Extreme characteristics and causes of"12·14"snowstorm process in Shandong
侯淑梅 1吴雪旭 1杨成芳 1高帆 2刘向科 1郭子彧 1李博 3贾斌4
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作者信息
1. 山东省气象防灾减灾重点实验室,山东济南 250031;山东省气象台,山东济南 250031
2. 济南市气象局,山东济南 250102
3. 菏泽市气象局,山东菏泽 274000
4. 聊城市气象局,山东聊城 252000
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摘要
利用国家级地面气象观测站、风廓线雷达、X波段双偏振相控阵雷达等多源观测资料和欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)第五代大气再分析(ECMWF Reanalysis v5,ERA5)资料,总结了2023年12月13-14日山东大范围暴雪、局地大暴雪(简称"12·14"暴雪)极端性的特征和成因,并与2021年11月7日山东极端暴雪过程(简称"11·7"暴雪)对比分析了降雪量和雪水比差异的原因.结果表明:(1)典型的暖平流型天气形势是产生极端暴雪有利的环流背景条件,低层切变线和风速辐合区在鲁西北叠加,形成强烈而持久的上升运动.(2)低空急流异常偏强,降水强度不仅与低空急流的强度有关,而且与其厚度有关.当3.0 km高度保持低空急流的强度时,10 m·s-1风速到达的高度越低,降雪强度越大.(3)700 hPa比湿超过4 g·kg-1、850 hPa比湿超过3 g·kg-1的持续时间均长达10 h以上,为极端暴雪过程提供了充足的水汽.850 hPa比湿和比湿平流远远高于"12·14"暴雪过程,是"11·7"过程最大累计降雪量大于"12·14"过程的原因之一.(4)"12·14"暴雪过程垂直运动旺盛,最大上升速度位于不稳定层顶的前沿,处于-20-10 ℃层,有利于树枝状冰晶生长,降雪效率高.对流层整层温度低于0 ℃,雪花下落过程中没有融化,雪水比高,积雪深度大."11·7"暴雪过程初期最大上升运动中心高度低,形成更多柱状冰晶,经过暖层时融化,雪水比低,积雪深度小于"12·14"暴雪过程.
Abstract
Multi-source observation data,such as national meteorological observation station,wind profile radar,X-band dual-polarization phased array radar,and ECMWF(European Centre for Medium-Range Weather Forecasts)Reanalysis v5(ERA5)are used to analyze the characteristics and causes of the large-scale snowstorm(partially severe snowstorm)process in Shandong from 13 to 14 December 2023("12 14"snowstorm for short),which is compared with the extreme snowstorm process on 7 November 2021("11·7"snowstorm for short)to study the reasons for differences in snowfall amount and snow-to-liquid ratio.The results are as follows.(1)The synoptic situation of typical warm advection type is a favorable circulation background for extreme snowstorm.The low-level shear line and wind speed convergence are overlapped in the northwest of Shandong Province,forming a strong and persistent ascending motion.(2)The low-level jet is abnormally strong,and the precipitation intensity is not only related to the intensity of the low-level jet,but also to its thickness.When the intensity of the low-level jet maintains at the height of 3.0 km,the lower the height of the 10 m·s-1 wind speed,the greater the snowfall intensity.(3)The duration of specific humidity exceeding 4 g·kg-1 at 700 hPa and 3 g·kg-1 at 850 hPa is both over 10 h,providing sufficient water vapor for the extreme snowstorm process.The 850-hPa specific humidity and specific humidity advection of the"11·7"snowstorm are much higher than those of the"12·14"snowstorm,which is one of the factors contributing to the maximum cumulative snowfall of the"11·7"snowstorm being greater than that of the"12·14"snowstorm.(4)For the"12·14"snowstorm,the vertical motion is vigorous,the maximum ascending velocity is located at the forefront of the unstable layer,and the temperature is between-20 and-10 ℃,which are all conducive to the growth of dendritic ice crystals and high snowfall efficiency.The temperature of the entire troposphere is below 0 ℃,and the snowflakes do not melt during the falling process,so the snow-to-liquid ratio is high,and the depth of snow is large.For the"11·7"snowstorm,the center of the maximum ascending motion during the early stage is lower,forming more columnar ice crystals that melt when passing through the warm layer.Therefore,the snow-to-liquid ratio is lower and its snow depth is smaller than that of the"12·14"snowstorm.
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