Unusual Atmospheric‐River‐Like Structures Coming From Africa Induce Extreme Precipitation Over the Western Mediterranean Sea

Abstract

AbstractLong filaments of high integrated water vapor transport (IVT) content, widely known as atmospheric rivers (ARs), play a relevant role in the water cycle being also associated to many extreme flooding events worldwide. In this work we inspect whether similar structures can be found over the western Mediterranean. The methodology used here to detect these AR‐like structures is based on standard ARs detection methods but imposing a strong IVT advection westward component. The ERA5 global reanalysis and Spain02 high‐resolution gridded observational data set are used covering the period 1979–2017 to analyze the composites of mesoscale features and associated impacts on rainfall. Results show that AR‐like structures over the Mediterranean (abbreviated here Med‐ARs) have an approximately once‐per‐year frequency, but they are associated with extreme orographic precipitation contributing to more than 40% to the annual precipitation in some cases. During Med‐AR, IVT increases due to high horizontal winds and water vapor contents. Med‐ARs are associated to a cutoff cyclone with a cold core over northwestern Africa and warmer air mass over northern Europe. The vertical structure of Med‐ARs suggests an occluded front with a low level jet in the warmer front where Med‐ARs reside and moisture penetrating into high atmospheric levels where cold and warm front intersect. In conclusion, long filaments of IVT can be found over the western Mediterranean Sea playing a relevant role on hydrometeorological impacts. Although these structures share some features with ARs over the Pacific/Atlantic Ocean, they may not be considered the same meteorological phenomenon.