Numerical Simulation On The 3D Structure Of Sea Breezes Over The Hainan Island

To study the three-dimensional structure of sea breeze and its diurnal evolution, a non-hydrostatic mesoscale model WRF, version 3.5, is used to simulate a typical case of sea breeze day on April 12,2012 over the Hainan Island. Compared with observational data, the results show that the evolution and characteristics of sea breeze can be reasonably simulated by WRF. Sea breezes over the Hainan Island begin later than other regions in China. Sea breezes in the north and south stay longer and develop stronger than those in the east and west.18:00 LST, two significant convergence lines are located in the north and northwest to the island which is the urban area, and a large convergence zone in the centre. Horizontally, owing to the effect of onshore background flow, sea breeze in the south penetrates approximately 80 km, which is far more than those in other parts of the island. Vertically, the mountains in the southwest play a role in lifting and intensifying sea breezes, and the dynamic effect of topography contributes to the development of land breeze in the evening as well. In addition, the return current is weakened by the effect of topography and onshore background flow, and only in the north and east can be shown clearly. So, the structure of sea breeze is the most complete in the eastern and northern plain areas. Sea breeze in the east can reach the height of 1.8 km, and that in the north can extend as far as 2.5 km. The potential temperature over Hainan Island enhances significantly since 12:00 LST, and the gradient near the coastline increase substantially, which engenders sea breezes. The gradient reach the maximum at 15:00 LST in the vicinity of SBF, and sea breezes develop intensely. The water vapor mixing ratio increases sharply during 15:00-18:00 LST, and the accumulation of ample amount of water vapor is at the back of SBF. Severe convctive weather tends to occur in the south of the mountain and northeast to the island. Finally, some surface heat fluxes, momentum variations and convective energy are analyzed, which turn out that sensible heat flux, latent heat flux and ground heat flux all play an important role in the development of sea breezes and convections in the island. The sensitivity of sea breeze structure characteristics to different horizontal resolutions and planetary boundary layer (PBL) parameterizations over complex terrain are also investigated. It indicates that impacts of both horizontal resolutions and PBL parameterizations on simulated sea breeze structureare quite evident in this study. Horizontal resolution has a generally significant impact on the sea breeze structure that WRF simulation at higher resolution reveals more exact surface conditions leading to more complicated and detailed sea breeze structure over complex terrain on the island. Additionally, comparisons between YSU and MYJ PBL parameterizations show that local (MYJ) scheme reproduces higher wind speeds, underestimates inland penetration distance and sea breeze depth, but wind fields are closer to realistic case and sea breeze structure is more precise in WRF simulation with YSU PBL scheme in this case over Hainan Island.