| 摘要: |
| 青藏高原及其周边地区降水的季节性具有显著的区域差异特征，且影响因子复杂，尤其在青藏高原西部及其邻近地区，春夏季降水异常的时空变化大，对当地的水资源、生态系统和人类生活具有重要影响。文章利用英国东安格利亚大学气候研究中心（CRU）整理的1961—2022年格点降水资料，采用奇异值分解（SVD），并结合经验正交函数分析（EOF）、相关与回归分析，研究了青藏高原西部及其邻近地区（主要为85°E以西地区）的春-夏降水的协同变化特征，并探讨其春季（3—5月）与夏季（6—8月）降水异常的主要模态、协同变化及其可能成因。结果表明，研究区春、夏两季降水场的SVD第一模态的协方差贡献为70%，指示春、夏两季降水场之间存在密切的协同变化。当帕米尔高原及其西部地区春季降水偏多（偏少）时，随后夏季青藏高原西北部与西南部降水呈偶极型变化，其中，高原西北部的天山一带降水偏多（偏少），而西南部从兴都库什山脉南侧至西藏西南部降水偏少（偏多）。进一步的分析表明，这种春-夏耦合的降水模态可能受到厄尔尼诺-南方涛动（ENSO）的调控。春季和夏季降水SVD第一模态时间序列与表征热带太平洋热力异常的超前一个月季节平均海洋尼诺指数（ONI）序列的相关系数分别达到0.5877和0.4282，这说明ENSO对研究区春-夏降水存在一定的滞后影响。ENSO通过持续影响春、夏季印度洋海温，导致两季分别出现不同的海温异常型，其中，春季为海温变化一致的印度洋盆地型（IOB），而夏季为东西异相的印度洋偶极子型（IOD）。印度洋不同海温异常引起印度洋上空环流的改变，促成了春-夏降水模态的协同变化。 |
| 关键词: 青藏高原 帕米尔高原 天山 降水 SVD ENSO |
| DOI：10.7515/JEE2025015 |
| CSTR：32259.14.JEE2025015 |
| 分类号: |
| 基金项目:国家自然科学基金项目（42375051）；崂山实验室科技创新项目（LSKJ202203300） |
| 英文基金项目: |
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| ENSO-modulated covariation of spring and summer precipitation patterns in the western Qinghai-Xizang Plateau and its neighboring areas |
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LU Wenxu1，2，LIU Xiaodong1，2
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1.State Key Laboratory of Loess Science, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061 , China ；2.University of Chinese Academy of Sciences, Beijing 100049 , China
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| Abstract: |
| Background, aim, and scope The western part of the Qinghai-Xizang Plateau and its adjacent areas with complex terrain (our study area), including the Pamir Plateau in the west and the Tianshan Mountains in the north, mostly lie within the arid climate zone of Central Asia west of 85°E, influenced by the westerly circulation, and a small part falls under the influence of the South Asian monsoon. Consequently, precipitation and its seasonality exhibit significant regional differences across the region. This study aims to identify the dominant spatial modes of spring (March-May) and summer (June-August) precipitation anomalies over the study area, reveal the covariation between spring and summer precipitation patterns, and explore possible physical mechanisms driving the covariation. Materials and methods Using gridded precipitation data for 1961—2022 compiled by the Climatic Research Unit (CRU), we applied empirical orthogonal function (EOF) analysis and singular value decomposition (SVD) to identify dominant spatial modes and the covariation between spring and summer precipitation fields over our study area. Using ERA5 reanalysis data and the Oceanic Niño Index (ONI), we revealed the modulating effect of the El Niño-Southern Oscillation (ENSO) on the dominant spring-summer coupled precipitation mode in the study area through correlation and regression analyses. Results The SVD analysis of spring and summer precipitation fields shows that the leading mode explains 70% of the total covariance, indicating a strong covariation between spring and summer precipitation anomalies. When spring precipitation is above (below) normal over the Pamir Plateau and its western areas, a dipole pattern emerges in the following summer: above (below) normal precipitation occurs over the Tianshan Mountains in the northwestern part of the Qinghai-Xizang Plateau, while below (above) normal precipitation appears from the southern Hindu Kush Mountains to southwestern Xizang. Further analysis suggests that this spring-summer coupled precipitation mode is related to the El Niño-Southern Oscillation (ENSO). The time series of the first SVD mode for spring and summer precipitation are correlated with the seasonal mean ONI leading by one month, with correlation coefficients of 0.5877 and 0.4282, respectively, indicating a lagged influence of ENSO on the covariation of spring and summer precipitation in the study area. Discussion The Indian Ocean may serve as an important pathway for the ENSO-induced spring-summer precipitation covariance in the study area. ENSO persistently influences Indian Ocean sea surface temperature (SST) anomalies from spring to summer, leading to different dominant patterns: the Indian Ocean Basin (IOB) mode in spring and the Indian Ocean Dipole (IOD) in summer. These SST anomalies induce atmospheric circulation variations. In spring, the IOB mode affects the westerly circulation south of the Plateau, thereby modulating spring precipitation over the Pamir region. In summer, the IOD mode induces opposite circulation anomalies north and south of the Qinghai-Xizang Plateau, resulting in the observed dipole pattern (increased precipitation over the Tianshan region and decreased precipitation from the southern Hindu Kush to southwestern Xizang, or vice versa). Together, these processes drive the observed covariation of spring and summer precipitation patterns. Conclusions This study demonstrates that there is a covariation between spring and summer precipitation anomaly patterns over the western Qinghai-Xizang Plateau and its neighboring areas, and that this covariation is physically linked through ENSO-driven Indian Ocean SST anomalies. The transition from the IOB mode in spring to the IOD mode in summer provides a coherent mechanism connecting the spring precipitation anomalies over the Pamir region with the subsequent summer dipole pattern over the northwestern and southwestern parts of the Qinghai-Xizang Plateau. Recommendations and perspectives These findings improve our understanding of cross-seasonal covariation of precipitation patterns in regions with complex topography and offer a scientific basis for water resources management and seasonal precipitation forecasting. |
| Key words: Qinghai-Xizang Plateau Pamir Plateau Tianshan Mountains precipitation SVD ENSO |
