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Atmospheric Rivers and Mei-yu Rainfall in China: A Case Study of Summer 2020

Abstract

Atmospheric rivers (ARs) are long, narrow, and transient filaments of strong horizontal water vapor transport that can lead to extreme precipitation. To investigate the relationship between ARs and mei-yu rainfall in China, the mei-yu season of 2020 in the Yangtze-Huaihe River basin is taken as an example. An adjusted AR-detection algorithm is applied on integrated water vapor transport (IVT) of the ERA5 reanalysis. The JRA-55 reanalysis and the data from Integrated Multi-satellite Retrievals for GPM (IMERG) are also utilized to study the impacts of ARs on mei-yu rainfall in 2020. The results reveal that ARs in East Asia have an average length of 5400 km, a width of 600 km, a length/width ratio of 9.3, and a northeastward orientation of 30°. ARs are modulated by the western North Pacific subtropical high. The IVT core is located at the south side of low pressure systems, moving eastward with a speed of 10° d−1. For the cross sections of ARs in the Yangtze-Huaihe River basin, 75% of the total flux is concentrated below 4 km with low-level jets near AR cores. Moreover, ARs occur mainly in the mei-yu period with a frequency of 20%–60%. The intensity of AR-related precipitation is 6–12 times that of AR-unrelated precipitation, and AR-related precipitation contributes about 50%–80% to total mei-yu precipitation. As shown in this case study of summer 2020, ARs are an essential part of the mei-yu system and have great impacts on mei-yu rainfall. Thus, ARs should receive more attention in research and weather forecast practices.

摘要

大气河是指狭长、 瞬变的强水平水汽输送带, 能够导致极端降水. 为了调查大气河与中国梅雨之间的关系, 本文以 2020 年中国江淮地区梅雨期为例, 基于 ERA5 再分析数据中的垂直积分的水汽输送值来筛选大气河, 并对现有的筛选大气河的方法做了改进. 本文使用到的数据还有 JRA-55 再分析数据以及 GPM 多卫星反演融合资料. 结果显示, 在东亚地区, 大气河平均长 5400 千米, 宽 600 千米, 长宽比平均为 9.3, 方向为东偏北 30°. 此外, 大气河受到西北太平洋副热带高压的调制, 大气河的核心位于低压系统的南侧, 以 10° d-1 的速度向东移动. 在江淮地区, 大气河截面上 75% 的水汽输送集中在4千米以下, 且大气河的轴心位于低空急流附近. 此外, 大气河主要发生在梅雨季, 出现频率为 20%-60%. 与大气河相关的降水的强度是与大气河无关的降水的强度的 6-12 倍, 与大气河相关的降水占梅雨期总降水的 50%-80%. 根据对 2020 年夏季的个例分析可知, 大气河是梅雨系统的重要组成部分, 对梅雨降水有着重要影响. 因此, 在中国梅雨研究和业务预报中, 应该对大气河加以关注.

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Acknowledgements

This research was supported jointly by the National Key Research and Development Program (Grant No. 2016YFA0600604), the National Natural Science Foundation of China (Grant No. 4191101005 and 4181101164), and the Alliance of the International Science Organizations (Grant No. ANSO-CR-KP-2020-01). In this study, the ERA5 data were provided by the ECMWF and are available online at http://apps.ecmwf.int/datasets/data/. The IMERG data were obtained from NASA and downloaded from https://disc.gsfc.nasa.gov/datasets/GPM_3IMER-GDL_06/summary?keywords=GPM. The JRA-55 reanalysis data were obtained from JMA and downloaded from https://jra.kishou.go.jp.

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Correspondence to Ke Wei.

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Article Highlights

• ARs are associated with mei-yu-related systems such as the WNPSH, LLJs, mei-yu fronts, and upper-level jets.

• During the summer of 2020, East Asian ARs mainly occurred in the mei-yu period.

• AR-related rainfall contributes 70%–90% to the total rainfall, with an intensity 6–12 times that of AR-unrelated rainfall.

This paper is a contribution to the special issue on Summer 2020: Record Rainfall in Asia—Mechanisms, Predictability and Impacts.

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Wang, T., Wei, K. & Ma, J. Atmospheric Rivers and Mei-yu Rainfall in China: A Case Study of Summer 2020. Adv. Atmos. Sci. 38, 2137–2152 (2021). https://doi.org/10.1007/s00376-021-1096-9

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Key words

  • atmospheric rivers
  • East Asian summer monsoon
  • mei-yu front
  • low-level jet
  • western North Pacific subtropical high

关键词

  • 大气河
  • 东亚夏季风
  • 梅雨锋
  • 低空急流
  • 西北太平洋副热带高压