Aircraft Observations Of Aerosol,cloud Properties In Beijing And Aerosol Impact On Cloud Microphysics Process

Aerosol and cloud are both of great importance in atmospheric environment.And aerosol affects cloud microphysical and radiative characteristics by providing cloud condensation nuclei.Therefore,it is essential to study the impact of aerosols on cloud microphysical characteristics.This paper analyzes the 11-year aerosol property and 12-year cloud porperty in Beijing through aircraft observations,supporting by Beijing Weather Modification Office.At the same time,two cases are selected for comparative analysis under different background aerosol concentration to investigate the impact of aerosol on clouds,especially on ice phase process.The data of PCASP probe on the aircraft Yun12 from 2007 to 2017 showed that the time variation of aerosol characteristics is very obvious.The aerosol number concentration in 2008 is significantly higher than that after 2008,and the effective diameter of aerosol before 2011 is significantly lower than that after 2011.The seasonal variation of aerosol is also very notable,which is closely related to the seasonal variation of boundary layer.The vertical profiles of aerosols can be divided into five categories,the most common two categories are:number concentration of aerosol remains unchanged in lower layer while decreases in the upper layer;aerosol number concentration peaks at an uncertain height.The situation that aerosol number concentration varies little with altitude is more likely to occur when the ground aerosol number concentration is relatively lower.Through aircraft observation by Yun 12 and King Air from 2007 to 2018,a set of 2959 cloud microphysical characteristic samples are analyzed.The cloud droplet concentration,’efifective diameter and droplet distribution of cloud droplets ranging from 2 to 50pm,vary significantly with the height above cloudbase,which is in good agreeIment with their vertical profile.The number concentration for cloud droplet smaller than 10μm increases with the height above cloudbase increases,while cloud droplets larger than 20μm increase with the height above cloudbase firstly,then decrease after reaching 2000m,but increase again at 4000m.The seasonal variation of cloud microphysical characteristics may be related to the aerosol concentration of each season,in addition to temperature.In September and October,most of precipitation particle and irregular ice particle are detected above melting layer in mountain area.Most of the time,the number concentration of precipitation particle and irregular ice particle is less than 5 L-1 or 2 L-1,respectively.Two flights on April 18,2015 and April 28,2015 are selected for investigating the impact of aerosol concentration on cloud microphysical characteristics.The near-ground aerosol concentrations are 4000 cm-3 and 1700 cm-3,respectively.By analyzing the number concentration time series and vertical profile of FCDP,2D-S and HVPS probes,we select two in-cloud ascending process with same height level,and analyze the particle size distribution and image data.The number concentration of cloud droplet with diameter ranging from 10 to 50μm in the higher aerosol concentration case is significantly higher than that in another case.At the same time,the increase in liquid water content promotes the formation of graupel,hence the aggregation of ice crystals and snow crystals is depressed,which induces the scarcity of irregular particles.