西太平洋副热带高压指数的修订与应用

Revision and application of the western pacific subtropical high indices

  • 摘要: 西太平洋副热带高压(以下简称副高)为影响东亚季风区气候异常的重要环流系统之一,气候监测业务中主要通过副高面积、强度、脊线、北界和西伸脊点5个指数来反映副高的强度、位置和空间形态。受全球变暖影响,北半球副热带位势高度整体增强,导致现行业务中的副高指数已不能准确刻画其变化特征,与区域性旱涝或高温等极端天气的关系也减弱,因此非常有必要对副高指数进行修订。修订内容主要包括:(1)先确定副高的空间形态,再计算其面积和强度指数;(2)考虑全球变暖背景下副高的西伸形态,将副高面积指数规定为西伸脊点所在经度至150°E范围内5880 gpm等值线所包围区域的实际面积;(3)补充西段和东段副高脊线和北界指数,更细致地表征副高形态变化及其对中国气候异常的影响。与现行指数对比结果显示,修订的副高指数提升了副高对中国气候异常演变的指示性。在变暖背景下,除副高脊线指数外,各月的副高指数显示副高明显增大、增强、北扩且西伸。盛夏时期副高更倾向于北扩影响中国北方地区,其他季节副高则更倾向于西伸影响西部地区。修订的副高指数与中国夏季降水和高温均存在较好的对应关系,且较现行业务指数与降水的关系更为显著,尤其是西伸脊点和西段脊线指数,它们与夏季各月降水和高温的空间相关分布,体现了随着东亚夏季风推进,降水和高温的高相关区也逐渐北抬的特征。

     

    Abstract: The Western Pacific Subtropical High (WPSH) is one of the major circulation systems that cause climate anomalies in the East Asian monsoon region. The WPSH is mainly described by five WPSH indices in the operational climate monitoring of the CMA National Climate Centre, including area (GM), intensity (GQ), ridgeline (GX), northern boundary (GB), and westernmost point (GD) indices. Under the background of global warming, the current operational WPSH indices can no longer accurately depict the WPSH spatial morphology due to the enhancement of the subtropical geopotential height in the Northern Hemisphere, and the corresponding relationship between the WPSH and regional extreme weather processes such as flood or summer heat also weakens. Thus, this work proposes several revisions necessary to improve the WPSH indices, including: (1) first determining the GD and GB indices, and then calculating the GM and GQ indices; (2) considering the western extension of the WPSH in the future under the warming background, the GM index is specified as the area enclosed by the 5880 gpm isoline from the WPSH westernmost point to 150°E; (3) adding the western and eastern GX indices, and the western and eastern GB indices, which can well characterize spatial variation of the WPSH and its impact on precipitation and high temperature anomalies in China. The comparison with the operational indices shows that the revised WPSH indices improve the inductiveness of the WPSH to the evolution of climate anomalies in China. Under a warming background, the WPSH in all months would significantly enlarge and strengthen and extend northwestward without a trend in the ridgeline location. Specifically, the WPSH would expand northward and affect northern China in mid-summer, while its westward extension would affect western China in other seasons. The revised indices have a better correspondence with both summer precipitation and high temperature in China than the operational indices, especially for the GD and western GX indices. Their spatial correlation distributions with summer precipitation and high temperature reflect that the high correlation area between precipitation and high temperature also gradually moves northward following the northward advance of the East Asian summer monsoon.

     

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