Differences in the Effects of 10–30-Day Oscillations on Persistent Precipitation across Diverse Mei-Yu Climate Regions in China

Abstract The mei-yu season is marked by persistent precipitation, often leading to floods and landslides. Due to significant spatial variability, the China National Climate Center has defined three mei-yu monitoring zones: south of the Yangtze River (SYR), the Yangtze River valley (YRV), and the Yangtze–Huaihe valley (YHV). Analyzing the differences of persistent precipitation events (PPEs) across these regions is crucial for accurately understanding precipitation patterns and effectively predicting natural disasters. This study employs ground-based observations, ERA5 reanalysis data, and Regional Climate Model, version 5.0 (RegCM5.0) to examine PPE characteristics and their physical processes concerning subseasonal oscillation in these three mei-yu climate regions, aiming to reveal how oscillation affects the PPEs. The observations indicate PPEs last about 4–5 days on average in all three regions, while the dominant subseasonal scales demonstrate a period of 10–30 days. However, notable disparities exist in the fundamental mechanisms influencing PPEs, and the trajectories of oscillations also differ. In SYR, PPEs are mainly influenced by mid- to high-latitude oscillations, whereas in YRV and YHV, they are influenced by both mid–high and low-latitude oscillations. Numerical simulation is consistent with observed results, which further elucidate the relative significance of 10–30-day oscillations at different latitudes on PPEs across the three regions. The PPEs of SYR are primarily influenced by mid- to high-latitude oscillations. The response of PPEs in YRV to 10–30-day oscillations is consistent across mid–high and low latitudes, with a slightly stronger effect at mid–high latitudes, while in YHV, low-latitude oscillations are the primary influence. The aforementioned results can provide a fundamental basis of precursor signals for predicting mei-yu precipitation.