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气象:2020,46(11):1415-1426
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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,张芳华,于超,马杰,张夕迪,沈晓琳,张芳,罗琪
(国家气象中心,北京 100081;中国气象局-河海大学水文气象研究联合实验室,北京 100081)
Synoptic Analysis of Extreme Meiyu Precipitation over Yangtze River Basin During June-July 2020
CHEN Tao,ZHANG Fanghua,YU Chao,MA Jie,ZHANG Xidi,SHEN Xiaolin,ZHANG Fang,LUO Qi
(National Meteorological Centre, Beijing 100081;CMA-HHU Joint Laboratory for Hydrometeorological Studies, Beijing 100081;Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082)
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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年以来排名第一。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,西太平洋副热带高压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。预报检验表明第一类梅雨暴雨过程可预报性较高,而第二类梅雨暴雨过程预报不确定性明显,在欧洲中心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) 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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基金项目:国家重点研发计划(2017YFC150210和2020YFC1510400)共同资助
引用文本:
陈涛,张芳华,于超,马杰,张夕迪,沈晓琳,张芳,罗琪,2020.2020年6—7月长江中下游极端梅雨天气特征分析[J].气象,46(11):1415-1426.
CHEN Tao,ZHANG Fanghua,YU Chao,MA Jie,ZHANG Xidi,SHEN Xiaolin,ZHANG Fang,LUO Qi,2020.Synoptic Analysis of Extreme Meiyu Precipitation over Yangtze River Basin During June-July 2020[J].Meteor Mon,46(11):1415-1426.