2018年5月江蘇極端降水事件發(fā)生前副熱帶高壓異常及原因分析

doi:10.3969/2018jms.0087

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2018年5月江蘇極端降水事件發(fā)生前副熱帶高壓異常及原因分析
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                        10.3969/2018jms.0087
                    
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中圖分類號(hào):P426.615
基金項(xiàng)目:國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目（2017YFC1502104）；國(guó)家自然科學(xué)基金資助項(xiàng)目（41575081）；江蘇省自然基金資助項(xiàng)目（BK20161603）；中國(guó)氣象局預(yù)報(bào)員專項(xiàng)（CMAYBY2018-028）；江蘇省氣象學(xué)會(huì)青年科研基金項(xiàng)目（KQ201804）

Analysis of anomalies and causes of subtropical high before the extreme precipitation events in Jiangsu in May 2018

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本文利用NCEP/NCAR提供的2.5°×2.5°全球再分析數(shù)據(jù)，以2018年5月江蘇兩次極端降水事件發(fā)生前副高異常變化為研究對(duì)象，根據(jù)全型渦度方程定量計(jì)算了凝結(jié)潛熱分布不均引起的渦源對(duì)副高迅速演變的誘發(fā)作用。研究發(fā)現(xiàn)，120°E處500 hPa 5月第1候副高脊線多年平均位置位于16°N附近，而2018年同期120°E的脊線則位于19°N附近，呈明顯偏北的狀態(tài)。2018年5月第1候東亞500 hPa位勢(shì)高度距平場(chǎng)表現(xiàn)出南高北低的形態(tài)，有利于我國(guó)華東地區(qū)成為暖濕空氣和干冷空氣的交匯區(qū)，構(gòu)成了江蘇5月兩次極端降水過(guò)程的有利環(huán)流背景。與對(duì)流層中層環(huán)流異常對(duì)應(yīng)的是，同期115°~125°E之間850 hPa上8 g·kg^-1等比濕線位于28°N附近，較多年氣候態(tài)偏北15°，強(qiáng)降水區(qū)內(nèi)同期850 hPa比濕較往年偏多2~4 g·kg^-1，相應(yīng)距平百分率可達(dá)50%~75%。且110°~120°E之間θ_se的340 K等值線5月第1候多年氣候態(tài)位于13°N以南，但2018年同期卻偏北至25°N附近，暖濕氣團(tuán)北進(jìn)有利于強(qiáng)降水的發(fā)生。副高西伸北抬前，副高主體西側(cè)和北側(cè)均有凝結(jié)潛熱加熱區(qū)存在，說(shuō)明潛熱加熱與副高演變關(guān)系密切。垂直剖面表明600 hPa為凝結(jié)潛熱加熱中心，向上加熱率隨高度減小，因此500 hPa處潛熱加熱率垂直梯度為負(fù)，使得500 hPa成為負(fù)渦源所在。因凝結(jié)潛熱分布不均產(chǎn)生的負(fù)渦源，1~2 d便可形成與副高自身十分接近的負(fù)渦度值，足以誘發(fā)副高突變，該時(shí)間尺度與副高真實(shí)演變時(shí)間相符。負(fù)渦源中與凝結(jié)潛熱垂直分布不均相關(guān)的部分起主要作用，而與凝結(jié)潛熱水平分布不均相關(guān)的部分同時(shí)期產(chǎn)生的負(fù)渦度最多僅為前者的1/3左右，對(duì)副高突然西伸的作用較小。與凝結(jié)潛熱相關(guān)的負(fù)渦源作為引發(fā)西太平洋副高異變的可能原因，其與副高的關(guān)系仍需進(jìn)一步研究。

Abstract:

The 2.5°×2.5° global reanalysis data provided by NCEP/NCAR were used in this paper. The anomalies of subtropical high before the two extreme precipitation events in Jiangsu in May 2018 were studied, and the inducing effect of vorticity source caused by the inhomogeneous distribution of condensation latent heat on the fast evolution of subtropical high was calculated quantitatively by the complete-form vorticity equation. The results showed that the average position of the subtropical high ridge on 500 hPa at 120°E at the first pentad in May was near 16°N, while the ridge at 120°E in the same period of 2018 was near 19°N, evidently moving towards the north. The 500 hPa geopotential height anomaly field in East Asia at the first pentad in May 2018 was high in the south and low in the north. This was conducive to forming an intersection of the warm and wet air and the dry and cold air in East China, thus providing a favorable circulation background for the two extreme precipitation events in Jiangsu in May. Relative to the middle-level circulation anomaly of the troposphere, the 8 g·kg^-1 equal specific humidity line at 850 hPa between 115°E and 125°E was near 28°N, moving 15° towards the north compared with the perennial climatic state. The specific humidity at 850 hPa in the area with heavy precipitation is 2-4 g·kg^-1 more than that in the same term in previous years, and the corresponding anomaly percentage is up to 50%-75%. The 340 K isoline of θ_se between 110°E and 120°E at the first pentad in May was located on the south of 13°N by referencing to the climate states of many years, but it was near the 25°N in the same period of 2018. The warm and wet air mass moving northward is conducive to generating the heavy precipitation. Before the subtropical high stretches westward and rises on the north, there is a condensation latent heating zone on the west and the north of the main body of subtropical high, indicating a close relation between the latent heating and the evolution of subtropical high. The vertical section shows that 600 hPa is the heating center of condensation latent, and the heating rate decreases as the height increases. Therefore, the vertical gradient of the latent heating rate at 500 hPa is negative, making 500 hPa the origin of the negative vortex source. The negative vortex source generated by the inhomogeneous distribution of condensation latent heat can form a negative vorticity value that approaches to the subtropical high itself within 1-2 days, so it is enough to induce the abrupt change of subtropical high. This time scale is consistent with the real evolution time of the subtropical high. The part that is related to the vertical inhomogeneous distribution of condensation latent heat in the negative vorticity source plays a prominent role, while the part that is related to the horizontal inhomogeneous distribution of condensation latent heat only generates about one third of negative vorticity source of the former at most, which has a minor effect on the abrupt western stretching of subtropical high. The relationship between the negative vortex source associated with the condensation latent heat, as the abrupt change of subtropical high in western Pacific, with the subtropical high still needs further study.

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沈陽(yáng),孫燕,吳海英,陳圣劼,韓桂榮.2018年5月江蘇極端降水事件發(fā)生前副熱帶高壓異常及原因分析.氣象科學(xué),2019,39(2):214-225 SHEN Yang, SUN Yan, WU Haiying, CHEN Shengjie, HAN Guirong. Analysis of anomalies and causes of subtropical high before the extreme precipitation events in Jiangsu in May 2018. Journal of the Meteorological Sciences,2019,39(2):214-225

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收稿日期:2018-08-28
最后修改日期:2018-10-10
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在線發(fā)布日期: 2019-06-01
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