Squall line in the Balearics producing extreme wind and meteotsunamis

Squall line in the Balearics producing extreme wind and meteotsunamis | 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 Squall line in the Balearics producing extreme wind and meteotsunamis Agusti Jansa, Joan Campins, Diego Carrio, Catalina Estarellas, and 6 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6655205/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 18 Mar, 2026 Read the published version in Natural Hazards → Version 1 posted 4 You are reading this latest preprint version Abstract On 22 January 2021, an active squall line embedded within cyclone Hortense swept across the Balearic Islands, significantly impacting Mallorca and Menorca. The event was characterized by extreme wind gusts, including a 130 km h-1 peak at Palma airport, an intensity breaking the 50-year record. Consequently, the squall line induced an outstanding long-lived pressure perturbation, which triggered moderate meteotsunami activity across several harbours and coastal inlets. Notably, a sea-level oscillation of 60 cm was recorded in the Port of Ciutadella (Menorca). The main objective of this paper is to investigate the coupled atmospheric and oceanic dynamics underlying a squall line event that produced extreme winds and meteotsunami activity, focusing on the role of an associated atmospheric pressure surge. In particular, we provide a comprehensive observational description of the combined event -squall and associated meteotsunamis- using land-based meteorological and oceanographic data, remote-sensing imagery, and ERA5 reanalysis products. Furthermore, the predictability of the event’s key dynamical features, including wind extremes and meteotsunami generation, is assessed through high-resolution atmospheric and oceanic numerical simulations. These findings highlight a rarely documented mechanism of compound atmospheric-oceanic hazard in the Mediterranean and underscore the critical need for improved mesoscale forecasting capabilities to support coastal risk mitigation strategies meteotsunamis convection squall line extreme w Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction According to the NOAA’s glossary of meteorology (NOAA, 2025), a squall line is “a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms”. The glossary of meteorology of the American Meteorological Society (AMS, 2025) specifies that a squall line as “a line of deep moist convection frequently associated with thunder, either continuous or with breaks, including contiguous precipitation areas. The squall line is a type of mesoscale convective system distinguished from other types by a larger length-to-width ratio”: Of course, the passage of squall line supposes strong wind gusts. In addition, it is widely accepted that a squall line is also usually accompanied by an atmospheric pressure surge or jump (Fujita, 1955, Mahoney III, 1988, Przybylinski, 1995, Adams-Selin and Johnson, 2010). At its turn, a rapid change in atmospheric pressure can affect the marine sea level. Atmospherically induced sea-level oscillations –commonly referred to as meteotsunamis– are long ocean wave generated by air-sea interactions, typically occurring at periods similar to seismic tsunamis. While they may not reach the catastrophic heights of extreme tectonic tsunamis, meteotsunamis can nonetheless cause significant coastal damage and pose risks to port infrastructure, vessels, and local communities. These phenomena are often under-recognized in coastal hazard frameworks, despite their frequent occurrence in several regions across the world, including Japan, the Adriatic Sea, or the Western Mediterranean (Hibiya and Kajiura, 1982, Šepić et al, 2012, Ramis and Jansà, 1983, Jansà and Ramis, 2021). Because of the widespread occurrence, meteotsunamis are known by different local names around the world (Monserrat et al, 2006). Within the Mediterranean region, the Balearic Islands -especially the Port of Ciutadella in Menorca- represent one of the most active meteotsunami hotspots worldwide (Fig. 1). This is due to a confluence of geographical and meteorological factors: complex topography, the presence of narrow harbours, and a regional predisposition to pressure disturbances capable of exciting long-period marine waves. Locally known as “rissaga”, these events have historically caused substantial damage and disruption, and have therefore become the subject of sustained research efforts (Ramis and Jansà, 1983, Jansà, 1986, Jansà et al, 2007, Jansà and Ramis, 2021, Villalonga et al, 2024). Unlike seismic tsunamis, which are generated by seabed displacements, meteotsunamis are triggered by atmospheric disturbances. In the Balearics, these include rapid atmospheric pressure changes, generated by internal atmospheric gravity waves or pressure jumps or surges (including squall lines) associated to convection ( Ramis and Jansà, 1983, Jansà, 1986, Jansà et al, 2007, Jansà and Ramis, 2021). Frontal passages and even hurricanes can also generate meteotsunamis (Vilibić et al., 2021). A fundamental mechanism underlying meteotsunami formation is the marine inverse barometer effect, where a change in atmospheric pressure induces a proportional adjustment in sea level in the form of long marine waves. In open waters, this relationship typically yields a 1 cm sea-level drop per 1 hPa increase in pressure. The magnitude of typical rapid pressure changes is about a few hPa, therefore changes of sea level may appear minor in deep water, although in exceptional cases, changes in pressure up to 7 hPa within a few minutes have also been recorded (Jansà et al, 2007). Even with such changes, to have sea-level oscillations large enough to produce significant impact in coasts and ports the long marine waves have to be dramatically amplified. For a meteotsunami to occur, three key amplification processes must typically be met: (1) Proudman resonance (Proudman, 1929), where the speed of the atmospheric disturbance matches that of the oceanic long wave; (2) shoaling, which enhances wave amplitude as the wave enters shallower regions; and (3) resonance within coastal basins, such as harbours, bays, or inlets (Monserrat et al, 2006). These mechanisms often act in combination to transform weak open-sea signals into impactful coastal sea-level oscillations. In this context, the event that affected the Balearic Islands on 22 January 2021 stands out as a well-documented case of a convectively driven meteotsunami, accompanied by hazardous winds. While not unprecedented, the event was nonetheless singular due to the combination of intense surface winds, a sharply defined atmospheric pressure surge, and the generation of moderate meteotsunamis in various ports and inlets across the islands. The phenomenon took place as a cold front associated with Storm Hortense moved through. A squall line formed within this front, crossed the eastern half of the Iberian Peninsula and reached the Balearic Islands. A pressure perturbation, reaching amplitudes of 3-4 hPa, was observed in the Balearics. This pressure change excited sea-level oscillations with final amplitudes that reached 60 cm in the Port of Ciutadella (Menorca), which is historically prone to resonant amplification. Simultaneously, the squall line produced intense convective rainfall and damaging wind gusts, peaking at 130 km h-1 at Palma Airport, thereby setting a new 50-year record for this long-term observing site. The multi-hazard event was extensively captured by a dense network of meteorological and oceanographic instruments across the Balearic Islands. These include conventional surface stations operated by the Spanish State Meteorological Agency (AEMET), the Balearic Islands Coastal Observing and Forecasting System (SOCIB), Balearsmeteo (a quality-controlled amateur network), the Balearic Islands Ports Agency (Ports-IB) and Puertos del Estado (PE). Complementary observations were also obtained from the AEMET weather radar in Mallorca and lighting network, as well as from satellite platforms, enabling a detailed reconstruction of the atmospheric dynamics involved. Some key geographic locations referenced throughout the study are indicated in Fig. 1. From a meteorological perspective, the event’s signature was both severe and unusual. The spatial and temporal coherence of the pressure surge, coupled with intense wind gusts, marks this squall line as an effective driver of coastal sea-level disturbances. This case underscores the potential of organized convective systems to generate complex, compound hazards in the Mediterranean coastal region. This study aims to provide an in-depth investigation of the coupled atmospheric-oceanic processes underlying the 22 January 2021 event. Specifically, we analyse the evolution of the squall line and the associated pressure perturbation, and their role in producing both extreme wind and meteotsunami activity. Observational data are complemented by analyses and high-resolution numerical simulations, allowing us to assess the event’s predictability. The paper is structured as follows. Section 2 examines the synoptic-scale meteorological conditions that lead to the development of the squall line. Section 3 provides a mesoscale diagnosis of the squall line event. Section 4 focuses on the observed sea-level response and the resonant mechanisms involved in meteotsunami amplification. Section 5 presents the results of atmospheric and oceanic numerical simulations, emphasizing the predictability of key processes. Finally, Section 6 summarizes the main conclusions and implications of the present study. 2. Overview of the synoptic meteorological conditions leading to the 22 January 2021 multi-hazard event On 22 January 2021, the synoptic situation over the Iberian Peninsula and the Western Mediterranean region was dominated by the presence of an intense cyclone, moving from west to east. This cyclone was officially named Hortense by the Spanish Meterorological Agency (AEMET, 2022), due to its potential for high-impact weather. A high resolution satellite image (Fig. 2) shows the cloud structure associated with Hortense, with its centre located south of France. Notably, a well-organized cluster of thunderstorms is visible approaching the Balearic Islands from the west, marking the leading edge of the squall line analysed in this study. At the synoptic scale, Hortense developed as a secondary cyclone within a larger extratropical system centered over Northern Europe. This parent system, officially named Christoph, was located over Scandinavia on 22 January and played a key role in shaping the downstream meteorological evolution. The process of secondary cyclogenesis, where a smaller cyclone forms along the frontal boundaries of a dominant low-pressure system, is a well-established mechanism in synoptic meteorology (Bjerkness & Solberg, 1922), and is particularly relevant in the Mediterranean basin. In this case, Hortense evolved along the southern flank of Christoph, deepening rapidly as it moved eastward across the Iberian Peninsula. The synoptic configuration and the position of the cyclone are illustrated in Fig. 3. While AEMET meteorologists identified a classical frontal system associated with Hortense, additional details emerge from ERA5 reanalysis (Hersbach et al, 2020), high-resolution numerical simulations and satellite imagery. Fig. 4 (left and centre) shows ERA5-derived 10 m wind fields and mean sea level pressure (MSLP) maps at 09 UTC (left) and 11 UTC (centre), respectively, on 22 of January. During this period, a significant wind shifts from south-south-westerly to westerly occurred over the Western Mediterranean. This change, first observed over the Iberian Peninsula, corresponds to a marked surface convergence line, interpreted