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索渺清, 丁一汇. 冬半年副热带西风南支槽结构和演变特征研究[J]. 大气科学, 2009, 33(3): 425-442. DOI: 10.3878/j.issn.1006-9895.2009.03.03
引用本文: 索渺清, 丁一汇. 冬半年副热带西风南支槽结构和演变特征研究[J]. 大气科学, 2009, 33(3): 425-442. DOI: 10.3878/j.issn.1006-9895.2009.03.03
SUO Miaoqing, DING Yihui. The Structures and Evolutions of the Wintertime Southern Branch Trough in the Subtropical Westerlies[J]. Chinese Journal of Atmospheric Sciences, 2009, 33(3): 425-442. DOI: 10.3878/j.issn.1006-9895.2009.03.03
Citation: SUO Miaoqing, DING Yihui. The Structures and Evolutions of the Wintertime Southern Branch Trough in the Subtropical Westerlies[J]. Chinese Journal of Atmospheric Sciences, 2009, 33(3): 425-442. DOI: 10.3878/j.issn.1006-9895.2009.03.03

冬半年副热带西风南支槽结构和演变特征研究

The Structures and Evolutions of the Wintertime Southern Branch Trough in the Subtropical Westerlies

  • 摘要: 南支槽是冬半年副热带南支西风气流在高原南侧孟加拉湾地区产生的半永久性低压槽, 本文从气候学角度探讨其结构和演变特征。结果表明: (1) 南支槽10月在孟加拉湾北部建立, 冬季 (11~2月) 加强, 春季 (3~5月) 活跃, 6月消失并转换为孟加拉湾槽; 10月南支槽建立表明北半球大气环流由夏季型转变成冬季型, 6月南支槽消失同时孟加拉湾槽建立是南亚夏季风爆发的重要标志之一。 (2) 南支槽在700 hPa表现明显, 其槽前干暖平流的输送有利于昆明准静止锋形成和维持, 槽后冷湿平流也与孟加拉湾冷涌关系密切。 (3) 冬季辐散环流下沉支抑制了南支槽前上升运动的发展, 这时低层辐合, 中层辐散, 南支槽前上升运动一般只伸展到对流层中层600 hPa左右。春季随着辐散环流减弱, 东亚急流入口区南侧辐散中心的出现使得垂直运动向上迅速伸展。 (4) 从气候平均看冬季水汽输送较弱, 上升运动浅薄, 无强对流活动, 南支槽前降水不明显, 雨区主要位于高原东南侧昆明准静止锋至华南一带。春季南支槽水汽输送增大, 同时副高外围暖湿水汽输送加强, 上升运动发展和对流增强, 南支槽造成的降水显著增加, 因此春季是南支槽最活跃的时期。

     

    Abstract: The structures and evolution characteristics of the wintertime southern branch trough in the subtropical westerlies (WEBTISR), as the semi-permanent trough generated by the subtropical southern branch westerlies (SBW) over the Bay of Bengal, to the south of the Tibetan Plateau, were studied for their climatological significance with the following results: 1) The WEBTISR is generated over the northern Bay of Bengal in October, maintained from November to the following February, and active from March to May, then disappears and transforms to the Bay of Bengal trough in June. The fact that the WEBTISR is established in October indicates that the northern hemispheric circulation transforms from summer pattern to winter pattern, while its disappearance in June, together with the Bay of Bengal trough establishment, is one of the important indications of summer monsoon onset. 2) The WEBTISR is noticeable at 700 hPa, in front of which the transmission of the warm-dry advection is favorable for the formation and maintenance of the Kunming quasi-stationary front. And the cold-wet advection behind the WEBTISR has a close relationship with the cold surge in the Bay of Bengal. 3) The descending branches of divergence circulation restrain the development of the vertical motion in front of the WEBTISR in winter, with concurrent convergence/divergence at the lower/middle levels, inducing that the ascending parts extend roughly to the middle troposphere at 600 hPa. Conversely the weakening of the divergence circulation in spring, and appearance of the divergence center on the south side of East Asia jet stream inlet lead to rapid upward extension of the vertical motions. 4) Climatologically, water vapor transport is weak; ascending motion is also restrained and there is not severe convection, therefore the precipitation is unobvious in front of the WEBTISR, while the rainfall is mostly over the areas from the Kunming quasi-stationary front to the southeast of the plateau to South China in winter. In spring, water vapor transport strengthens in the WEBTISR, with increased transport of warm-wet moisture outside the subtropical high as well as developing upward motion and convection, leading to a distinct increase in the rainfall produced by the WEBTISR. Therefore, spring is the period the WEBTISR is most active.

     

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