柴达木盆地尘卷风的时空分布特征

Spatial and Temporal Distribution Characteristics of Dust Devils in the Qaidam Basin

沙尘气溶胶是大气气溶胶的重要组成部分,其通过辐射效应和对云的形成及降水过程影响全球天气和气候变化,而尘卷风对全球沙尘气溶胶排放的贡献不容忽视。青藏高原北部的柴达木沙漠为高原尘卷风的发生提供了沙源。为研究柴达木盆地尘卷风的发生条件及其时空特征,本文利用1991-2020年ERA5再分析资料评估了尘卷风发生的热力学阈值,分析青藏高原尘卷风发生时数(PDDP_(hours))和柴达木盆地尘卷风起沙量的时空分布特征,探究了1991-2020年近地面温度递减率(LR)、对流比(w*/u*)和PDDP_(hours)的变化趋势。利用2016-2020年德令哈国家基本气象站的地面降水数据、德令哈空气质量监测站的细颗粒物PM_(2.5)和PM_(10)数据以及Aura卫星臭氧监测仪的紫外吸收性气溶胶指数(UVAI)数据,分析柴达木盆地夏季尘卷风对PM_(2.5)和PM_(10)的可能贡献。结果表明,w*/u*和LR是影响尘卷风形成的关键因素,不同热力条件下PDDP_(hours)均具有单峰日变化特征,在12:00-16:00(北京时)达到峰值。结合柴达木盆地PDDP_(hours)累计贡献的日变化特征,确定尘卷风发生的热力学阈值是w*/u*>5和LR>10 K·m^(-1)。分析表明,青藏高原夏季北部的柴达木盆地和西南部PDDP_(hours)较大。柴达木盆地夏季尘卷风的起沙量最大,起沙范围也较大,平均起沙量可达1.28×10^(5)t,占全年平均起沙量的69.8%。1991-2020年柴达木盆地LR呈现明显的减小趋势,w*/u*呈增加趋势,导致PDDP_(hours)有明显的减小趋势。虽然夏季德令哈降水明显较其他季节多,但夏季UVAI较大,说明夏季除沙尘暴外尘卷风可能对该地区PM_(2.5)和PM_(10)有重要贡献。

Dust aerosols are significant components of atmospheric aerosols,and they play a crucial role in global weather and climate changes through radiative effects and the formation of cloud and precipitation.The impact of dust devils on the worldwide emissions of dust aerosols should not be underestimated.The Qaidam Desert located in the northern part of the Tibetan Plateau is a source of dust devils.To investigate the meteorology conditions that lead to the occurrence of dust devils and to understand their spatial and temporal distribution characteristics in the Qaidam Basin,the thermodynamic criteria of dust devils are examined using the ERA5 reanalysis data from 1991 to 2020.The spatio-temporal distributions of the potential dust devil and dust plumes occurrence(PDDP_(hours))across the Tibetan Plateau and the estimation of dust emission caused by dust devils and dust plumes in the Qaidam Basin have been carried out based on these criteria.In the analysis of trends from 1991 to 2020,lapse rate(LR),convective ratio(w*/u*),and PDDP_(hours)have been examined.The precipitation from the Delingha National Basic Meteorological Station,PM_(2.5)and PM_(10)from the Delingha Air Quality Monitoring Station,and ultraviolet aerosol index(UVAI)data derived from the Aura satellite from 2016 to 2020 have been utilized to investigate the contribution of dust devils to PM_(2.5)and PM_(10)in summer in the Qaidam Basin.The results show that w*/u*and LR are the primary factors that influence the formation of dust devils.The PDDP_(hours)reveals a diurnal cycle with peaking at 12:00-16:00(Beijing Time)under different thermodynamic conditions.Based on the diurnal variation of the cumulative contribution of PDDP_(hours),the combined w*/u*>5 and LR>10 K·m^(-1)criteria are considered to be the most appropriate for determining the occurrence of dust devils in the Qaidam Basin.On the basis of the PDDP_(hours)criteria,the analysis highlights the significant presence of PDDP_(hours)in the Qaidam Basin and the southwestern part of the Tibetan Plateau in summer.The results also reveal that the larger dust devil emissions occur in summer with the average dust emission of up to 1.28×10^(5)t,which accounts for 69.8%of annual dust emissions.The lapse rate has shown a significant downward trend and the convective ratio has shown an upward trend in the Qaidam Basin,which finally lead to an obvious downward trend of PDDP_(hours).The observations indicate that the annual variation of UVAI shows a larger magnitude in summer,despite there is more precipitation in Delingha during this season compared to others.It indicates that,in addition to the dust storm,dust devils may attribute to PM_(2.5)and PM_(10)in summer.