Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018,the microphysical structural characteristics of cumulus(Cu)cloud at the precipitation stage were investigated.The c...Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018,the microphysical structural characteristics of cumulus(Cu)cloud at the precipitation stage were investigated.The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform(STF)cloud.In the Cu cloud,most cloud particles were between 7 and 10μm in diameter,while in the STF cloud the majority of cloud particles grew no larger than 2μm.The sensitivity of cloud properties to aerosols varied with height.The cloud droplet effective radius showed a negative relationship with the aerosol number concentration(Na)in the cloud planetary boundary layer(PBL)and upper layer above the PBL.However,the cloud droplet concentration(Nc)varied little with decreased Na in the high liquid water content region above 1500 m.High Na values of between 300 and 1853 cm-3 were found in the PBL,and the maximum Na was sampled near the surface in August in the Hebei region,which was lower than that in autumn and winter.High radar reflectivity corresponded to large FCDP(fast cloud droplet probe)particle concentrations and small aerosol particle concentrations,and vice versa for low radar reflectivity.Strong updrafts in the Cu cloud increased the peak radius and Nc,and broadened cloud droplet spectrum;lower air temperature was favorable for particle condensational growth and produced larger droplets.展开更多
Aerosols in the atmosphere not only degrade visibility,but are also detrimental to human health and transportation.In order to develop a method to estimate PM2.5 mass concentration from the widely measured visibility,...Aerosols in the atmosphere not only degrade visibility,but are also detrimental to human health and transportation.In order to develop a method to estimate PM2.5 mass concentration from the widely measured visibility,a field campaign was conducted in Southwest China in January 2019.Visibility,ambient relative humidity(RH),PM2.5 mass concentrations and scattering coefficients of dry particles were measured.During the campaign,two pollution episodes,i.e.,from 4-9 January and from 10-16 January,were encountered.Each of the two episodes could be divided into two periods.High aerosol hygroscopicity was found during the first period,when RH was higher than 80%at most of the time,and sometimes even approached 100%.The second period experienced a relatively dry but more polluted condition and aerosol hygroscopicity was lower than that during the first period.An empirical relationship between PM2.5 mass concentration and visibility(ambient aerosol extinction)under different RH conditions could thus be established.Based on the empirical relationship,PM2.5 mass concentration could be well estimated from visibility and RH.This method will be useful for remote sensing of PM2.5 mass concentration.展开更多
基金funded by the National Key Research and Devel-opment Program of China[grant number 2017YFC1501405]the National Natural Science Foundation of China[grant numbers 41975180,41705119,and 41575131]the National Center of Meteorology,Abu Dhabi,AE(UAE Research Program for Rain Enhancement Science)。
文摘Based on cloud-probe data and airborne Ka-band cloud radar data collected in Baoding on 5 August 2018,the microphysical structural characteristics of cumulus(Cu)cloud at the precipitation stage were investigated.The cloud droplets in the Cu cloud were found to be significantly larger than those in stratiform(STF)cloud.In the Cu cloud,most cloud particles were between 7 and 10μm in diameter,while in the STF cloud the majority of cloud particles grew no larger than 2μm.The sensitivity of cloud properties to aerosols varied with height.The cloud droplet effective radius showed a negative relationship with the aerosol number concentration(Na)in the cloud planetary boundary layer(PBL)and upper layer above the PBL.However,the cloud droplet concentration(Nc)varied little with decreased Na in the high liquid water content region above 1500 m.High Na values of between 300 and 1853 cm-3 were found in the PBL,and the maximum Na was sampled near the surface in August in the Hebei region,which was lower than that in autumn and winter.High radar reflectivity corresponded to large FCDP(fast cloud droplet probe)particle concentrations and small aerosol particle concentrations,and vice versa for low radar reflectivity.Strong updrafts in the Cu cloud increased the peak radius and Nc,and broadened cloud droplet spectrum;lower air temperature was favorable for particle condensational growth and produced larger droplets.
基金supported by a National Science and Technology Major Project(Grant No.2016YFC0200403)the National Natural Science Foundation of China(Grant Nos.41675037 and 41675038)。
文摘Aerosols in the atmosphere not only degrade visibility,but are also detrimental to human health and transportation.In order to develop a method to estimate PM2.5 mass concentration from the widely measured visibility,a field campaign was conducted in Southwest China in January 2019.Visibility,ambient relative humidity(RH),PM2.5 mass concentrations and scattering coefficients of dry particles were measured.During the campaign,two pollution episodes,i.e.,from 4-9 January and from 10-16 January,were encountered.Each of the two episodes could be divided into two periods.High aerosol hygroscopicity was found during the first period,when RH was higher than 80%at most of the time,and sometimes even approached 100%.The second period experienced a relatively dry but more polluted condition and aerosol hygroscopicity was lower than that during the first period.An empirical relationship between PM2.5 mass concentration and visibility(ambient aerosol extinction)under different RH conditions could thus be established.Based on the empirical relationship,PM2.5 mass concentration could be well estimated from visibility and RH.This method will be useful for remote sensing of PM2.5 mass concentration.
