| Dust storms are one of the major meteorological disasters affecting the world.It has a profound impact on climate change,atmospheric environment,human health and urban construction.Northern China,as an important part of dust sources in East Asia,has always been attacked by dust storms.The Hexi region is located in the key throat area of the ?Belt and Road?,which is not only an important dust source in northern China but also an area heavily affected by dust storms.Therefore,it is of great significance to clarify the characteristics,transport process and potential dust sources of dust storms in the Hexi region in order to reveal the mechanism of dust sources in East Asia.This study systematically studied the spatiotemporal changes of dust storms in the Hexi region by using measured data from national air quality monitoring stations,paleoclimate proxy indicators,remote sensing satellite data,spaceborne lidar and dust emission experience models,and discussed both in terms of meteorological factors.Coupling relationship.On this basis,the dust trajectories in the study area in the past four years were screened out and their main potential dust source contributions were quantified.The main findings are as follows:A statistical survey of the frequency of dust storms recorded in North China from 1960 to 2007 found that the dust storms in the Taklimakan Desert in the west and the Hunshandake Sandy Land in the east mainly occurred in the early(77.1%)and late(72.1%).In contrast,the frequency of dust storms in the Hexi region(middle)differed slightly at the end of the 30 s,only slightly higher in the middle(45.8%).The annual changes and high incidences of dust storms in the three regions indicate that 1985 and 2000 were the years when the frequency of dust storms changed abruptly.Meteorological factors are the main factors influencing the frequency of dust storms.Corresponding to the high incidence of the three dust storm centers in northern China,the low critical wind velocity,strong solar radiation,and large evaporation can provide a reasonable explanation for the temporal and spatial differences on the scale of the dust storm.However,temperature,relative humidity,and precipitation are weakly explained.Multivariate factors reveal that the maximum wind speed is the determinant of the ten-day difference,followed by relative humidity,evaporation and solar radiation.Temperature and precipitation are not the main influencing factors.The combination of maximum wind speed,relative humidity and solar radiation has the greatest impact on dust storms.The multi-factor and single-factor explanations for the ten-day differences in dust storms are basically the same.Compared with the western and eastern regions,the frequencies of dust storms in the Hexi region(middle region)have not shown a significant downward trend in recent years,so this area is analyzed emphatically.The research of modern dust storms and meteorological factors mainly relies on monitoring instruments,but the records are limited.In order to better explore the occurrence mechanism of dust storms and analyze the future development trend of dust storms,it is necessary to obtain the records before the observation records.Therefore,this study used tree ring,glaciers,stalagmites,coral reefs,lake deposits and other proxy indicators to characterize the paleoclimate to reconstruct the dust storm frequency,gale frequency,NDVI(Normalized Difference Vegetation Index),temperature and precipitation data in the study area in the past 300 years.The results showed that the frequency of dust storms was higher from 1700 to 1800 and the fluctuations were smaller;from 1800 to 1820,it was deeply affected by the strong winter monsoon and the frequency of dust storms was the highest;after 1820,the frequency of dust storms showed a downward trend.In addition,there are significant quasi-35 years and quasi-56 years periodic changes in the frequency of dust storms in the study area.This study uses climate factors and meteorological factors to jointly explain the results of dust storm frequency reconstruction.The frequency of dust storms in the study area is positively correlated with the intensity of the East Asian winter monsoon,but negatively correlated with the total solar radiation in the northern hemisphere and the frequency of sunspots.Meteorological factors are specific manifestations of the climate system,and the results of the frequency of dust storm reconstruction within the study area are significantly different from meteorological factors.The frequency of spring dust storms in the western part of the study area was negatively correlated with NDVI and temperature,and positively correlated with the frequency of gale and precipitation.Multivariate factor analysis results show that the frequency of gale frequency(> 11.35)and NDVI(< 0.08)are the main factor combinations for dust storms in the west.The frequency of spring dust storms in the middle part of the study area was negatively correlated with temperature and positively correlated with the frequency of high winds.The relationship with NDVI was not significant.The frequency of gale frequency(> 6.83),precipitation(< 43.32),and PDSI(< 2.32)are the most likely factors to cause dust storms.Contrary to the middle and western regions,precipitation in the eastern part of the study area is inversely related to the frequency of dust storms in the area.The factor that has the greatest impact on dust storms is precipitation,which is related to the long-distance transport of dust in this area.The main factor combinations affecting the frequency of dust storms in the eastern part of the study area are precipitation(> 93.86)and gale frequency(> 4.21).In addition to reconstructing the characteristics of the temporal and spatial variation of the frequency of dust storms in the study area,it is also necessary to identify the main potential dust sources affecting the Hexi region in order to reduce the dust storm hazards in the study area according to local conditions.Therefore,this paper studies the dust emissions in northern China during the dust event in Hexi region from 2015 to 2018 and found that compared with local sources,foreign potential dust sources have a greater impact on the Hexi region.The main potential dust sources in the study area are the Taklimakan Desert,the Gobi area at the border between Xinjiang and Mongolia,the Badain Jaran and Tengger Deserts,the Kumtag Desert and the Qaidam Basin.In this paper,spaceborne lidar,satellite remote sensing data and HYSPLIT model are used to screen out dust trajectories at different heights in five cities in the study area,and then to quantify the potential foreign dust sources.Among them,dust trajectories from the Kumtag Desert,Badain Jaran Desert,and Tengger Desert contributed greatly to the study area.These source areas are rich in surface loose materials,with strong dust intensity,close to the study area,and in the upwind direction,and there is no high terrain obstruction in the path,so it has a greater impact on the Hexi region.Although the Gobi area at the border between Xinjiang and Mongolia has the highest maximum wind speed in the dust path,due to the high vegetation coverage,high precipitation,and the large particle size of the dust particles,its dust trajectory contributes less to the study area.Dust intensity in the Taklimakan Desert is relatively strong,but the dust is mainly concentrated in the lower layers and is not easy to be transported out of the source area,so its dust trajectory does not contribute much.In the Qaidam Basin,due to the low dust intensity and the obstruction of Qilian Mountains in the path,the impact on the Hexi region is small. |
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