2011年秋季河南持续降水的低频环流特征

Low-frequency Circulation Characteristic of Persistent Precipitation over Henan in the Autumn of 2011

利用河南119站的降水观测资料以及NCEP/NCAR各层高度场、风场和垂直速度场的再分析资料,研究2011年9月在河南发生的一次持续的区域性连阴雨过程。对降水进行的墨西哥帽小波分析发现,降水存在着低频特征。通过对造成低频降水的高度场和风场资料滤波计算,分析了造成降水的低频环流特征,结果表明:2011年9月河南秋季持续性降水低频振荡最主要的周期是32 d左右;低频降水的周期分为4个位相,降水从低频谷值和峰值之间的过渡位相开始,在峰值位相达到最大。低频环流场的配置在低频降水的谷值位相和峰值位相有着显著的差异,环流场的高低层配置从不利于对流发展转为有利于对流发展;同时低层水汽输送在过渡位相开始逐渐加强。降水的发生在850 hPa上主要是与低频正涡度的分布相一致,低频正涡度有着明显的波列变化及北跳;500hPa、200 hPa上的低频负涡度变化和降水变化相一致。降水的峰值(谷值)位相散度场的高低空配置主要为低层辐合(辐散)、中高层辐散(辐合),有利于(不利于)对流的发展。

By using daily precipitation data of 119 observation stations in Henan and NCEP INCAR reanalysis data （height field, wind field and vertical velocity field） the persistent continuous rain process over Henan in September 2011 was researched. The low-frequency circulation characteristics of precipitation was analyzed through the filter calculation of height field and wind field data of low-frequency precipitation. It showed that, the autumn persistent precipitation of Henan in September 2011 oscillated for a cycle of 32 days by Mexican Hat wavelet analysis. The period of low-frequency precipitation was divided into 4 phases. Precipitation started from a transition phase between low-frequency valley values to peak value, and reached the maximum in the peak value phase. The configuration of low-frequency circulation field was obviously different in the phases of valley value and peak value; the high and low level configuration turned to be helpful to the development of convection from not conducive. Meanwhile, there was strong water vapor input at the low levels. The distribution of precipitation was in keeping with low-frequency relatively positive vorticity in 850 hPa, low-frequency positive vorticity has an obvious waveform variation and northward jump; the change of precipitation was same with the low-frequency relatively negative vorticity in 500 hPa and 200 hPa. The high and low level configuration in of divergence field of a phase of peak value （valley value） of precipitation is the low-level convergence （divergence） , the highlevel divergence （convergence） , which is benefit （not benefit） the development of convection.