Impact of potential vorticity anomalies around the eastern Tibetan Plateau on quasi-biweekly oscillations of summer rain
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Impact of potential vorticity anomalies around the eastern Tibetan Plateau on quasi‑biweekly oscillations of summer rainfall within and south of the Yangtze Basin in 2016 Guanshun Zhang1,2 · Jiangyu Mao1,2 · Guoxiong Wu1,2 · Yimin Liu1,2 Received: 26 May 2020 / Accepted: 13 October 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Six persistent heavy rainfall events that occurred mostly over Hubei–Anhui–Jiangxi (HAJ) provinces within and south of the middle–lower Yangtze Basin during the summer of 2016 were regulated by the 10–20-day quasi-biweekly oscillation (QBWO). The characteristics and mechanisms of the QBWO associated with the HAJ rainfall events were examined using ERA-Interim reanalysis data. Composite analysis shows that during a QBWO cycle, the extreme wet (dry) phase of the HAJ rainfall was characterized by the strongest ascending (descending) motion associated with an anomalous upper-tropospheric saddle-shaped circulation field resulting from an eastward-propagating middle–high latitude wave train and westwardmigrating tropical potential vorticity (PV) anomalies. The wet (dry) phase was preceded by the corridor establishment of significant anomalous poleward-directed (equatorward-directed) moisture transport over southern China on the northwestern side of the western North Pacific subtropical high in the lower troposphere. The corridor-related moisture convergence (divergence) over the HAJ tended to intensify as an anomalous anticyclone (cyclone) propagated northwestward to the northern South China Sea, in conjunction with the eastward-propagating mid-latitude wave train. The QBWO of the HAJ rainfall was closely linked with upstream PV anomalies generated over the eastern slope of the Tibetan Plateau (TP) due to topographic lateral friction. The PV budget analysis demonstrates that the horizontal PV advection and subsequent topographic friction with a four-day phase-lag between them dictated the QBWO of PV anomalies around the eastern TP. The TP-generated PV anomalies then migrate downstream to facilitate the development of the anomalous circulation over the HAJ. Keywords Quasi-biweekly oscillation · Summer yangtze rainfall · Potential vorticity · Tibetan Plateau · Topographic friction
1 Introduction In eastern China and the entire East Asian subtropical region, the major rainy season is summer (May–August) (Tao and Chen 1987; Mao and Wu 2006), during which regionally persistent heavy rainfall (RPHR) events often result in severe floods in China owing to their long duration and high intensity (Chen and Zhai 2013; Ren et al. 2013; * Jiangyu Mao [email protected] 1
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, P.O. Box 9804, Beijing 100029, China
University of Chinese Academy of Sciences, Beijing 100049, China
2
Li and Zhou 2015; Li and Mao 2018). The RPHR event refers roughly to a spatially coherent long-lasting heavy rainfall event, in whi
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