Numerical Study Of The Regional Climate Effect Of Lake Clusters In Tibetan Plateau And Its Working Mechanisms During Summer

To reveal the regional climate effect of lake clusters in Tibean Pleteau(TPL)during summer,we conducted 7-summer simulations from 2008 to 2014 by utilizing the WRF-Lake model.In this paper,we firstly investigate the sensitivity of the WRF-Lake model to land surface and cumulus parameterizations in simulating the summer climate over the entire model domains.Based on the optimal combining schemes,we designed the control and sensitive experiments with or without TPL to assess their impacts on the regional summertime climate and associated atmospheric responses.The major findings are listed as follows:The performances of precipitation simulations mainly depends on the choices of cumulus parameterizations.The land surface schemes only have apparent influences on precipitation simulations over the arid and semi-arid regions,such as the Tibetan Plateau and the vast northwest parts of China.Further comparisons reveal that the Grell-Devenyi(GD)scheme outperforms than the other cumulus schemes in simulating the spatial distributions of summer mean precipitation,the probability and contribution density function of rainfall with different intensity.These significant improvements can be attributed to the more realistic simulations of the South Asia high,the low pressure over India and Tibetan Plateau,which will lead to better descriptions in the intensity of the lower convergence,the aloft divergence and the water vapor transportation.All the ten experiments simulated the spatial distribution of summer mean 2-m temperature quite well.According to the integrated score by considering the spatial correlation coefficients,the ratio of standard deviation,the mean bias,the root mean square errors and the taylor score simultaneously,the Noah GD and CLM4_GD are the optimals schemes in simulating the summer 2-m temperature.The TPL can hugely influence the 2-m temperature and precipitation over the lake areas and the nearby regions.The lakes in the central and eastern Tibetan Plateau can increase the 2-m temperature and the convective precipitation,while the others show cooling effects on 2-m temperature and decreasing effects on large-scale precipitation.In terms of intra-seasonal variations,the cooling effects of TPL on 2-m temperature decrease with the summertime evolutions due to the gradual reduction of the negative sensible heat anomaly and the enhancement of positive latent heat anomaly.As for the diurnal variations,the TPL mostly reduce the 2-m temperature variations by increasing the minimum 2-m temperature and largely decreasing the maximum 2-m temperature.In addition,the TPL can enhance the nighttime convective precipitation and reduce the late-afternoon convective precipitation.The enhancement of nighttime precipitation amount,frequency,and intensity of total rainfall over TPL is jointly contributed by short-duration(?6h)and long-duration(>6h)rainfall,while the decrease of daytime precipitation amount and frequency of total rainfall is due to the short-duration rainfall.During the daytime,the TPL absorbs the incoming solar radiation,cools the above air,and inhibits the upward turbulent heat transport.Moreover,the valley breeze triggered by the mountain-valley thermal contrast can further enhance the over-lake katabatic flow and the secondary circulations,which jointly stabilize the over-lake atmospheric column and inhibit the daytime convections.At night,the TPL releases large amounts of latent heat,warm and moisten the above air,and lead to the formation of destabilized atmospheric column,as reflected by the decreased equivalent potential temperature over lake.Hence,the nighttime convective precipitation over lakes is significantly enhanced due to the presence of TPL.