长江中下游地区夏季降水年际差异的多尺度分析

Multiscale Analysis of Interannual Variability of Summer Precipitation over Middle and Lower Reaches of Yangtze River

关键词:  长江中下游地区  多尺度诊断  年际差异  区域差异

Key words:  middle and lower reaches of the Yangtze River  multiscale diagnosis  interannual differences  regional differences

摘要:

基于中国气象局（CMA）提供的降水站点观测数据和 ECMWF 提供的 ERA5 再分析数据集，通过尺度分离方法，对降水率进行定量诊断，探究了长江中下游地区1980—2020年夏季降水年际差异形成的多尺度特征。结果表明该区域降水呈现显著的天气尺度（小于 10 天）和次季节主导周期（10~30 天以及 30~60 天）。通过定量诊断背景尺度（大于 60天）、季节内尺度（30~60天）、准双周尺度（10~30天）和天气尺度（小于 10天）变量之间的相互作用，发现长江中下游地区夏季降水主要决定于背景水汽、背景风和天气尺度风，并且降水强年背景环流贡献最大，降水弱年天气尺度扰动贡献更大。针对长江中下游地区的两个降水大值中心进行了进一步的分析，发现长江中游平均降水更多依赖于天气尺度扰动，下游降水更多依赖于背景环流。在长江中游降水强年，西北太平洋副热带高压更加西伸，且强度更强。在次季节尺度两个降水大值中心也存在较大差异，下游地区30~60天振荡更为显著，尤其表现在降水偏强年份。

Abstract:

Based on observational data from meteorological stations of the China Meteorological Administration and the ERA5 reanalysis dataset provided by the European Centre for Medium-Range Weather Forecasts, this study conducted a quantitative diagnosis of precipitation rates using the scale separation method to explore the multi-scale characteristics of interannual variability of summer precipitation in the middle and lower reaches of the Yangtze River from 1980 to 2020. The results indicate that the precipitation variability in the region exhibited two dominant timescales, one with a synoptic period (less than 10 days) and the other with a subseasonal period (10-30 days and 30-60 days). By quantitatively diagnosing the interactions between background-scale (greater than 60 days), intraseasonal scale (30-60 days), quasi-biweekly-scale (10-30 days), and synoptic-scale (less than 10 days) variables, we found that summer precipitation in the middle and lower reaches of the Yangtze River was mainly determined by ambient water vapor, ambient wind, and synoptic-scale wind. Moreover, background circulation contributed the most in years with strong precipitation, while synoptic-scale disturbances contributed more in years with weak precipitation. Further analysis of the two precipitation centers in the middle and lower reaches of the Yangtze River reveals that the average precipitation in the middle reaches was more dependent on synoptic-scale disturbances. In comparison, precipitation in the lower reaches was more dependent on background circulation. In years with strong precipitation in the middle reaches, the subtropical high in the Northwestern Pacific extended further westward and exhibited stronger intensity. There was also a significant difference between the two precipitation centers at the subseasonal scale, with the 30-60-day oscillation being more significant in the downstream areas, especially in years with stronger precipitation.