PNNL

Abstract

The present study explores the mechanism governing wintertime (November–April) precipitation over the Arabian Peninsula (AP) using a 17-yr-long (2002–18) high-resolution WRF simulation. The composite analysis of strong precipitation events suggests that the equatorward extension of the upper-level jet together with the embedded upper-level trough creates a positive (cyclonic) midlevel vorticity and subsequently generates an anomalous lower-level convergence through Ekman pumping. This leads to the development of an anomalous surface low, which is further enhanced in the presence of the existing Red Sea trough over the AP. This surface low weakens the persistent anticyclone over the AP, shifting it further eastward to the Arabian Sea. The eastward shift in the lower-level anticyclone contributes to the transport of warm, moist air from the Arabian Sea and the Red Sea toward the AP. This warm, moist air converges with the cold and dry air advected by the midlatitude jet and creates a moisture convergence zone, leading to the initiation of convection. We test the proposed mechanism through numerical experiments with modified upper-level wind and demonstrate that a strong, southward intrusion of the jet can indeed lead to precipitation over the AP. The above mechanism also explains the interannual variability of precipitation over the AP. During wet years, we notice approximately 3 m s-1 stronger jet core magnitude and about a 2° equatorward shift of the jet compared to dry years. While the equatorward extension of the jet explains about 21% of the interannual variability, the jet magnitude explains around 7% of the variability during wet years. Significance Statement Understanding the mechanism governing rainfall variability is crucial for the arid Arabian Peninsula. We conducted 17-yr (2002–18) high-resolution simulations using the WRF Model to understand the rainfall variability and the model’s ability to capture rainfall patterns. We propose a mechanism behind winter–spring (November–April) season precipitation over the Arabian region and its connections with the subtropical jet. The results reveal that an equatorward shift of the jet is associated with above-normal rainfall over the Arabian Peninsula. Our study has identified a new pathway through which the subtropical jet’s location influences rainfall patterns over this region. This finding assumes significant importance, especially considering the anticipated changes in the subtropical jet’s position in a warmer climate.