2008年1月18-22日南阳市强降雪过程诊断分析

Diagnostic Analysis of the Strong Snowfall Process in Nanyang in January 18-22,2008

利用NCEP再分析资料,从大尺度环流背景、影响系统、水汽条件、动力条件等方面对2008年1月18-22日南阳市出现的强降雪天气过程进行了诊断分析。结果表明:欧亚地区持续稳定的大气环流异常为雨雪天气提供了大的环流背景;中低层切变线和西南风急流是强降雪的主要影响系统。在降雪集中时段,水汽输送带与700hPa急流相对应,西南急流为强降雪提供了充分的水汽输送和能量。700 hPa的正涡度大值区的演变与该层西南急流区有很好的对应关系,且正涡度大值区位于急流轴的左侧。正涡度核的生成和强烈的垂直上升运动为强降雪提供了动力条件。在整个降雪过程中,ζMPV1的大小变化与降雪的强弱变化一致,强降雪落区与|ζMPV2<0|的大值带有很好的对应关系。湿位涡的斜压项证明了大气的湿斜压性很强,等压面上的温度梯度较大,对强降温和水汽输送较为有利。

From large-scale circulation background, influence system, water vapor condition and dynamic condition aspects, this article carries on a diagnostic analysis of the strong snowfall synoptic process appearing in Nanyang during January 18-22, 2008 by the use of NCEP reanalysis data. The resuits indicate that sustainable and stable atmospheric circulation anomalies in Europe and Asia area provide the large-scale circulation background for the sleet weather; and the middle low-level shear line and southwest jet are the major effect systems. In the snowing centralized time interval, the water vapor conveyor belt corresponds, with the 700 hPa jet stream, and southwest jet provides for the snowfall with sufficient water vapor transport and energy. The 700 hPa positive vorticity great value area＇ s evolution has very good corresponding relationships with the southwest jet stream area in this level, and positive vorticity great value area locates at the left side of the jet axis. Positive vorticity nuclear generation and a strong vertical ascending motion provide the dynamic condition. In the whole snowfall process, the ζMPV1 size changes are consistent with the strong and the weak snowfall changes, and strong snowfall district has the very good corresponding relationships with the great value belt of the 1ζMPV2 〈 01. The baroclinic item of the moist potential vorticity proves that the atmospheric wet barocliny is very strong, and the temperature gradient on isobaric surface is bigger, which are more advantageous to the strong temperature decrease and the water vapor transfer.