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河北省2023年7月持续性高温过程成因和预报研究

Causes and Predictability of the Persistent Heatwave in July 2023 in Hebei

  • 摘要: 持续性高温热浪严重影响经济社会活动,对高温天气过程的成因和预报研究具有重要的科学意义。基于河北省142个观测站1961~2023年历年7月的逐日最高气温观测资料以及NCEP/NCAR全球逐日/月再分析资料等,本文分析了河北省2023年7月高温过程成因,并采用深度学习算法(LSTM)提出了高温热浪预报模型。结果表明:2023年7月河北省平均高温日数较常年偏多7.8 d,共出现3次持续性高温过程,最强时段为5~11日。副热带高压偏西、偏北、面积异常偏大,南亚高压的持续偏东和偏北是此次高温持续性发展的环流背景,强烈的下沉运动伴随的非绝热增温是导致干热型高温热浪的直接成因。采用LSTM对河北省中南部4站进行了预测,预测结果均通过了显著性检验。预测评估结果显示:ROC曲线的下面积AUC值在0.55~0.65,其中预报效果最好的是保定,表明该模型对逐日最高气温有一定的预报能力。进一步分析表明,LSTM能够很好地预测出各站的高温过程,但在高温起止时段和最高气温值上存在较大差异。

     

    Abstract: Persistent heatwaves severely impact economic and social activities; thus, it is crucial to study their causes and predictability. Using daily maximum temperature data from 142 stations in Hebei Province for July, along with NCEP/NCAR global daily and monthly reanalysis data from 1961 to 2023, this study analyzed the causes of heatwaves in July in Hebei. A heatwave forecasting model was developed using a deep learning algorithm LSTM (Long Short Term Memory networks). The results indicated that the average number of heatwave days in July 2023 in Hebei was 7.8 d more than normal. There were three prolonged heatwave events, with the strongest occurring from 5 July to 11 July. The anomalous westward and northward expansion and the large area of the western Pacific subtropical high, along with the persistent eastward and northward extension of the South Asian high, served as the background circulation patterns contributing to the ongoing development of this heatwave. Diabatic heating accompanied by strong descending motion was the direct cause of the hot and dry conditions. LSTM was employed to forecast conditions at four stations in central and southern Hebei Province, and the model predictions were all statistically significant. The assessment results showed that the AUC (Area Under Curve) values ranged from 0.55 to 0.65, with Baoding demonstrating the highest forecasting accuracy, indicating that the LSTM model has a moderate ability to predict daily maximum temperatures. Further analysis revealed that LSTM can effectively capture the heatwave trends at each station. However, significant discrepancies existed in the predicted start and end dates of the heatwaves and in the maximum air temperature values.

     

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