Characteristics of Coastal Low-Level Jets in the Bohai Sea, China, During the Early Warm Season

Abstract

We investigate coastal low-level jets (CLLJs) in the early warm season during 2006–2011 over the Bohai Sea using a 9-km horizontal resolution output data from the Weather Research and Forecasting model. CLLJs mainly occur in May when large-scale low is located over land to the north and the Pacific high is located to the southeast of the study area. The occurrence of the CLLJs exhibits an obvious diurnal cycle with two different peaks: one at night, located mainly in the central region, and the other in the afternoon, located in the northern region with mountains at both eastern and western sides. A momentum budget analysis shows that inertial oscillations, triggered by land-sea thermal contrast, results in the formation of nocturnal CLLJs in the Bohai Sea. In addition, sensitivity experiments show that the enhanced atmospheric baroclinicity, caused by unbalanced solar radiation over the western mountain of the northern region, dominates the occurrence of afternoon CLLJs in the northern area of the Bohai Sea. Besides that, the eastern topography plays a main role as barrier and, therefore, traps CLLJs by topography blocking to its western side.