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ISSN 1006-9895

CN 11-1768/O4

梅雨期东亚副热带西风急流纬向振荡特征
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南京大学大气科学学院

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国家自然科学基金重点项目资助(41930969)


Characteristics of the East Asian subtropical westerly jet's zonal oscillation during the Mei-yu period
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School of Atmospheric Sciences,Nanjing University

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    摘要:

    利用1979-2020年EAR5逐日再分析资料和中国站点降水观测资料,分析了梅雨期东亚副热带西风急流的纬向振荡特征及其与东亚大气环流和梅雨期降水的联系。通过对比200 hPa纬向风标准差大值区(37o~47oN, 100o~120oE)与西太平洋(37o~47oN, 140o~160oE)、青藏高原(37o~47oN, 80o~100oE)上空两个急流中心区域平均纬向风速距平值发现,梅雨期间东亚副热带西风急流主要存在两种强度和位置变化类型,第一种类型前期急流中心位于西太平洋上空,随后强度减弱,并在其西侧出现一个增强的急流中心,最大纬向风表现为快速西进特征,称为快速西进型;第二种类型前期急流中心位于青藏高原上空,随后逐渐增强并东移,最大纬向风表现为渐进东移特征,称为渐进东移型。分析两种急流振荡类型对应的环流及降水演变发现,与急流快速西进类型相对应,南亚高压东伸脊点位置偏东,西太平洋副热带高压强度增强西伸,中高纬环流形势为“两槽一脊”型,伴随200 hPa辐散经向增强,700 hPa水汽输送向北抬升,雨带出现由南向北的位置变化;而与急流渐进东移型相对应,南亚高压东伸脊点位置偏西,西太平洋副热带高压强度减弱东缩,中高纬环流形势为“两脊一槽”型,鄂霍次克海出现阻高的频数偏多,同时长江下游高层辐散减弱,而长江上游的高层辐散和低层水汽输送加强,从而在长江上游和长江下游地区形成降水强度的反相变化。

    Abstract:

    Based on the EAR5 daily reanalysis data and observational precipitation data at 2437 stations in China from 1979 to 2020, this study analyzes the zonal oscillation characteristics of the East Asian subtropical westerly jet and its relationship with the East Asian atmospheric circulation and precipitation during the Mei-yu period. The results reveal that there are two intensity and position variation types for the East Asian subtropical westerly jet during Mei-yu period by comparing the 200 hPa regional mean zonal wind anomalies in a large value area of standard deviation (37o-47oN, 100o-120oE) with the two jet stream centers over the Western Pacific (37o-47oN, 140o-160oE) and the Tibetan Plateau (37o-47oN, 80o-100oE). For the first type, the jet stream center is situated over the western Pacific Ocean in the early stage, then the intensity of the jet stream over the western Pacific weakens, and an enhanced jet stream center appears on the western side of the jet stream. The maximum zonal wind shows a rapid westward migration feature, which is called the rapid westward migration type. For the second type, the jet stream center is located over the Tibetan plateau in the early stage, then steadily strengthens and moves eastward. The maximum zonal wind exhibits a gradual eastward migration feature, which is referred to as the gradual eastward migration type. The analyses of circulation and precipitation corresponding to the two jet stream oscillation types indicate that, with the rapid westward migration of the jet stream, the east ridge point of the South Asian High is located to the east, and the western Pacific Subtropical High’s intensity is increased and moved to the west, and the circulation pattern in the middle and high latitudes is characterized as "two troughs and one ridge". Furthermore, as the meridional increase of 200 hPa divergence and the 700 hPa water vapor transport rises to the north, the position of the rain belt shifts from south to north. Corresponding to the gradual eastward migration type, the east ridge point of the South Asian High is located to the west, and the western Pacific Subtropical High’s intensity is decreased and contracted to the east, the circulation pattern in the middle and high latitudes is featured as "two ridges and one trough," and the blocking highs occur more frequently over the Okhotsk Sea region. Meanwhile, the upper-level divergence in the lower reaches of the Yangtze River weakens, while the upper-level divergence and lower-level water vapor transport strengthen in the upper reaches of the Yangtze River, thus forming an antiphase change in precipitation intensity between the upper and lower reaches of the Yangtze River.

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  • 收稿日期:2023-08-01
  • 最后修改日期:2024-03-10
  • 录用日期:2024-03-15
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