as the leading edge of a low level cold front. High-resolution numerical weather models, such as TRAM (Romero, 2024), capture this convergence line with greater clarity than ERA5 (Fig. 4, right). According to both ERA5 and TRAM outputs, maximum wind gusts over open waters on either side of the convergence line, reached 90-100 km h-1. Fig. 5 shows the vertical atmospheric stability, through the CAPE distribution, as well as the equivalent potential temperature distribution at 850 hPa, which can be an indicator of a low level front. The convergence line identified in Figure 4 corresponds to a band of moderate, though not extreme, CAPE values, indicative of a conditionally unstable environment. In addition, the low-level temperature distribution of equivalent potential temperature exhibits a sharp horizontal gradient, reinforcing the interpretation of the convergence line acting as a low-level front (Fig. 5, right). As this feature propagates eastward, the combination of low-level convergence, moderate convective instability and frontal upward forcing provides sufficient upward motion to generate deep convection along the convergence-frontal band. The observed thermodynamics and dynamic conditions are consistent with lightning activity recorded during the event, which confirms the presence and evolution of an organized convective line (Fig. 6). This line of thunderstorms extended over a broad region, from the foothills of the Pyrenees to the southern Balearic Islands, highlighting the extent of the convective structure. Although the convection appears as a quasi-continuous band, the lightning map reveals the presence of several distinct convective nuclei. Four main clusters of lightning strikes are evident, with the southernmost cell corresponding to the thunderstorm in which a severe squall line developed, ultimately sweeping across Mallorca and Menorca. The water vapour satellite image (Fig. 7) reveals that, as the line of active convection approaches the Balearics, a moist upper-level band is located to the east of the archipelago. In the classical framework introduced by Browning (1997), such a moist band, interpreted as an upper-level front, marks the leading edge of the warm conveyor belt, a stream of ascending warm air that becomes increasingly saturated with height, leading to condensation and cloud development. To the west of this upper-level structure lies a distinctly drier region, evident as a dark band over the Balearic Islands. This area corresponds to a descending intrusion of cold dry air from the upper levels, consistent with the dry intrusion concept also described by Browning (1997). Such intrusions can, under certain conditions, enhance convective intensity and organization by increasing static instability, particularly when they interact with surface-base lifting mechanisms. A further dynamic element is inferred from a small dry patch over the north-eastern Iberian Peninsula and a thin band of cirrus clouds extending toward the southern Balearics (Fig. 7 and Fig. 2): these features indicate the presence of a jet streak approximately oriented perpendicularly to the frontal upper level and low-level frontal bands. According to Uccellini and Johnson (1979), the left-exit region of a jet streak is typically associated with enhanced upper-level divergence and upward motion, providing an additional forcing for deep convection. While the role of jet-induced forcing in convective organization can vary between cases, the spatial overlap between the jet exit region and the convective system in this event suggests a contributing influence. The observed convective line (Fig. 6) developed within the region influenced by this dry intrusion. Although large-scale subsidence generally inhibits deep convection, in this case the combination of low-level convergence, conditional instability, and frontal lifting provided sufficient mesoscale forcing to initiate and sustain deep convective development, as already commented. In parallel with the upper-level structures discussed in Fig. 7, lightning observations (Fig. 6) offer further insight into the evolution of the convective structures. The figures show that a convective line, which initially developed over the Iberian Peninsula, underwent continuous reactivation as it advanced eastward across the Western Mediterranean. Several discrete convective nuclei are identifiable along the main line, although radar imagery occasionally depicts it as a quasi-continuous band of high reflectivity. In the following section, we will pay special attention to the southernmost convective nucleus, which is also the most intense and organized one. This convective nucleus also hosted the development of a severe squall line, which ultimately swept across Mallorca and Menorca, producing both extreme surface winds and a pronounced atmospheric pressure disturbance that triggered sea-level oscillations. 3. Structure and evolution of the 22 January 2021 squall line The AEMET weather radar located in the south of Mallorca (Fig. 1) provides detailed observations of the evolution of the main line of thunderstorms, as it approached and traversed Mallorca and Menorca. Fig. 8 presents a sample of radar reflectivity images taken at 30-minute intervals (09:10, 09:40, 10:10, 10:40, 11:10 and 11:40 UTC, respectively). Higher-frequency data, recorded every 10 minutes, are also available but are not shown here. Among the convective cells along the line, the southernmost convective nucleus, active since approximately 08:00 UTC, became the most intense and well-organized. This convective nucleus includes the formation of the squall line that impacted Mallorca and Menorca. At 09:10 UTC, radar imagery shows a continuous band of high reflectivity approaching Mallorca (Fig. 8a). As the system evolves, the northern portions become more fragmented, while the southern segment remains compact. By 09:40 UTC, this southern nucleus makes landfall in Mallorca, by Andratx (Fig. 8b). The leading edge of the convective nucleus forms a well-defined, straight squall line, which soon begins to exhibit bowing characteristics. At 10:10 UTC, when the nucleus is almost arriving at the airport of Palma, the bow-shaped radar echo is clearly evident (Fig. 8c). Such bowing is commonly associated with severe convective activity, including intense downburst and damaging surface winds (Przybylinski, 1995). As the system progresses toward Porto Cristo, it becomes less organized, although the linear squall line structure remains discernible (Fig. 8 d-f). Beyond radar data, surface wind observations across the Balearic Islands (Fig. 1; Table 1) also confirm the passage of a squall line. A sequential pattern of strong wind gusts was recorded at multiple stations across Mallorca and Menorca. Table 1. Approximate chronology and magnitude of the maximum gusts, pressure surge and height of sea level oscillations registered in some locations of the Balearic Islands Location Gust (Km/h) Pressure surge (hPa) Sea level oscillations height (cm) Time (ECT) Andratx (Mallorca) 64 4,0 --- 11:10 Calvià (Mallorca) 94 11:10 Estellencs (Mallorca) 86 4,2 --- 11:10 Palma, port (Mallorca) 111 --- 33 11:20 Palma, airport (Mallorca) 130 2,8 --- 11:20 Binissalem (Mallorca) 103 --- --- 11:30 Sa Ràpita (Mallorca) 122 2,4 30 11:40 Campos Salines (Mallorca) 105 11:40 Manacor (Mallorca) 97 11:40 Portocolom (Mallorca) 93 -- -- 11:50 Porto Cristo (Mallorca) --- 2,2 25 12:00 Port de Pollença (Mallorca) 89 2,2 --- 11:40 Port de Ciutadella (Menorca) 88 3,2 60 12:10 Es Mercadal (Menorca) 122 --- --- 12:20 Airport of Menorca 111 1,9 --- 12:20 Sources: AEMET, SOCIB, Balearsmeteo and Ports IB According to Table 1, 7 of 14 surface stations registered wind gusts exceeding 100 km/h (28 m/s). Stations at mountainous tops recorded wind gusts even stronger than those listed in Table 1. The record-setting gusts observed at Palma Airport can be attributed to the combination of strong general winds of synoptic scale (associated to the intense cyclone Hortense) and to a convective outflow, generated by the thunderstorms downdrafts. Looking at Fig. 9, the wind peak appears as an almost instantaneous gust, although the winds before and behind the peak are quite strong. Before the wind peak, the sustained winds are about 50 km/h, with gusts up to 70 km/h. Behind it, the winds are stronger, with sustained speeds of 60-70 km /h and gust up to 80-90 km/h. These observations suggest that the extreme wind gust at Palma Airport was partially convective in origin. Approximately half of the total wind speed can be attributed to the squall-line-associated convective downdrafts, while the remaining contribution reflects the strong synoptic flow driven by cyclone Hortense. Note that the wind-record at the airport of Palma is significant, since it refers to a 50-year-long time series (1975-2025), according to AEMET (https://www.aemet.es/es/serviciosclimaticos/datosclimatologicos/efemerides_extremos*?w=0&k=bal&l=B278&datos=det&x=B278&m=13&v=VMX ). The passage of a squall line, in addition to producing strong wind gusts, is typically evident in the radar imagery as a narrow, high-reflectivity band, either straight or exhibiting a bow-shaped structure (see Fig. 8). This radar signature is usually associated with a well-defined convective nucleus. It is common for such systems to be accompanied by a pressure surge or abrupt pressure jump coinciding with the peak wind gusts. A classical conceptual model describing the relationship between wind, pressure, temperature and rainfall in convective systems can be found in Fujita (1955). Other references can be Mahoney III (1988), Johnson and Hamilton (1988), Przybylinski, (1995), Adams-Selin and Johnson (2010). The pressure surge associated with a squall line can consist in a rapid increase in surface pressure, followed by a sharp drop, a few minutes later. In some cases, this pattern is asymmetric and may even appear as a single abrupt jump rather than a symmetric surge. With regard to the squall line of 22 January 2021, it was accompanied by a relatively symmetric pressure signal. The magnitude of the pressure increases and subsequent drops recorded at various observation sites, which ranged from 1.9 to 4.2 hPa, are indicated in Table 1. The high temporal resolution from AEMET’s automatic weather stations enables a detailed analysis of the evolution of wind and/or pressure. Figure 9 shows 1-minute observations of the evolution of pressure and wind at the airport of Palma. The pressure peaks coincide closely with the arrival of the squall line and the associated wind gust. These findings support the interpretation of the event as convective structures capable of producing compound atmospheric hazards. The red lines in Fig. 10 show the shape and magnitude of the pressure surge changes, as observed at several locations in Ibiza, Mallorca and Menorca Islands on 22 January 2021. While the pressure jump is not detected in Ibiza, it is detected in all stations in Mallorca and Menorca, yet with differences in its shape and magnitude. The most abrupt changes were found in Andratx, Sa Rapita, Porto Cristo, Ciutadella and Mahon recording stations. 