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中高纬和低纬10~30天大气低频振荡对中国夏季降水的影响

Effects of 10–30-day Atmospheric Low-Frequency Oscillations at Mid-High and Low Latitudes on Summer Precipitation in China

  • 摘要: 大气低频振荡与中国夏季降水及灾害性天气密切相关,研究10~30天低频振荡对天气气候的影响具有重要意义。本文利用站点观测和ERA5再分析数据等,研究了1991~2020年间中高纬和低纬10~30天低频振荡对中国夏季平均降水的影响及机理。由奇异值分解(SVD)分析得到,中高纬10~30天振荡与长江—华南反位相降水分布有密切关系,贝加尔湖以北振荡偏弱,贝加尔湖以南振荡偏强时,长江流域降水显著偏少,南海至华南地区降水显著偏多;低纬10~30天振荡的关键区则位于西北太平洋,该区域振荡偏强时,华南地区降水为显著正异常。中高纬10~30天振荡主要通过波流相互作用影响夏季副热带西风急流的平均位置,使得急流附近次级环流的位置发生相应异常,从而间接影响长江流域和南海至华南地区的降水多寡,使其呈现异常的反位相分布;区别于中高纬度的是,低纬西北太平洋10~30天振荡通过向西-西北传播至华南地区,直接引起华南地区的降水异常。

     

    Abstract: Atmospheric low-frequency oscillations are closely related to summer precipitation and catastrophic weather events in China, and studying the effects of 10–30-day low-frequency oscillations on weather and climate is of great significance. In this paper, the effects and mechanisms of 10–30-day oscillations at mid-high and low latitudes on average summer precipitation in China during 1991–2020 are investigated using station observation data, ERA5 reanalysis data, etc. According to the singular value decomposition analysis, 10–30-day oscillations at mid-high latitudes are closely related to the spatial distribution of inverse-phase precipitation over the Yangtze River and South China. When 10–30-day oscillations in the north of Lake Baikal are weak, and oscillations in the south of Lake Baikal are strong, precipitation significantly decreases in the Yangtze River basin while showing a notable increase from the South China Sea to South China. The key region of 10–30-day oscillations at low latitudes is located in the northwestern Pacific, where precipitation in southern China exhibits a significant positive anomaly during periods of strong oscillations within this region. Furthermore, 10–30-day oscillations at mid-high latitudes mainly affect the mean position of the summer subtropical westerly jet stream through wave–current interactions, which makes the position of the secondary circulation near the jet stream anomalous. This indirectly affects precipitation in the Yangtze River basin and the South China Sea to South China and causes anomalous inverse-phase distributions. Distinguishing them from mid-high latitudes, 10–30-day oscillations at low latitudes over the northwest Pacific propagate northwestward to southern China, directly inducing precipitation anomalies.

     

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