利用宁夏25个常规地面观测站逐时资料和欧洲中期天气预报中心(ECMWF)ERA-Inter-im逐6 h 0.125°×0.125 °分辨率再分析资料,对宁夏2016年5月11日大风扬沙天气过程的天气形势、影响系统及其热力、动力条件和形成机制进行了分析.结果表明:(1)大风和扬沙呈现出时间位相上的不一致性,沙尘超前大风约6h.(2)200hPa高空急流、500hPa锋区、700hPa低空急流和地面冷锋是此次过程的主要影响系统.(3)大风在不同阶段对扬沙起不同作用,在初期有利于扬沙的传输,后期对扬沙起抑制作用.(4)动量下传和变压风是大风形成和发展的直接原因,感热通量通过加强地面湍流形成混合层,从而引导动量下传是其间接原因,动量下传的重要机制是对流层高层高位涡的下传,过程风力最强时位涡高值区(≥2.0 PVU)由200hPa下传至520hPa.(5)扬沙的产生主要是冷平流和感热通量形成的热力不稳定共同作用的结果,变压风和动量下传大风是扬沙的输送机制,次级环流缺失和冷平流中心过低(750hPa)对沙尘输送高度的抑制作用是沙尘天气偏弱的主要原因.
Mechanism of a strong wind and blowing sand process in Ningxia
By using the data from 25 observation stations in Ningxia,the sounding data from Yinchuan observatory and the ECMWF ERA-Interim 6-hourly reanalysis data with resolution 0.125°×0.125°,the weather situation,the influence system,the thermal,the dynamic conditions and the formation mechanism of the strong wind and weak dust process on May 11,2016 are analyzed.The results show that the strong wind and dust present a time phase inconsistency characteristics,the dust reaches its strongest stage ahead the wind 6 hours and tends to die out at the strongest stage of the wind.The 200 hPa high-level jet flow,500 hPa frontal zone,700 hPa low-level jet flow and the ground cold front is the main influencing system.Strong wind in different stages plays different roles in dust,conducive to the transmission of the sand in the early stage and restrains the development of the sand in the later stage.Further analysis shows that the high momentum carried by the 200 hPa high-level jet flow passes down through 500 hPa frontal zone,which is momentum down,and contributes to the formation of 700 hPa jet flow.The important mechanism of momentum transfer is the downward transmission of high level high vortex in the troposphere,potential vorticity region (≥2.0 PVU) down to 520 hPa with the strongest wind.At the same time,the downward momentum transmission is accompanied by the downward transmission of the cold advection in the upper air,which leads to the increase of the ground air pressure and the formation of the isallobar wind.Cold advection that is transmitted to the lower layer and surface sensible heat flux makes the atmospheric stratification unstable,through strengthening the ground turbulence to form a hybrid layer,which makes the high momentum of the 700 hPa jet flow spread to the ground and increase the surface wind speed and the maintenance and development of the dust.It can be seen that the momentum transportation downward and isallobar wind are the direct mechanisms for the formation and the development of strong winds,and the sensible heat flux is the indirect mechanism.The occurrence and development of dust is due to thermal unstable stratification,which is caused by the cold advection and the surface sensible heat.Isallobar wind and the wind formed by downward momentum are the transport mechanism of the dust.Furthermore,the inhibition effect of cold advection center (750 hPa) and the absence of secondary circulation lead to the weakness of the dust.Atmospheric stratification tends to bring the end of the dust,and the downward momentum transportation is the direct cause of the demise of the windy weather.
国家科技期刊平台
NSTL
万方数据
维普
