Numerical Simulation Study Of The Effects Of Sulfate And Black Carbon Aerosols On The Onset Of The East Asian Summer Monsoon

Previous studies have shown that scattering aerosol sulfate(SO₄^2-)and absorptive aerosol black carbon(BC)can affect the climate system by scattering or absorbing solar radiation as well as changing the microscopic and macroscopic characteristics of clouds.As subsystems of the East Asian monsoon,the East Asian subtropical monsoon and the South China Sea summer monsoon have an important impact on the East Asian atmospheric circulation and precipitation.However,there is still a lack of understanding of the differences in the effects of sulfate and black carbon aerosols on the onset of monsoons in different regions,as well as their effects and mechanisms on the SCS summer monsoon.This study uses the CESM(The Community Earth System Model)model CAM5.1 module to simulate the effects of SO₄^2-and BC on the onset and advancement of the East Asian subtropical monsoon,as well as the onset time of the South China Sea summer monsoon.We also highlight the thermal and dynamic mechanism induced by SO₄^2-and BC on the onset of South China Sea summer monsoon.The simulation results show that for the East Asian subtropical monsoon,the turbulent diffusion cooling effect of sulfate in the central region of the monsoon(27.5-32.5°N,105-120°E,namely the Yangtze River Delta)causes the cooling of the middle and lower troposphere in spring,delaying the reversal of land and sea temperature,and delaying the onset of the monsoon by about 1.4 pentad.BC increases the temperature in the lower troposphere through short-wave heating,which leads to the reversal of land and sea temperature,thus leading to the onset of monsoon about 0.5 pentad earlier.The combined effect of the two is biased to the black carbon effect,which makes the reversal of land and sea temperature advance,and thus makes the onset of east Asian subtropical monsoon advance by0.5 pentad.(All the phenology statements in this paper are based on the mean of the 25-year aggregate experiment).In the northern monsoon region(35-40°N,105-120°E,namely The Beijing-Tianjin-Hebei region),the turbulent diffusion cooling effect of SO₄^2-is not obvious,and there is advection warming effect.Sulfate makes the middle and lower troposphere warm in spring,and the reversal of land and sea temperature is advanced,so the time of monsoon advancing to the Beijing-Tianjin-Hebei region is about 0.5 pentad earlier.BC increases the temperature of the lower troposphere through heating,and reverses the temperature of the land and sea in advance,thus advancing the time of monsoon to the Beijing-Tianjin-Hebei region by about 0.7 pentad.The combined effect of the two is biased towards the black carbon effect,which leads to the reversal of land and sea temperature and the advance of monsoon to the northern part of monsoon by about 1 pentad.For the south China Sea monsoon,the effects of SO₄^2-and BC on the South China Sea-South China meridional sea-land thermal difference,the convection in the Indo-China Peninsula,the breakup of the western Pacific subtropical high,and the onset of the South China Sea summer monsoon.The dynamic and thermodynamic mechanisms of aerosols affecting SCSM onset are emphatically discussed.The simulation results show that both SO₄^2-and BC are conducive to the enhancement of the stability of the entire troposphere in the Indo-China Peninsula,triggering the anomalous subsidence airflow over the Indo-China Peninsula,dynamically inhibiting the convection in the Indo-China Peninsula,and causing the subtropical high belt breakup delayed by 2 and 1 pentad respectively,in late spring and early summer.At the same time,thermally,the reversal time of spring meridional sea-land temperature difference was delayed(advanced)by SO₄^2-(BC).Integratedly,the consistent kinetic and thermal effects of SO₄^2-delay the onset of SCSM by 1 pentad.While,BC exerts insignificant effect on the onset of SCSM,which may be due to the opposite dynamic and thermal effects of BC.