Numerical Simulation Study of a Collision-Type Sea Breeze Front Case in the Bohai Bay Region

A collision-type sea breeze front that occurred in the Bohai Bay region, China on September 26, 2009, is simulated using the Weather Research and Forecasting (WRF) model. The process related to this case, and the structure and characteristics of sea breeze front are reproduced successfully by the simulation. The results show that the development of significant and relatively strong convective instability energy and accumulation of ample amount of water vapor are at the back of the sea breeze front. The formation of a huge amount of water vapor can mainly be attributed to the banking and vertical transportation of sea breeze behind the sea breeze front. On the other hand, the large convective instability energy is caused by the lowering of the lifting condensation level and level of free convection, and rising of the equilibrium level, which result from the decrease in temperature and increase in moisture content of the lower atmosphere, caused by the colder and moister sea breeze. Increase in the moisture content is the primary impact factor. The abundant convective instability energy is triggered when the convective system enters into the back of the sea breeze front after colliding with it, leading to a strong convective motion. Meanwhile, weak convective inhibition enhances the occurrence of the convective motion. Vertical transportation of the water vapor formed behind the sea breeze front by the strong convective motion results in heavy precipitation. In addition, development and maintenance of convective motion may be favored when the convective system moves along the back of the sea breeze front after the collision.