4. Generation and amplification of meteotsunamis on 22 January 2021 event According to the observations of SOCIB, Puertos del Estado -PE- and Ports IB, some of the sea level oscillations generated by the passage of the pressure surge associated with the squall line reached heights from 25 to 60 cm (see Table 1 and Fig. 10). These values suggest total amplification factors of approximately 10 to 20, relative to the initial open-water response. Among the amplification mechanisms, the Proudman resonance is particularly relevant in this case. It occurs when an atmospheric perturbation (pressure surge or pressure jump) advances coupled to its marine response, that is, in the same direction and at the same speed. According to the shallow water approach, the phase speed (c) of long marine waves depends only on the water depth (h) according to the relation ( c = ), where g is the gravitational acceleration When the speed of the pressure perturbation closely matches the propagation of the marine wave, then the Proudman amplification is possible. The combined analysis of the event chronology (Table 1) and radar imagery allows for an estimation of the propagation speed of the squall line (or of the pressure jump). The direction can be seen in Figure 11 left), and the estimated speed is approximately 100 km/h (25-30 m/s). Notably, the distance between Palma Airport and Menorca Airport is about 100 km, and the system passed over Palma roughly one hour before it reached the airport of Menorca, supporting the inferred propagation speed. Figure 11 (right) presents a bathymetric map in which the isobaths are labelled with the corresponding phase speed of long marine gravity waves. The pink-shaded area highlights the zone where the marine long-wave speed ranges from 80 to 100 km/h, condition favourable for the Proudman resonance. This region, located primarily in the Menorca Channel, is the only relatively extended area along the squall line path where the Proudman resonance condition is met. As a result, amplification due to this resonance is expected to be strongest at the Port of Ciutadella than in other ports or inlets. Although Proudman resonance is less effective outside this zone, some degree of amplification still occurs at other coastal locations, due to harbour/inlet/bay amplification and/or shoaling effect. The particular contribution of the Proudman resonance to the total amplification that occurs in the Menorca Chanel is a key mechanism of wave amplification that is important, not only in this event, but also in many other historical meteotsunami cases affecting Ciutadella (Ličer et al, 2017). This mechanism is a major factor behind Port of Ciutadella classification as global hotspot for meteotsunamis. 5. Predictability The meteorological models accurately forecasted the large scale meteorological pattern, including the intense Hortense cyclone in which the severe squall line developed. Looking to high resolution models and, particularly, to the forecasted maximum gusts, the results are still quite good, but not perfect. Fig. 12 shows maximum gusts forecasted by the high resolution model of the ECMWF. Apart from wind peaks at the mountains tops, the maximum gusts forecasted in the Balearic Sea are around 43-49 kts (80-90 km/h), with some areas with 49-54 kts, that is, 90-100 km/h. In a more restricted area, to the north of the Balearic Islands, the foreseen maximum gusts exceed 100 km/h. Nevertheless, the airport of Palma, representative of an extended area and located in flat terrain, is situated in the zone where the maximum gusts forecasted by the model are under 90 km/h. The model has well forecasted strong gusts, in the Balearic zone, even very strong gusts, probably combining general and convective wind, but has not foreseen the record wind at the airport of Palma: note that the area of maximum winds exceeding 100 km/h is to the north of the location where the squall line developed. Regarding the rissaga (local Balearic name for meteotsunami), in 1985, the Spanish meteorological service (AEMET, nowadays) was able to start an experimental service of rissaga warning. This service is, in principle, based on the meteorological identification of weather situations in which meteotsunamis have more probability to develop (Jansà and Ramis, 2021). That service, which still exists, is basically subjective, although at present the forecaster has the important aid of objective methods. The potential of using ocean models to predict sea-level oscillations from known atmospheric initial conditions was first explored by Vilibić et al. (2008). Building on this concept, a high-resolution modelling system integrating meteorological and oceanographic components demonstrated promising results in subsequent studies (Renault et al., 2011; Ličer et al., 2017; Mourre et al., 2021). The Balearic Islands Coastal Observing and Forecasting System (Tintoré et al., 2013) developed an operational forecasting system — BRIFS (Balearic Islands Regional Forecasting System) based on such high-resolution atmosphere and ocean models, to provide daily predictions of high-frequency sea level oscillations in Ciutadella harbour. The system is accessible at https://www.socib.es/en/what-we-do/ocean-forecasting/brifs. Additional objective approaches to meteotsunami forecasting and modelling have been developed by Šepić et al. (2016) and Romero et al. (2019), further contributing to the advancement of operational capabilities in this domain. Both, the model TRAM (Romero, 2024) and BRIFS models (the atmospheric component of BRIFS is produced by the WRF model with a 4km spatial resolution), are forecasting some kind of strong squall line or intense thunderstorm, but not in the correct zone. Fig. 10 compares the observed and BRIFS-forecasted atmospheric pressure anomaly evolution at several locations. While pressure jumps associated with the squall line were observed at several locations over Mallorca and Menorca Islands, no significant jump was predicted by the model at these locations. . Looking into more details, the model represented a squall line and the associated significant surface pressure changes but at a distance around 100km north of Menorca Island. Figure 10 shows the representation of a pressure jump of around 2hPa in the model prediction at the station 8 located in the open sea north of Menorca. The capacity to generate these small-scale atmospheric processes at the proper location is still an important challenge from the perspective of the prediction systems. Due to this spatial mismatch, Ciutadella harbour didn't feel the effects of this specific atmospheric pressure jump in the prediction and the BRIFS system significantly underestimated the magnitude of the sea level oscillations (37 cm in the prediction versus 60cm in the observations). The same kind of spatial offset was found in TRAM forecasts, where a strong pressure jump was produced to the north of the Balearic Islands, (see Fig. 13), leading similarly to an underestimation of the magnitude of the rissaga . To have rissaga prediction (according to the Romero et al, 2019 method), the pressure jump has to be moved to the zone where the squall line did exist. Indeed, when the rissaga -prediction system of Romero et al. (2019) is forced with the squall-line induced surface pressure signal, that is, as if the system shown in Fig. 13 to the north of the islands had been simulated about 100 km further south, a rissaga of fairly the correct magnitude (50-60 cm wave height) is obtained (Fig. 14). The above method is highly simplified and operates in 2D to save computing time, but it incorporates all essential atmospheric and oceanic physical components, namely: (i) the genesis upstream from the Balearic Islands of high amplitude atmospheric gravity waves - and concomitant sea level pressure signal- travelling in the SW–NE direction; for this convectively driven case we simply took this SLP signal from a 150 km-long cross section centred in the TRAM-simulated mature squall line; (ii) the oceanic response to the pressure fluctuations along the Menorca channel, in the form of long oceanic waves subject to Proudman resonance; these processes are simulated with a shallow-water model applied over a 80-m depth channel; (iii) shelf amplification, which accounts for a doubling of the wave amplitude for a depth jump; and (iv) harbour resonance within Ciutadella inlet, a crucial mechanism solved again with the shallow-water equations over an idealized 5-m deep channel. The marine response to mesoscale atmospheric pressure perturbations can be correctly forecasted only if the atmospheric disturbances are sufficiently realistically represented in terms of intensity and location. This kind of atmospheric disturbance are in principle predictable, with high-resolution convective solving models, as demonstrated by BRIFS and TRAM prediction systems. However, a certain degree of uncertainty inevitably affects the exact location of the generation of these small-scale disturbances. The use of high resolution ensemble predictions represents a way to deal with these uncertainties (Homar et al, 2020, Mourre et al, 2021). 6. Conclusions The severe squall line that crossed the Balearic Islands on 22 January 2021 represents a rare yet highly instructive case of a compound atmospheric–marine hazard in the Western Mediterranean. The event was associated with extreme surface wind gusts—reaching a record-breaking 130 km/h at Palma Airport—and generated rapid atmospheric pressure surges of up to 4.2 hPa. These pressure perturbations triggered significant sea-level oscillations, including a 60 cm meteotsunami recorded in the Port of Ciutadella (Menorca). This combined impact, driven by mesoscale convective processes embedded within a synoptic cyclone, exemplifies the need for integrated analysis of convective dynamics and ocean response in insular coastal regions. Through the joint interpretation of radar and lightning observations, high-resolution numerical simulations, and marine and meteorological measurements, this study offers a comprehensive diagnosis of the atmospheric and oceanic evolution of the event. In particular, the identification of a well-organised convective nucleus—with clear severe squall-line characteristics, such as a bow echo and sharp pressure jump—demonstrates the capacity of mesoscale systems to produce both destructive wind phenomena and pressure-forced sea-level responses. The link between the convective structure and the meteotsunami was substantiated through both timing and spatial alignment, highlighting the atmospheric source mechanism with rare clarity. The Proudman resonance emerged as a key amplification mechanism for the meteotsunami, especially in the Menorca Channel, where the propagation speed of the pressure disturbance matched the phase speed of long ocean waves. This physical alignment explains the high amplitude recorded in Ciutadella and reaffirms the region’s status as a global hotspot for meteotsunamis. The results also illustrate the importance of detailed bathymetric and kinematic analysis in diagnosing and forecasting such events, particularly when multiple amplification mechanisms—shoaling, coastal resonance, and atmospheric forcing—may interact. Finally, this study underscores both the strengths and current limitations of existing forecasting systems. While high-resolution meteorological models successfully captured the broad meteorological context, including the cyclone Hortense and associated gust fronts, they failed to resolve the precise location and timing of the severe squall line and its associated pressure jumps. This highlights the critical need for ensemble-based, convection-permitting forecasting systems and tightly coupled atmosphere-ocean models to improve predictability of compound hazards. The event analysed here stands as a benchmark for future research on mesoscale convective systems and their coastal impacts, and as a vivid example of how scientific insight, grounded in multi-source data integration, can advance our understanding of Mediterranean hazards. Declarations Conflict of interest Not applicable Acknowledgements Observational data used in this work have been provided by AEMET, SOCIB, Balearsmeteo, Port IB, PE, EUMETSAT, ECMWF. UIB and AEMET authors acknowledge financial support by the “Ministerio de Ciencia e Innovación” of Spain through the grant TRAMPAS (PID2020-113036RB-I00/AEI/10.13039/501100011033). UIB authors also acknowledge the more recent grant HYDROMED, PID2023-146625OB-I00, funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU. SOCIB acknowledges the support of the EDITO-Model Lab project funded by the European Climate, Infrastructure and Environment Executive Agency (project number 101093293). References Adams-Selin, R. D., and R. H. 