低层大气季节变化及与黄海雾季的关系

Seasonal Variations in the Atmospheric Stratification and the Relations with the Yellow Sea Fog Season

根据2005～2006年青岛气象台逐日L波段探空雷达资料和地面观测资料,计算、分析了低层大气湍流混合高度、湍流混合强度和温度层结的季节变化,并分析了其与黄海海雾季节变化的关系。结果表明:温度层结、湍流强度和高度均有明显的季节变化,这些变化与海雾的季节变化密切关联。春、夏季节湍流强度较强,湍流混合高度相对较低,有利于近海面的凝结水汽在低空聚集而形成雾。雾季典型的层结结构是"上稳下湍",即:近地(海)面至150 m左右为条件性不稳定,其上方为大约400 m厚的稳定层。盛雾期稳定层的稳定性减弱,湍流强度加强。另外,黄海雾季由7月最盛到8月突然结束,与东海雾季逐渐结束明显不同。8月黄海终雾期迅速的原因与风向的突然转变有关。偏东风为整个黄海带来较冷的空气,使条件性不稳定发展,雾季终止。风向的突然转变与区域性海陆热性质差异和大尺度背景环流的调整有关。

Based on the daily soundings by L-band radar data from 2005--2006 in Qingdao and the surface in situ fog observations in the Yellow Sea（YS）, this paper calulated the seasonal variation in the turbulent mixing height and intensity（TMHI） and the stratification in the atmospheric boundary layer and analyzed their relations with the sea fog occurrence frequencies（FOFs）. The results show that the variations in the TMHI, the stratification and the FOFs are highly seasonal, and the relations among them are obvious. The turbulent height is relatively lower and the turbulence is strengthened in spring-summer period. These benefit the FOFs increasing. The typical stratification in the sea fog season is ＂a hanging stable layer with turbulent mixing beneath＂. The thickness of the stable laYer maintains about 300-400 meters capping a conditional instability layer that is about 100--150 meters in thickness in the fog season. The stability becomes weaker and the turbulence becomes stronger with the development of the sea fog season. The wet adiabatic neutral Stability appears when the sea fog season peaks. Besides, the sea fog season in the YS is marked by a sudden withdrawal in August which differs from that in the East China Sea. With the sudden changes, the solar radiation and the differentia in land-ocean heat capacity play a vital role in the turning of the prevailing winds from southerly to easterly, and the easterlies bring dry and cool air to the Yellow Sea, thus stimulating the conditional instability and contributing to the sudden retreat of the sea fog season.