Abstract
Using ERA-Interim daily reanalysis and precipitation data, the combined effects of East Asia-Pacific (EAP) and Silk Road (SR) teleconnection patterns on summer precipitation in Southern China were investigated on synoptic to sub-monthly timescales. Combined EAP and SR patterns lead to more persistent and extreme precipitation in the Yangtze River Valley (YRV) and exhibit an obvious zonal advance between the South Asia High (SAH) and Western Pacific Subtropical High (WPSH) prior to its onset. During typical combined events, an overlap between the SAH and WPSH remains in a favorable position for Persistent Extreme Precipitation (PEP). Furthermore, SR-induced acceleration of the westerly jet stream and extra positive vorticity advection provide persistent upper-level divergence for YRV precipitation. An anomalous EAP-related cyclone/anticyclone pair over East Asia induces enhanced low-level southwesterlies to the northern anticyclone flank and northerlies from the mid-latitudes, advecting anomalously abundant moisture toward the YRV, resulting in clear moisture convergence. Moreover, the strong ascent of warmer/moister air along a quasi-stationary front may be crucial for PEP. During decay, the SAH and WPSH diverge from each other and retreat to their normal positions, and the strong ascent of warmer/moister air rapidly weakens to dissipation, terminating PEP in the YRV.
Highlights
Variations of East Asian summer monsoon circulation are complicated, owing to the existence and persistence of summer teleconnection patterns, including the well-known EastAsia-Pacific (EAP)/Pacific-Japan (PJ) and Silk Road (SR) teleconnection patterns, recognized as the most dominant modes and most influential teleconnection patterns of the boreal summer [1,2].The East Asia-Pacific (EAP) teleconnection pattern tends to be confined and propagates northward along the EastAsian coast in both the lower and middle troposphere, with the poleward propagation of Rossby waves triggered by anomalous cumulus convection over the western Pacific warm pool [3,4]
This study aims to explore the effects of the combined EAP and SR patterns on summer precipitation in Southern China
The criteria of the typical EAP/SR-C events include the following: (1) the EAPI must be greater than +1.0σ for at least three consecutive days and the SRI must be less than −1.0σ for at least three days during the specific event; and (2) the 500 hPa (200 hPa) height anomalies corresponding to the three anomaly centers in Equation (1). (Equation (2)) should be arranged as ‘+, −, +’ (‘−, +, −’)
Summary
Variations of East Asian summer monsoon circulation are complicated, owing to the existence and persistence of summer teleconnection patterns, including the well-known East. Subsequent studies have indicated that this circumglobal pattern can significantly affect climate and weather over a broad area, including but not limited to East Asia and the latitudes of the Asian jet stream It may induce precipitation anomalies over Europe, Japan, Northern China, and the Indian Monsoon regions [16,17,18,19]. Highlighted the relationship between summer Mei-Yu-baiu precipitation anomalies and these two key teleconnection patterns on inter-annual timescales According to these previous studies, such a combination may result in extraordinary anomalous features of the East Asian summer monsoon circulation. How does the combination influence rainfall? The rest of the paper is arranged as follows: Section 2 describes the data and methods; Section 3 introduces the definition of typical combined and single patterns; Section 4 investigates combined and separate effects on summer precipitation in Southern China; and Section 5 summarizes the key conclusions
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