山东省冰雹频数月际变化的时空特征与成因探究

基于观测数据，统计分析了1999—2017年山东省冰雹频数月际变化的时空特征；基于大气再分析数据，通过对大尺度环流客观分型与物理量场的合成分析，探究了月际变化的成因。统计结果显示，山东省冰雹频数存在显著的月际变化，逐月冰雹落区具有明显的空间差异。成因探究结果表明：1）约88%的冰雹发生于低槽槽前，或槽后西北气流的环流形势下，此两种形势发生频率之和的月际变化与冰雹频数的月际变化呈现一致的起伏特征；2）水汽与热力条件影响了冰雹发生频数，对4—6月和9—10月而言，充足的水汽与强不稳定对应了较高的冰雹频数，其中6月冰雹频数最高归因于水汽含量与K指数均达到最大，且距平正异常最小；3）4—9月冰雹落区的空间分布与低层水汽输送及辐合存在较好的对应关系，而10月对应关系不明显。

A study on monthly spatiotemporal variation of hail frequency over Shandong Province and its formation mechanism

The monthly temporal and spatial characteristics of hail frequency (HF) over Shandong Province from 1999 to 2017 are statistically analyzed based on observation data. In addition, the reasons of the monthly variations are explored by the objective classification of circulation patterns and the composite analysis of physical characters based on atmospheric reanalysis data. The statistic results show that there are obvious monthly variations of HF and spatial differences in the monthly hailfall area over Shandong. The exploration of formation mechanism is shown below. 1) About 88% of hail occurs in the trough or the northwest airflow behind trough, and the monthly variation of the above two circulation patterns'' cumulative frequency is consistent with the monthly variation of HF. 2) Low-level water vapor and thermal conditions affect the HF. From April to June and from September to October, sufficient water vapor and strong instability correspond to higher HF. The HF is the highest in June because both water vapor and K index reach their maximum and the positive anomaly is the smallest. 3) From April to September, the spatial distribution of hailfall area is well correlated to low-level water vapor transport and convergence, while such correlation is not obvious in October.