| The Asian long-distance transport process is one of the largest dust transport activity in the world.It can sweep across the Tibetan Plateau and transport to most of China,and even across the Pacific Ocean to the Americas.On the one hand,the dust suspended in the atmosphere affects the local radiative budget through direct or indirect effects;On the other hand,dust deposition during transport provides rich mineral elements and nutrients for the Asian continent and the Pacific Ocean,enhancing the growth of land vegetation and marine plankton.Therefore,the Asian dust cycle is closely related to the land-atmosphere-ocean biochemical cycle,and has a profound impact on regional and global ecological health,weather and climate.Currently,model simulation is an ideal tool to study the Asian dust cycle and provide information on the mechanism of dust cycle.However,due to the parameterization scheme and related assumptions,there is still a great uncertainty in the simulation results.Therefore,relevant data of dust cycle based on remote sensing observations are urgently needed to constrain and validate the model.This paper takes advantage of CALIOP polarization detection and the 3D dust optical properties data it provides to accurately extract dust aerosol from the total aerosol based on the dust and non-dust depolarization ratio thresholds;then,combined with the dust mass extinction efficiency provided by Dust COMM,we construct a long-term 3D remote sensing dataset of Asian dust optical thickness,mass concentration and mass transport fluxes.The transport contributions of dust sources,transport characteristics and deposition fluxes of Asian dust are further studied systematically.The dust radiative heating rate over the Tibetan Plateau is also quantified by combining the SBDART radiative transfer model.The main conclusions of this paper are as follows.(1)There are two main dust transport belts in Asia,one of which runs from Central Asia in the west,through the Taklimakan desert and Gobi Desert,and extends to the North China Plain and even the Pacific Ocean.It is the strongest dust transport belt from Central Asia to East Asia and exists all the year round.The other dust transport belt started from Central and West Asia,mixed with the dust emitted from Thar Desert in South Asia,and then crossed the Hengduan Mountains and Yunnan-Guizhou Plateau before arriving southern China,which is a weaker dust transport belt.The two transport belts converge in eastern China and its downstream areas.The scope of dust transport belt is basically consistent with the location of high dust mass concentration.However,it is worth noting that the center location of dust transport belt is not always consistent with the dust mass center axis.This is because the dust transport process is not only affected by dust mass loading,but also by wind speed and terrain.(2)The dust mass transport center axis(TCA)has significant temporal and spatial variation.In the near-surface layer,the dust TCA is controlled by the topography of inland northwest China and crosses the Taklamakan and Gobi Deserts throughout the year,while with the increase of dust transport distance,the dust TCA is influenced by the location of the western Pacific subtropical high pressure and Aleutian low pressure,and moves in the range of 35-50°N throughout the year.As the altitude increases,the dust TCA is gradually weakened by the influence of topography and gradually distributed in a zonal straight line.(3)There are significant differences among the downstream transport contributions of different dust sources in Asia.The transport contributions of dust from Central and West Asia to South Asia is the strongest,with an annual value of about 164 Tg and its strongest transport height is about 0-5 km;due to the blocking effect of the Tibetan Plateau and the surrounding terrain,the annual transport contributions of Central Asian dust across Northwest China and South Asian dust across the Yunnan-Guizhou Plateau are about 78 and 30 Tg,respectively,and their strongest transport heights are 3-6 km and 2-4 km,respectively;comparing the two major desert sources in East Asia,the Gobi Desert has the largest transport contribution to inland China and adjacent seas,with an annual value of about 146 Tg,which is 2.1 times larger than that of Taklamakan Desert(68 Tg).This is because the dust from the Taklamakan Desert needs to be lifted above 3 km before it can be transported downstream,while the strongest dust transport layer in Gobi Desert can extend from near the surface to a higher altitude(5 km).(4)The Asian dust budget and deposition in the downstream regions are significantly different due to the effects of long-range dust transport and local dust emissions.Under the combined effect of long-range dust transport and local anthropogenic dust emission,the net dust budget rate in northern China is 21.58 g m-2,which is significantly larger than that in southern China(2.75 g m-2).The deposition of Asian dust in adjacent seas decreases with increasing transport distance,and its maximum value occurs in the Yellow Sea,where the annual deposition flux rate is 40 g m-2,which is about 2 and 10 times higher than that in the Japan Sea(20.41 g m-2)and the Northwest Pacific Ocean(4.01 g m-2),respectively.(5)Dust aerosols significantly affect the thermal structure of the atmosphere over the Tibetan Plateau and its surrounding areas.Over there,dust aerosols significantly heat the atmosphere in the short-wave band,while exhibit a weaker cooling effect on the atmosphere in the long-wave band.Therefore,the net dust radiative heating rate exhibits a warming effect on the atmosphere,and its warming center is exactly the same as the dust load center.The peak centers of net dust radiative heating occur in the Taklamakan Desert in spring(?7 K/month)and in the Ganges Plain of India in summer(?6 K/month).The net radiative heating rates of different sub-regions on the Tibetan Plateau vary significantly due to the effects of long-range transport and local dust emissions,and their peak centers are mainly located in the northeastern of the plateau with a maximum values occur in spring and summer(?2.4 K/month),this can attribute to the large amount of dust emitted by the Qaidam Basin,which is located in the northeastern of the Tibetan plateau.In addition,the dust radiative heating rate decreases with height over all regions,and its maximum value occurs near the surface,which is 3-3.6 times higher than the averaged column radiative heating rate.In this paper,we develop a satellite-based lidar remote sensing algorithm for dust mass concentration and transport flux in Asia,which takes fully into account all the dust suspended in the atmosphere and the seasonal and spatial variability of dust mass extinction efficiency.Further,important parameters in the Asian dust cycle are quantified,including dust transport fluxes,transport contributions from different dust sources,dust radiative heating rates,and even dust deposition fluxes into the ocean.These results not only provide new insights into the Asian dust cycle and lay the foundation for further exploration of aerosol-cloud-climate interactions and the radiative balance of the Earth-Atmosphere system;but also help to validate and constrain the simulation results of regional and global climate models,and improve the simulation capability of aerosol-related modules in climate models,which can significant improve the climate prediction capacity of models. |
PDF Full Text Request