孙继松,雷蕾,于波,丁青兰. 2015. 近10年北京地区极端暴雨事件的基本特征[J]. 气象学报, 73(4):609-623, doi:10.11676/qxxb2015.044
近10年北京地区极端暴雨事件的基本特征
The fundamental features of the extreme severe rain events in the recent 10 years in the Beijing area
投稿时间:2015-01-16  修订日期:2015-02-15
DOI:10.11676/qxxb2015.044
中文关键词:  极端暴雨事件  中尺度对流系统  列车效应
英文关键词:Extreme severe rain event  MCS  Train Effect
基金项目:公益性行业(气象)科研专题(GYHY 201506006)、国家科技支撑项目"中期灾害性天气过程及其预报方法研究"、中国气象局强对流预报专家创新团队、北京市气象局强对流天气机理研究创新团队。
作者单位
孙继松 北京市气象台, 北京, 100089
中国气象局北京城市气象研究所, 北京, 100089 
雷蕾 北京市气象台, 北京, 100089 
于波 北京市气象台, 北京, 100089 
丁青兰 北京市气象台, 北京, 100089 
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中文摘要:
      利用北京地区5 min间隔的自动气象站降水观测资料,SA雷达观测资料、FY-2卫星TBB(Temperature of Black Body)资料、常规气象探空资料和1°×1°NCEP/NCAR最终分析资料,对2006—2013年发生的10次极端暴雨事件(14个区(县)中,任意一个区县代表站24 h内降水量≥ 100 mm,且暴雨区内至少有一个自动气象站降水强度≥ 40 mm/h)的基本特征进行了对比分析。结果表明:(1)长生命周期的单体或多单体组织合并的中尺度对流系统(第Ⅰ类中尺度对流系统)形成的暴雨中心一般位于北京西部山前地区或中心城区,这种分布与低空偏东气流的地形强迫作用或城市强迫作用有关;"列车效应"对应的多单体中尺度对流系统(第Ⅱ类中尺度对流系统)形成的极端暴雨事件往往与两次不同属性的降水过程有关:锋前暖区对流过程和锋面附近的对流过程。因此,降水分布往往平行于低空急流轴或锋面。(2)第Ⅰ类中尺度对流系统形成的极端暴雨过程局地性更强,全市平均降水量远小于暴雨量级(50 mm),其中,由混合型降水主导的极端暴雨事件一般是由几乎不移动的长生命周期单体反复生消造成的,对流高度相对较低;而深对流主导的极端暴雨事件一般由多单体组织、合并、加强造成,由于对流单体的上冲云顶很高,最低TBB一般低于-55℃,这类极端暴雨事件的短时强降水具有显著的间歇性:第一阶段的强降水与单体对流发展过程对应,以后的短时强降水与对流单体组织、合并过程对应。(3)"列车效应"对应的多单体中尺度对流系统暴雨过程,初始阶段一般表现为相互独立的两个对流带,即与锋面系统对应的对流带和与低空急流轴对应的暖区对流带,随着锋面对流带逐渐向暖区对流带移动,低空冷空气逐渐侵入到暖区对流带中,两条对流云带逐渐合并,对流活动进一步发展;或者由于暖区对流带截断锋面对流带的水汽入流,造成锋面对流减弱,而暖区对流带组织性更强,发展更加旺盛。与第Ⅰ类中尺度对流系统形成的极端暴雨过程不同,这类暴雨过程往往造成全市平均降水量达到暴雨(≥ 50 mm)甚至大暴雨(≥ 100 mm)。(4)不同类型的极端暴雨过程,大尺度水汽输送条件不同:"列车效应"造成的暴雨过程多数情况下由源于孟加拉湾和源于西太平洋的两支暖湿季风气流共同构成,大尺度水汽供应充沛;而第Ⅰ类中尺度对流系统中的混合型降水造成的暴雨过程的水汽来源主要与低空东南气流造成的近海水汽输送有关;第Ⅰ类中尺度对流系统中的深对流主导的深对流暴雨过程中整层水汽含量并不大,多数情况下水汽输送仅出现在对流层低层甚至仅在近地面层内。(5)大多数情况下,无论哪类性质的极端暴雨过程,在强降水发生时刻,雷达强回波高度一般在4 km以下,仅有极个别时刻强回波中心高于5 km。极端暴雨过程中,环境大气对流有效位能(CAPE)的大小一般与对流发展高度(雷达回波顶高)具有较好的对应关系,但与强降水发生时刻回波强度、最强回波高度、降水强度的对应关系较差。
英文摘要:
      This paper analyses the fundamental properties of 10 extreme severe rain events (the event is defined as its precipitation≥ 100 mm/(24 h) at any representative weather station among the 14 Districts or Counties with the rain intensity≥ 40 mm/h over at least one automatic weather station) during 2006-2013 in the Beijing region, based on the rainfall data per 5 min of automatic weather stations, the data series of SA radar, TBB (Temperature of Black Body) of FY-2, routine sounding and 1°×1° NCEP/NCAR final analysis. The investigation results show that the severe rain centers, formed from long periodic convective cells or MCS organized/amalgamated by multi cells (typeⅠ), are usually located before the mountain or central urban areas, and the distribution feature is related to the terrain forcing caused by easterlies airflow under the lower layer or the urban forcing. However, the extreme severe rain events which are dominated by the Train Effect associated with MCS of multi cells (typeⅡ) are connected with two different properties of raining process: The convective activity happening on the warming area and the other near a front, so