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Tintoré, 2021, On the potential of ensemble forecasting for the prediction of meteotsunamis in the Balearic Islands: sensitivity to atmospheric model parameterizations, Natural Hazards, 106, 229-250 https://doi.org/10.1007/s11069-020-03908-x NOAA, acceded 2025, https://forecast.weather.gov/glossary.php?word=squall Proudman, J., 1929. The effects on the sea of changes in atmospheric pressure, Geophisical Journal Internation , Vol. 183 , pp. 114–125. https://doi.org/10.1111/j.1365-246X.1929.tb05408.x Przybylinski, Ron, 1995, The Bow Echo: Oservations, Nurical Simulations, and Severe Weather Detection Methods, Weather and Forecasting, 10, 203-218 Ramis, C. y A. Jansà, 1983: Condiciones meteorológicas simultáneas a la aparición de oscilaciones del nivel del mar de amplitud extraordinaria en el Mediterráneo occidental (in Spanish), Revista de Geofísica , 39, 35-42. Renault, L., Vizoso, G., Jansá, A., Wilkin, J., & Tintoré, J., 2011. 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Strelec Mahović, 2012, Northern Adriatic meteorological tsunamis: Observations, link to the atmosphere, and predictability, Journal of Geophysical Research , 117, C02002, doi:10.1029/2011JC007608 Tintoré, J., Vizoso, G., Casas, B., Heslop, E., Pascual, A., Orfila, A., Ruiz, S., Martínez-Ledesma, M. M., Torner, M., Cusí, S., Diedrich, A., Balaguer, P., Gómez-Pujol, L., Álvarez-Ellacuria, A., Gómara, S., Sebastian, K., Lora, S., Beltrán, J. P., Renault, L., Juzà, M., Álvarez, D., March, D., Garau, B. B., Castilla, C., Cañellas, T., Roque, D., Lizarán, I., Pitarch, S., Carrasco, M. A., Lana, A. A., Mason, E., Escudier, R., Conti, D., Sayol, J. M., Barceló, B., Alemany, F. F., Reglero, P., Massuti, E., Vélez-Belchí, P., Ruiz, J., Oguz, T., Gómez, M., Álvarez, E., Ansorena, L. L., Manriquez, M., Barceló-Llull, B., Alemany, F. F., Reglero, P., Massutí, E., Vélez-Belchí, P., Ruiz Segura, J., Oguz, T., Gómez, M., Álvarez-Fanjul, E., Ansorena, L. L., and Manríquez, M.: 2013. SOCIB: The Balearic Islands Coastal Ocean Observing and Forecasting System Responding to Science, Technology and Society Needs, Mar Technol Soc J, 47, 101–117, https://doi.org/10.4031/MTSJ.47.1.10. Uccellini, L., and D. Johnson, 1979, The Coupling of Upper and Lower Tropospheric Jet Streaks and Implicatins for the Development of Severe Convective Storms, Mon. Wea. Rev., 107, 682-703 Vilibić, I., Monserrat, S., Rabinovich, A., & Mihanović, H., 2008. Numerical modelling of the destructive meteotsunami of 15 June, 2006 on the coast of the Balearic Islands. Pure and Applied Geophysics , 165 (11–12), 2169–2195. https://doi.org/10.1007/s00024‐008‐0426‐5 Vilibić, I., Rabinovich, A., Anderson, E, , 2021. Special issue on the global perspective on meteotsunami science: editorial, Natural Hazards , 106 , 1087–1104. https://doi.org/10.1007/s11069‐021‐04679-9 Villalonga, J., Monserrat, S., Gomis, D., & Jordà, G., 2024. Observational characterization of atmospheric disturbances generating meteotsunamis in the Balearic Islands. Journal of Geophysical Research: Oceans , 129 , e2024JC020910. https://doi.org/10.1029/ 2024JC020910 Cite Share Download PDF Status: Published Journal Publication published 18 Mar, 2026 Read the published version in Natural Hazards → Version 1 posted Reviewers agreed at journal 21 May, 2025 Reviewers invited by journal 20 May, 2025 Editor assigned by journal 16 May, 2025 First submitted to journal 14 May, 2025 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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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-6655205","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":459449225,"identity":"bab406d3-33a0-48da-9875-41768eea31ef","order_by":0,"name":"Agusti Jansa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYNACAwZmMP0BiNnYidFxAKqFcQZICzNRWqA0Mw+YJKCav3+N8ecPBQzs/LPbH362+bVNno+ZgfHDxxzcWiRuvDGTADlM4s4ZY+ncvtuGbcwMzJIzt+Gx5sYZM4hfbuQwSOf23GYEamFj5sWjRf7GGeMPIC3yN9If/7bsuW1PUIvB+R4DsMMMbiSYSTP8uJ1IUIvhDbYyiTMGEsyGN3LMLHsbbie3MTM24/WL3PnDmz9U/LFJlgM67MaPP7dt57c3H/zwEZ/3JRLAZDKYw9gGJhvwqAcC/gNgyg7C+4Nf8SgYBaNgFIxMAAACy0+SeAaxvwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-3321-3881","institution":"Universitat de les Illes Balears Departament de Fisica","correspondingAuthor":true,"prefix":"","firstName":"Agusti","middleName":"","lastName":"Jansa","suffix":""},{"id":459449226,"identity":"b8ed24a3-8623-4686-a9bf-ed3a86a875c9","order_by":1,"name":"Joan Campins","email":"","orcid":"","institution":"AEMET: Agencia Estatal de Meteorologia","correspondingAuthor":false,"prefix":"","firstName":"Joan","middleName":"","lastName":"Campins","suffix":""},{"id":459449227,"identity":"317dc931-fe96-4870-8946-5ce3f9aac0f0","order_by":2,"name":"Diego Carrio","email":"","orcid":"","institution":"University of the Balearic Islands: Universitat de les Illes Balears","correspondingAuthor":false,"prefix":"","firstName":"Diego","middleName":"","lastName":"Carrio","suffix":""},{"id":459449228,"identity":"d4e29a75-7fa1-4268-81d8-cbfe59be1daf","order_by":3,"name":"Catalina Estarellas","email":"","orcid":"","institution":"AEMET: Agencia Estatal de Meteorologia","correspondingAuthor":false,"prefix":"","firstName":"Catalina","middleName":"","lastName":"Estarellas","suffix":""},{"id":459449229,"identity":"4cfc3096-7645-474c-bcf7-bc6876e3c830","order_by":4,"name":"Victor Homar","email":"","orcid":"","institution":"Universitat de les Illes Balears","correspondingAuthor":false,"prefix":"","firstName":"Victor","middleName":"","lastName":"Homar","suffix":""},{"id":459449230,"identity":"f5b755e7-ab95-43fe-99fc-8488abb8c8c4","order_by":5,"name":"Baptiste Mourre","email":"","orcid":"","institution":"IMEDEA: Institut Mediterrani d'Estudis Avancats","correspondingAuthor":false,"prefix":"","firstName":"Baptiste","middleName":"","lastName":"Mourre","suffix":""},{"id":459449231,"identity":"a95e0c15-2da8-4440-8422-6040f0e89d1c","order_by":6,"name":"Maria Angeles Picornell","email":"","orcid":"","institution":"AEMET: Agencia Estatal de Meteorologia","correspondingAuthor":false,"prefix":"","firstName":"Maria","middleName":"Angeles","lastName":"Picornell","suffix":""},{"id":459449232,"identity":"390a7483-8ebe-4136-8921-7519ced1cb8a","order_by":7,"name":"Climent Ramis","email":"","orcid":"","institution":"Universitat de les Illes Balears","correspondingAuthor":false,"prefix":"","firstName":"Climent","middleName":"","lastName":"Ramis","suffix":""},{"id":459449233,"identity":"2c1903a2-38ba-43cc-8714-c6d78ce005f9","order_by":8,"name":"Romualdo Romero","email":"","orcid":"","institution":"Universitat de les Illes Balears","correspondingAuthor":false,"prefix":"","firstName":"Romualdo","middleName":"","lastName":"Romero","suffix":""},{"id":459449234,"identity":"70301cc8-40df-4057-b12b-063b02564ade","order_by":9,"name":"Joaquin Tintore","email":"","orcid":"","institution":"ICTS SOCIB: Sistema d'observacio i prediccio costaner de les Illes Balear","correspondingAuthor":false,"prefix":"","firstName":"Joaquin","middleName":"","lastName":"Tintore","suffix":""}],"badges":[],"createdAt":"2025-05-13 11:59:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6655205/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6655205/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11069-026-08048-2","type":"published","date":"2026-03-18T15:57:30+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83325466,"identity":"39dac97e-e122-4a0c-90d7-6bf2cb1d207d","added_by":"auto","created_at":"2025-05-23 06:17:15","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":39456,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eGeographical context of the study region. Left panel: large-scale view showing the location of the Balearic Islands within the Western Mediterranean basin. Right panel: zoomed-in view highlighting some specific locations in the Balearic Islands, particularly in Mallorca and Menorca, that were affected by the squall line and the associated meteotsunami event.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/ad1da5181af16c3583094bad.jpg"},{"id":83325463,"identity":"ae392fce-5ef9-4a81-8696-174f6716459f","added_by":"auto","created_at":"2025-05-23 06:17:15","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":155087,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eHigh-resolution visible satellite image (HRVIS) from MSG at 09:00 UTC on 22 January 2021, showing storm Hortense with its centre located south of France. (Source: AEMET, 2022)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/eff87960ba882a64e7bc1b92.jpg"},{"id":83325472,"identity":"bb1397c0-85d2-4de4-90a6-c736aceaf675","added_by":"auto","created_at":"2025-05-23 06:17:15","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":225699,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eSurface synoptic weather forecast for 22 January 2021 at 12 UTC, showing the position of cyclone Hortense south of France (outlined in black). This chart illustrates the large-scale meteorological context in which Hortense developed as a secondary cyclone. (Source: AEMET, 2022)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/83222b47536b94b211fbf361.jpg"},{"id":83326246,"identity":"83910fcd-3e1e-470e-b5bf-859a4c416d09","added_by":"auto","created_at":"2025-05-23 06:33:15","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":357431,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e10-m wind and MSLP from ERA5 at 09 UTC (top-left) and 11 UTC (top-right) on 22 January 2021. The bottom panel shows a 10-m wind field from the high-resolution TRAM model, valid at 10 UTC on the same day.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/aa865df23a6c21369178bd89.jpg"},{"id":83325475,"identity":"196ce8e8-be62-433f-8242-ac380206e8d0","added_by":"auto","created_at":"2025-05-23 06:17:16","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":146608,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eCAPE values (left) and equivalent potential temperature at 850 hPa (right), at 09 UTC on 22 of February 2021, derived from ERA5.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/2f6bf940b4c1c4631b8eab7a.jpg"},{"id":83326032,"identity":"9ae4352f-fa54-4f77-9b57-96f19d7df524","added_by":"auto","created_at":"2025-05-23 06:25:15","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":122361,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eLightning strikes recorded between 04-05 \u0026nbsp;\u0026nbsp;UTC (deep blue) and 09-10 UTC (red), with colour indicating time progression. \u0026nbsp;\u0026nbsp;Each dot represents a detected lightning strike (Source: AEMET)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/e6043788c960f591bd803a4f.jpg"},{"id":83326030,"identity":"d4c3a1ad-02c8-48af-8fd7-11ba264fea66","added_by":"auto","created_at":"2025-05-23 06:25:15","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":87503,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEUMETSAT water vapour imagery from 22 January 2021 at 09 UTC. 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White (dark) shades indicate moist (dry) air masses.