Numerical Simulation and Mechanism of the Influence of Poyang Lake on the Intensity of Severe Convection over the Lake
The inhomogeneity of the lake and land underlying surfaces has large influences on the development and evolution of severe convective weather.Poyang Lake is the largest freshwater lake in China,and its area exhibits distinct monthly and seasonal variations.However,the underlying surface of the lake in the Weather Research and Forecast(WRF)model is usually assumed to be constant,which is different from the real situation and leads to model forecast errors.In this paper,the WRFV3.9 model was used to simulate a severe convective weather event that occurred over the Poyang Lake region during a summer night.Lake area sensitivity experiments were conducted to analyze the influence of Poyang Lake on the development and evolution of severe convective weather and its mechanism.The results showed that the 2 m temperature over the lake surface was significantly higher than that over the land surface during summer night.The land breeze converged and rose over the lake region,while there was a sinking and divergent airflow over the shore,which caused precipitation to decrease over the west bank of the lake but increased over the lake.The subsequent lake-removing sensitivity experiment further confirmed the warming effect of Poyang Lake.Poyang Lake could inhibit precipitation occurred over the west bank of the lake and intensify precipitation over the lake by stimulating the secondary circulation of land-breeze.The precipitation of the lake-removing experiment increased by 20%over the west side of the lake,and decreased by 16%over the lake,suggesting the impact of the lake on precipitation intensity.In addition,it was found that the precipitation over the lake increased by 7%,16%,30%and 43%in the lake-expanding sensitivity experiments,where the lake area was expanded by 1.5,2.5,3.5 and 4 times,respectively,further confirming the sensitivity of severe convection intensity to the area of Poyang Lake.These results indicated that attention should be paid to the possible trend of convections weakening(enhancing)before(after)entering the Poyang Lake region during summer nights.Meanwhile,when a numerical model was used to simulate the severe convection weather,the real lake area could be introduced into the underlying surface of the model when the real lake area differed greatly from the default climatic value used in the numerical model,to improve the forecasting capability for severe convective weather occurring over lake regions.
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