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Climate Diagnosis of Lanzhou Dustfall

LI xu et al(Key laboratory of Semi-arid climate change,Minister of Education,College of Atmospheric Sciences,Lanzhou University,Lanzhou,Gansu 730000))  
By using the NCEP/NCAR reanalysis data,climate diagnosis method was used to analyze the characteristics of Lanzhou dustfall.After analyzing the 60 years' average vertical velocity field and vorticity field,the following conclusions were gained,in winter,the middle and low level descending motion were strong and evident.Moreover,during the heating period,because of the impact of sandstorm and basin climate,the dustfall in winter was evident. In spring,Lanzhou was the margin of descending motion area,the ascending motion was weaker.But for the reason that there existed ascending motion in the dust source region which made for the dust ascending,and Lanzhou located in the leeward region of Gansu Corridor where sandstorm frequently occurring region,adventives dust will speed dust falling,dustfall was the heaviest in spring compared with other seasons.In summer,the low level ascending motion was obvious in Lanzhou for the effect of the earth's surface heating source.Since the rain can clean out the particulate matter,the dustfall was obvious in summer than in autumn.There existed good coherence between the multiyear average vorticity field situation and vertical motion field.It intuitively reflected evolvement states of the main systems which affected Lanzhou in different seasons,and it reasonably explained the evolvement rules of dustfall distributing in Lanzhou area.
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