An Improved Parameterization Scheme For Dust Devil Formation In Northern China And Numerical Simulation Of Dust Aerosol Radiation Effects

The dust aerosol is one of the main aerosol components of the atmosphere,which is an important connection between the atmosphere,the biosphere,and the lithosphere,as well as a key link in the global mass cycle and the climate change.The amount of dust aerosol emission is the core factor that describes the dust aerosol.The dust aerosol emission is believed to originate from the dust weathers such as dust storms and blowing sands caused by strong winds.However,such kinetic-driven mechanisms cannot explain the fact that the aerosol concentration rises in some deserts under sunny weather and weak winds.Moreover,the kinetic dust emission is not able to fulfill the huge dust aerosol deficiency at the global scale.Some studies have proposed a different dust emission mechanism in the boundary layer caused by dynamic vortex convections,which mainly consists of dust devils and dry convections.Based on the observation data and other frontier researches,the present research has retrofitted a parameterization scheme for the dust devil in order to match up the weather conditions in Northern China,and coupled it with the atmospheric chemical model WRF-Chem.The study area was set in Northern China,over which the diurnal and yearly variation of dust devils,the vertical distribution of dust aerosol at sunny days,and the total dust devil emission were simulated.At the same time,the dust devil scheme was combined with the dust storm scheme,in order to quantify the contributions of dust devils and dust storms to the total dust aerosol.The results clarified the significant impact of dust devils on the dust aerosol,which can offset the dust aerosol simulation deficiency to some extent.After taking the dust devil emission into consideration,the possible elevated heat pump(EHP)in Northern China was re-analysed.The main conclusions are listed as follows:1.The existing parameterization scheme for the dust devil emission in Northern China was proved,in order to better simulate the diurnal and annual evolution of the dust devils and the total dust devil emission.According to an observation lasting for two years and the frontier researching achievements,several major weather criteria that influence the dust devil formation were determined.By integrating the weather criteria with the dust source mask distribution and the dust devil emission formula,a parameterization for dust devil formation in Northern China was established,and then coupled with WRF-Chem.Compared to the observation,the simulated surface temperature in the deserts was lower,which makes up the main reason for the simulation error.After applying error correction to the parameterization scheme,the simulation results were examined by comparison to the observation data from meteorological stations and the MODIS satellite,which validates the reliability if the dust devil scheme.Thus,the dust devil scheme can be trusted to illustrate the spatial and temporal distribution of dust devils in Northern China,forming the basis of the analyses in the temporal and spatial distribution of the dust devils.2.It was confirmed that dust storms occur most frequently in the desert and gobi areas.The dust devils featured an obvious single-peak distribution in its diurnal and yearly variation.The dust aerosol emitted by dust devils can be brought to high altitudes up to 700-400 hPa by the convention.As what is shown in the simulation results,the dust devils are formed in the deserts in Northern China.The diurnal and yearly variation of the dust devil emission both shows a single-peak distribution.Generally,dust devils occur from 8:00 to 20:00 LST in a day,and the peak is at 14:00 LST.At sunny days in the summer,the high frequency area and high intensity area first show up in Badan Jaran,moving from east to west.The frequency center and intensity center are located in Badan Jaran and Taklimakan.Dust devils show up from March to October,being most active in the middle of June.At sunny days,the dust aerosol emitted by dust devils form a dust layer at 1?6 km above the dust source.The dust aerosol by dust devils features a burst at daytime,and a sudden fall at night.A dust devil is able to carry the dust aerosol to an altitude up to 700-400 hPa.The ratio of the convective buoyancy to the fiction velocity,w*/u*,is the major limiting factor for the dust devil formation in Northern China.3.The dust devil applies a significant impact on the total amount of atmospheric dust aerosols.In Northern China,the dust devil contributes 30.4 ± 13%to the atmospheric dust aerosol budget.Dust devils contribute less than 17%in the inactive period from November to May in the next year,but over 93%from June to October to the total dust aerosol.The contribution of dust devils to the total dust emission varies with the season,sorted as following:summer>fall>spring>winter.The estimated total dust devil emissions in East Asia comprised 4.6 × 107t in the present research,which contributed 30.4 ±13%to the atmospheric dust aerosol budget in East Asia.4?A conceptional model of the EHP effect driven by dust aerosols to demonstrate the circulation anomalies in Northern China during spring and summer.If there are only dust storms in Northern China,it is difficult to determine whether the EHP is still active.After taking the dust devil parameterization scheme,the EHP is notably enhanced,and the pumping mechanism remains active constantly.After sensitivity experiments,it can be concluded that the dust aerosol heats the atmosphere,forming an updraft current to pump the air at low altitudes if there only exists dust storms,thus there exists the EHP effect.An EHP model is then presented to further investigate the climate effects of the dust aerosols in East Asia.After comparison of the simulated and the observed annual dust emission during 1961-2015,it is difficult to verify the existence of EHP effect in those years when dust storms rarely take place.After introducing the parameterization scheme for dust devil emissions,the EHP effect is significantly enhanced in Northern China.Under the impacts of dust storms and dust devils,the existence of EHP in Northern China is validated.