Spatial And Temporal Variations Of Spring Dust Aerosol And Its Effects On Radiative Forcing In China Over The Past 20 Years

Dust aerosol is an important part of tropospheric atmospheric aerosol in arid and semi-arid areas,accounting for about half of the total tropospheric atmospheric aerosol.Dust aerosol directly affects the radiation balance of the earth atmosphere system by scattering and absorbing solar short wave radiation and surface long wave radiation.At the same time,it can also indirectly affect the climate system by changing the formation process of clouds.It is one of the important influencing factors of global energy balance and climate change.The arid and semi-arid region in Northwest China is prone to dust weather in spring.It is one of the important sources of global dust aerosols.It is easy to transport southward with the prevailing wind,which has a long-term impact on China’s climate change.Therefore,the quantitative evaluation of the temporal and spatial distribution and radiative forcing effect of dust aerosols is of great significance to reveal the impact mechanism of dust aerosols on regional climate change in China.At present,the research on the radiative forcing effect of dust aerosol in China is mainly limited to case analysis or observation data analysis of small-scale and limited stations,while the distribution of dust aerosol in large-scale and long-time series and its climate impact are not clear.Therefore,this paper uses the atmospheric chemical transport model（WRF Chem）to simulate and quantify the temporal and spatial process and radiative forcing effect of dust aerosols in northern China from 2000 to 2020.The main research results are as follows:（1）The temporal and spatial processes of dust emission and dust aerosol concentration in spring in China are simulated.The spring dust emission in China is mainly distributed in the arid and semi-arid areas of Northwest China,and there are obvious temporal and spatial differences.From 2000 to 2020,the national average annual spring dust emission flux was 82.43?g m^-2 s^-1.The maximum and minimum years of dust emission flux were 2018(107.79?g m^-2 s^-1)and 2008(62.01?g m^-2 s^-1)respectively.The dust aerosol concentration decreases from northwest to Southeast.The annual average dust aerosol concentration in spring across the country is 26.95?g kg^-1,of which the dust aerosol concentration in 2018 is the largest(35.42?g kg^-1)and the dust aerosol concentration in 2008 is the smallest(20.13?g kg^-1).From the perspective of monthly variation,the annual average dust emission flux and dust aerosol concentration in May are the largest,96.43?g m^-2 s^-1and 34.13?g kg^-1respectively,and the annual average dust emission flux and dust aerosol concentration in March are the smallest,55.43?g m^-2 s^-1and 16.89?g kg^-1 respectively.（2）The effects of dust aerosols on the radiative forcing at the top of the atmosphere,atmosphere and surface are quantified.It is found that the radiative forcing effects of dust aerosols at different altitudes in China have obvious temporal and spatial differences.The long wave and short wave radiation of dust aerosol on the top layer of the atmosphere shows obvious positive radiation forcing effect(about 0.38 W m^-2),which is mainly distributed in Northwest China and North China Plain,while the long wave and short wave radiation on the atmosphere show negative and positive effects respectively,and its net radiation forcing value is 1.54W m^-2,which shows warming effect.Dust aerosol has a positive forcing effect on surface long wave radiation,but a negative forcing effect on short wave radiation.Both of them have a good corresponding relationship with the spatial distribution of dust aerosol concentration.Its net radiation forcing value is-1.16 W m^-2,which shows a cooling effect.From the perspective of monthly variation,the net radiative forcing value of dust aerosol at the top of the atmosphere and the atmosphere is in the form of may(0.94 W m^-2 and 2.42 W m^-2)>April(0.48 W m^-2 and 1.44 W m^-2)>March(-0.20 W m^-2 and 0.68 W m^-2),while on the surface,it is in the form of March(-0.88 W m^-2)>April(-0.96 W m^-2)>may(1.48 W m^-2).（3）The asymmetric effects of radiative forcing of dust aerosol on diurnal sensible/latent heat flux and temperature are revealed.The results show that the radiative forcing effect of dust aerosol has obvious asymmetry on the climate during the day and at night.The impact of dust aerosol on sensible heat flux in most regions of the country is positive(1.80 W m^-2),and its spatial distribution shows a gradual decreasing trend from northwest to Southeast,while the impact on sensible heat flux is negative(-1.23 W m^-2),with obvious spatial difference.In summary,the impact degree in northwest is greater than that in southeast,and the negative effect of latent heat flux in central and eastern regions is the most obvious.Dust aerosol has obvious negative effects on white weather temperature（2m height）and surface temperature.The more significant the surface negative radiation forcing is,the more obvious the cooling effect is.The nocturnal dust aerosol has a negative effect on the surface sensible heat flux(-0.92 W m^-2),but it has a weak positive effect on the latent heat flux(0.12 W m^-2).Dust aerosol has obvious warming effect on night temperature and surface temperature,and the warming range of surface temperature is greater than that of air temperature.