Characteristics of Coastal Low‐Level Jets Over Beibu Gulf, China, During the Early Warm Season
Hoiio Kong, Qinghong Zhang, Yu Du, Fan Zhang
Abstract
Abstract We investigated coastal low‐level jets (CLLJs) over Beibu Gulf, China, during the warm season (May to July) using hourly model simulations from a mesoscale weather research and forecasting model with a 9‐km horizontal resolution. Two high‐incidence CLLJ areas were identified over Beibu Gulf: one located on the leeward side of the Annamite Range that prevailed after sunset and the second off the northwestern coast of Hainan Island that reached its maximum intensity at midnight. The upstream wind of the Annamite Range was too weak to pass over the range during the daytime due to strong turbulent mixing near the land surface of Indochina; however, due to the suppression of the turbulent mixing after sunset, the flow intensified and crossed over the Annamite Range and further formed a hydraulic jump jet downstream. In addition to advection effect from upstream, topographic blocking effect of Hainan Island contributed to the CLLJ off the northwestern coast of Hainan Island, which persisted during the day but became more prevalent at midnight. Further momentum budget analysis and sensitivity experiments indicated that the upstream inertial oscillation due to the diurnal variation in turbulence over land was the primary source of the CLLJ over the ocean. These findings reveal the primary mechanism of CLLJs over Beibu Gulf, providing insight into CLLJ formation in other coastal regions with complex mountain ranges.