| In this paper, a coupled Weather Research and Forecasting (WRP) model with the Noah land surface model is used to investigate the impact of lake land use changes on the evolution of the severe thunderstorms, which attacks Tai Lake region and caused extensive damage in the vicinity of Taihu area during the afternoon hours of18August2010. The control run and two sensitivity experiments are designed. The control run (CNTL) is carried out with the original surface characteristics. The first sensitivity experiment (CROP) is designed to replace Tai Lake with cropland. In the second sensitivity experiment (WATER) the underlying surface is considered as water. Firstly, the control run results from lkm domain compared with observation show that the control run simulates well both lake-land breeze circulation and remarkable lake-land breeze evolution on18August2010. The lake breeze set up at9:00LST, then become enhanced with the horizontal temperature contrast between land and lake being pronounced at12:00LST, and turn to land breeze at18:00LST. It is found that the wind speed and depth of Lake Breeze are horizontal asymmetries on the east and west coast of Tai Lake affected by southeasterly gradient flows and valley breeze. At the leading edge of lake breeze circulation called lake breeze front, convergence lines spread along the lake shore where is a zone of enhanced upward vertical motion, moisture air and low-level vertical wind shear, which act to trigger the development of thunderstorm at12:00LST. The characteristics of the diurnal evolution of the thunderstorm are reproduced by WRF model, which including the initiation of convection along the lake breeze front and the formation of thunderstorm, then collision between outflow from thunderstorm and Lake Breeze trigger a new thunderstorm. The convective cloud not develop in the CROP, and in the WATER the whole area shows cloudless. The comparison experiments show that the lake breeze front triggered and strengthen the severe convective weather. In the course of thunderstorm development, on the one hand, the exchange of sensible heat fluxes can change the structure of the boundary layer, and make the atmosphere more unstable. On the other hand, the surface fluxes moistened the boundary layer atmosphere and enhance horizontal convergence and divergence which can accelerate the development of cloud and precipitation.Based on the work afore, the impact of the two different land surface models coupled with the Weather Research Forecasting (WRF) model on the thunderstorm is studied. The model results are compared with observed rainfall, surface temperature and wind speed over two stations, model results shows that the NOAH scheme has a fairly better performance than the RUC scheme and the simulated thunderstorm is sensitive to the chosen land surface model (LSM). Different LSMs can lead to the difference of location, timing and intensity of the simulated thunderstorm and the maximum values of daily precipitation differences between two schemes can be40mm. The results from the model experiments analyzed in this study show the convection initialization has two-hour delays in RUC experiment relative to NOAH experiment and provide additional evidences that land surface representation has a prominent feedback on the representation of mesoscale convection. The changes in land surface model can affect both thermal and dynamic effects which influence the development of thunderstorm, then resulting in the differences of convection initialization, development and maintenance for each of the two WRF runs with different LSMs. Due to parameterization of vegetation properties for different land use categories in two land surface models, Noah scheme describes the characteristics of underlying surface reasonably better than RUC scheme, especially the urban land use category, which can improve the ability of WRF run with NOAH LSM to simulate the thunderstorm. |
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