天津平流雾过程及其空中微物理特征个例研究

Advection fog process and its microphysical properties:a case study in Tianjin

2016/2017冬季在天津开展了平流雾微物理特征观测试验,结合距地66 m高度处雾滴谱和255 m气象塔大气边界层资料,借助突变和趋势一致性非参数检验方法对重度霾后接连发生的两次平流雾过程发展阶段进行客观划分,揭示雾体内部一定高度处雾滴微物理特征和尺度分布特征的观测事实,讨论其生消演变规律。结果表明,伴随西南暖湿平流,饱和层首先在空中出现并向地面扩展,雾过程中成熟阶段观测高度范围内升温,雾层处于中性或弱不稳定层结状态。66 m高度处大雾滴持续存在,微物理特征与地面能见度准同步变化,数浓度高值出现在成熟阶段初期,而含水量、特征直径高值出现在成熟阶段后期,对应成熟阶段后期雾滴数浓度减少、地面能见度小幅跃升。消散阶段各尺度数浓度因雾滴蒸发同步减小。

The microphysical characteristics observation test of advection fog was carried out in Tianjin in the winter of 2016/2017.Combined with the droplet spectrum at a height of 66 m above the ground and the atmospheric boundary layer data of 255 m meteorological tower,the development stages of two consecutive advection fog processes after heavy haze were objectively divided by means of change-point detection and trend consistency nonparametric test,which reveals the observation facts of droplet microphysical characteristics and size distribution characteristics at a certain height in the fog,and discusses the evolution law of its generation and disappearance.The results show that with the southwest warm and humid advection,the saturated layer first appears in the air and extends to the ground.During the fog process,the temperature rises within the observation height range in the mature stage,and the fog layer is in a neutral or weakly unstable stratification state.At the height of 66 m,large fog droplets persist,and the microphysical characteristics change quasi synchronously with the ground visibility.The high value of number concentration appears in the early stage of maturity,while the high value of water content and characteristic diameter appears in the late stage of maturity,corresponding to the decrease of fog droplet number concentration and a small jump in ground visibility in the late stage of maturity.In the dissipation stage,the number concentration of each size decreases synchronously due to droplet evaporation.