Modeling Study On The Impact Of Black Carbon And Sulfate Aerosol On East Asian Upper-level Jet

The East Asian upper-level jet is a strong and narrow wind,which mainly exits in the upper troposphere or stratosphere.The Asian upper-level jets include subtropical jet and polar front jet.And the intensities of them are strongest in winter and weakest in summer.Under the influence of human activities,the emissions of aerosol and their precursors are increased in East Asia,that have an influence on radiation forcing and may have an influence on the jets through thermodynamics and dynamics process.In this study,the black carbon and sulfate aerosol impact on the East Asian upper-level jet in winter was simulated using The Community Earth System Model(CESM),and investigated the thermodynamic and dynamics mechanism and the impact on the precipitation.The concentration of black carbon increased significantly at 20-42.5°N,100-130°E;In the large value of black carbon concentration increased,black carbon absorbs solar shortwave radiation and heated the atmosphere in the middle and low-atmosphere(below 500 h Pa),and the atmospheric stability decreased;there was deep-convection at middle atmosphere.While strong ascending motion at the north of 30°N,the precipitation increased which caused releases latent heat and heated atmosphere.Under combined action of shortwave heat and condensational heating from moisture processes,the local atmosphere warmed up.The concentration of black carbon on the land was larger than that on the sea,and the black carbon concentration diffused higher at the plateau,so the atmosphere on the land warmed up,and the strongest warming was at the plateau,so the temperature meridional gradient was strengthened in the north of the plateau,so the polar front jet increased.Due to the land warmd up,there was a high pressure anomaly in the land and low pressure anomaly in the western Pacific Ocean.The polar front jet was located at the north side of the high pressure anomaly on the land,the low pressure on the ocean anomaly increased.Subtropical jet was located on the north side of the low pressure anomaly,there was east wind anomaly,subtropical jet was weakened.The precipitation reduced at the East China Sea where was at the south of subtropical jet.The concentration of sulfate increased significantly at 15-35°N,100-130°E.The impact of the direct effect of sulfate was very weak.Sulfate could be cloud condensation nuclei,the concentration of sulfate increased,the concentration of cloud droplets increased,and the effective radius of cloud droplet decreased;Sulfate could also increase the liquid water path that caused the cloud cover increased.Under the first-indirect effect and second-indirect effect,the cloud shortwave radiation forcing decreased,that caused local atmosphere cooling.Due to the cooling effect of sulfate,there was a high pressure anomaly at the surface,which caused the adjustment of circulation field.There was an accumulation of cold air over southern Japan and the western Pacific Ocean.The temperature meridional gradient was weakened at 40°N,the zonal wind decreased at upper atmosphere,so subtropical jet and polar front jet kept away from each other.At the south of Japan,the precipitation increased.Under the impact of sulfate and black carbon on East Asian jet in winter,black carbon played a leading role in the direct effect,that caused atmosphere warming;sulfate played a leading role in the indirect effect,that caused atmosphere cooling.Black carbon played a leading role of the change of local temperature,so the local atmosphere temperature increased.The impact of black carbon and sulfate made subtropical jet weaken and polar front jet strengthen.The change of intensities jets were stronger,so the change of precipitation was stronger.Compared the impact of each aerosol on temperature,jet with the combined action of black carbon and sulfate,we can found that the impact of different aerosol was nonlinear superposition.