Numerical simulation of summer katabatic wind at Zhongshan Station,Antarctica: A case study

Katabatic winds are airflows that occur above a cold sloped surface. They are driven by gravity that causes colder and denser air masses to move downhill. Katabatic winds play a crucial role in the surface wind regime of Antarctica. Chinese Zhongshan Station,Antarctica,is strongly influenced by the katabatic wind all the year round. In sunny summer days,the katabatic wind at Zhongshan Station usually begins in the evening. The wind reaches its maximal speed at mid-night and then decreases before the next noon,with a significant diurnal cycle characteristics. The katabatic wind case in austral summer,January 2010,at Antarctic Zhongshan Station is analyzed with employing of conventional meteorological observations and the Polar WRF model. The results indicate that when katabatic wind emerges at nights of clear sky,the wind speed near the ground and surface air temperature trends are negatively correlated to-0.91. Simulations from Polar WRF show that the height of the maximum speed of the katabatic wind,15-21 m/s,is between 100 and 150 m from the ground. Near surface air temperature inversion always accompany with the katabatic wind. With the thickness of 200 to 300 m,the inversion has its strength of about 4-6℃. The near-ground katabatic wind at Zhongshan Station always blows from the southeast due to the ground friction. The wind direction deflects counterclockwise and eventually becomes parallel with the terrain contours while the height increasing. When there is no direct solar radiation,continuous inversion presents at Antarctica continent and enhances the katabatic air flow. With the enhancement of the inversion,windy area gradually shifts westward and the acreage increases. In the short time when inversion disappears due to solar radiation in summer times,the katabatic wind would not completely disappear,thus forming a relatively stable spatial distribution of wind direction.