Analyses of the winter low‐level jet over the southern Red Sea using the Weather Research and Forecasting model

Abstract

The three-dimensional structure of the Red Sea Low-Level Jet (RSLLJ) that occurs over the southern Red Sea during the winter season is examined using the Weather Research and Forecasting (WRF) model. The causes of the jet formation are investigated, and the simulations confirm that the jet is a terrain-induced phenomenon. It initiates as a gap flow as the jet forms north of the strait of Bab el-Mandab as a result of a hydraulic effect when a stably stratified cool layer is channeled through the mountainous gap at low levels over the strait into the southern Red Sea. The jet intensity is enhanced by the Red Sea trough over the southern Red Sea. The cool dense air mass south of the strait is supported by a generally persistent synoptic regime that includes a high-pressure system over most of the eastern Arabian Peninsula and the Sudan low-pressure system over Sudan. The jet extends more than 500 km northward to slightly north of 17 • N from the strait around 12.5 • N, with a width of 100-150 km over the southern Red Sea. The jet core lies at 500-600 m above sea level between 14 • N and 16 • N, with wind speeds exceeding 25 m/s. The north-south pressure gradient along the strait, as well as the depth of the stratified cool layer south of the strait, are directly responsible for the jet length and speed over the southern Red Sea, with stronger pressure gradients and deeper cool layers resulting in longer and stronger jets. Sea/land breezes also directly influence the spatial scale, intensity, and diurnal variation of the jet, with land breezes causing faster and more constricted jets at night and divergence due to sea breezes leading to relatively slower jets during the daytime.