true},\"keywords\":\"Space weather, geomagnetically induced current (GIC), geomagnetic storms, solar wind and IMF\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-1980192/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-1980192/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003eThe association of GIC (geomagnetically induced current) with various solar and geophysical conditions has been known. However, what determines the time of occurrence and amplitude of the largest GIC during geomagnetic storms, which during extreme storms can cause sudden damage of vulnerable utility systems, is not yet known. We address this important question by analyzing the GIC data measured in Finland for 21 years (1999\\u0026ndash;2019) during 106 geomagnetic activities (DstMin \\u0026le;-50 nT) at low, mid and high latitudes and the corresponding solar wind velocity V, dynamic pressure P, north-south component of interplanetary magnetic field (IMF Bz), and the products V\\u0026times;Bz and P\\u0026times;Bz. The results show for the first time that the largest GIC (\\u0026ge;\\u0026thinsp;10 A) occurs at the time of the largest -(V\\u0026times;Bz) in all seasons and solar activity levels with its time determined by the time of the largest -Bz and magnitude determined by both V and -Bz, except in one case. The two power outages happened in the 21-year period (06 November 2001 and 30 October 2003) also occurred at the UT time of the largest GICmax. The correlation of largest GICmax is also highest (0.92) with the largest -(V\\u0026times;Bz) at September equinox. The results highlight the importance of the single station GIC measurements and possibility of improving the forecasting of the rate of change of the local horizontal geomagnetic field (dH/dt) directly related to GIC.\\u003c/p\\u003e\",\"manuscriptTitle\":\"Relationship of the largest GIC during geomagnetic storms with solar wind-IMF parameters\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2022-09-21 18:16:51\",\"doi\":\"10.21203/rs.3.rs-1980192/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"researchsquare\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":true,\"externalIdentity\":\"\",\"sideBox\":\"\",\"snPcode\":\"\",\"submissionUrl\":\"/submission\",\"title\":\"Research Square\",\"twitterHandle\":\"researchsquare\",\"acdcEnabled\":true,\"dfaEnabled\":false,\"editorialSystem\":\"\",\"reportingPortfolio\":\"\",\"inReviewEnabled\":false,\"inReviewRevisionsEnabled\":true}}],\"origin\":\"\",\"ownerIdentity\":\"4f1aece7-6e8d-42e2-967f-bc9819274e8c\",\"owner\":[],\"postedDate\":\"September 21st, 2022\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"posted\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2022-10-24T22:20:11+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2022-09-21 18:16:51\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-1980192\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-1980192\",\"identity\":\"rs-1980192\",\"version\":[\"v1\"]},\"buildId\":\"cBFmMYwuxLRRLfASyISRj\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}