Spatiotemporal Patterns Of Dust Events And Its Response To Surface Frozen Period In Northern China

Dust storm is one kind of meteorological disasters with suddenness,high strength,and great destructive force,especially in arid and semi-arid areas.Considering that more than 30 percent of the total land area is covered by arid and semi-arid ecosystems in China.The dust storms frequently occurred in China.Dust storms can cause huge economic losses in source regions and downstream areas.The dust released into the atmosphere has important impacts on ecosystems and climate change due to the long-distance transportation and deposition.The surface temperature is an important physical parameter in the processes of material,energy,and momentum exchange between the ground and atmosphere.The surface frozen period in dust source regions has the potential to mitigate or promote dust events during the occurrence and transmission.Studies on the effect of surface frozen period on dust storms could help to improve the forecast of dust storms and dust controls in the source areas.Therefore,climate data were analyzed using China's strong sandstorm sequence and its supporting datasets,as well as Chinese ground log dataset(V3.0)from 1962 to 2007 obtaining from the China Meteorological Science Data Sharing Service in this study.By analyzing the data over the past 46 years,the spatial and temporal patterns of dust events in northern China and responses of dust storms to surface frozen period were explored.The dust event frequency varied strongly across the grassland and desert regions in northern China.In general,the dust event frequency gradually reduced from west to east.Dust event mainly occurred in Southern Sinkiang,Midwestern Inner Mongolia,and Hexi Corridor regions,such as the Taklamakan Desert,the Badain Jaran Desert,Tengger Desert,and Otindag Sandy Land and Mu Us Desert,etc.Dust weather was rare in the Northeastern Inner Mongolia,Heilongjiang,and Jilin.The frequency of dust events showed a declining trend with fluctuations from 1962 to 1997,but increased since 1998.The average annual dust event frequency was 4.96 times/station.The highest and lowest dust event frequency were 11.45 times/station in 1966 and 1.26 times/station in 1997,respectively.During 1962-1985,average annual dust event frequency was 7.19 times/station.During 1985-2007,however,average annual dust event frequency was 2.72 times/station,which was decreased by 62.2%.The dust event occurrence could be divided into strong dust storms,moderate dust storms,dust storms,and flying sand dust,which were accounting for 3%,9%,22%,and 65%of average annual dust event frequency,respectively.The interannual variations of dust events varied with the dust intensity.The strong dust storm frequency did not significantly vary over the past five decades,whereas other categories of dust events were decreased.The spatial distribution of the dust events showed seasonal variations.Dust events were frequently occurred in spring,followed by summer and winter.The dust weather in the source regions rarely happened in autumn.In the grassland and desert ecosystems of Northern China,57.8%of dust events occurred in spring and 25.1%of dust events occurred in April.Dust events occurred in autumn and October only accounted for 6.5%and 1.8%,respectively.The interannual variation of surface frozen periods was decreased with fluctuations over the past 46 years in Northern China.The surface frozen period ranged from 110(2001)to 130(1970)days.The spatial distribution of the surface frozen period had obvious latitudinal and altitudinal zonality.The surface frozen period increased with latitude.It had significant elevation effects in Qinghai Plateau,such as it was longer in Qinghai Plateau than it in Gansu and Northern Qinghai.There were regional differences in the length of surface frozen period,such as the surface frozen period of Northern Sinkiang was shorter than that in Eastern Inner Mongolia.The interannual variability of surface frozen time was not significant and slightly delayed over the nearly past 50 years.Dust event frequency showed positive dependence on frozen time(R2 = 0.17,P<0.05).The interannual fluctuation of surface thawing time was large.The surface thawing time advances significantly,and it explained 26%variations of dust event frequency.The dust event frequency showed significantly negative dependence on the surface frozen period(R2 = 0.23,P<0.001).The augment of the surface frozen period could suppress the occurrence of dust event.The numbers of strong dust storms(R2 = 0.12,P<0.001),moderate dust storms(R2 = 0.16,P<0.001),dust storms(R2 = 0.17,P<0.001),and flying sand dust(R2 = 0.23,P<0.001)showed significantly negative relationships with the surface frozen period length.However,the response of dust intensity to surface frozen period length was different.The weaker the dust storm strength,the more negative relationship with the surface frozen period was.The different sensitivity of the response of dust intensity to the surface frozen period is the main reason,and negatively related to the gradient distribution.The surface frozen period in different vegetation types had different impacts on dust event frequency.Dust events were not correlated with the surface frozen period in the temperate zone subshrub dwarf trees desert(R2 = 0.10,P>0.05),the meadow grassland(R2 = 0.05,P>0.05),and the desert grassland(R2 = 0.13,P>0.05).The dust event frequency showed negative dependence on temperate subshrub desert(R2 = 0.32,P<0.01),the warm temperate zone subshrub desert(R2 = 0.33,P<0.01),and the typical grassland(R2 = 0.45,P<0.01).32.0%and 32.9%variations of dust event frequency could have been accounted for by the surface frozen period in temperate subshrub desert and warm temperate zone subshrub desert,respectively.The surface frozen in the typical grassland explained 45.4%variations of dust event frequency,which was the highest.The shorter the surface frozen period,the more dust event frequency of these areas.Under global climate change,this study preliminarily explored the effects of surface frozen period on dust events.It suggests that the surface frozen period is one of the important factors affecting dust events occurrence.The surface frozen period plays an important role in suppressing the occurrence of dust events.With shortened frozen period under climate warming,the dust event frequency is expected to increase.