A dipole pattern of July precipitation between South China and the eastern Tibetan Plateau and impacts of ENSO

Abstract

Based on observations, reanalysis data, and numerical experiments, the present study investigates the link between the interannual variation in precipitation over South China (SC) and the eastern Tibetan Plateau (ETP) in July during 1979–2019 and the underlying mechanisms. Results show that during May–September the variation in precipitation exhibits a dipole pattern between the two regions in July and August only, with more significance in July. The correlation coefficients of precipitation between the two regions in July and August are − 0.60 and − 0.34, statistically significant at the 99% and 95% confidence levels, respectively. The role of developing ENSO in the formation of the precipitation dipole in July is further investigated. During El Niño’s development in July, precipitation increases over the tropical central–eastern Pacific, and decreases from India to the Maritime Continent and tropical Atlantic. These conditions cause anomalous cyclones over SC and the northern Bay of Bengal, and an anomalous anticyclone over Lake Balkhash to Northwest China in the middle and lower troposphere via the tropical atmospheric bridge and upper-tropospheric wave trains over Eurasia. This favors the July precipitation dipole with increased (decreased) precipitation over SC (the ETP). In La Niña’s developing phase in July, the opposite is true. Moreover, numerical experiments with the ECHAM5 model can reproduce the above physical processes.

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Vol.:(0123456789)
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Climate Dynamics (2023) 61:5785–5804
https://doi.org/10.1007/s00382-023-06884-7
A dipole pattern ofJuly precipitation betweenSouth China
andtheeastern Tibetan Plateau andimpacts ofENSO
JuanWang1· KeFan1 · ZhiqingXu2· ShaofengLiu1
Received: 23 March 2023 / Accepted: 1 July 2023 / Published online: 18 July 2023
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023
Abstract
Based on observations, reanalysis data, and numerical experiments, the present study investigates the link between the inter-
annual variation in precipitation over South China (SC) and the eastern Tibetan Plateau (ETP) in July during 1979–2019
and the underlying mechanisms. Results show that during May–September the variation in precipitation exhibits a dipole
pattern between the two regions in July and August only, with more significance in July. The correlation coefficients of
precipitation between the two regions in July and August are − 0.60 and − 0.34, statistically significant at the 99% and 95%
confidence levels, respectively. The role of developing ENSO in the formation of the precipitation dipole in July is further
investigated. During El Niño’s development in July, precipitation increases over the tropical central–eastern Pacific, and
decreases from India to the Maritime Continent and tropical Atlantic. These conditions cause anomalous cyclones over SC
and the northern Bay of Bengal, and an anomalous anticyclone over Lake Balkhash to Northwest China in the middle and
lower troposphere via the tropical atmospheric bridge and upper-tropospheric wave trains over Eurasia. This favors the July
precipitation dipole with increased (decreased) precipitation over SC (the ETP). In La Niña’s developing phase in July, the
opposite is true. Moreover, numerical experiments with the ECHAM5 model can reproduce the above physical processes.
Keywords A dipole pattern of precipitation· South China· Eastern Tibetan Plateau· Interannual variability· Developing
ENSO
1 Introduction
South China (SC), affected by the South China Sea summer
monsoon, East Asian summer monsoon, and typhoons, is
one of the main regions with abundant precipitation. The
interannual variability of summer precipitation over SC has
strengthened since the 1990s (Fan etal. 2014), and extreme
droughts and floods occur frequently (Hu etal. 2023), which
has brought tremendous challenges to the prediction of
summer precipitation in this region. The Tibetan Plateau
(TP) plays a significant role in the variability of the Asian
monsoon and East Asian climate via both dynamic and ther-
mal effects (Wu etal. 2016; Yao etal. 2021; Duan and Zhang
2022). Some studies have suggested that spring atmospheric
heat sources over the TP are an indicator of summer precipi-
tation over eastern China, and there is a negative correlation
between spring heating over the TP and summer precipita-
tion over SC (e.g., Zhao and Chen 2001). Furthermore, the
interannual variation of summer atmospheric heat source
over the TP is mainly contributed by the latent heat released
by precipitation over the central and eastern TP (ETP) (Jiang
etal. 2016). Therefore, it is unclear whether there is a cou-
pling variation of summer precipitation over the TP and SC
on the interannual timescale. If there is, realizing it would be
beneficial to understanding the interannual variation in sum-
mer precipitation and improving its prediction over SC and
the TP. At present, most studies focused on the interannual
variation and physical mechanism of summer precipitation
in these two regions separately.
As the East Asian summer monsoon moves northward,
the summer precipitation over SC presents pronounced sub-
seasonal changes. From May to June, SC receives abundant
* Ke Fan
fank8@mail.sysu.edu.cn
* Shaofeng Liu
liushaof5@mail.sysu.edu.cn
1 School ofAtmospheric Sciences, Sun Yat-Sen University,
andSouthern Marine Science andEngineering Guangdong
Laboratory (Zhuhai), Zhuhai519082, China
2 Institute ofAtmospheric Physics, Chinese Academy
ofSciences, Beijing100029, China
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