Study Of Boundary Layer Wind Characteristics In Hangzhou Bay Area

Human activities are closely related to the physical and Chemical processes in the atmospheric boundary layer.The structure of the wind field in the atmospheric boundary layer greatly affects the transport and diffusion of pollutants.In order to guide the activities of daily life and production reasonably,it is of great significance to study the wind field in the atmospheric boundary layer.Aiming at the wind field in the atmospheric boundary layer of Hangzhou Bay,using observation data,including ground conventional observation data,wind profiler radar data,sounding data,etc.the basic characteristics of the wind field in the boundary layer,such as the shear coefficient of the near-surface wind profile and the low level jet,are analyzed,and the characteristics of the sea-land winds are counted.A typical land-sea breeze process was selected and the transport characteristics of pollutants in the process were analyzed by using WRF-Chem numerical simulation.The main conclusions are as follows:(1)Based on the ground routine observation data of Ningbo,Baoshan and Shengsi stations,the northwest and southeast winds dominate Ningbo all year round.In summer,they are affected by the Pacific high,and more than one third of them are southeast winds.In winter,northwest winds prevail under the control of Mongolian high.The east-northeast wind dominates Baoshan station,the south wind and north-northeast wind dominates Shengsi Station,and the west wind is less.Taking Shengsi station as background wind,the east-west wind component of Baoshan station and Ningbo station increased obviously,and the west wind component of Ningbo station increased mainly.(2)Based on the wind profiling radar data of Ningbo and Shanghai stations,the average wind speed in autumn is the smallest,and the average wind speed below the boundary layer is 5.91 m/s.The diurnal variation of wind speed in spring is not obvious,and the variation of wind shear is stronger in high level than in winter.The data show that the wind profile follows the power exponential law,and the wind shear coefficient(power exponent)is fitted by the data.The results show that the wind shear coefficient at night is generally larger than that at daytime,and the wind shear coefficient of Shanghai station is obviously larger than that of Ningbo station.(3)The characteristics of low-level jet flow are analyzed by using wind profiler radar data from Ningbo and Shanghai stations.Overall,the occurrence rate of low-level jet in the boundary layer at night is higher than that at daytime.Hangzhou Bay is affected by sea-land breeze,and the frequency of low-level jet in the boundary layer at night in autumn and winter is close to or even lower than that in daytime.Through the analysis of wind direction when the low-level jet appears,it is found that the abnormal increase of the low-level jet frequency in the daytime of autumn and winter is mainly due to the influence of weather system.In addition,the increase of westerly and westerly winds caused by land-sea breezes is also one of the reasons.Influenced by the branch of sea breeze reflux,when the background wind is westly,the low-level jet in the boundary layer frequently occurs at 1000m altitude.(4)The relationship between the development trend of sea-land breeze and the difference of sea-land temperature is analyzed by using surface observation data and sea-land temperature data.The development trend of land-sea breeze(disturbance intensity of sea-land breeze)is proportional to the difference of sea-land temperature in Hangzhou Bay.The deterministic coefficient of the equation(R2)is 0.5611.The greater the difference of sea-land temperature,the stronger the disturbance intensity of sea-land breeze.The trend of sea-land breeze increases by 0.16m/s/hr with the increase of sea-land temperature difference by 5?.Between 2014 and 2016,when the wind direction is westerly,there were 319 daytime low-level jet days,of which 32 were land-sea breeze days,and 10%were sea-land breeze days in daytime low-level jet days.The highest proportion is in autumn,6 of the 33 low-level jet days are land-sea breeze days,accounting for 18%.To some extent,this explains the occurrence rate of daytime low-level jet in autumn(5)WRF-Chem is used to simulate an example of the interaction between a low-level jet and sea-land breeze.The sea breeze started at about 10 o'clock,and the main pollutants were removed by sea breeze.Influenced by the disturbance of surface air pressure,pollutants will be transported in the region,and the convergence of local flow field will lead to the high concentration of pollutants at night.