湖南涝年主汛期降水低频振荡特征分析

本文基于1986—2015年湖南逐日降水数据以及同期NCEP/NCAR再分析资料,分析旱涝年主汛期(5—7月)降水低频振荡特征,并利用位相合成方法研究涝年主汛期20～50 d低频环流演变特征。结果发现,湖南地区20～50 d和10～20 d的低频降水方差贡献比都具有南高北低的分布特征,10～20 d的低频振荡在旱涝年中皆较普遍存在,而20～50 d的低频振荡只在涝年普遍存在,20～50 d低频振荡对涝年有一定的指示意义。对涝年主汛期20～50 d低频降水进行位相合成发现,在活跃位相(中断位相),夏季南亚高压和西太平洋副热带高压(简称西太副高)纬向异常接近或者重叠(分离),湖南地区降水偏多(偏少),且两个高压的强度、范围、以及脊线位置和湖南地区主汛期降水关系较密切。南海反气旋(气旋)、河套地区槽(脊)系统以及湖南地区的垂直速度和比湿配合度高,且随位相变化存在明显的周期振荡,其中南海反气旋(气旋)和河套地区槽脊系统配置与湖南低频降水有着高度的时间一致性,湖南地区的低频垂直速度和低频比湿较低频降水有一个位相的超前滞后关系。此外,随着位相的演变,低频南北风高值区皆有明显的北传特征。

Analysis on the characteristics of low frequency oscillation in precipitation in flood season in Hunan Province

Based on the daily precipitation data in Hunan during 1986-2015 and the NCEP/NCAR reanalysis data in the same period, this paper analyzed the characteristics of low frequency oscillations in precipitation during the main flood season (from May to July) in drought and flood years and studied the evolution characteristics of low-frequency circulation in the man flood seasons in drought and flood years for 20-50 days. The results showed that the distributions of variance of low-frequency precipitation at 20-50 days and 10-20 days in Hunan Province both had the characteristics of high in the south and low in the north. The low-frequency oscillations of 10-20 d are more common during the droughts and floods, while the low-frequency oscillations of 20-50 d are common only during the flood years. Low frequency oscillation of 20-50 d has some indications for the flood years. The phase composition of 20-50 d low-frequency precipitation in the flood seasons shows that in the active phase (discontinuous phase), when the latitudinal direction of the South Asian High and the latitudinal direction of the Western Pacific Subtropical High (WPSH) are abnormally close to or overlap (separate), the precipitation in Hunan is relatively more (less), and the intensity of two high-pressure, range, and ridge location are more closely related to flood season precipitation in Hunan. The anticyclone (cyclone) in the South China Sea, the trough (ridge) system in Hetao region and the vertical velocity and specific humidity in Hunan Province are well coordinated, and there is obvious periodic oscillation along with the phase change. The anticyclone (cyclone) and Hetao systems in the South China Sea have a high degree of temporal consistency with low-frequency precipitation in Hunan. The low-frequency vertical velocity in Hunan Province has a phase-lead lag relation with the low-frequency precipitation. In addition, with the evolution of the phase, the low-frequency NW wind region has obvious northward transmission characteristics.