Analysis And Discussion On The Reason Of Two Continuous Thunderstorm Processes At Beijing Capital Airport

Thunderstorms and the accompanying weather such as gale,heavy rainfall,low-level wind shear pose a great threat to aviation safety.The frequent thunderstorms in summer easily cause a sharp decline in airport traffic capacity and large-scale delays in flights,seriously affecting aviation safety and the efficiency of civil aviation operation,especially when continuous thunderstorms occur in the airport or near the airport area,flights are even more affected.Therefore,it is necessary to explore the occurrence and development mechanism of thunderstorms and provide timely and effective weather forecasting and decision-making services for the control and airport.Based on the monthly mean reanalysis data of NCEP(2.5° x 2.5°),the reanalysis data of NCEP(1° x 1°)every six hours,and the ground observation data of Beijing Capital Airport(ZBAA)every half hour from 2000 to 2018,the characteristics of summer precipitation in eastern China and Beijing(June-August)were analyzed by using meteorological statistics and diagnostic methods.A continuous thunderstorm(TS)occurring in the observation message of Beijing Capital Airport for 2 days or more from 2000 to 2018 is recorded as a continuous thunderstorm process with 16 UTC per day as the boundary.Two continuous thunderstorms were selected.The C-band dual polarization Doppler weather radar data of Beijing Capital International Airport(ZBAA)were used to analyze and discuss the weather situation,dynamic and thermal conditions and mesoscale characteristics.The accuracy of WAFS(World Area Forecast System)numerical prediction products for two continuous thunderstorms is analyzed by comparing the forecast products with the actual data.The results show that:(1)By using EOF analysis method,it is found that the summer rainfall in eastern China from 1989 to 2018 has a certain spatial and temporal distribution characteristics.In some years of more(less)rain in North China and South China,the corresponding years in East China are less(more)rain;in some years,the precipitation in North China and South China is more synchronous,and these characteristics have obvious interannual variation characteristics.(2)From 2000 to 2018,there were 138 continuous thunderstorms occurred in Beijing Capital Airport.The most continuous thunderstorms occurred in June-August and the least in April and October.The average number of continuous thunderstorms occurred in Beijing Capital Airport(ZBAA)was 7.26.The effects of cold vortex system and the thunderstorms generated by the periphery of subtropical high were longer.(3)Two cases of continuous thunderstorms at Beijing Capital Airport(ZBAA)from July 6 to 9,2017 and July 16 to 22,2018 were selected for analysis.It was found that the effects of the systematic cold eddy thunderstorms on the terminal had the characteristics of long time span and large regional impact.The impact of cold air was limited before the system approached,and the duration of thunderstorms was not very long.Squall line weather may occur when the high and low level jet acts together under the control of the cold eddy system.The continuous thunderstorms occurring in the periphery of the subtropical high often require the cooperation of weather systems such as low-level jet and high-level trough.(4)The 6-36 hour forecast of WAFS has a good grasp of the circulation situation and a high reference value.However,WAFS products mainly provide high-altitude meteorological service products.The types of forecast products are limited,and there is a lack of near-ground observation data and forecast.It needs to be combined with other numerical forecast products for reference.(5)The generation and development of mesoscale weather systems in continuous thunderstorms are complicated.At present,meteorological science is not well aware of its microphysical processes.Doppler weather radar products can reflect many details,such as the observation of ultra-low-level jet and outflow boundary,which can provide some guidance and reference for the proximity forecast of severe convective weather and the issuance of airport warnings.