钤伟妙,罗亚丽,曹越,张晓,车少静. 2022. 多种探测资料对华北中部一次回流暴雪的观测分析[J]. 气象学报, (0):-, doi:[doi]
多种探测资料对华北中部一次回流暴雪的观测分析
Analysis of a backflow heavy snowfall event in central North China using multisource data
投稿时间:2021-12-31  修订日期:2022-05-11
DOI:
中文关键词:  回流暴雪,天气背景,低空急流指数,降雪微物理特征
英文关键词:backflow heavy snowfall, synoptic background, LLJ, snow microphysical characteristics
基金项目:灾害天气国家重点实验室开放课题(2018LASW-B02)、国家重点研发计划(2018YFC1505604)、河北省青年科学基金(D2019106042)、河北省气象局面上项目(20ky14)和河北省气象局指导性项目(21zc03)
作者单位邮编
钤伟妙 石家庄市气象局 050081
罗亚丽 中国气象科学研究院灾害天气国家重点实验室 050021
曹越 石家庄市气象局 050081
张晓  050001
车少静  050021
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中文摘要:
      2020年1月5日07时至6日04时华北中部出现一次回流暴雪天气,过程最大降雪量15.5 mm。本文应用ERA5再分析和多种高分辨观测资料分析此次暴雪的大尺度天气背景和本地动、热力状况,探讨了暴雪落区、强度演变和降雪微物理特征及成因。结果表明,受河套地区地面倒槽和东北平原高压影响,900 hPa以下东北气流(被称为“回流”)自我国东北平原经渤海抵达华北平原,早于降雪7 h开始影响华北中部,受太行山阻挡在华北平原形成地面中尺度辐合线,对应暴雪落区;暴雪落区位于500 hPa高空槽前、700 hPa南北走向切变线东侧,700 hPa西南低空急流在200 hPa高层辐散影响下北伸发展,其出口区左侧朝暴雪区输送水汽。降雪前1 h石家庄市观测到800 m以下转为东北风,1 km以下气温迅速下降到-5至-1℃,形成“冷垫”;暴雪区上空700 hPa附近低空急流较降雪提早2 h出现,随后急流变厚、向下伸展至2 km,其下部暖湿空气沿“冷垫”爬升,触发降雪,急流最大风速(19 m s-1)和急流指数峰值(约8)与大于1 mm h-1强降雪时段重合,此时700 hPa附近为上升运动和水汽输送的大值中心。本次降雪粒子直径多为0.35—0.55 mm,降雪强度与粒子数浓度线性正相关;降雪云层位于1.3—5.5 km高度,大致以3 km(约-10℃)为分界线,下层为冰雪混合层,上层为冰雪层,冰雪层相对湿度与地面雪花粒子浓度及降雪强度正相关。雨滴谱仪探测的地面反射率因子(Z)与降雪强度(R)拟合关系为Z=149.85×R1.14。本研究结果为华北强降雪精细化预报提供参考。
英文摘要:
      A backflow heavy snowfall event occurred in central North China from 07:00 BJT January 5 to 04:00 BJT January 6, 2020, producing the maximum snowfall of 15.5 mm. The ERA5 reanalysis and high-resolution observation data from multisource are utilized to analyze the synoptic background, local dynamic and thermal conditions of this event, as well as the spatiotemporal distribution and microphysical features of snowfall. The results show that 7 h earlier than the snowfall, the northeast airflow below 900 hPa (called ‘backflow’) originating in the northeast plain of China across the Bohai Sea reached the North China Plain, under the influence of an inverted trough over Huang river bend and a high pressure in northeast plain. A surface mesoscale convergence line in the North China Plain was formed under the blocking effect of Taihang mountain, corresponding to the heavy snowfall area. Likely influenced by the 200 hPa divergence, the 700 hPa southwest low-level jet (LLJ) extended northward and transported abundant water vapor towards North China. Northeasterly wind below 800 m was observed in Shijiazhuang about 1 h before snowfall, then the temperature below 1 km dropped rapidly to -5~-1℃, forming a ‘cold pad’. An LLJ near 700 hPa over the heavy snowfall area appeared 2 h earlier than the snowfall, then the LLJ became thicker and extended down to 2 km, inducing the warm and humid air below it to climb along the ‘cold pad’ and triggering the snowfall. The maximum wind speed of LLJ (19 m s-1) and the peak value of LLJ index (about 8) coincide with occurrence of the heavy snowfall greater than 1 mm h-1. At the same time, the maximum center of ascending motion and water vapor transport was near 700 hPa. The snow particles were 0.35-0.55 mm in diameter. There was a positive linear correlation between snow intensity and particle number concentration. The snow-producing cloud layer was located at 1.3-5.5 km heights. The lower layer (below 3km; about -10℃) was ice-snow mixing layer and the upper layer (3-5.5 km) was ice-snow layer. The relative humidity of ice-snow layer was positively correlated with snow particle concentration and snowfall intensity. The fitting relationship between ground reflectivity factor (Z) and snowfall intensity (R) detected by disdrometer was Z=149.85×R1.14. The results obtained provide a reference for the precise forecasting of heavy snowfall in North China.
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