the rainfall distributions are frequently parallel to the axis of low level jets or fronts. The precipitation distributions of the extreme rain events caused by MCS of typeⅠare more localized, and each of their average precipitation of the whole administrative area is much lower than 50 mm. One of them is led by mixed convection, and its extreme rainfall is usually caused by long periodic or hardly moving convective cells to be generated and dissipated repeatedly,with the convection height relatively low. However, the extreme rain events led by deep convection are usually caused by multi cells to develop, organize and combine, and the lowest TBB of this typical MCS is usually lower than -55℃ since convective cloud top develops high. Short-time strong rainfall of these extreme events is intermittent: the initial rainfall corresponds with convective cells developing, and the second period is connected to the process of their organizing and combining. This study indicates that typeⅡMCS (Train Effect) shows often the two independent convection zones in the first stage: One is connected with the front and the other is a warm convection zone related to a low level jet. When the front moves toward the warm convection zone, the cold air in the low layer passes into the warm convection area gradually, the two convection zones begin to amalgamate slowly into single one while convective activity becomes to flourish, or since convection in the warm side prevents inflow of vapor, the front convection zone becomes weaker and weaker, meanwhile, the warm convection develops with more blossoming and organizing. The MCS , unlike MCS of typeⅠ, is usually to give rise to the city wide torrential rain (≥ 50 mm) even heavy rainstorm (≥ 100 mm). The large scale vapor conditions are obviously different among the various typical convective severe precipitation processes. In most cases the vapor sources of the severe rain to be connected with Train Effect are related to two warmly moist monsoon flows: one originates from the Bay of Bengal and the other is from the western Pacific Ocean, so the large scale vapor supplies are abundant. However, the vapor of the severe precipitation led by mixed convection of the typeⅠMCS is connected principally with offshore southeasterly wind in the low level; the vapor of the typeⅠMCS dominated by deep convection exists mostly in the lower troposphere even only near the surface, and in most cases the total vapor content of large scale is much less than others. No matter which extreme severe rain events, the strongest radar echo heights are rarely higher than 5 km, in most cases are lower than 4 km during the heaviest rainfall. The CAPE levels of the ambient atmosphere have often good relationship with convective heights (Top of Radar reflectivity), but correspondence among the ambient CAPE, momentary convection intensity and level of the strongest reflectivity or the maximum rainfall intensity is completely heterogeneous.
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