Analysis on causes of extreme high temperature in Zhejiang Province during July-September in 2024

doi:10.11755/j.issn.1006-7639-2025-04-0499

Abstract

Abstract:

Under the background of global warming, the extreme high-temperature events become more frequent in recent years. During July-September in 2024, Zhejiang Province experienced a record-breaking high temperature event. The average high-temperature days there were 46 days, and the return period of this extreme high temperature event reached 82 years. Based on the observation data from the national meteorological stations in Zhejiang Province, High Resolution China Meteorological Administration Land Data Assimilation System (HRCLDAS), sea surface temperature from National Oceanic and Atmospheric Administration (NOAA), and reanalysis data from European Centre for Medium-Range Weather Forecasts Reanalysis v5 (ERA5), this study explored the atmospheric circulation background and the role of sea surface temperature over the North Atlantic by using the statistical analysis and dynamic diagnosis. The results are listed as below: (1) The enhancement and westward displacement of the western Pacific subtropical high, together with the strengthening and eastward movement of the South Asian high, lead to the persistent descending over Zhejiang Province, resulting in the decrease of in-situ cloud cover. The associated adiabatic warming and radiation warming contribute to the high temperature. (2) The tropical North Atlantic plays a key role. The anomalous warming of sea surface temperature over the tropical North Atlantic during the preceding April-June influences the atmospheric circulation over the region from East Asia to the western Pacific through the atmospheric teleconnection, inducing the enhancements of western Pacific subtropical high and South Asian high, thus the extreme high temperature in Zhejiang Province. (3) Decreased meridional circulation inhibit the southward movement of cold air. Meanwhile, the typhoons affecting Zhejiang Province were fewer than the climatology, and the associated precipitation anomalies couldn’t relief high temperature.

Key words: Zhejiang Province, extreme high temperature, western North Pacific subtropical high, South Asian high, tropical North Atlantic SST

摘要：

在全球气候变暖背景下，极端高温事件频发，浙江省2024年7—9月经历破纪录极端高温事件，全省平均高温日数达46 d，重现期估算为82 a一遇。基于浙江省气象站观测数据、中国气象局高分辨率陆面数据同化系统（High Resolution China Meteorological Administration Land Data Assimilation System，HRCLDAS）、美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration，NOAA）海温及欧洲中心第五代再分析资料（European Centre for Medium-Range Weather Forecasts Reanalysis v5，ERA5），采用统计分析与动力诊断等方法，综合分析此次事件的大气环流特征及其与北大西洋海温异常的联系。结果表明：（1）西太平洋副热带高压西伸和南亚高压的东扩同时增强是造成2024年浙江省极端高温事件的关键动力成因，在此环流控制下，全省为持续性异常下沉运动，云系偏少，绝热增温和辐射增温叠加，直接引发极端高温事件。（2）热带北大西洋海温异常是重要外强迫因子。前期（4—6月）热带北大西洋海温异常偏暖通过激发大气遥相关波列，显著影响东亚至西太平洋的环流，促成西太平洋副热带高压和南亚高压同时增强，诱发极端高温天气。（3）中高纬度环流经向分量偏弱不利于冷空气南下。同时，影响浙江的台风偏少偏弱，降水量偏少，导致浙江异常高温持续时间长、极端性强。

关键词: 浙江, 极端高温, 西太平洋副热带高压, 南亚高压, 热带北大西洋海温

CLC Number:

P423
P466

HU Yuepeng, ZHAO Junping, LIU Hanhua, FU Yuan, SUN Shanlei, SONG Ziyi. Analysis on causes of extreme high temperature in Zhejiang Province during July-September in 2024[J]. Journal of Arid Meteorology, 2025, 43(4): 499-509.

胡跃鹏, 赵军平, 刘汉华, 付远, 孙善磊, 宋子祎. 2024年7—9月浙江省极端高温成因分析[J]. 干旱气象, 2025, 43(4): 499-509.

Figures/Tables 8

Fig.1 The temperature anomalies during July-September in 2024 （a， Unit： ℃） and the evolution of daily maximum temperature during June-September in 2024 （b） in Zhejiang Province （The dotted areas indicate that the outliers in 2024 exceeded the 90th percentile during 1991-2020）

Fig.2 Normalized time series of July?September daily mean maximum temperature （a） and high-temperature days （b） during 1980-2024 （Dashed lines denote anomalies in 2024）， and the monthly distribution of differences of area influenced by high temperature with different levels between 2024 and 2022 （c） in Zhejiang Province

Fig.3 The 500 hPa geopotential height anomaly regressed by high-temperature days from July to September during 1980-2023 in Zhejiang Province （a， the dotted area indicates a confidence level of 90%）， and the 500 hPa geopotential height anomaly from July to September 2024 （b， the dotted area exceeding the 90th percentile during 1991-2020）（Unit： gpm）

Fig.4 The 500 hPa geopotential height contour of 5 880 gpm （a） and the 100 hPa geopotential height contour of 16 760 gpm （b） during July?September in 2024 and the climatological mean states， the anomalies of 200 hPa zonal wind during July-September in 2024 （c， Unit： m·s-1； the dotted area exceeding the 90th percentile during 1991-2020）， and the July-September 200 hPa zonal wind regressed with the high-temperature days in Zhejiang Province during 1980-2023 （d， Unit： m·s-1； the dotted area indicates a confidence level of 90%）

Fig.5 The 500 hPa vertical velocity （a， Unit： Pa·s-1） and total cloud cover （b， Unit： %） anomalies during July?September in 2024

Fig.6 The surface net shortwave radiation （a）， net longwave radiation （b）， sensible heat flux （c） and latent heat flux （d） anomalies during July?September in 2024 （Unit： W·m-2）

Fig.7 Correlations of April-June sea surface temperature with the July-September high-temperature days in Zhejiang Province during 1980-2023 （a， the dotted area indicates a confidence level of 90%） and the time series of the Atlantic sea surface temperature index during 1980-2024 （b， the dashed line denotes the anomaly in 2024）

Fig.8 The July-September sea surface temperature （a， Unit： °C） and 500 hPa geopotential height （b， Unit： gpm） anomalies regressed with the Atlantic sea surface temperature index during April-June from 1980 to 2023 （The dotted area indicates a confidence level of 90%）

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