高级检索

冬奥赛期及同期北京两次雨雪过程的微物理特征及其积雪效率差异

Analysis of Microphysical Characteristics and SLR of Two Rain and Snow Weather Processes in the Same Period of Winter Olympics

  • 摘要: 利用粒子谱观测、人工加密积雪观测和显微镜雪花观测,分析冬奥赛期及同期2月北京两次雨雪过程的微物理特征及积雪效率差异发现:粒子平均谱均呈单峰型,峰值浓度雪花谱最大,雨滴谱最小,而同一降雪过程中板状或柱状雪花峰值浓度高于辐枝状雪花。粒子平均下落速度降至2m/s以下可以作为转雪的指标,干雪的平均粒子下落速度不足1m/s。2020年2月13-14日雨转雪过程的环境温度相对较高,雨夹雪阶段的雪花增长主要来源于雪花凇附;随着低层温度降低至-8~-4℃,-18~-12℃温度层明显增湿,降水相态转为雪,雪花凇附现象依旧存在,雪花凇附和粘连聚并机制并存使得粒子最大直径达到19mm;此次过程以凇附的湿雪为主,积雪效率较小,仅0.6cm/mm。2022年2月13日冬奥赛期降雪过程中,温度更低,低层云区始终维持在-18~-12℃,雪花下落速度接近未凇附雪花的经典下落速度,整个过程均为未凇附的干雪,凝华增长、贝吉龙过程和攀附钩连的聚并机制共同发挥作用,粒子最大直径为11mm;冬奥现场观测发现雪花形态由辐枝状变为板状或柱状,辐枝状雪花的积雪效率高,加密观测积雪效率最高可达4cm/mm,随着雪花形态改变,对应的粒子数浓度极值增大而粒子谱宽明显减小,积雪效率也急剧下降。

     

    Abstract: The microphysical characteristics and different snow liquid ratios (SLR) of rain to snow and snowfall processes during the same period of Beijing Winter Olympics were analyzed based on Parsivel data, densely artificial snow-depth measurement and microscopic snowflake shape observation. The average particle spectrum showed a unimodal pattern, with snowflake spectrum having the highest peak number concentration and raindrop spectrum having the lowest. During the same snowfall process, the peak number concentration of plate or column ice crystals was higher than that of dendritic snowflakes. The average falling speed of particles falling below 2 m/s can be used as an indicator of phase transfer. The average falling speed of dry snow particles was less than 1 m/s. The ambient air temperature during the rain to snow process on February 13-14, 2020 was relatively high. The growth of snowflakes in the sleet stage mainly came from the riming process. With the decrease in temperature at lower levels and the significant increase in humidity at -18~-12℃ layer, precipitation phase turned to snow and the riming process still existed. Under the joint action of riming and adhesive aggregation processes, the maximum crystal diameter reached 19mm, but the snow liquid ratio was low to 0.6cm/mm. In the snow process during the Winter Olympics, the temperature was lower with low level cloud region between -18 and -12℃, and the falling velocity was close to the classical curve of the unrimed ice crystals, so the snowflakes were all unrimed. The combined action of sublimation, Bergeron process, and hook aggregation made the particle diameter grow to 11mm. But the snowflakes’ shape changing to plate or column was observed at Shougang Venue, resulting in the increase of the number concentration and reduction of particle spectrum width, while the corresponding SLR sharply reduced.

     

/

返回文章
返回