“丝绸之路”型与东亚—太平洋型遥相关的低频特征及其对江淮流域夏季降水的影响

Low-frequency Characteristics of Silk-road and East Asia-Pacific Patterns and Their Effects on Summer Precipitation in Jianghuai River Basin,China

江淮流域夏季洪涝灾害主要归因于大气环流异常的稳定维持。不同大气遥相关的低频振荡及其协同变化对江淮流域夏季降水的影响机理是大气科学领域热点问题之一。利用ERA5逐日再分析资料和中国气象局提供的逐日站点降水资料,揭示了“丝绸之路”(SR)型和东亚—太平洋(EAP)型遥相关的低频特征及其对江淮流域夏季降水的影响机理。结果表明:SR型和EAP型遥相关的10~30 d低频周期与江淮流域夏季降水关系密切,SR型和EAP型遥相关各低频系统都经历了正负位相转换并逐渐达到峰值(谷值)。其主要表现为:①10~30 d低频200 hPa等压面经向风沿西风急流呈偏北风与偏南风的交替分布,当SR型达到负位相峰值时,江淮流域为偏北风控制,中纬度低频气旋加强,加速西风急流;②10~30 d低频西太平洋副热带高压西伸东退、南亚高压东移西撤,二者相向而行,在峰值位相重叠于对江淮流域降水有利的位置;③由东亚沿岸向西北移动的向外长波辐射异常波列亦表现出显著的10~30 d低频振荡特征,处于峰值位相时,向外长波辐射在江淮流域为负异常,有利于江淮流域降水;④10~30 d低频低层正涡度、高层负涡度的配置有利于低层辐合、高层辐散,导致上升运动增强,进而触发江淮流域低频降水。

The summer flood disaster in Jianghuai River Basin(JRB)is mainly due to the stable maintenance of abnormal atmospheric circulation.The influence mechanism of low-frequency oscillations and their synergistic changes on summer precipitation in JRB is one of the hot issues in the field of atmospheric science.Based on the daily reanalysis data of ERA5 and daily station precipitation data provided by China Meteorological Administration,the low-frequency characteristics of silk-road(SR)and East Asia-Pacific(EAP)patterns,and their influence mechanism on summer precipitation in JRB were analyzed.The results show that the low-frequency periods of 10-30 d of SR and EAP patterns are closely related to the summer precipitation in JRB.The low-frequency systems of SR and EAP patterns have undergone positive and negative phase conversion and gradually reach the peak(valley)phase.The main results are as follows:①The 10-30 d low-frequency meridional winds at the isobaric surface of 200 hPa present alternating distribution of northerly and southerly winds along the westerly jet;when SR pattern reaches the peak of negative phase,JRB is controlled by the northerly wind,and the low-frequency cyclone in the middle latitude is strengthened,accelerating the westerly jet.②Western Pacific subtropical high(WPSH)and South Asian high(SAH)have a low-frequency scale of 10-30 d;the two low-frequency highs move towards each other and overlap in JRB at the peak phase,which is in favor of persistent precipitation.③The anomalous outgoing longwave radiation(OLR)wave train moving northwest from East Asia also shows a significant low-frequency oscillation characteristic of 10-30 d;when it is in the peak phase,OLR is a negative anomaly in JRB,which is conducive to the precipitation.④The configuration of positive vorticity at lower level and negative vorticity at upper level with a low-frequency scale of 10-30 d is in favor of convergence at lower level and divergence at upper level,which leads to the enhancement of upward motion and triggers precipitation in JRB.