茂名地区海雾含水量的演变特征及其与大气水平能见度的关系

Characteristics of liquid water content of sea fog in Maoming area and its relationship with atmospheric horizontal visibility

2008年3月16—19日,在广东茂名博贺海洋气象科学试验基地,利用美国DMT公司生产的FM-100型雾滴谱仪,连续观测了海雾的雾滴谱、数浓度等微物理量。在此基础上分析了海雾液态含水量的演变特征,并结合同期的气象观测与分析数据,进行了海雾中低能见度成因的天气学分析。研究表明,海雾发展过程中含水量有着上下起伏变化的特点;直径10μm以上雾滴的增多是含水量增大的主要原因;随着含水量的增大,雾滴谱分布有向大雾滴方向增宽的趋势,其峰值高度也不断增大。在相同的含水量区间,不同的大气能见度样本表现出明显不同的谱分布特征;在相同高数浓度区间的情况下,导致大气能见度降低的主要原因是含水量的增大。而海雾过程中低能见度的出现,是众多天气因素共同影响的结果:地面天气图上的均压场范围更大,大气低空及地面风速小,大气低层处于弱不稳定状态,以及高湿度层主要在近地层等等。

By using the Fog Monitor （FM-100, DMT Inc. USA） droplet collector, the droplet size distribution and droplet number concentration of sea fog from 16 to 19 March 2008 were investigated in the Science Experiment Base for Marine Meteorology at Bohe, Guangdong Province. The microphysical structure and evolution of this sea fog event, especially the LWC （liquid water content） of sea fog, are analysed. According the observational data during the same period, the synoptic factors accounting for the low atmospheric visibility assocaited with this sea fog event were also analysed. It is shown that liquid water content of sea fog had, a wave-variation during the sea fog development period. The main factor for the increasement of LWC was due to the increasement of larger droplets greater than 10μm. Accompanied with the increasement of LWC, the droplet size distribution of sea fog became wider towards larger size, and the peak value kept increasing either. In the same range of LWC, different visibility samples exhibited various droplet size distributions. In the same large drolet number concentrations range, the main reason for lower atmospheric visibility was due to the increasement of the LWC. The low atmospheric visibility caused by sea fog were affected by many synoptic factors, such as wider homogeneous pressure field, weaker low-level wind speed, slightly unstable low-level atmosphere, higher humidity at the surface level and so on.