| Dust devils are convective vertical vortices caused by uneven surface heating,commonly happening in arid and semi-arid regions.Since dust storms usually occur in spring and winter but rarely in summer,dust devils become a major means of transporting dust aerosols into the atmosphere in summer which could further impact on weather and climate with aerosol–radiation and aerosol–cloud interactions.In addition,the dust that has been lifted in the atmosphere could function as a carrier of bioaerosols and cause adverse effects on livestock and human health.Therefore,dust devils have great research significance.In this study,we investigated the long-term trend of favorable conditions for dust devil occurrence and defined it as potential dust devil and dusty plume（PDDP）.Using this definition,we give the distribution and trends of PDDP occurrence in East Asia over the past 63 years,discuss the meteorological factors affecting the variation of PDDP frequency,and further estimate the contribution of dust devils to dust and bioaerosols emissions in East Asia.Results are shown below:（1）Dust devils in East Asia occur mostly in arid areas with dust sources,and almost no dust devils occur at latitudes higher than 50°N as well as in humid areas;we classified the different intensities of dust devils according to the frequency distribution of the near-surface temperature lapse rate during the occurrence of dust devils.The results show that weak dust devils account for about 68%of the total frequency,moderate dust devils occur at about 27%,and strong dust devils occur at less than 5%.（2）The frequency of dust devils in East Asia showed an overall decreasing trend from 1959 to 2021,in which strong dust devils declined at the fastest rate and weak dust devils had a strong interannual variability,showing a trend of first decreasing and then increasing in 63 years;although strong dust devils brought a large amount of dust each time,strong dust devils accounted for less than 5%of the time of dust devil occurrence;Therefore,weak dust devils might be a major means of transporting dust aerosols into the atmosphere.（3）For seasonal distribution,the frequency of dust devils is highest in summer,followed by spring,and dust devils hardly occurs in winter;annual variation of dust devil shows a single-peak distribution,with dust devils increasing from March,reaching the maximum in June-July,and almost no dust devil occurring after September;the interannual peak of dust devil tends to move from June to July,which may be related to the change of circulation and the extension of summer.The Pinatubo eruption in June1991 suppressed the occurrence of dust devils in the following two years by lowering the Earth’s temperature and reducing solar radiation.（4）For small regions,the interannual variability of dust devils in different subregions shows distinct trends:the potential dust devil frequency in the Taklamakan Desert decreases during 1959-2021,while dust devils increase significantly in the Gobi Desert;dust devils in the Qaidam and Turpan basins and the Kuruqtag show a decreasing trend;similar to the characteristics of the larger East Asian region,dust devils in small regions occur most frequently in summer,and dust devils shows a unimodal distribution;dust devils occur mainly between 10:00 LT and 16:00 LT throughout the day,with the frequency of dust devils between 12:00 LT and 14:00 LT accounting for more than 60%of the total frequency;compared with the basin,dust devils in desert areas occur for a shorter period of time throughout the year and start later in the day.（5）Applying the dust fluxes given by the results of different studies,the average annual amount of dust from dust devils varies from 104 to 1013 kg.The bacterial emission fluxes from dust devils are in the range of 2.4×10-6 kg m-2 s-1 and 5.2×10-6kg m-2 s-1,and the bacterial emission from ecosystems has been given by models to be about 5.49×10-13 kg m-2 s-1,ecosystem average bacterial emission has been given by the model as about 5.49×10-13 kg m-2 s-1,which is 7 orders of magnitude smaller than the bacterial flux of dust devils.The average annual bacterial emissions in the Taklamakan Desert,Turpan Basin and Kuruqtag,Qaidam Basin,and Gobi Desert were9.8×106,7.0×106,6.9×106 and 1.2×107 kg,respectively.This study provides a comprehensive understanding of favorable conditions for dust devil occurrence in East Asia over the past decades,which is of great importance to further evaluate its impact on climate,environment as well as ecosystem. |
