The Extraordinary Rainfall over the Eastern Periphery of the Tibetan Plateau in August 2020

Abstract

A large amount of accumulated precipitation was recorded over the Eastern Periphery of the Tibetan Plateau (EPTP) in August 2020. Using hourly rain gauge records and the ERA5 reanalysis dataset, we analyzed the unique characteristics of rainfall in August and the accompanying circulation conditions and conducted a comparison with previous data. This record-breaking amount of accumulated rainfall was centered on the northern slope of the EPTP. This location was in contrast with the historical records of the concentration of rainfall over the middle and southern slopes. The hourly rainfall in August 2020 was both more frequent and more intense than the climatological mean rainfall. An amplification effect of the topography was observed, with the precipitation over the EPTP showing a more significant change with terrain height in August 2020. A circulation analysis showed that cold (warm) anomalies existed over the north (south) of approximately 35°N compared with those in the years when the southern EPTP received more rain. The western Pacific subtropical high was more intense and extended to the west, and the low-level cold air from the north was more active. The enhanced low-level southerly winds on the periphery of the subtropical high injected warm, moist air further north than the climatological mean. These winds became easterly near the northern EPTP and were forced to ascend by the steep terrain.

摘要

2020 年 8 月在青藏高原东坡出现了异常大的累积降水量. 利用逐小时站点观测资料和 ERA5 再分析数据, 本文分析了 2020 年 8 月降水的独特特征和对应的环流条件, 并与历史记录进行了比较. 这一创纪录的累积降水量集中在青藏高原东坡的北段. 该位置与历史记录中降水集中在中坡和南坡的情况明显不同. 相比气候平均, 2020 年 8 月的小时降水更加频繁、 强度更强. 2020 年 8 月, 青藏高原东坡地形对降水的增幅效应比以往更加明显. 环流分析表明, 与降水集中在青藏高原东坡南段的年份相比, 降水集中在北段时, 在约 35°N 以北 (以南) 存在冷 (暖) 异常. 西太平洋副热带高压强度更强, 并向西延伸, 来自北部的低层冷空气更活跃. 副热带高压外围增强的低层偏南风将暖湿空气注入比多年平均更北的地方, 并在青藏高原东坡北段附近转为偏东风, 在陡峭地形的作用下强迫上升.