| Heat conduction properties and roughness between lake and land have significant difference, led directly to the lake-atmosphere exchange has important influence on the regional weather and climate, thus affecting the atmospheric environment of surrounding city. Observation data of the Lake Taihu meso-scale flux net which is from March2012—February2013is firstly utilized to drive the CLM4-LISSS. While optimizing the important parameters of the calculation of the lake-atmosphere exchange and assessing the suitability of the offline model for different seasons in Lake Taihu. Then we used WRF-Lake which successfully coupled between CLM4-LISSS and WRF/NOAH model to study the impact of Lake Taihu on the urban heat island of the surrounding city and further to explore how the interaction of lake breeze and the heat island circulation affect air pollution.The main research conclusions are:(1) Seasonal changes of submerged macrophytes growth determines the purification degree of lake water quality, water flow rate and the turbulent mixing inside the lake. Thus affecting extinction coefficient, turbulent diffusion coefficient, roughness parameters and so on in lake model. According to the characteristics of submerged macrophytes dominated the east Lake Taihu, by analyzing and summarizing multiple susceptibility test, we have optimized five parameters in the lake model as follows:extinction coefficient valued3m"1in spring and winter, while it valued2.5m-1in summer and autumn; The turbulent diffusion coefficients of four seasons were2%,1.4%,1.1%,2%of the value calculated with the Henderson-Sellers parameterization respectively; Turbulent diffusion coefficient valued6×10-6m2s-1when276K<T20<277.15K, while it valued1×10-5m2s-1when T20≤276K particularly; Momentum roughness of four seasons valued by1.9×10-6,1.9×10-6,6×10-5,1.9×10-7m, respectively; Heat roughness all valued8×10-5m and moisture roughness all valued3.9×10-8m.(2) After parameter optimized, the consistency coefficient of lake surface temperature simulated by CLM4-LISSS in spring, summer and winter all increased by0.01. The consistency coefficient of sensible heat flux increased by0.1,0.1and0.01respectively. The consistency coefficient of latent heat flux increased by0.09,0.06,0.04respectively. But the simulated results in autumn was not ideal.(3) WRF-Lake which successfully coupled between CLM4-LISSS and WRF/NOAH model, the accuracy of both the results of horizontal wind speed and air temperature were better than WRF-Default.(4) The simulated results of WRF-Lake showed that, the urban heat island effect around Lake Taihu was strong at daytime and weak at night. The temperature difference between urban and suburban areas was not obvious at02:00, and there was no significant urban heat island phenomenon; Land breeze gradually decreased while the onset of lake breeze begin at8:00, with no urban heat island phenomenon as well; At14:00since the temperature differences between lake and land caused by the underlying surface difference reached to the highest level, the lake breeze became mature and diverged from the center of the lake, then coupling with the heat island circulation at the urban area, the intensity of urban heat island reached about3℃at this time; At20:00the intensity of urban heat island decreased to1℃or so with lake breeze break up.(5) The simulated results of WRF-Lake also showed that, temperature on the lake was comparatively higher at02:00, there appeared obvious hot tail feathers above Suzhou city at the leeward side, thus there was distinct temperature inversion in local city which maximum value reached100m height, it had adverse influence on the diffusion of pollutants above the city; At08:00, temperature on the lake was comparatively higher, Lake Taihu generated distinct calescence to leeward side, the scope of influence reached about50-60km; Lake breeze developed exuberant at16:00, the coupled between lake breeze and the urban heat island circulation made turbulent kinetic energy above Suzhou city achieved2.4m2s-2. |
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