平凉一次暴雨前对流层顶异常特征分析

Analysis of Abnormal Characteristics of Tropopause before a Rainstorm in Pingliang

利用NCEP/NCAR 1°×1°再分析资料和常规气象观测资料,以2016年7月18日出现在平凉的区域性暴雨为例,分析暴雨发生前对流层顶高度、温度以及各高度的垂直速度、位涡、风场变化特征。结果表明,暴雨发生前4 d至前2 d对流层顶高度有明显的下降,并于暴雨发生前2 d降至最低,最低为14.6 km,相反地,对流层顶温度在暴雨发生前5 d至前2 d开始上升,并于暴雨发生前2 d升至最高,可达-65.6℃。对流层顶高度在暴雨发生前2 d的空间形变主要体现在南北方向上,高度的经向梯度变化比纬向梯度变化明显;从纬向看,暴雨发生前2 d,2 PVU等位涡线可以向下发展至380 hPa附近,凹陷最明显,即暴雨发生前2 d平凉地区对流层顶会出现折卷现象,暴雨发生当天,上升运动最强盛,最大垂直速度可达-0.3 Pa/s;对流层顶高度下降主要原因是由高层向下侵入的高位涡冷空气及对流层顶折卷过程影响。以上结果表明,对流层顶附近异常信号对暴雨预测有较好的指示意义。

By using the NCEP/NCAR global reanalysis data with the resolution of 1°×1°and conventional meteorological data,taking the regional rainstorm in Pingliang on July 18,2016 for example,the variation characteristics of tropopause height,temperature and the vertical velocity,potential vorticity and wind fields of each height were analyzed.The results showed that the tropopause height decreased significantly from 4 days to 2 days before the rainstorm,and decreased to the lowest(14.6 km)2 days before of the rainstorm.Conversely,the tropopause temperature began to rise from 5 days to 2 days before the rainstorm,and rose to the highest 2d before the rainstorm,reaching-65.6℃.The tropopause height was mainly reflected in the north-south direction 2 days before the rainstorm,and the meridional gradient change was more significantly than that in the zonal direction.From the zonal direction,the 2 PVU potential vorticity line could be developed down to 380 hPa 2 days before the rainstorm,and the depression was the most obvious,that was,2 days before the rainstorm,the tropopause would appear folding in the Pingliang area,while the ascending movement was the strongest in the day of the rainstorm,and the maximum vertical speed could reach to-0.3 Pa/s.It was proposed that the lowering of the tropopause height was mainly due to the cold air from the high vorticity invaded by the upper layer and tropopause fold event process.Therefore,the characteristics of anomalous near the top of the tropopause could be applied to forecast rainstorm in Pingliang.