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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、CIPAS3.1西北太平洋副热带高压指数和ERSSTv5海温月数据,首先分析了2024年梅雨期降水的时空分布特征,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,呈典型特征。但降水时空分布呈非典型特征,整体表现为“西多东少”,降水强度及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、西太平洋副热带高压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个梅雨正常年份中,并不一定表现为典型的“浙中北梅雨”降水格局,且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”并不等同于“降水空间分布正常”。

     

    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 during June-August of 1973-2024, together with the NCEP/NCAR daily reanalysis, the CIPAS3.1 index of the Northwestern Pacific Subtropical High (NWPSH), and ERSSTv5 monthly sea surface temperature (SST) data, this study first analyzes the spatial and temporal characteristics of the 2024 Meiyu precipitation, then examines its intraseasonal evolution, associated atmospheric circulation, and preceding SST background, and finally provides a preliminary discussion of the diversity and complexity of climatologically normal Meiyu years. The results are as follows. (1) The 2024 Meiyu season in Zhejiang Province was statistically close to normal, with the onset on 9 June and withdrawal on 4 July. Both the total Meiyu precipitation and the Meiyu intensity index were within the climatological range, indicating typical overall characteristics. However, the spatial distribution of precipitation was atypical, exhibiting a "more in the west and less in the east" pattern. Precipitation intensity and the number of moderate-to-heavy precipitation days were above normal, while some non-Meiyu regions also experienced remarkable precipitation anomalies. The non-Meiyu precipitation amounted to nearly 90% of the Meiyu precipitation. (2) The 2024 Meiyu process exhibited distinct stage-dependent characteristics. Heavy rainfall was mainly concentrated over southwestern Zhejiang during 9-18 June and shifted to northwestern Zhejiang after 19 June. Around 19 June, a critical transition occurred, during which the strengthening of the East Asian summer monsoon, the development and northward jump of the NWPSH, and the adjustment of the South Asian High jointly enhanced precipitation and caused the precipitation center to migrate northward. In terms of the SST background, the preceding winter-spring El Niño event and SST anomalies over multiple ocean basins influenced the early-summer circulation by enhancing moisture transport and suppressing the southward intrusion of cold air. The combined and competing effects of these SST anomalies likely contributed to the near-normal overall Meiyu intensity in 2024. (3) Among the nine climatologically normal Meiyu years identified in Zhejiang Province, the precipitation pattern did not necessarily conform to the typical "central and northern Zhejiang Meiyu" pattern, and substantial differences existed in the spatial distribution of precipitation among different years. Significant rainfall could also occur in non-Meiyu regions, indicating that a normal total Meiyu precipitation does not necessarily imply a normal spatial distribution of precipitation.

     

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