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.