2014年4月22日新疆寒潮天气过程锋面结构演变特征分析

Characteristics of frontal structure evolution during the cold wave weather process in Xinjiang on 22 April 2014

摘要:

中亚是寒潮强冷空气爆发的关键区，天山陡峭高大地形阻挡了冷气团前锋面系统的东移南下的移动，呈准静止状态，在中亚强天气中扮演着重要角色，目前研究不多。本文选取2014年4月22日08时开始北疆发生大风降温，南疆发生强沙尘暴的一次寒潮天气过程，利用常规气象观测数据和分辨率为1o×1o的NCEP再分析资料，分析了这次寒潮天气锋面过程的500 hPa天气形势和地面气压场形势；计算了和锋面密切相关的冷暖平流、温度梯度和锋生函数；分析了三个物理量在水平面以及西北东南向的垂直剖面上的三维立体结构和演变特征。研究表明： 500 hPa东欧脊在暖平流作用下快速发展，西西伯利亚槽在冷平流作用下加强并东移南下。受其影响，中亚地区地面图上锋面气旋发展旺盛，地面冷锋在东移过程中遇到平均海拔高度3000m的天山高大陡峭地形，温度梯度增大，产生较强的锋生。该锋面在对流层中下层的水平面图上表现为等位温线沿天山密集分布，位温梯度很大；在垂直剖面上，在天山位置表现为锋生，等位温线变为准垂直分布，梯度增大，宽度变窄。

Abstract:

The Tianshan Mountain quasi-stationary front, which forms due to the effect of the steep terrain, influences the variation of temperature and precipitation on the two sides of the mountain, playing an important role in the severe weather processes over the region of central Asia. Affected by such quasi-stationary front, a severe cold weather process took place in Xinjiang on 22 April 2014, during which strong wind and temperature decline occurred in the northern Xinjiang while strong sand-dust storm appeared in southern Xinjiang. Adopting conventional observation and NCEP 1o×1o reanalysis data, this paper analyzes the 500 hPa synoptic situation and surface pressure field during this cold wave frontal process, calculates the cold and warm advections, temperature gradient and front genesis function which are closed related to the frontal surface, and also analyzes the 3-dimensional structure and evolution characteristics of three physical quantities on the horizontal plane chart and vertical cross-section in the northwest-southeast direction. The results suggest that, before the formation of the Tianshan Mountain quasi-stationary front, the 500 hPa European ridge developed quickly northward affected by warm advection while the West Siberian trough strengthened and moved southward under the influence of cold advection. Thus, the frontal cyclone over central Asia developed vigorously and the surface cold front met with the Tianshan Mountain that is high and steep with average altitude of 3000 m, causing the temperature gradient to increase, strong front genesis to break out and strong quasi-stationary front to form in the northern part of Tianshan Mountain. This frontal surface assumes the isotherms that distribute densely on the horizontal plane chart of mid-low troposphere, which means the temperature gradient is very large. Meanwhile, front genesis is seen in the Tianshan Mountains on the vertical cross-section where θ becomes vertical, and temperature gradient increases, but the width decreases.