| As a main source area of dust aerosols in China,the Taklamakan Desert has a unique floating dust phenomenon,which has an important impact on air quality,weather and climate changes.The evolution of the atmospheric boundary layer structure,weather conditions,and the deep basin topography have an important influence on the formation and maintenance of the floating dust process in the Tarim Basin,and the study of these important mechanisms has scientific significance for the environment and climate change,as well as application value for modelling and forecasting of weather and air quality.The main research conclusions of this paper are as follows.1.Diurnal differences in the effects of floating dust aerosols on the structure of the desert atmospheric boundary layer and the mechanisms of actionUsing four daily enhanced soundings and ground-based meteorological observations in the Taklamakan Desert hinterland in July 2016,the diurnal differences in the atmospheric boundary layer structure and the differences in surface radiation income and expenditure between clear days and dusty days in the Taklamakan Desert in summer were compared and analyzed to reveal the diurnal differences and mechanisms of the effects of floating dust aerosols on the atmospheric boundary layer structure.The results show that the stable boundary layer height is 270 m on clear days and 360 m on dusty days,and the inverse temperature intensity of the stable boundary layer reaches 3.1 K·100 m-1on clear days,which is stronger than that of 1.6 K·100 m-1on dusty days,while the convective boundary layer height is nearly 3600 m on clear days and only 2700 m on dusty days.This raises the height of the stable boundary layer and weakens its stability.The strong net solar shortwave radiation heats the desert surface on sunny days,and its strong thermal effect creates an ultra-high convective atmospheric boundary layer.Floating dust aerosols significantly reduce the surface shortwave radiation and sensible heating,lowering the daytime convective boundary layer height.The unique radiation effect of floating dust aerosols in the Tarim Basin has a diurnally opposite effect on the atmospheric boundary layer structure in the desert region.2.Modulation of floating dust in the Tarim Basin by weather circulationThe number of days with floating dust in the Tarim Basin from 2011 to 2020 was screened.The PCT objective classification method was used to identify the daily surface,500h Pa and 700h Pa circulation patterns in the Tarim Basin,to determine the configuration of high and low-level synoptic systems affecting the occurrence of floating dust,and to clarify the relationship between weather systems and dust aerosol emission and transport.The results show that the surface weather patterns on floating dust days are summarized as high-pressure frontal,high-pressure bottom and even pressure field patterns.At 500h Pa and 700h Pa,potential height fields can be identified as flat latitudinal type,high pressure ridge type,and westerly trough post type.The highest number of vertical weather system configurations from500h Pa to700h Pa are of the flat latitudinal type,accounting for 43%of the total.system configurations of 500h Pa and 700h Pa are mostly the direct latitudinal types and the ground is accounting for 17%with the uniform pressure pattern.Analysis of an individual case of dusty weather from 30 April to 6 May 2016 shows that when the ground Siberian cold high pressure moved southeastward,the upper trough after the Iranian subtropical high-pressure control,dusty weather significantly aggravated.When the ground-level even pressure field with no obvious pressure system,and high altitude is flat zonal circulation,it changes to light dust floating.3.The influence degree and underlying mechanism of the topography of the Tarim Basin on the spatial and temporal variations of dust aerosolsThe WRF-Chem model was used to simulate a typical dust floating process in spring2015 with a sensitivity modeling experiment with filling the Tarim Basin to reveal the extent and mechanism of the effect of basin topography on the spatial and temporal variations of dust aerosols,and the simulation experiement results showed that the topographic effect of the deep Tarim basin increased the surface concentrations of dust aerosols in the parts of the basin by 240-1100?g·m-3.Dust aerosol concentrations in the northern part of the Tibetan Plateau decreased significantly,reaching 360-800?g·m-3.The upper boundary layer caused a significant increase in dust aerosol concentrations in the basin as a whole,reaching a maximum of 600?g·m-3.For the entire basin region,the topographic effect lead to significant increases in dust aerosol concentrations below 4.6 km height in the basin,with the largest increase of 278?g·m-3near the surface,while dust aerosol concentrations decrease above 4.6km height in the free troposphere.The unique near-surface wind fields of the Tarim Basin significantly influence surface dust aerosol emissions.When cold air pours into the basin,it is affected by the topographic narrow tube,increasing the near-surface wind speed along the Pamir Plateau,along the Tianshan Mountains and in the open northeastern mouth of the basin.The increase in near-surface wind speed intensifies the emission of dust aerosols.The vertical circulation within the basin plays a decisive role in the transport and dispersion of dust aerosols.Due to the topography of the Tibetan Plateau,a large amount of dust aerosols accumulated in the southern basin.Only a small amount of dust aerosols can be lifted to free troposphere and transported to downwind China and East Asia by the mid-latitude westerly airflow. |
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