Long-Term Variability of Wind Speed and Direction in the Mediterranean Basin

Abstract

In this work, the ERA5 reanalysis dataset, with its fine spatial and temporal resolution, is used to study the wind speed and direction characteristics in the Mediterranean basin from 1979 to 2020. Their variability, trend and mean values, as well as their association, are examined in the monthly, annual and interannual/decadal time scales. The long-term variability of the wind direction is assessed using the angular variance, while the mean annual and interannual variability are used for the wind speed. The most characteristic and constant flow systems appear in the Gulf of Lion (Mistral) and the Aegean Sea during the summer (Etesian winds). The mean annual variability maximizes in the northern part of the basin, while the western part appears to have the most variable wind directions, while the fastest increasing wind speeds appear in the southwestern Levantine sub-basin. The long-term linear trend for the mean, the 95th and 99th quantiles of annual wind speed and the number of occurrences of extreme wind events have been also assessed. For particular areas, there is an increasing tendency in both intensity and frequency of occurrence of extreme wind events. Τhe linear-circular correlation coefficient has been implemented in order to quantify the linear association between the wind direction and the wind speed. This parameter demonstrates higher annual values for the Mistral wind in the Gulf of Lion and the Etesian winds in the Aegean Sea during the summer. Finally, the comparison of the results of ERA5 with the results of ERA-Interim highlighted significant differences in the Mediterranean wind speed and direction characteristics.

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“…The two winds interact with an additive effect due to their prevailing direction [ 102 ]. In the eastern part of the basin, along the coast of Tuscany, the prevailing wind during winter blows from the east in offshore direction and this air mass converges with that coming from the western part of the basin up to Cap Corse, in the northernmost part of Corsica Island (also observed in [ 101 ]), generating a southerly wind blowing towards the coast of Liguria. During summer, the southwestern part of the LPB is characterized by strong westerly winds, while intense winds blowing from the southwest direction can be observed in the central part of the basin.…”

“…As highlighted in [ 88 , 101 ], the winter season wind regime in the western part of the LPB is dominated by the cold and dry Mistral, which reaches the northern part of the Tyrrhenian Sea and the Ligurian Sea blowing from the north–northwestern direction through the Rhone Valley and the Gulf of Lion, and by the Tramontana northerly wind. The two winds interact with an additive effect due to their prevailing direction [ 102 ].…”

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“…north Tunisia). Arrows in the map indicate the most persistent wind systems in the Mediterranean Sea, Mistral (Gulf of Lyon) and Etesian winds (Aegean Sea) 31 . …”

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“…The Mediterranean is also known for its distinctive regional features, which include strong seasonal temperature and precipitation contrasts, strong wind systems, heavy precipitation, and Mediterranean cyclones (Lionello et al, 2006;Nadia et al, 2006;Allam et al, 2020). The Mediterranean Sea is considered a hotspot of climate change (Skliris et al, 2012;Pastor et al, 2020;Soukissian and Sotiriou, 2022). Moreover, it is an area where offshore wind energy is currently in the development phase.…”

“…The main intense wind regimes found in the Mediterranean Sea are, for example, the sirocco, a wind that blows from the Sahara desert towards the Mediterranean Sea and reaches high speeds especially in spring and autumn, the tramontana, a northerly wind that occurs in many Mediterranean countries, Mistral is a strong northwesterly wind that blows across the Rhone Valley into the Gulf of Lion in France, the Etesians are seasonal northerly winds that blow across the Aegean Sea in summer, and Bora is a northeasterly wind that blows in the Adriatic Sea, especially from November to March (Soukissian and Sotiriou, 2022). These wind systems shape the wind climate of the basin and influence SST variability and water circulation in the Mediterranean Sea (Soukissian and Sotiriou, 2022). The Mediterranean region is not only a climate change hotspot, but also a true biodiversity hotspot (Mannino et al, 2017;Criado-Aldeanueva and Soto-Navarro, 2020).…”