Impact of Subtropical Jet on the Precipitation Variabilities over the Arabian Region Using a Gray-Zone Regional Model

A 17-year (2002-2018) simulation was performed using the Weather Research and Forecasting (WRF) model at a gray-zone resolution (9 km) to understand the climatological, intraseasonal, and interannual variability of precipitation and associated processes over the Arabian region. WRF realistically captures the precipitation and circulation climatology along with its interannual variabilities. The current study identifies that winter (Nov–Apr) precipitation contributes around 70% of its annual mean over the Arabian region, specifically the United Arab Emirates. The mechanism behind wintertime precipitation is further explored, and it is found that the intrusion of subtropical jets helps to initiate wintertime precipitation events by modulating the physical processes. The composites of all events during these 17 years suggest that equatorward extension of upper-level jets creates a positive middle-level vorticity and subsequently generates an anomalous lower-level convergence through Ekman pumping, which weakens the persistent anticyclones over the Arabian region, shifting them further eastward over the Arabian Sea. The eastward shift in the lower-level anticyclones brings anomalous warm and moist air from the Arabian Sea and the Red Sea towards the Arabian Peninsula. This warm and humid air converges with the cold and dry air from the mid-latitude jet and creates a moisture convergence zone leading to the initiation of convection. The above mechanism can also explain the interannual variabilities of precipitation over the Arabian region during wet-to-dry years. A 3 ms^-1 stronger jet peak magnitude and ~2^o equatorward shift of the jet is noticed during wet years compared to dry years. Equatorward extension of the jet can explain about 21% of the variability of Arabian precipitation compared to around 7% by the jet magnitude during the wet years.