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2020年6-7月长江中下游极端梅雨天气特征分析
陈涛1, 张芳华2, 于超2, 马杰2, 张夕迪2, 沈晓琳2, 张芳2, 罗琪2
(1.国家气象中心,北京;2.国家气象中心,北京1 00081)
Synoptic analysis of extreme Meiyu precipitation over Yangtze River Basin during June to July 2020.
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投稿时间:2020-08-10    修订日期:2020-10-12
中文摘要: 2020年6~7月我国长江中下游地区出现极端梅雨,长江中下游地区累积降水量超过1998年同期,为1961年以来长江流域最大累积降水量。梅雨降水过程持续时间长、间隔短、空间重叠度高、夜间增强特征明显,强降水中心空间分布与大别山、皖南山区和鄂西山区地形特征存在显著相关。分析表明6月降水过程移动性特征明显;7月上旬主雨带稳定在长江中下游沿江地区,降水强度更强,极端性更显著。6~7月亚洲中高纬度维持异常稳定的阻塞形势,西太平洋副高脊线西段始终维持在20°N附近,导致梅雨锋长时间在江淮地区活动;整层水汽输送通量达到3倍气候标准差以上,有利于出现异常强的梅雨降水;在低空西南急流、高空西风急流和东风急流共同作用下,长江中下游地区低空辐合、高空辐散形势显著。梅雨暴雨从天气形势可分为准静止锋、气旋锋生两类过程;前者高空环流较为平直,低层切变和降水带稳定少动;气旋锋生梅雨暴雨伴随显著高空波动,伴有江淮或黄淮气旋东移发展,梅雨锋低涡附近往往伴随有长生命史中尺度对流系统发展,并具有更复杂的β中尺度对流雨带结构。预报检验表明第1类梅雨暴雨过程可预报性较高,而第2类梅雨暴雨过程预报不确定性明显,在EC数值预报中往往出现低涡急流系统和降水潜热之间的非自然正反馈,导致较明显的天气系统和降水预报偏差。
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.
文章编号:202008100284     中图分类号:P458    文献标志码:
基金项目:2019YFC1510400以及2017YFC150210
引用文本:
陈涛,张芳华,于超,马杰,张夕迪,沈晓琳,张芳,罗琪,0.[en_title][J].Meteor Mon,():-.
Chen Tao,Zhang Fanghua,Yu Chao,Ma Jie,Zhang Xidi,Shen Xiaolin,Zhang Fang,Luo Qi,0.Synoptic analysis of extreme Meiyu precipitation over Yangtze River Basin during June to July 2020.[J].Meteor Mon,():-.