造成东北地区暴雪过程的温带气旋暖输送带特征研究

Characteristics of Warm Conveyor Belts in Extratropical Cyclones Causing Snowstorms in Northeastern China

利用欧洲中期天气预报中心(European Center for Medium-Range Weather Forecasts,ECMWF)的ERA5再分析资料与拉格朗日分析工具(Largrangian analysis tool,LAGRANTO),对2006-2021年期间引发东北地区暴雪天气的温带气旋暖输送带进行统计,研究了暖输送带对气旋和降水发展的作用及其与锢囚锋的关系。结果表明:(1)气旋的加深率与暖输送带强度有明显的正相关,两者相关系数为0.63,通过α=0.01的显著性检验。大部分气旋在迅速加深24 h期间锢囚,以暖式锢囚为主。(2)强烈发展的锢囚型气旋通常具有强暖输送带,暖输送带低空入流主要位于气旋中心和气旋暖区附近,暖输送带的出流有两个分支:一支上升至气旋西北侧高空,另一支随高空西风带向气旋下游移动;气旋锢囚阶段低空正位涡异常与高空正位涡异常相互作用,形成贯穿整个对流层的位涡柱。(3)未锢囚或晚锢囚的气旋虽然有强暖输送带,但缺少对流层上层的干侵入,仅在低空有正位涡异常,气旋发展较弱。弱的锢囚型气旋存在明显干侵入,但暖输送带及降水均较弱。(4)具有强(弱)暖输送带的气旋造成的降水更多(少),且降水落区与暖输送带分布有密切关系。移动到气旋中心附近的暖输送带气块对气旋的发展有重要作用,其水平运动引起的暖平流及上升运动组织形成的低空非绝热位涡均能加强气旋式环流,进而促进气旋发展。

The role of warm conveyor belts(WCBs) on the development of cyclones and precipitation and their relationship to occluded fronts are investigated for extratropical cyclones causing snowstorms in northeastern China during 2006-2021,using ERA5 reanalysis data and Lagrangian Analysis Tool(LAGRANTO).Main results show that:(1) The correlation coefficient of 0.63 which could pass significance test of α=0.01 implies strong correlation between cyclone intensification and WCB strength.Most of cyclones have occluded in the 24 h period of strongest deepening,and these occluded fronts are mainly warm-type occlusions.(2) Rapidly intensifying occluded cyclones typically have strong WCBs,which low-level inflow mainly locates in the center and warm sector of cyclones,while the outflow has two branches:some trajectories rise to the high levels northwest of the cyclone,and others ascend to the downstream of cyclone following the upper westerly winds;the interaction between low-level potential vorticity(PV) and upper-level PV in cyclone occluding stage eventually forms a PV tower throughout the troposphere.(3) Non-occluded cyclones also have strong WCBs and positive low-level PV anomalies,but lack of significant upper-level PV forcing.The development of these cyclones is weak.Weakly intensifying occluded cyclones have a PV tower,but their WCBs and precipitation are weak.(4) Cyclones with strong(weak) warm conveyor belts cause more(less) precipitation,and the distribution of rainfall is closely related to the location of warm conveyor belts.The WCB trajectories moving towards to cyclone center play an important role for cyclone development.The warm advection and low-level diabatic PV production generated by these trajectories both enhance the low-level circulation and contribute to the cyclone intensification.