ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Synoptic analysis of extreme Meiyu precipitation over Yangtze River Basin during June to July 2020.
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Abstract:
Extreme Meiyu struck Yangtze River Basin (YRB) during June to July 2020 which was ranked first in history exceeding Meiyu season of 1998 since 1961. Meiyu rainfall events were characterized with long time duration, short intervals and spatial overlapping with nocturnal rainfall peak. Accumulated precipitation centers were obvious correlated with topographical features of Dabie Mountain, Wannan Mountain and mountainous territory in west of Hubei Province. It was revealed that main rainbelt swung over YRB in June compared 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 pressure staging at about 20°N during July with significant positive vapor flux anomaly beyond 3\sigma 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 characterized with quasi-stationary Meiyu front, and the other type was characterized with 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 accompanied with long-life mesoscale convective systems organized with complicated β-mesoscale convective rainbelt adjoining to low-level vortexes. Forecast verifications indicated that high predictivity for the first type of heavy rain events, while the second type of Meiyu events were associated with low predictivity and more uncertainty. Obvious forecast deviations occurred 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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P458
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