Analysis Of The Characteristics Of The Land-Sea Boundary Layer During The Active And Inactive Periods Of South China Sea Summer Monsoon—Guangdong Dianbai Area

The characteristics of the land-sea atmospheric boundary layer and sea-air flux and land-air flux during the active and inactive periods of the South China Sea Summer Monsoon (SCSSM) are analyzed by using the observation data obtained from the Dianbai meteorological station and the Marine Meteorological Science Experiment Base at Bohe from June to September in the year 2012. It is found that the structure of the atmospheric boundary layer in the active and inactive periods of SCSSM differs significantly not only above the land but also over the sea. (1) In the active period, a southeast wind dominates during the whole day which is observed in both the sea and the land sites, and the wind speed is relatively high. In contrast, the wind direction in the inactive period changes irregularly, and the wind speed is smaller than that in the active period. Moreover, in the active period, continuous precipitation is observed. As a result, the average daily temperature in the active period within the surface layer over land is reduced by approximately 2℃ than that in the inactive period. (2) Based on the sounding data, during the active period, a prevailing wind along southeast exists in the boundary layer, and the wind speed persists larger than 8 m/s above the altitude of 200m. However, during the inactive period, the wind speed is relatively small, and the wind direction changes frequently. The deviation of the wind direction between the upper and lower layers of the boundary reaches up to 180 degree in the inactive period. The temporal behavior of the potential temperature vertical profile in the land-type boundary layer is also analyzed. It is shown that the boundary layer height reaches the maximum of 937m in the inactive period. In contrast, due to the existence of the precipitation and the clouds during the active period the height of the mixing layer decreases heavily. The highest boundary layer found in the active period has the thickness of only about 700m.(3) In the active period, daily variation trend of Rn and Rs is consistent with the trend of Rn and Rs in the inactive period, only individual moment diurnal variation curve suddenly of Rn and Rs fall because of the influence of cloud. Sensible heat flux during the active period is smaller than the inactive period.(4)In the inactive period momentum flux is mainly affected by radiation in the Dianbai station, and turbulent is mainly affected by thermodynamic activity;In the active period momentum flux is greatly influenced by wind speed, and the turbulence energy due to kinetic energy.Turbulence of land-air and sea-air increases during the active period, because wind speed increases in the active period, and the kinetic energy enhance.In order to study the characteristics of the land-sea atmospheric boundary layer and sea-air flux and land-air flux during the active and inactive periods of the South China Sea Summer Monsoon, WRF model is used to evaluate the model performances of boundary layer structural characteristics in the Dianbai station. The simulation results show that during the active period a prevailing wind along southeast exists in the boundary layer and the wind speed increases, the temperature decrease, humidity increases.