A Numerical Study Of Impact Of Topography On Sea Breeze Circulation Over The Hainan Island

One sea breeze circulation process over the Hainan Island is simulated by the WRF (Version3.7) model on 25 May, 2014. Firstly, the impact of topography on the sea breeze circulation is studied by changing the terrain height. The results show that the land-sea thermal difference, which is the trigger mechanism of sea breeze,reaches its top at 15:00 LST in CNTL experiment. In FLAT experiment, the main variations are embodied in two aspects, one is in the horizontal direction: the duration of the sea breeze becomes shorter, and the propagation distance of sea breeze reduces about 1?5 km. At the same time, the intensity of sea breeze weakens more than 1 m s-1. Meanwhile, the kinetic energy of sea breeze exists great attenuation area in the coastal and southwest region, and the corresponding range of sea breeze convergence zone narrows down and the sea breeze convergence line also moves to the coastal regions. The other is in the vertical direction: the impacted location of different directions of sea breeze moves to the west and north, the backflow in high altitude and sea breeze thickness become lower. The intensity of the vertical circulation around sea breeze front reduces more than 10 cm s-1.Moreover, the effect which the valley wind strengthens the sea breeze disappears. Its Influence mechanism can be summarized as the following two parts: in the dynamical aspect, the updraft and flow caused by mountains disappeared. In the thermal aspect, net radiation absorbed by the earth's surface decreases, which causes the releasing of sensible heat flux and latent heat flux decline about 9%, respectively.Ultimately, land-sea thermal difference and the corresponding air pressure difference all get smaller than CNTL, which weakens the basic characteristics of the sea breeze circulation. In addition, the results of the two experiments which only part of the mountains is removed show that the kinetic energy and convergence zone of sea breeze become weaker in the corresponding regions, and the structure of the vertical circulation also changes, the influence of Limu Mountain (RMLM) on sea breeze is greater than Wuzhi Mountain (RMWZ). The second purpose is to study the impact of planetary boundary layer parameterizations (YSU, MYNN2.5, MYNN3, ACM2,BouLac, UW, SH, GBM) on simulated sea breeze circulation over the Hainan Island.YSU, ACM2, SH are nonlocal closure schemes, and the MYNN2.5, MYNN3,BouLac, UW, GBM are local TKE schemes. The results show that: In the simulation of horizontal structure of sea breeze,the intensity of YSU?ACM2?BouLac?UW?SH in the north are strong and the inland wind speed of SH, GBM are relatively high at 15:00 LST. Meanwhile, the variations of temperature and intensity of sea breeze are corresponding, MYNN2.5 and MYNN3 simulated low temperature, so their land-sea thermal difference are less than other 6 schemes, the intensity of sea breeze are weak. In the simulation of vertical structure of sea breeze, which occurs at 09:00 LST, but the strength is small and exists remanent land breeze, the propagation distance of sea breeze is short, YSU, MYNN2.5, SH simulated strong sea breeze. At 12:00 LST, the circulation structure of sea breeze is clear, YSU and ACM2 simulated thick sea breeze depth and long propagation distance, but the circulation structure of MYNN3 is not clear and the propagation distance is short, so the intensity of sea breeze is weak. At 15:00 LST, sea breeze develops intensely, MYNN2.5 and MYNN3 simulated weak sea breeze vertical strength, ACM2 simulated the clearest sea breeze circulation structure. At 18:00 LST, the intensity of sea breeze and vertical disturbance are weaker than 15:00 LST, ACM2, BouLac, UW simulated strong sea breeze. At 21:00 LST, sea breeze changed into land breeze and BouLac,UW simulated powerful circulation. The characteristics of potential temperature,water vapor, intensity of vertical circulation are corresponding with sea breeze.ACM2 simulated strong sea breeze due to the fact that vertical mixing action is strong within the planetary layer. With regard to the simulated planetary layer height,ACM2 has the highest height, which is coincident with the intensity of sea breeze.While the heights of other schemes are not consistent with the sea breeze strength.