The Temporal And Spatial Distribution Of Taihu Lake Breeze And Its Interaction With Urban Heat Island

Hourly wind speed and direction, air temperature over land surface temperature data from 19 stations, heat flux, wind speed and direction, air temperature over lake surface temperature data from 4 stations of Eddy Covariance Mesonet on Lake Taihu, and the wind profile data per 6minutes on Suzhou city are analysed in order to characterize lake breezes at Lake Taihu at 2012. A set of criteria based on the land-lake temperature difference, threshold of the synoptic wind and diurnal reversal of wind direction is used to identify sea breeze. WRF model while existing land surface process model programs on Taihu lake shore and near surface wind and temperature field simulation were compared to assess, and then simulate the effect of the best programs on the model and the Suzhou Taihu Lake Monsoon interaction between the urban heat island and its impact on urban air pollution were explored, the main conclusions are as follows.(1) Statistics are presented that describe the occurrence, duration and strength of the sea breezes.) Lake breezes are found to show a pronounced seasonal variation. The frequency of occurrence shows clearly regime characterized by summer and autumn (June, August and October), while the mean monthly frequency reach 25.3%.Lake breezes occurred most commonly on the north shore of the Taihu lake in spatial. The mean onset and cessation times are 1112 LST and 1541 LST (local standard time) respectively. The monthly wind speed range from 1.5 to 3.3ms-1, which reaches a maximum in August. The mean height of the lake breezes range from 300-500m during 1200 LST to 1400 LST.(2) An analysis of four physical factors affecting the lake breeze:the heat flux and temperature difference between lake and land, synoptic wind and urban area, shows that the temperature difference between lake and land is the most crucial factor that drive the lake Taihu breezes, while the heat flux difference between lake and land are less Significant somehow. The mean synoptic wind speed before lake breezes occurrence is low in autumn and winter while high in spring and summer. The reversal of wind direction, the development and the characteristics of the lake breeze are more intense as the presence of urban and convex shoreline.(3) CLM4-LISSS model WRF/NOAH mode coupling of success horizontal wind speed and air temperature than the accuracy of the simulation results WRF/NOAH mode and WRF/CLM4.0 mode significantly increased.(4) The simulation results indicate that WRF/CLM-LISSS, Taihu Lake in Suzhou wind circulation and urban heat island circulation significant interactions. Suzhou urban heat island circulation 10:00 start building a complete form, lake breeze circulation at the time near the urban heat island circulation of its extended speed inland improved significantly, from 11:00 to 12:00 between the lake breeze front in the inland forward the 20km and the urban heat island circulation mutual coupling, this time lifting speeds up the heart of the airflow 2m/s.14:00 lake breeze fronts hampered urban surface friction factors in inland extension slowed noticeably, while the urban heat island move another 2km to the east side.(5) WRF/CLM-LISSS simulation results show that the presence of the urban heat island for the temporal and spatial distribution of wind circulation in the lake has a significant influence, when the existence of the urban heat island, significantly increased the temperature difference between the east coast of Lake land, the east coast of Lake corresponding wind strength more large lake wind lasts longer. The existence of the urban heat island lake wind so divergent center closer to the center of the lake, but not the city center to the lake wind divergence northeastern coast of displacement. Suzhou city for the existence of the lake there is significant cooling effect, so that the pace of development and the intensity of the heat island circulation heat island circulation slowed down significantly closer to the center of Suzhou city center, while the east coast shore wind farm is more stable in the air flow to the city near the lower strata the collaboration with the center spoke more significant, more easily lead to the accumulation of pollutants in the city center.