Relating 27-day Averages of Solar, Interplanetary Medium Parameters and Geomagnetic Activity Proxies in Solar Cycle 24

Abstract Correlations between solar, interplanetary medium parameters and geomagnetic activity proxies in 27-day averages (a Bartels’ rotation) were analysed for the 2009-2016 time interval. In this analysis, two new proxies were considered: 1) B ZS GSM, calculated as the daily percentage of the IMF southward component along the GSM Z-axis and then averaged every 27 days; 2) four magnetospheric indices (T-indices), calculated from the local North-South (X) contributions of the magnetosphere's cross-tail (TAIL), the symmetric ring current (SRC), the partial ring current (PRC) and the Birkeland current (FAC), derived from Tsyganenko and Sitnov 2005 (TS05) semi-empirical magnetospheric model. Our results suggest that, among the parameters tested in this study, solar facular areas, interplanetary magnetic field intensity and new proxies derived from TS05 model could be taken into account in an empirical model, with a 27-day resolution, to explain geomagnetic activity felt on the Earth's surface in terms of solar surface features and the IMF condition. We further retrieve a clear annual oscillation in series of 27-day-mean values of toward/away asymmetries of geomagnetic activity indices, which can be interpreted in the light of Russell-McPherron hypothesis for the semiannual variation of geomagnetic activity.