Based on the dynamic framework of WRF and Morrison 2-moment explicit cloud scheme, a salt-seeding scheme was developed and used to simulate the dissipation of a warm fog event during 6–7 November 2009 in the Beijing ...Based on the dynamic framework of WRF and Morrison 2-moment explicit cloud scheme, a salt-seeding scheme was developed and used to simulate the dissipation of a warm fog event during 6–7 November 2009 in the Beijing and Tianjin area. The seeding effect and its physical mechanism were studied. The results indicate that when seeding fog with salt particles sized 80 μm and at a quantity of 6 gm^（-2） at the fog top, the seeding effect near the ground surface layer is negative in the beginning period, and then a positive seeding effect begins to appear at 18 min, with the best effect appearing at 21 min after seeding operation. The positive effect can last about 35 min. The microphysical mechanism of the warm fog dissipation is because of the evaporation due to the water vapor condensation on the salt particles and coalescence with salt particles.The process of fog water coalescence with salt particles contributed mostly to this warm fog dissipation. Furthermore, two series of sensitivity experiments were performed to study the seeding effect under different seeding amounts and salt particles sizes. The results show that seeding fog with salt particles sized of 80 μm can have the best seeding effect, and the seeding effect is negative when the salt particle size is less than 10 μm. For salt particles sized 80 μm, the best seeding effect, with corresponding visibility of 380 m, can be achieved when the seeding amount is 30 g m^（-2）.展开更多
A comprehensive measurement of planetary boundary layer(PBL)meteorology was conducted at 140 and 280 m on a meteorological tower in Beijing,China,to quantify the effect of aerosols on radiation and its role in PBL dev...A comprehensive measurement of planetary boundary layer(PBL)meteorology was conducted at 140 and 280 m on a meteorological tower in Beijing,China,to quantify the effect of aerosols on radiation and its role in PBL development.The measured variables included four-component radiation,temperature,sensible heat flux(SH),and turbulent kinetic energy(TKE)at 140 and 280 m,as well as PBL height(PBLH).In this work,a method was developed to quantitatively estimate the effect of aerosols on radiation based on the PBLH and radiation at the two heights(140 and 280 m).The results confirmed that the weakened downward shortwave radiation(DSR)on hazy days could be attributed predominantly to increased aerosols,while for longwave radiation,aerosols only accounted for around onethird of the enhanced downward longwave radiation.The DSR decreased by 55.2 W m^(-2) on hazy days during noontime(1100–1400 local time).The weakened solar radiation decreased SH and TKE by enhancing atmospheric stability,and hence suppressed PBL development.Compared with clean days,the decreasing rates of DSR,SH,TKE,and PBLH were 11.4%,33.6%,73.8%,and 53.4%,respectively.These observations collectively suggest that aerosol radiative forcing on the PBL is exaggerated by a complex chain of interactions among thermodynamic,dynamic,and radiative processes.These findings shed new light on our understanding of the complex relationship between aerosol and the PBL.展开更多
基金partially supported by the National Science Foundation of China(Grant Nos.41205100,41375136 and 41405127)the Beijing Municipal Science and Technology Commission(Project No.Z141100001014017)the National Department of Public Benefit Research Foundation of China(Grant No.GYHY201306065)
文摘Based on the dynamic framework of WRF and Morrison 2-moment explicit cloud scheme, a salt-seeding scheme was developed and used to simulate the dissipation of a warm fog event during 6–7 November 2009 in the Beijing and Tianjin area. The seeding effect and its physical mechanism were studied. The results indicate that when seeding fog with salt particles sized 80 μm and at a quantity of 6 gm^（-2） at the fog top, the seeding effect near the ground surface layer is negative in the beginning period, and then a positive seeding effect begins to appear at 18 min, with the best effect appearing at 21 min after seeding operation. The positive effect can last about 35 min. The microphysical mechanism of the warm fog dissipation is because of the evaporation due to the water vapor condensation on the salt particles and coalescence with salt particles.The process of fog water coalescence with salt particles contributed mostly to this warm fog dissipation. Furthermore, two series of sensitivity experiments were performed to study the seeding effect under different seeding amounts and salt particles sizes. The results show that seeding fog with salt particles sized of 80 μm can have the best seeding effect, and the seeding effect is negative when the salt particle size is less than 10 μm. For salt particles sized 80 μm, the best seeding effect, with corresponding visibility of 380 m, can be achieved when the seeding amount is 30 g m^（-2）.
基金the National Key Research and Development Program of China(2017YFC0209604 and 2018YFF0300101)Beijing Natural Science Foundation(8204062)。
文摘A comprehensive measurement of planetary boundary layer(PBL)meteorology was conducted at 140 and 280 m on a meteorological tower in Beijing,China,to quantify the effect of aerosols on radiation and its role in PBL development.The measured variables included four-component radiation,temperature,sensible heat flux(SH),and turbulent kinetic energy(TKE)at 140 and 280 m,as well as PBL height(PBLH).In this work,a method was developed to quantitatively estimate the effect of aerosols on radiation based on the PBLH and radiation at the two heights(140 and 280 m).The results confirmed that the weakened downward shortwave radiation(DSR)on hazy days could be attributed predominantly to increased aerosols,while for longwave radiation,aerosols only accounted for around onethird of the enhanced downward longwave radiation.The DSR decreased by 55.2 W m^(-2) on hazy days during noontime(1100–1400 local time).The weakened solar radiation decreased SH and TKE by enhancing atmospheric stability,and hence suppressed PBL development.Compared with clean days,the decreasing rates of DSR,SH,TKE,and PBLH were 11.4%,33.6%,73.8%,and 53.4%,respectively.These observations collectively suggest that aerosol radiative forcing on the PBL is exaggerated by a complex chain of interactions among thermodynamic,dynamic,and radiative processes.These findings shed new light on our understanding of the complex relationship between aerosol and the PBL.
