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2024年浙江梅雨期降水的典型与非典型时空特征分析

Analysis on typical and atypical spatiotemporal characteristics of Meiyu precipitation over Zhejiang Province in 2024

  • 摘要: 浙江省梅雨期降水时空分布不均、年际差异显著,分析其典型与非典型特征对理解降水异常具有重要意义。利用1973—2024年6—8月浙江省66个国家级气象观测站逐日降水量观测、NCEP/NCAR逐日再分析、国家气候监测预测分析系统(CIPAS3.1)的东亚夏季风、西北太平洋副热带高压(以下简称副高)和南亚高压指数以及ERSSTv5海温月数据,首先分析了2024年梅雨期降水的典型与非典型时空分布特征,然后研究其阶段性特征及环流和前期海温背景,最后初步探讨了历年梅雨正常年份的多样性和复杂性。结果表明:(1) 2024年浙江省梅雨在统计特征上总体接近常年,6月9日入梅、7月4日出梅,梅雨量和梅雨强度指数均处于正常水平,属于典型的梅雨正常年份。但降水空间分布呈非典型特征,整体表现为“西多东少”,降水强度偏强,中雨以上降水日数偏多,同时部分非梅雨区出现显著异常降水,非梅雨量接近梅雨量的90%。(2) 2024年浙江省梅雨过程具有明显阶段性特征。6月9—18日强降水主要出现在浙西南地区,6月19日以后转移至浙西北地区。6月19日前后为关键转折时期,因东亚夏季风增强、副高发展并北跳以及南亚高压调整等多系统协同影响,浙江省降水增强并出现降水中心北移。海温背景上,前冬春季厄尔尼诺及多海域海温异常通过增强水汽输送并抑制冷空气南下共同影响初夏环流,其相互制约可能使2024年浙江梅雨强度总体接近常年。(3)浙江省9个梅雨正常年份的降水空间分布并不完全呈典型的“浙中北梅雨”特征,不同年份降水空间分布差异较大,非梅雨区亦可能出现强降水,“梅雨量正常”并不意味着降水空间分布特征接近气候平均态。

     

    Abstract: The spatial distribution of Meiyu precipitation in Zhejiang Province is highly heterogeneous, with pronounced interannual variability. Investigating both its typical and atypical characteristics is therefore essential for understanding precipitation anomalies. Using daily precipitation observations from 66 national meteorological stations in Zhejiang Province from 1973 to 2024 (June-August), daily NCEP/NCAR reanalysis data, the East Asian summer monsoon, western North Pacific subtropical high (hereafter referred to as the subtropical high), and South Asian high indices from the Climate Monitoring and Prediction Analysis System (CIPAS3.1), as well as monthly ERSSTv5 sea surface temperature (SST) data, this study first analyzes the spatial and temporal characteristics of the 2024 Meiyu precipitation, then investigates its stage-dependent characteristics, associated atmospheric circulation, and preceding SST background, and finally preliminarily explores the diversity and complexity of normal Meiyu years. The results are as follows. (1) The statistical characteristics of the 2024 Meiyu over Zhejiang Province were generally close to the climatological mean. The Meiyu season started on 9 June and ended on 4 July, and both the Meiyu precipitation amount and Meiyu intensity index were within the normal range, indicating a typical normal Meiyu year. However, its precipitation exhibited atypical spatial distribution characteristics, with an overall pattern of “more precipitation in the west and less precipitation in the east”. Precipitation intensity was relatively strong, the number of days with moderate or heavier precipitation increased significantly, and some non-Meiyu regions also experienced notable precipitation anomalies, with the non-Meiyu precipitation amount reaching nearly 90% of the Meiyu precipitation amount. (2) The 2024 Meiyu precipitation process showed distinct stage-dependent characteristics. During 9-18 June, heavy precipitation mainly occurred in southwestern Zhejiang, while after 19 June, the precipitation center shifted to northwestern Zhejiang. Around 19 June, a critical transition occurred due to the coordinated influences of an enhanced East Asian summer monsoon, the development and northward shift of the subtropical high, and the adjustment of the South Asian high, leading to intensified precipitation and a northward migration of the precipitation center. The preceding winter-spring El Niño event and multi-basin SST anomalies affected the early-summer circulation by enhancing moisture transport and suppressing southward cold-air intrusions. Their opposite effects may have partially offset each other, contributing to the near-normal Meiyu intensity in Zhejiang Province in 2024. (3) The precipitation spatial patterns of the nine normal Meiyu years in Zhejiang Province did not always exhibit the typical “central and northern Zhejiang Meiyu” pattern. Large interannual differences existed in precipitation distributions, and heavy precipitation could also occur in non-Meiyu regions. These findings indicate that a normal Meiyu precipitation amount does not necessarily correspond to a precipitation spatial pattern close to the climatological mean state.

     

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