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/67003b87ead4050212859882.jpg"},{"id":83326035,"identity":"73bf2fa7-2f3c-4c9f-a288-335cd9955d18","added_by":"auto","created_at":"2025-05-23 06:25:15","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":179588,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eAEMET weather radar imagery (reflectivity) between 09:10 UTC and 11:40 UTC\u003c/em\u003e\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/c16674051454f2dc5c07b711.jpg"},{"id":83325470,"identity":"9d740485-4772-4524-9bbe-91f867c8b567","added_by":"auto","created_at":"2025-05-23 06:17:15","extension":"jpg","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":62994,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eEvolution of pressure (left) and wind gusts (right) at the airport of Palma, from 09 UTC to 12 UTC, on 22 January, 2021. (Data from AEMET)\u003c/em\u003e\u003c/p\u003e","description":"","filename":"9.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/bb4378a985206928eb2b8b73.jpg"},{"id":83326247,"identity":"f74a080c-5494-4392-ab92-fb7da5477dbc","added_by":"auto","created_at":"2025-05-23 06:33:15","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":106279,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eObserved (red lines) and forecasted (blue lines) atmospheric surface pressure anomaly evolution at different locations in the Balearic Islands on 22 January 2021: 1-Sant Antoni, 2- Andratx, 3-Sa Rapita, 4-Pollença, 5-Porto Cristo, 6- Ciutadella, 7- Maó-Mahon, 8-northern location in open sea. At each location, anomalies are computed with respect to the mean value over the period displayed in the time series. Observations and forecasts were provided by SOCIB, all represented here with a 1-minute temporal resolution.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"10.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/162d9677794a566a28326821.jpg"},{"id":83326635,"identity":"9cc3bbad-7913-4e12-92bf-9da719dfed28","added_by":"auto","created_at":"2025-05-23 06:41:15","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":40032,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eDirection of advance of the squall line (blue arrows; left). The speed of displacement of the atmospheric disturbance is around 100 km/h. Shallow water wave velocity (right): the pink band corresponds to the range of 80-100 km/h, that is, it is the zone in which the Proudman amplification is possible\u003c/em\u003e\u003c/p\u003e","description":"","filename":"11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/7b642626106afa0fd24c7ba8.jpg"},{"id":83326036,"identity":"91822b89-b738-4581-a912-01acdaff8e22","added_by":"auto","created_at":"2025-05-23 06:25:16","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":197073,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eMaximum gusts forecasted by the high resolution model of the ECMWF (HRES-IFS), valid on 22 of January, 2021, at 12 UTC, and referred to the three hours before (09-12 UTC).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/b90cbbad9add590c26c65643.jpg"},{"id":83325479,"identity":"e0d9906d-e96f-4756-a5ca-1f749208fe6b","added_by":"auto","created_at":"2025-05-23 06:17:16","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":225525,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eTRAM forecast, valid at 10:00 UTC of 22 January 2021 for mean sea level pressure (hPa) and vertical integrated liquid (Kg m-2).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/05fae5a4ad06f7bbe18a9217.jpg"},{"id":83325480,"identity":"a05f8973-5c07-4408-b3aa-878efb653c0c","added_by":"auto","created_at":"2025-05-23 06:17:16","extension":"jpg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":51468,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eTime series of the atmospheric pressure anomaly (in hPa) at the position of the TRAM-simulated squall line of Fig. 13, and the hypothetical water depth response (as anomaly, in cm) at the Ciutadella harbour (see text for details).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"14.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/3a5d2d4d713d98e02614fa2a.jpg"},{"id":105223294,"identity":"8cc151d4-35ee-4388-87b0-267a74798998","added_by":"auto","created_at":"2026-03-23 16:02:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2591951,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6655205/v1/e65473a3-92e2-4f8f-b41a-846c46433733.pdf"}],"financialInterests":"","formattedTitle":"Squall line in the Balearics producing extreme wind and meteotsunamis","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAccording to the NOAA’s glossary of meteorology (NOAA, 2025), a squall line is “a line of active thunderstorms, either continuous or with breaks, including contiguous precipitation areas resulting from the existence of the thunderstorms”. The glossary of meteorology of the American Meteorological Society (AMS, 2025) specifies that a squall line as “a line of deep moist convection frequently associated with thunder, either continuous or with breaks, including contiguous precipitation areas. The squall line is a type of mesoscale convective system distinguished from other types by a larger length-to-width ratio”: Of course, the passage of squall line supposes strong wind gusts. In addition, it is widely accepted that a squall line is also usually accompanied by an atmospheric pressure surge or jump (Fujita, 1955, Mahoney III, 1988, Przybylinski, 1995, Adams-Selin and Johnson, 2010). At its turn, a rapid change in atmospheric pressure can affect the marine sea level.\u003c/p\u003e\n\u003cp\u003eAtmospherically induced sea-level oscillations –commonly referred to as meteotsunamis– are long ocean wave generated by air-sea interactions, typically occurring at periods similar to seismic tsunamis. While they may not reach the catastrophic heights of extreme tectonic tsunamis, meteotsunamis can nonetheless cause significant coastal damage and pose risks to port infrastructure, vessels, and local communities. These phenomena are often under-recognized in coastal hazard frameworks, despite their frequent occurrence in several regions across the world, including Japan, the Adriatic Sea, or the Western Mediterranean (Hibiya and Kajiura, 1982, Šepić et al, 2012, Ramis and Jansà, 1983, Jansà and Ramis, 2021). Because of the widespread occurrence, meteotsunamis are known by different local names around the world (Monserrat et al, 2006). Within the Mediterranean region, the Balearic Islands -especially the Port of Ciutadella in Menorca- represent one of the most active meteotsunami hotspots worldwide (Fig. 1). This is due to a confluence of geographical and meteorological factors: complex topography, the presence of narrow harbours, and a regional predisposition to pressure disturbances capable of exciting long-period marine waves. Locally known as “rissaga”, these events have historically caused substantial damage and disruption, and have therefore become the subject of sustained research efforts (Ramis and Jansà, 1983, Jansà, 1986, Jansà et al, 2007, Jansà and Ramis, 2021, Villalonga et al, 2024).\u003c/p\u003e\n\u003cp\u003eUnlike seismic tsunamis, which are generated by seabed displacements, meteotsunamis are triggered by atmospheric disturbances. In the Balearics, these include rapid atmospheric pressure changes, generated by internal atmospheric gravity waves or pressure jumps or surges (including squall lines) associated to convection ( Ramis and Jansà, 1983, Jansà, 1986, Jansà et al, 2007, Jansà and Ramis, 2021). Frontal passages and even hurricanes can also generate meteotsunamis (Vilibić et al., 2021).\u003c/p\u003e\n\u003cp\u003eA fundamental mechanism underlying meteotsunami formation is the marine inverse barometer effect, where a change in atmospheric pressure induces a proportional adjustment in sea level in the form of long marine waves. In open waters, this relationship typically yields a 1 cm sea-level drop per 1 hPa increase in pressure. The magnitude of typical rapid pressure changes is about a few hPa, therefore changes of sea level may appear minor in deep water, although in exceptional cases, changes in pressure up to 7 hPa within a few minutes have also been recorded (Jansà et al, 2007). Even with such changes, to have sea-level oscillations large enough to produce significant impact in coasts and ports the long marine waves have to be dramatically amplified. For a meteotsunami to occur, three key amplification processes must typically be met: (1) Proudman resonance (Proudman, 1929), where the speed of the atmospheric disturbance matches that of the oceanic long wave; (2) shoaling, which enhances wave amplitude as the wave enters shallower regions; and (3) resonance within coastal basins, such as harbours, bays, or inlets (Monserrat et al, 2006). These mechanisms often act in combination to transform weak open-sea signals into impactful coastal sea-level oscillations.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this context, the event that affected the Balearic Islands on 22 January 2021 stands out as a well-documented case of a convectively driven meteotsunami, accompanied by hazardous winds. While not unprecedented, the event was nonetheless singular due to the combination of intense surface winds, a sharply defined atmospheric pressure surge, and the generation of moderate meteotsunamis in various ports and inlets across the islands. The phenomenon took place as a cold front associated with Storm Hortense moved through. A squall line formed within this front, crossed the eastern half of the Iberian Peninsula and reached the Balearic Islands. A pressure perturbation, reaching amplitudes of 3-4 hPa, was observed in the Balearics. This pressure change excited sea-level oscillations with final amplitudes that reached 60 cm in the Port of Ciutadella (Menorca), which is historically prone to resonant amplification. Simultaneously, the squall line produced intense convective rainfall and damaging wind gusts, peaking at 130 km h-1 at Palma Airport, thereby setting a new 50-year record for this long-term observing site.\u003c/p\u003e\n\u003cp\u003eThe multi-hazard event was extensively captured by a dense network of meteorological and oceanographic instruments across the Balearic Islands. These include conventional surface stations operated by the Spanish State Meteorological Agency (AEMET), the Balearic Islands Coastal Observing and Forecasting System (SOCIB), Balearsmeteo (a quality-controlled amateur network), the Balearic Islands Ports Agency (Ports-IB) and Puertos del Estado (PE). Complementary observations were also obtained from the AEMET weather radar in Mallorca and lighting network, as well as from satellite platforms, enabling a detailed reconstruction of the atmospheric dynamics involved. Some key geographic locations referenced throughout the study are indicated in Fig. 1.\u003c/p\u003e\n\u003cp\u003eFrom a meteorological perspective, the event’s signature was both severe and unusual. The spatial and temporal coherence of the pressure surge, coupled with intense wind gusts, marks this squall line as an effective driver of coastal sea-level disturbances. This case underscores the potential of organized convective systems to generate complex, compound hazards in the Mediterranean coastal region.\u003c/p\u003e\u003cp\u003eThis study aims to provide an in-depth investigation of the coupled atmospheric-oceanic processes underlying the 22 January 2021 event. Specifically, we analyse the evolution of the squall line and the associated pressure perturbation, and their role in producing both extreme wind and meteotsunami activity. Observational data are complemented by analyses and high-resolution numerical simulations, allowing us to assess the event’s predictability.\u003c/p\u003e\n\u003cp\u003eThe paper is structured as follows. Section 2 examines the synoptic-scale meteorological conditions that lead to the development of the squall line. Section 3 provides a mesoscale diagnosis of the squall line event. Section 4 focuses on the observed sea-level response and the resonant mechanisms involved in meteotsunami amplification. Section 5 presents the results of atmospheric and oceanic numerical simulations, emphasizing the predictability of key processes. Finally, Section 6 summarizes the main conclusions and implications of the present study.