北疆棉花一次严重障碍型冷害天气过程的诊断分析

[目的]从天气学角度揭示北疆棉花严重障碍型冷害的致灾特点和成因,探讨其致灾机理,给出天气概念模型,为此类天气过程的预报提供参考和依据.[方法]以2001年7月28日～8月2日北疆棉花一次严重障碍型冷害天气过程为例,采用1°×1°NCEP再分析资料对其进行物理量的诊断分析.[结果]障碍型冷害天气过程的大气环流背景为100 hPa盛夏南亚高压及其北侧的副热带锋区上的低槽,南亚高压双体型致使副热带大槽位于中亚到新疆之间,造成新疆较大降水.500 hPa上,伊朗高压突然北挺,其高压脊顶向东北方向延伸,引导北方冷空气南下至中亚地区,形成深厚的冷性低值系统--中亚低涡,该低值系统深厚、稳定,其槽底伸到25°N,且低涡中心冷空气强度达-20.0℃,这在盛夏新疆较为罕见,从而造成持续性低温过程.高空西南急流对水汽输送起重要作用,它还可造成高空辐散,增强高空正涡度平流,从而使空气产生强烈的上升运动,为此次天气过程提供动力条件.[结论]南亚高压呈双体型分布,副热带大槽位于中亚至新疆之间,且大槽位置在40°N以南;500 hPa在中亚地区形成深厚冷性影响系统,冷空气中心强度在-20.0℃左右,新疆上空有较强的西南急流相配合,该天气形势在盛夏出现易造成新疆棉花严重障碍型冷害.

Diagnostic Analysis on a Severe Cold Disasters Event on Cotton Plants in the North of Xinjiang

【Objective】The aim of this study is to open out the characteristics and the cause of the severe cold disasters from the angle of synoptic meteorology,discuss the mechanism of the cold disasters and give some scientifical reasons for weather forecast on this weather course.【Method】In this paper,a severe cold disaster event on cotton plants in the north of Xinjiang on July 28,2001 to August 2,2001 is studied,the diagnostic analyses are given by using daily 1°×1° grid reanalyzed data from NCEPA/NCAR.【Result】The atmospheric circulation background of the durative low temperature process in midsummer is the trough of subtropical front of South Asian high pressure at 100 hPa.Double centers of South Asian high pressure bring about the subtropical trough to be among the central Asian and Xinjiang,which result in the heavy rain.The effect system of this cold disaster event is central Asian whorl at 500 hPa.The deep and stable cold whorl with temperature below-20.0℃ forms over Central Asia,and a continuous low temperature process occurs.The upper-level jet not only transport the water vapor but result in the divergence,and make the positive vorticity advection added,and induced the strong upward motion which provide the dynamical condition for this process.【Conclusion】If in midsummer,the South Asian high pressure takes on double centers,the subtropical trough among the central Asian and Xinjiang and the trough locate in north from 40°N;the deep and stable cold whorl at 500 hPa with temperature below-20.0℃ were formed over Central Asia,and the strong upper-level jet work in Xinjiang will bring on severe cold disaster for cotton in Xinjiang.