2021年宁夏中北部一次强沙尘暴天气分析

Analysis of a Strong Sandstorm Weather in 2021in Central and Northern Ningxia

利用1961—2020年宁夏地面观测资料、MICAPS4常规资料、NCEP再分析资料,对2021年3月15—19日宁夏中北部地区发生的1次强沙尘暴天气过程(简称“3·15”沙尘暴)进行了分析。结果表明,1961—2020年沙尘及沙尘暴天气出现次数呈下降趋势,但2021年银川市沙尘天气发生频次高、出现时间早、沙尘暴强度强。此次出现的强沙尘暴为输入型,其沙源地主要为蒙古国和我国河套以北的沙漠地带。在蒙古气旋作用下,强冷空气自蒙古国由北南下,蒙古气旋不断发展,500 hPa正涡度中心、850 hPa散度中心、地面冷锋后强气压梯度带及强偏北大风造成了这次起源于蒙古国东部、影响我国北方大范围地区的沙尘暴过程。蒙古气旋的发展、移动缓慢,地面密集气压梯度区长时间维持,沙尘暴暴发区低层散度场有-12×10^(-6)s^(-1)的强辐合区,中层涡度场有18×10^(-6)s^(-1)的辐合区,蒙古国50~52°N的低层至高层有-5×10^(-2)Pa/s的强上升运动区维持沙源输送,为沙尘暴的暴发和持续创造了条件。

A strong sandstorm weather process(referred to as “3·15” sandstorm) occurred in the central and northern part of Ningxia from March 15 to 19, 2021. Based on the ground observation data of Ningxia from 1961 to 2020, conventional data retrieved by MICAPS4 and NCEP reanalysis data, this paper conducted relevant analysis. The results show that: the frequency of dust and sandstorm weathers from 1961 to 2020 is on a decreasing trend, but in 2021, such weathers in Yinchuan City occurr frequently, and early, and the intensity of sand and dust is strong. The “3·15” sandstorm is of the input type, whose sand source is mainly in Mongolia and the desert area north of the Hetao Plain. Under the action of the Mongolian cyclone, strong cold air from Mongolia move southward, and the Mongolian cyclone continue to develop, with positive vorticity center at 500 hPa,divergence center at 850 hPa, strong pressure gradient after the cold front on the ground and strong northerly winds, resulting in the “3·15” sandstorm, affecting a large area of northern China. The development and movement of Mongolian cyclones are slow,and the dense surface pressure gradient area maintain for a long time. The divergence field in the lower layer of the sandstorm outbreak area has a strong convergence area of-12×10^(-6)s^(-1), and the vorticity field in the middle layer is 18×10^(-6)s^(-1), and the strong upward movement area from the lower layer of 50~52°N to the upper layer of Mongolia has a strong upward movement area of-5×10^(-2)Pa/s to maintain sand source transport, which has created favorable conditions for sandstorm outbreak and persistence.