Influence of the MJO and sea surface temperature anomalies on spring drought in 2019 in Yunnan

doi:10.11755/j.issn.1006-7639-2026-01-0028

Abstract

Abstract:

In the spring of 2019, Yunnan experienced a severe seasonal drought characterized by its extensive impact area and high intensity, which significantly affected agricultural production and water resources. By utilizing precipitation data from 125 meteorological stations in Yunnan, reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and high-resolution sea surface temperature data from the National Oceanic and Atmospheric Administration (NOAA), and employing statistical analysis methods such as correlation and synthesis analysis, this study analyzed the causes of the spring drought in Yunnan from the perspective of tropical atmospheric intraseasonal oscillation (Madden-Julian Oscillation, MJO) and abnormal sea surface temperature changes. The results are as follows: (1) The spring precipitation in Yunnan region is significantly modulated by the phase of MJO. When MJO is in the third and fourth phases, it usually leads to an increase in precipitation. However, during the critical period of precipitation from April and May 2019, MJO was mainly active in the Western Hemisphere and the African region, corresponding to its 8th and 1st phases, resulting in weak convection over the Indian Ocean-West Pacific region and blocking the northward transport of moisture by high-pressure systems and resulting in unfavorable moisture convergence conditions over Yunnan. (2) From March to May in 2019, there was a persistent sea surface temperature positive anomaly in the central-eastern Pacific, which weakened the tropical zonal circulation, and the convective activities over southeast Asia and South China Sea were suppressed, further weakening the conditions for water vapor transport to Yunnan. Most areas of Yunnan were in a moisture divergence zone, which was unfavorable for water vapor accumulation and resulted in less precipitation. (3) The positive anomaly of sea surface temperature in the central-eastern Pacific caused a weakening of the Walker circulation, and coupled with the circulation anomalies induced by the active MJO over the Western Hemisphere, both the two factors worked together and caused the strong and westward extension of the low-latitude subtropical high pressure system, which blocked the transport of water vapor from the Bay of Bengal to Yunnan, resulting in significant decrease of precipitation there in spring of 2019.

Key words: Madden-Julian Oscillation （MJO）, sea surface temperature, Yunnan, spring drought in 2019, causes

摘要：

2019年春季，云南经历了一次严重的季节性干旱，其影响范围广、强度大，对当地农业生产和水资源造成了严重影响，利用云南125个气象站降水资料、美国国家环境预报中心和国家大气研究中心的再分析数据、美国国家海洋和大气管理局的高分辨率海面温度资料等，采用相关及合成分析等统计分析方法，从热带大气季节内振荡（Madden-Julian Oscillation，MJO）及海温异常变化的角度分析此次云南春旱成因。结果表明：（1）云南地区春季降水受MJO位相的显著调制，当MJO处于第3和第4位相时，通常有利于降水增多；而2019年4—5月降水关键期，MJO主要活跃于第8、第1位相所在的西半球及非洲区域，导致印度洋—西太平洋对流偏弱，向北水汽输送受到高压系统阻隔，致使该区域水汽辐合条件整体偏差。（2）2019年3—5月，中东太平洋持续的海温正距平削弱了热带纬向环流，进而抑制了东南亚及南海的对流活动，导致向云南输送的水汽减弱。云南大部地区处于水汽辐散区，不利于水汽聚集，降水偏少。（3）中东太平洋海温正距平导致Walker环流减弱，叠加MJO在西半球活跃所引发的环流异常，两者协同作用促使低纬副热带高压偏强西伸，阻断了孟加拉湾水汽向云南的输送，导致2019年春季降水显著偏少。

关键词: 热带大气季节内振荡（MJO）, 海温, 云南, 2019年春旱, 成因

CLC Number:

P466

LUO Dongli, ZHAO Erxu, WAN Yunxia. Influence of the MJO and sea surface temperature anomalies on spring drought in 2019 in Yunnan[J]. Journal of Arid Meteorology, 2026, 44(1): 28-36.

罗冬莉, 赵尔旭, 万云霞. MJO及海温异常对云南2019年春季干旱的影响[J]. 干旱气象, 2026, 44(1): 28-36.

Figures/Tables 11

Fig.1 The yearly variation of the average precipitation anomaly percentage in spring from 1961 to 2019 in Yunnan

Fig.2 Distribution of average geopotential height field (black solid lines, Unit: gpm)，temperature field (red dashed lines, Unit: ℃），and wind field（green arrow vectors, Unit: m·s-1) at 500 hPa (a) and 700 hPa (b) in spring of 2019 (The black box indicates the Yunnan region, the same as below)

Fig.3 Composition of the daily average precipitation anomaly percentage at 125 stations in Yunnan during MJO phases1-8 in spring from 1979 to 2018

Fig.4 Phase diagram of the MJO from April 22 to May 31，2019

Fig.5 The distribution of the average OLR anomaly fields in the spring of 2019 (a) and May 2019 (b)（Unit: W·m-2） (The shaded area represents the value greater than or equal to 10)

Fig.6 The longitudinal-altitude cross-section of the wind field （arrow vectors，Unit： m·s-1） and vertical velocity （the color shaded，Unit： -10-2 Pa·s-1） along the equator averaged from March to May during the period 1979-2018

Fig.7 Yearly variations of the Ni?o3.4 index, WYI, and WI in March (a) and April (b) during the period of 1979-2018

Tab.1 The correlation coefficients between WYI and WI，and between the Ni?o3.4 index and WYI，WI from March to May during the period of 1979-2018

月份	WI与WYI	Niño3.4与WYI	Niño3.4与WI
3	0.35*	-0.32*	-0.76**
4	0.42**	-0.49**	-0.87**
5	0.42**	-0.49**	-0.72**

Fig.8 The distribution of the difference between the average sea surface temperature field in spring (a) and May (b) of 2019 and the average sea surface temperature field of the same period from 1979 to 2018 (Unit: °C)

Fig.9 The correlation coefficients between the average OLR over the 0°-10°N，80°E-90°E region in spring from 1982 to 2018 and the sea surface temperature field in the same period （The yellow and red areas pass the significance tests at the 0.05 and 0.01 levels，respectively）

Fig.10 Distribution of the 700 hPa water vapor flux （arrow vectors，Unit： 10-5 kg·m-1·hPa-1·s-1） and the water vapor flux divergence （the colored shaded，Unit： 10-8 kg·m-2·hPa-1·s-1） in spring of 2019

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