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DIAGNOSTIC ANALYSIS OF HEAVY RAINFALL EVENTS OVER THE YANGTZE RIVER VALLEY DURING THE MEI-YU SEASON 2020
|Title:||DIAGNOSTIC ANALYSIS OF HEAVY RAINFALL EVENTS OVER THE YANGTZE RIVER VALLEY DURING THE MEI-YU SEASON 2020|
|Contributors:||Chen, Yi-Leng (advisor)|
Atmospheric Sciences (department)
|Publisher:||University of Hawai'i at Manoa|
|Abstract:||During the early summer rainy season of the southern China plain in 2020, series of unprecedented heavy Mei-Yu precipitation occurred over the Yangtze River Valley region accompanied by a widespread inundation. Compared with the past ten-year mean conditions (2011-2019), the Mei-Yu precipitation over the Yangtze River Valley in 2020 shows that there was an occurrence of downpour over a longer lasting period (62 days in total). By using the CFSv2 reanalysis data with 6-hourly interval (2011-2020), a low-level boundary layer jet over the north part of South China Sea is diagnosed and referred to as Marine Boundary Layer Jet (MBLJ) by previous studies (Chen et al. 2018, Tu et al. 2019). This boundary layer jet has shown its wind maximum around 925-hPa with relatively large horizontal moisture transport is confined to the boundary layer for almost the entire Mei-Yu season (from June 1st to July 31st) in 2020. The MBLJ is mainly related to the large sub-synoptic scale pressure gradients between a stronger than normal WPSH and a South-West Vortex (SWV) originating from the lee side of the Tibet Plateau (Tu et al. 2019, Tu et al. 2020). Accompanied with a relatively stronger low-level wind (>10 ms^(-1)) within the MBL During the Mei-Yu season in 2020, the MBLJ over the Northern South China Sea played a key role in transporting the low-level moisture from the subtropical ocean to the southern China plain, contributing to the heavy precipitation over the Yangtze River valley that lasted almost for the entire rainy season. In addition to the S-N moisture supply by the MBLJ, a southwesterly sub-synoptic Low-Level (SLLJ) along the Mei-Yu front was (Chen and Yu 1988) present as a result of the secondary circulation associated with the Mei-Yu frontal circulation (Chen et al., 1994). During the Mei-Yu season in 2020, the MBLJ encountered the SLLJ along with the Mei-Yu front after reaching the southern China plain. The MBLJ brings in excessive moisture from the northern South China Sea to the central China plain where the rainfall production is mainly related to the secondary circulation associated with the Mei-Yu jet/front system. Moreover, the moisture transport is dominated by the mean flow with much less contribution in the transient mode. With this favorable synergistic effect caused by both MBLJ and SLLJ together, series of unprecedented long-lasting rainfall events occurred over the Yangtze River Valley during the entire 2020 Mei-Yu season.|
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|Appears in Collections:||
M.S. - Atmospheric Sciences|
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