An Observational Study And Numerical Simulation On Lake Breeze Over Poyang Lake Area

Lake-breeze circulations, which occur due to the differential heat content between lake and land, have a large impact on local weather and climate. However, what we know about lake-breeze related to Poyang Lake is still limited, including its activity characteristics, three-dimentional structure and generation mechanism. In this study, statistical features of lake-breeze events over Poyang Lake area are analyzed based on National Automatic Meteorological Station data from 2010 to 2015. And two cases are selected to learn the diurnal pattern of lake-breeze circulations. Then WRF3.6.1, coupled with a lake model is employed to explore the lake-breeze circulation structure in 8th Aug, 2004. Finally, the impacts of Poyang water bodies on lake-breeze’s intensity are investigated by two sensitivity experiments.Statistical and observational analysis indicates that there are about 69 lake-breeze days annualy, and the number varies with year, season and month. Lake-breeze days tend to occur more frequently in autumn, less frequently in summer, especially on October and June. Lake-breeze offen begins at 09-14 LST(Local Stantard Time) at the day, while land-breeze at 21-01 LST at night. Generally, lake-breeze, usually lasting about 3-10 hours, is greater than land-breeze in intensity. Lake-breeze events along the eastern and western shores have also showed their differences. Lake-breeze events occur more frequently on eastern shores, and the time of onset and end is later than that in western lake shore. Obviously differential heat content can be observed in lake-breeze days, especially along the eastern shores.Numerical study suggests that lake-breeze circulation can be well-simulated over Poyang Lake area, which clearly shows the diurnal pattern of wind, temperature, humidity and divergency relate to lake-breeze. The air over lake is divergent in the daytime, accompanied with downward wind and low humidity. The lake breeze can penetrate to 100 km inland, where lake-front may occur. There is a return flow to the lake above 850 hPa, forming a secondary circulation below 700 hPa. At night, land-breeze flows onshore, weaker than lake-breeze, while a convergent line of land-breeze and return flow still could be found near the lake.Sensitivity experiments on water body scope of Poyang Lake demonstrate that Poyang Lake water is the main reason for the occurrence of the local circulation over Poyang Lake area. The differences on temperature between lake and land would be dissipated(reduced) if water bodies were removed(narrowed), resulting in the disappearance(weakening) of lake breeze. Moreover, it is found that the lake-breeze circulation is the main component of local circulation over Poyang Lake basin.