\u003c/p\u003e"},{"header":"2.\tOverview of the synoptic meteorological conditions leading to the 22 January 2021 multi-hazard event","content":"\u003cp\u003eOn 22 January 2021, the synoptic situation over the Iberian Peninsula and the Western Mediterranean region was dominated by the presence of an intense cyclone, moving from west to east. This cyclone was officially named Hortense by the Spanish Meterorological Agency (AEMET, 2022), due to its potential for high-impact weather. \u0026nbsp;A high resolution satellite image (Fig. 2) shows the cloud structure associated with Hortense, with its centre located south of France. Notably, a well-organized cluster of thunderstorms is visible approaching the Balearic Islands from the west, marking the leading edge of the squall line analysed in this study.\u003c/p\u003e\n\u003cp\u003eAt the synoptic scale, Hortense developed as a secondary cyclone within a larger extratropical system centered over Northern Europe. This parent system, officially named Christoph, was located over Scandinavia on 22 January and played a key role in shaping the downstream meteorological evolution. The process of secondary cyclogenesis, where a smaller cyclone forms along the frontal boundaries of a dominant low-pressure system, is a well-established mechanism in synoptic meteorology (Bjerkness \u0026amp; Solberg, 1922), and is particularly relevant in the Mediterranean basin. In this case, Hortense evolved along the southern flank of Christoph, deepening rapidly as it moved eastward across the Iberian Peninsula. The synoptic configuration and the position of the cyclone are illustrated in Fig. 3.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWhile AEMET meteorologists identified a classical frontal system associated with Hortense, additional details emerge from ERA5 reanalysis (Hersbach et al, 2020), high-resolution numerical simulations and satellite imagery. Fig. 4 (left and centre) shows ERA5-derived 10 m wind fields and mean sea level pressure (MSLP) maps at 09 UTC (left) and 11 UTC (centre), respectively, on 22 of January. During this period, a significant wind shifts from south-south-westerly to westerly occurred over the Western Mediterranean. This change, first observed over the Iberian Peninsula, corresponds to a marked surface convergence line, interpreted as the leading edge of a low level cold front. High-resolution numerical weather models, such as TRAM (Romero, 2024), capture this convergence line with greater clarity than ERA5 (Fig. 4, right). According to both ERA5 and TRAM outputs, maximum wind gusts over open waters on either side of the convergence line, reached 90-100 km h-1.\u003c/p\u003e\n\u003cp\u003eFig. 5 shows the vertical atmospheric stability, through the CAPE distribution, as well as the equivalent potential temperature distribution at 850 hPa, which can be an indicator of a low level front. The convergence line identified in Figure 4 corresponds to a band of moderate, though not extreme, CAPE values, indicative of a conditionally unstable environment. \u0026nbsp;In addition, the low-level temperature distribution of equivalent potential temperature exhibits a sharp horizontal gradient, reinforcing the interpretation of the convergence line acting as a low-level front (Fig. 5, right). As this feature propagates eastward, the combination of low-level convergence, moderate convective instability and frontal upward forcing provides sufficient upward motion to generate deep convection along the convergence-frontal band.\u003c/p\u003e\n\u003cp\u003eThe observed thermodynamics and dynamic conditions are consistent with lightning activity recorded during the event, which confirms the presence and evolution of an organized convective line (Fig. 6). This line of thunderstorms extended over a broad region, from the foothills of the Pyrenees to the southern Balearic Islands, highlighting the extent of the convective structure. Although the convection appears as a quasi-continuous band, the lightning map reveals the presence of several distinct convective nuclei. Four main clusters of lightning strikes are evident, with the southernmost cell corresponding to the thunderstorm in which a severe squall line developed, ultimately sweeping across Mallorca and Menorca.\u003c/p\u003e\n\u003cp\u003eThe water vapour satellite image (Fig. 7) reveals that, as the line of active convection approaches the Balearics, a moist upper-level band is located to the east of the archipelago. In the classical framework introduced by Browning (1997), such a moist band, interpreted as an upper-level front, marks the leading edge of the warm conveyor belt, a stream of ascending warm air that becomes increasingly saturated with height, leading to condensation and cloud development. To the west of this upper-level structure lies a distinctly drier region, evident as a dark band over the Balearic Islands. This area corresponds to a descending intrusion of cold dry air from the upper levels, consistent with the dry intrusion concept also described by Browning (1997). Such intrusions can, under certain conditions, enhance convective intensity and organization by increasing static instability, particularly when they interact with surface-base lifting mechanisms. A further dynamic element is inferred from a small dry patch over the north-eastern Iberian Peninsula and a thin band of cirrus clouds extending toward the southern Balearics (Fig. 7 and Fig. 2): these features indicate the presence of a jet streak approximately oriented perpendicularly to the frontal upper level and low-level frontal bands. According to Uccellini and Johnson (1979), the left-exit region of a jet streak is typically associated with enhanced upper-level divergence and upward motion, providing an additional forcing for deep convection. While the role of jet-induced forcing in convective organization can vary between cases, the spatial overlap between the jet exit region and the convective system in this event suggests a contributing influence. The observed convective line (Fig. 6) developed within the region influenced by this dry intrusion. Although large-scale subsidence generally inhibits deep convection, in this case the combination of low-level convergence, conditional instability, and frontal lifting provided sufficient mesoscale forcing to initiate and sustain deep convective development, as already commented.\u003c/p\u003e\n\u003cp\u003eIn parallel with the upper-level structures discussed in Fig. 7, lightning observations (Fig. 6) offer further insight into the evolution of the convective structures. The figures show that a convective line, which initially developed over the Iberian Peninsula, underwent continuous reactivation as it advanced eastward across the Western Mediterranean. Several discrete convective nuclei are identifiable along the main line, although radar imagery occasionally depicts it as a quasi-continuous band of high reflectivity.\u003c/p\u003e\n\u003cp\u003eIn the following section, we will pay special attention to the southernmost convective nucleus, which is also the most intense and organized one. This convective nucleus also hosted the development of a severe squall line, which ultimately swept across Mallorca and Menorca, producing both extreme surface winds and a pronounced atmospheric pressure disturbance that triggered sea-level oscillations.\u003c/p\u003e"},{"header":"3.\tStructure and evolution of the 22 January 2021 squall line","content":"\u003cp\u003eThe AEMET weather radar located in the south of Mallorca (Fig. 1) provides detailed observations of the evolution of the main line of thunderstorms, as it approached and traversed Mallorca and Menorca. Fig. 8 presents a sample of radar reflectivity images taken at 30-minute intervals (09:10, 09:40, 10:10, 10:40, 11:10 and 11:40 UTC, respectively). Higher-frequency data, recorded every 10 minutes, are also available but are not shown here.\u003c/p\u003e\n\u003cp\u003eAmong the convective cells along the line, the southernmost convective nucleus, active since approximately 08:00 UTC, became the most intense and well-organized. \u0026nbsp;This convective nucleus includes the formation of the squall line that impacted Mallorca and Menorca.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAt 09:10 UTC, radar imagery shows a continuous band of high reflectivity approaching Mallorca (Fig. 8a). As the system evolves, the northern portions become more fragmented, while the southern segment remains compact. By 09:40 UTC, this southern nucleus makes landfall in Mallorca, by Andratx (Fig. 8b). The leading edge of the convective nucleus forms a well-defined, straight squall line, which soon begins to exhibit bowing characteristics. At 10:10 UTC, when the nucleus is almost arriving at the airport of Palma, the bow-shaped radar echo is clearly evident (Fig. 8c). Such bowing is commonly associated with severe convective activity, including intense downburst and damaging surface winds (Przybylinski, 1995). As the system progresses toward Porto Cristo, it becomes less organized, although the linear squall line structure remains discernible (Fig. 8 d-f).\u003c/p\u003e\n\u003cp\u003eBeyond radar data, surface wind observations across the Balearic Islands (Fig. 1; Table 1) also confirm the passage of a squall line. A sequential pattern of strong wind gusts was recorded at multiple stations across Mallorca and Menorca.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u003cem\u003eTable 1.\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cem\u003eApproximate chronology and magnitude of the maximum gusts, pressure surge and height of sea level oscillations registered in some locations of the Balearic Islands\u003c/em\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"601\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 37.1048%;\"\u003e\n \u003cp\u003e\u003cem\u003eLocation\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e\u003cem\u003eGust (Km/h)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e\u003cem\u003ePressure surge (hPa)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e\u003cem\u003eSea level oscillations height (cm)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e\u003cem\u003eTime (ECT)\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eAndratx (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e4,0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eCalvi\u0026agrave; (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:10 \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eEstellencs (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e86\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e4,2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003ePalma, port (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e111\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003ePalma, airport (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e2,8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eBinissalem (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eSa R\u0026agrave;pita (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e122\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e2,4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eCampos Salines (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e105\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:40\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eManacor (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003ePortocolom (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e--\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003ePorto Cristo (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e2,2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e12:00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003ePort de Pollen\u0026ccedil;a (Mallorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e2,2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e11:40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003ePort de Ciutadella (Menorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e3,2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e12:10\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eEs Mercadal (Menorca)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e122\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e12:20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 37.1048%;\"\u003e\n \u003cp\u003eAirport of Menorca\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.6423%;\"\u003e\n \u003cp\u003e111\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 14.1431%;\"\u003e\n \u003cp\u003e1,9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 18.9684%;\"\u003e\n \u003cp\u003e---\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 15.1414%;\"\u003e\n \u003cp\u003e12:20\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"5\" valign=\"top\" style=\"width: 100%;\"\u003e\n \u003cp\u003e\u003cem\u003eSources: AEMET, SOCIB, Balearsmeteo and Ports IB\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAccording to Table 1, 7 of 14 surface stations registered wind gusts exceeding 100 km/h (28 m/s). Stations at mountainous tops recorded wind gusts even stronger than those listed in Table 1. The record-setting gusts observed at Palma Airport can be attributed to the combination of strong general winds of synoptic scale (associated to the intense cyclone Hortense) and to a convective outflow, generated by the thunderstorms downdrafts. Looking at Fig. 9, the wind peak appears as an almost instantaneous gust, although the winds before and behind the peak are quite strong. \u0026nbsp;Before the wind peak, the sustained winds are about 50 km/h, with gusts up to 70 km/h. Behind it, the winds are stronger, with sustained speeds of 60-70 km /h and gust up to 80-90 km/h. These observations suggest that the extreme wind gust at Palma Airport was partially convective in origin. Approximately half of the total wind speed can be attributed to the squall-line-associated convective downdrafts, while the remaining contribution reflects the strong synoptic flow driven by cyclone Hortense. Note that the wind-record at the airport of Palma is significant, since it refers to a 50-year-long time series (1975-2025), according to AEMET\u003c/p\u003e\n\u003cp\u003e(https://www.aemet.es/es/serviciosclimaticos/datosclimatologicos/efemerides_extremos*?w=0\u0026amp;k=bal\u0026amp;l=B278\u0026amp;datos=det\u0026amp;x=B278\u0026amp;m=13\u0026amp;v=VMX ).\u003c/p\u003e\n\u003cp\u003eThe passage of a squall line, in addition to producing strong wind gusts, is typically evident in the radar imagery as a narrow, high-reflectivity band, either straight or exhibiting a bow-shaped structure (see Fig. 8). This radar signature is usually associated with a well-defined convective nucleus. It is common for such systems to be accompanied by a pressure surge or abrupt pressure jump coinciding with the peak wind gusts. A classical conceptual model describing the relationship between wind, pressure, temperature and rainfall in convective systems can be found in Fujita (1955). Other references can be Mahoney III (1988), Johnson and Hamilton (1988), Przybylinski, (1995), Adams-Selin and Johnson (2010).\u003c/p\u003e\n\u003cp\u003eThe pressure surge associated with a squall line can consist in a rapid increase in surface pressure, followed by a sharp drop, a few minutes later. In some cases, this pattern is asymmetric and may even appear as a single abrupt jump rather than a symmetric surge. With regard to the squall line of 22 January 2021, it was accompanied by a relatively symmetric pressure signal. The magnitude of the pressure increases and subsequent drops recorded at various observation sites, which ranged from 1.9 to 4.2 hPa, are indicated in Table 1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe high temporal resolution from AEMET\u0026rsquo;s automatic weather stations enables a detailed analysis of the evolution of wind and/or pressure. Figure 9 shows 1-minute observations of the evolution of pressure and wind at the airport of Palma. The pressure peaks coincide closely with the arrival of the squall line and the associated wind gust. These findings support the interpretation of the event as convective structures capable of producing compound atmospheric hazards.\u003c/p\u003e\n\u003cp\u003eThe red lines in Fig. 10 show the shape and magnitude of the pressure surge changes, as observed at several locations in Ibiza, Mallorca and Menorca Islands on 22 January 2021. While the pressure jump is not detected in Ibiza, it is detected in all stations in Mallorca and Menorca, yet with differences in its shape and magnitude. The most abrupt changes were found in Andratx, Sa Rapita, Porto Cristo, Ciutadella and Mahon recording stations.\u003c/p\u003e"},{"header":"4.\tGeneration and amplification of meteotsunamis on 22 January 2021 event","content":"\u003cp\u003eAccording to the observations of SOCIB, \u003cem\u003ePuertos del Estado\u003c/em\u003e -PE- and \u003cem\u003ePorts IB,\u0026nbsp;\u003c/em\u003esome of the sea level oscillations generated by the passage of the pressure surge associated with the squall line reached heights from 25 to 60 cm (see Table 1 and Fig. 10). These values suggest total amplification factors of approximately 10 to 20, relative to the initial open-water response.\u003c/p\u003e\n\u003cp\u003eAmong the amplification mechanisms, the Proudman resonance is particularly relevant in this case. It occurs when an atmospheric perturbation (pressure surge or pressure jump) advances coupled to its marine response, that is, in the same direction and at the same speed. According to the shallow water approach, the phase speed (c) of long marine waves depends only on the water depth (h) according to the relation \u0026nbsp;( c = \u003cimg width=\"26\" height=\"22\" src=\"data:image/png;base64,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\" alt=\"image\"\u003e\u0026nbsp;), where g is the gravitational acceleration When the speed \u0026nbsp;of the pressure perturbation closely matches \u0026nbsp;the propagation of the marine wave, then \u0026nbsp;the Proudman amplification is possible.\u003c/p\u003e\n\u003cp\u003eThe combined analysis of the event chronology (Table 1) and radar imagery allows for an estimation of the propagation speed of the squall line (or of the pressure jump). The direction can be seen in Figure 11 left), and the estimated speed is approximately 100 km/h (25-30 m/s). Notably, the distance between Palma Airport and Menorca Airport is about 100 km, and the system passed over Palma roughly one hour before it reached the airport of Menorca, supporting the inferred propagation speed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 11 (right) presents a bathymetric map in which the isobaths are labelled with the corresponding phase speed of long marine gravity waves. The pink-shaded area highlights the zone where the marine long-wave speed ranges from 80 to 100 km/h, condition favourable for the Proudman resonance. This region, located primarily in the Menorca Channel, is the only relatively extended area along the squall line path where the Proudman resonance condition is met. As a result, amplification due to this resonance is expected to be strongest at the Port of Ciutadella than in other ports or inlets. Although Proudman resonance is less effective outside this zone, some degree of amplification still occurs at other coastal locations, due to harbour/inlet/bay amplification and/or shoaling effect. The particular contribution of the Proudman resonance to the total amplification that occurs in the Menorca Chanel is a key mechanism of wave amplification that is important, not only in this event, but also in many other historical meteotsunami cases affecting Ciutadella (Ličer et al, 2017). This mechanism is a major factor behind Port of Ciutadella classification as global hotspot for meteotsunamis.\u003c/p\u003e"},{"header":"5. Predictability","content":"\u003cp\u003eThe meteorological models accurately forecasted the large scale meteorological pattern, including the intense Hortense cyclone in which the severe squall line developed. Looking to high resolution models and, particularly, to the forecasted maximum gusts, the results are still quite good, but not perfect. Fig. 12 shows maximum gusts forecasted by the high resolution model of the ECMWF. Apart from wind peaks at the mountains tops, the maximum gusts forecasted in the Balearic Sea are around 43-49 kts (80-90 km/h), with some areas with 49-54 kts, that is, 90-100 km/h. In a more restricted area, to the north of the Balearic Islands, the foreseen maximum gusts exceed 100 km/h. Nevertheless, the airport of Palma, representative of an extended area and located in flat terrain, is situated in the zone where the maximum gusts forecasted by the model are under 90 km/h. The model has well forecasted strong gusts, in the Balearic zone, even very strong gusts, probably combining general and convective wind, but has not foreseen the record wind at the airport of Palma: note that the area of maximum winds exceeding 100 km/h is to the north of the location where the squall line developed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eRegarding the \u003cem\u003erissaga\u003c/em\u003e (local Balearic name for meteotsunami), in 1985, the Spanish meteorological service (AEMET, nowadays) was able to start an experimental service of \u003cem\u003erissaga\u003c/em\u003e warning. This service is, in principle, based on the meteorological identification of weather situations in which meteotsunamis have more probability to develop (Jansà and Ramis, 2021). That service, which still exists, is basically subjective, although at present the forecaster has the important aid of objective methods.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe potential of using ocean models to predict sea-level oscillations from known atmospheric initial conditions was first explored by Vilibić et al. (2008). Building on this concept, a high-resolution modelling system integrating meteorological and oceanographic components demonstrated promising results in subsequent studies (Renault et al., 2011; Ličer et al., 2017; Mourre et al., 2021). The Balearic Islands Coastal Observing and Forecasting System (Tintoré et al., 2013) developed an operational forecasting system — BRIFS (Balearic Islands Regional Forecasting System) based on such high-resolution atmosphere and ocean models, to provide daily predictions of high-frequency sea level oscillations in Ciutadella harbour. The system is accessible at https://www.socib.es/en/what-we-do/ocean-forecasting/brifs.\u003c/p\u003e\n\u003cp\u003eAdditional objective approaches to meteotsunami forecasting and modelling have been developed by Šepić et al. (2016) and Romero et al. (2019), further contributing to the advancement of operational capabilities in this domain.\u003c/p\u003e\n\u003cp\u003eBoth, the model TRAM (Romero, 2024) and BRIFS models (the atmospheric component of BRIFS is produced by the WRF model with a 4km spatial resolution), \u0026nbsp;are forecasting some kind of strong squall line or intense thunderstorm, but not in the correct zone.