Numerical simulation of the climate effect of high-altitude lakes on the Tibetan Plateau

摘要

Lakes regulate the water and heat exchange between the ground and the atmosphere on different temporal and spatial scales.However,studies of the lake effect in the high-altitude Tibetan Plateau(TP)rarely have been performed until recently,and little attention has been paid to modelling of frozen lakes.In this study,the Weather Research and Forecasting Model(WRF v.3.6.1)is employed to conduct three numerical experiments in the Ngoring Lake Basin(the original experiment,an experiment with a tuned model,and a no-lake experiment)to investigate the influences of parameter optimization on the lake simulation and of the high-altitude lake on the regional climate.After the lake depth,the roughness lengths,and initial surface temperature are corrected in the model,the simulation of the air temperature is distinctly improved.In the experiment using a tuned model,the simulated sensible-heat flux(H)is clearly improved,especially during periods of ice melting(from late spring to early summer)and freezing(late fall).The improvement of latent-heat flux(LE)is mainly manifested by the sharp increase in the correlation coefficient between simulation and observation,whereas the improvement in the average value is small.The optimization of initial surface temperature shows the most prominent effect in the first year and distinctly weakens after a freezing period.After the lakes become grassland in the model,the daytime temperature clearly increases during the freezing and melting periods;but the nocturnal cooling appears in other stages,especially from September to October.The annual mean H increases by 6.4 times in the regions of the Ngoring Lake and the Gyaring Lake,and the LE declines by 56.2%.The sum of H and LE increases from 71.2 W/m2(with lake)to 84.6 W/m2(no lake).For the entire simulation region,the sum of H and LE also increases slightly.After the lakes are removed,the air temperature increases significantly from June to September over the area corresponding to the two lakes,and an abnormal convergence field appears;at the same time,the precipitation clearly increases over the two lakes and surrounding areas.