青海湖夏秋季局地气候效应数值模拟研究

Numerical Simulation of Seasonal Local Climate Effect in Qinghai Lake

由于水陆热力性质差异,湖泊对局地天气气候具有显著影响,占中国湖泊总面积一半以上的高原湖泊对区域天气气候的影响不可忽视,但目前对高原湖泊局地气候效应的研究依然存在不足。本研究利用WRF-FLake动态耦合模式,设计了有湖与无湖两组实验,对高原最大湖泊青海湖的局地气候效应进行了整年的模拟研究。结果表明,耦合模式的模拟性能良好,青海湖在16月使得区域气温降低,而712月使得区域气温升高,且青海湖的存在降低了19月的日最高气温,增加了612月的日最低气温,使得气温日变化减小,白天青海湖为冷湖效应,而夜间青海湖为暖湖效应。26月青海湖轻微减少区域降水量,712月明显增加了区域降水量,且8月增加量最显著。青海湖对局地年降水量的贡献率在湖面上最大可达50%~60%,而在周边陆地为10%~30%,夏季青海湖增加的降水量最多,而秋季青海湖对总降水的贡献率最大,青海湖增加的降水在20:00(北京时,下同)至次日02:00最多,而14:0020:00最少,夏季增加的对流性降水较多,秋季增加的对流性降水较少。白天青海湖的冷湖效应使湖面产生下沉辐散气流,抑制对流的发展和水汽的扩散,导致湖泊降水效应减弱,而夜间青海湖的暖湖效应使湖面产生辐合上升气流,促进对流的发展和水汽的扩散,导致湖泊降水效应增强。

Due to the difference of the thermal properties between water and land,the lake has a significant impact on the local weather and climate,lakes on Qinghai-Tibetan Plateau account for more than half of China's total lake area,the effects of plateau lakes on regional weather and climate cannot be neglected,but studies on the local climate effect of the plateau lake are still insufficient.In this study,two simulation experiments that with and without lake were conducted by using the WRF-FLake dynamic coupling model to study the local climate effect of Qinghai Lake,the largest lake on TP,in a whole year.The results show that coupled model have a good performance on TP lake,Qinghai Lake reduce regional mean air temperature from January to June,while increase it from July to December.Moreover,daily maximum air temperature was decreased from January to September and daily minimum air temperature was increased from June to December,which also reduced the daily variation of air temperature.Qinghai lake have a cold lake effect in the daytime and turns to a warm lake effect in the nighttime.Qinghai lake slightly reduced the amount of precipitation in the lake area from February to June and significantly increased the regional precipitation from July to December,especially in August.The contribution rate of Qinghai lake to local annual precipitation is up to 50%~60%on the lake surface,and 10%~30%on the surrounding land.Qinghai lake increased the maximum amount of precipitation in summer,while has the largest contribution to total precipitation in autumn.The increased precipitation caused by Qinghai lake distribute most from 20:00(Beijing Time,same below)to 02:00 of nighttime,while least from 14:00 to 20:00 of daytime.Most of them is convective precipitation in summer but not in autumn.During the daytime,the cold lake effect of Qinghai lake produces a sinking and divergent flow on the surface of the lake that inhibit the development of convection and the diffusion of water vapor,leading to a weaken of the lake effect precipitation,while the warm lake effect of Qinghai Lake in the night generate convergence and upward airflow on the lake surface,promote the development of convection and the diffusion of water vapor,strengthen the lake precipitation effect.