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFig. 10 compares the observed and BRIFS-forecasted atmospheric pressure anomaly evolution at several locations. While pressure jumps associated with the squall line were observed at several locations over Mallorca and Menorca Islands, no significant jump was predicted by the model at these locations. . Looking into more details, the model represented a squall line and the associated significant surface pressure changes but at a distance around 100km north of Menorca Island. \u0026nbsp;Figure 10 shows the representation of a pressure jump of around 2hPa in the model prediction at the station 8 located in the open sea north of Menorca. \u0026nbsp;The capacity to generate these small-scale atmospheric processes at the proper location is still an important challenge from the perspective of the prediction systems. Due to this spatial mismatch, \u0026nbsp;Ciutadella harbour didn't feel the effects of this specific atmospheric pressure jump in the prediction and the BRIFS system significantly underestimated the magnitude of the sea level oscillations (37 cm in the prediction versus 60cm in the observations).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe same kind of spatial offset was found in TRAM forecasts, where a strong pressure jump was produced to the north of the Balearic Islands, \u0026nbsp;(see Fig. 13), leading similarly to an underestimation of the magnitude of the \u003cem\u003erissaga\u003c/em\u003e. To have \u003cem\u003erissaga\u0026nbsp;\u003c/em\u003eprediction (according to the Romero et al, 2019 method), the pressure jump has to be moved to the zone where the squall line did exist.\u003c/p\u003e\n\u003cp\u003eIndeed, when the \u003cem\u003erissaga\u003c/em\u003e-prediction system of Romero et al. (2019) is forced with the squall-line induced surface pressure signal, that is, as if the system shown in Fig. 13 to the north of the islands had been simulated about 100 km further south, a \u003cem\u003erissaga\u003c/em\u003e of fairly the correct magnitude (50-60 cm wave height) is obtained (Fig. 14). The above method is highly simplified and operates in 2D to save computing time, but it incorporates all essential atmospheric and oceanic physical components, namely: (i) the genesis upstream from the Balearic Islands of high amplitude atmospheric gravity waves - and concomitant sea level pressure signal- travelling in the SW–NE direction; for this convectively driven case we simply took this SLP signal from a 150 km-long cross section centred in the TRAM-simulated mature squall line; (ii) the oceanic response to the pressure fluctuations along the Menorca channel, in the form of long oceanic waves subject to Proudman resonance; these processes are simulated with a shallow-water model applied over a 80-m depth channel; (iii) shelf amplification, which accounts for a doubling of the wave amplitude for a depth jump; and (iv) harbour resonance within Ciutadella inlet, a crucial mechanism solved again with the shallow-water equations over an idealized 5-m deep channel.\u003c/p\u003e\n\u003cp\u003eThe marine response to mesoscale atmospheric pressure perturbations can be correctly forecasted only if the atmospheric disturbances are sufficiently realistically represented \u0026nbsp;in terms of intensity and location. This kind of atmospheric disturbance are in principle predictable, with high-resolution convective solving models, as demonstrated by BRIFS and TRAM prediction systems. However, \u0026nbsp;a certain degree of uncertainty inevitably affects the exact location of the generation of these small-scale disturbances. The use of high resolution ensemble predictions represents a way to deal with these uncertainties (Homar et al, 2020, Mourre et al, 2021).\u003c/p\u003e"},{"header":"6. Conclusions","content":"\u003cp\u003eThe severe squall line that crossed the Balearic Islands on 22 January 2021 represents a rare yet highly instructive case of a compound atmospheric–marine hazard in the Western Mediterranean. The event was associated with extreme surface wind gusts—reaching a record-breaking 130 km/h at Palma Airport—and generated rapid atmospheric pressure surges of up to 4.2 hPa. These pressure perturbations triggered significant sea-level oscillations, including a 60 cm meteotsunami recorded in the Port of Ciutadella (Menorca). This combined impact, driven by mesoscale convective processes embedded within a synoptic cyclone, exemplifies the need for integrated analysis of convective dynamics and ocean response in insular coastal regions.\u003c/p\u003e\n\u003cp\u003eThrough the joint interpretation of radar and lightning observations, high-resolution numerical simulations, and marine and meteorological measurements, this study offers a comprehensive diagnosis of the atmospheric and oceanic evolution of the event. In particular, the identification of a well-organised convective nucleus—with clear severe squall-line characteristics, such as a bow echo and sharp pressure jump—demonstrates the capacity of mesoscale systems to produce both destructive wind phenomena and pressure-forced sea-level responses. The link between the convective structure and the meteotsunami was substantiated through both timing and spatial alignment, highlighting the atmospheric source mechanism with rare clarity.\u003c/p\u003e\n\u003cp\u003eThe Proudman resonance emerged as a key amplification mechanism for the meteotsunami, especially in the Menorca Channel, where the propagation speed of the pressure disturbance matched the phase speed of long ocean waves. This physical alignment explains the high amplitude recorded in Ciutadella and reaffirms the region’s status as a global hotspot for meteotsunamis. The results also illustrate the importance of detailed bathymetric and kinematic analysis in diagnosing and forecasting such events, particularly when multiple amplification mechanisms—shoaling, coastal resonance, and atmospheric forcing—may interact.\u003c/p\u003e\n\u003cp\u003eFinally, this study underscores both the strengths and current limitations of existing forecasting systems. While high-resolution meteorological models successfully captured the broad meteorological context, including the cyclone Hortense and associated gust fronts, they failed to resolve the precise location and timing of the severe squall line and its associated pressure jumps. This highlights the critical need for ensemble-based, convection-permitting forecasting systems and tightly coupled atmosphere-ocean models to improve predictability of compound hazards. The event analysed here stands as a benchmark for future research on mesoscale convective systems and their coastal impacts, and as a vivid example of how scientific insight, grounded in multi-source data integration, can advance our understanding of Mediterranean hazards.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eObservational data used in this work have been provided by AEMET, SOCIB, Balearsmeteo, Port IB, PE, EUMETSAT, ECMWF.\u003c/p\u003e\n\u003cp\u003eUIB and AEMET authors acknowledge financial support by the “Ministerio de Ciencia e Innovación” of Spain through the grant TRAMPAS (PID2020-113036RB-I00/AEI/10.13039/501100011033). UIB authors also acknowledge the more recent grant HYDROMED, PID2023-146625OB-I00, funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSOCIB acknowledges the support of the EDITO-Model Lab project funded by the European Climate, Infrastructure and Environment Executive Agency (project number 101093293).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAdams-Selin, R. D., and R. H. Johnson, 2010: Mesoscale surface pressure and temperature features associated with bow echoes. \u003cem\u003eMon. Wea. Rev.\u003c/em\u003e, 138, 212\u0026ndash;227.\u003c/li\u003e\n \u003cli\u003eAEMET, 2022. 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Observational characterization of atmospheric disturbances generating meteotsunamis in the Balearic Islands. \u003cem\u003eJournal of Geophysical Research: Oceans\u003c/em\u003e, \u003cem\u003e129\u003c/em\u003e, e2024JC020910. https://doi.org/10.1029/ 2024JC020910\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"natural-hazards","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nhaz","sideBox":"Learn more about [Natural Hazards](https://www.springer.com/journal/11069)","snPcode":"11069","submissionUrl":"https://submission.nature.com/new-submission/11069/3","title":"Natural Hazards","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"meteotsunamis, convection, squall line, extreme w","lastPublishedDoi":"10.21203/rs.3.rs-6655205/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6655205/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"On 22 January 2021, an active squall line embedded within cyclone Hortense swept across the Balearic Islands, significantly impacting Mallorca and Menorca. The event was characterized by extreme wind gusts, including a 130 km h-1 peak at Palma airport, an intensity breaking the 50-year record. Consequently, the squall line induced an outstanding long-lived pressure perturbation, which triggered moderate meteotsunami activity across several harbours and coastal inlets. Notably, a sea-level oscillation of 60 cm was recorded in the Port of Ciutadella (Menorca). The main objective of this paper is to investigate the coupled atmospheric and oceanic dynamics underlying a squall line event that produced extreme winds and meteotsunami activity, focusing on the role of an associated atmospheric pressure surge. In particular, we provide a comprehensive observational description of the combined event -squall and associated meteotsunamis- using land-based meteorological and oceanographic data, remote-sensing imagery, and ERA5 reanalysis products. Furthermore, the predictability of the event’s key dynamical features, including wind extremes and meteotsunami generation, is assessed through high-resolution atmospheric and oceanic numerical simulations. These findings highlight a rarely documented mechanism of compound atmospheric-oceanic hazard in the Mediterranean and underscore the critical need for improved mesoscale forecasting capabilities to support coastal risk mitigation strategies","manuscriptTitle":"Squall line in the Balearics producing extreme wind and meteotsunamis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-23 06:17:11","doi":"10.21203/rs.3.rs-6655205/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-05-21T06:07:15+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-05-20T16:15:34+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-16T10:56:14+00:00","index":"","fulltext":""},{"type":"submitted","content":"Natural Hazards","date":"2025-05-14T11:15:41+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"natural-hazards","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nhaz","sideBox":"Learn more about [Natural Hazards](https://www.springer.com/journal/11069)","snPcode":"11069","submissionUrl":"https://submission.nature.com/new-submission/11069/3","title":"Natural Hazards","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4daa4982-e825-498a-b723-130c6db757a8","owner":[],"postedDate":"May 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-23T16:00:50+00:00","versionOfRecord":{"articleIdentity":"rs-6655205","link":"https://doi.org/10.1007/s11069-026-08048-2","journal":{"identity":"natural-hazards","isVorOnly":false,"title":"Natural Hazards"},"publishedOn":"2026-03-18 15:57:30","publishedOnDateReadable":"March 18th, 2026"},"versionCreatedAt":"2025-05-23 06:17:11","video":"","vorDoi":"10.1007/s11069-026-08048-2","vorDoiUrl":"https://doi.org/10.1007/s11069-026-08048-2","workflowStages":[]},"version":"v1","identity":"rs-6655205","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6655205","identity":"rs-6655205","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}