The extraordinary atmospheric rivers analysis over the Middle East: Large-scale drivers, structure, effective sources, and precipitation characterization

Abstract

The study investigates the characteristics of Extraordinary Atmospheric Rivers (EARs), including large-scale atmospheric patterns, structure, effective sources, and precipitation in the Middle East. For this purpose, ARs with maximum Vertically Integrated Water Vapor Transport (IVT) ≥ 1000 kg m−1 s−1 were extracted from 1981 to 2020. ERA5 and PERSIANN-CCS-CDR data were used to analyze the characteristics of the EARs. The latter was applied to show the precipitation risk level. Atmospheric patterns indicated the state of the merging cyclones. Sudan's low pressure was the more recurrent system in all the patterns and alternately integrated with one or two cyclonic tongues over the Mediterranean, the Black Sea, the Caspian Sea, and then the polar vortex. Atmospheric blocking was present in all events, affecting the lifetime of the EARs and the maximum IVT anomaly, which averaged 4.5 days and 622 kg m−1 s−1, respectively. The EARs are the result of the simultaneous feeding of several moisture pathways from different sources. Both regional (mainly below 850 hPa) and trans-regional (above 700 hPa, except for the western Mediterranean) water sources played a crucial role in their formation. Dynamically, most events were characterized by merging the subtropical and polar jets, with maximum central speeds between 70 and 85 m s−1. EARs were also accompanied by strong near surface wind gusts up to 28 m s−1. In the IVT core wind structure, the low-level jet with a speed of 30 m s−1 deepened to a maximum of 925 hPa. There were also intense upward velocities between − 3 and − 5 Pa s−1 near the precipitation maxima areas in the EARs. The spatial character of the precipitation was of a continuous or intermittent nature, and a considerable part of it fell in short periods (up to 286 mm in 3 h). The daily maximum was 390 mm. Accordingly, the importance of using high-resolution data was represented for such events with devastating hydrological effects.