ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Archive > Volume 46 Issue 11 > 2020,46(11):1415-1426. DOI:10.7519/j.issn.1000-0526.2020.11.003 Prev Next
Synoptic Analysis of Extreme Meiyu Precipitation over Yangtze River Basin During June-July 2020
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Abstract:
Extreme Meiyu struck Yangtze River Basin (YRB) from June to July 2020. The accumulated precipitation in the middle and lower reaches of Yangtze River exceeded that of the same peroid in 1998 and was the most accumulated precipitation since 1961. The Meiyu rainfall events this year were characterized by long-time duration, short intervals and spatial overlapping with nocturnal rainfall peak. Accumulated precipitation centers were obviously correlated with topographical features of Dabie Mountain, Wannan Mountain and mountainous territory in the west of Hubei Province. Analysis reveals that main rainbelt swung significantly over YRB in June with quasi-stationary rainbelt along Yangtze River in July. Staggering of Meiyu front over YRB was correlated with persistence of strong blocking high pressure systems in mid-high latitude zones of Asia and abnormal position of the Western Pacific subtropical high staging at about 20°N during July with significant positive vapor flux anomaly beyond 3σ over YRB. Due to the interaction of low-level southwest jet, upper-level westerly jet and upper-level easterly jet, displacement of low-level convergence with upper-level divergence was conducive to intense precipitation along Meiyu front. Heavy rainfall events on Meiyu front could be identified into two synoptic types. One type was quasi-stationary Meiyu front, and the other type featured mesoscale cyclogenesis on Meiyu frontal zone. The former type was dominated by steady quasi-zonal upper-level flow, and staggered low-level wind shear zones with quasi-stationary rainbelts. The other type of rainstorm events developed with distinct cyclonegenesis along Meiyu front, and was accompanied by long-life mesoscale convective systems organized with complicated meso-β scale convective rainbelt adjoining to low-level vortexes. Forecast verifications indicate that there is high predictivity for the first type of heavy rain events, while the second type of Meiyu events has low predictivity and more uncertainty. Obvious forecast deviations tend to occur due to unrealistic positive feedback between over-intensified low-level vortex, precipitation latent heat releasing and low-level jet enhancing in ECMWF-HR forecast.
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