EVOLUTION OF LIQUID WATER CONTENT IN A SEA FOG CONTROLLED BY A HIGH-PRESSURE PATTERN

On March 16–17, 2008, a sea fog occurred in Dianbai in the west of Guangdong Province and was accompanied by a high-pressure synoptic system. Using comprehensive observation datasets, this study analyzes the evolution of liquid water content during this sea fog and investigates the relationships between liquid water content and the average diameters and count densities of fog droplets, air temperature, wind speed and turbulence exchanges. The main results are presented as follows. (1) The sea fog showed a quasi-periodic oscillation characteristic, i.e., it developed, disappeared and then developed again. (2) During the sea fog, the number of fog droplets changed significantly while the changes in average diameter of the fog droplets were relatively small. The development and disappearance of the sea fog correlated significantly with the fog droplet numbers. (3) The air-cooling mechanism played a significant role in sea fog formation and development. However, the influences of this mechanism were not evident during fog persistence. (4) During sea fog formation, weak turbulence exchanges were helpful for fog formation. During sea fog development and persistence, liquid water content increased when turbulence exchanges weakened, and vice versa. The changes in turbulence exchanges were closely related to the quasi-periodic oscillations observed in sea fog presence.

The spring Yellow Sea fog：synoptic and air–sea characteristics associated with different airflow paths

The fog occurs frequently over the Yellow Sea in spring（April–May）, a climatical period of Asian monsoon transition. A comprehensive survey of the characteristic weather pattern and the air-sea condition is provided associated with the fog for the period of 1960–2006. The sea fog is categorized by airflow pathways of backward trajectory cluster analysis with the surface observations derived from international comprehensive oceanatmosphere dataset（I_COADS） I_COADS datasets and contemporaneous wind fields from the National Centers for Environmental Prediction（NCEP）/National Center for Atmospheric Research（NCAR） reanalysis. On the basis of the airflow paths, the large-scale lower-tropospheric circulation patterns and the associated surface divergence,the distribution of a vertical humidity, the horizontal water vapor transportation and the air-sea temperature difference are investigated and the major findings are summarized as follows.（1） Four primary clusters of the airflow paths that lead to spring sea fog formation are identified. They are originated from the northwest, east,southeast and southwest of the Yellow Sea, respectively.（2） Springtime Yellow Sea fog occurs under two typical weather patterns： the Yellow Sea high（YSH） and cyclone and anticyclone couplet（CAC）. Each pattern appears by about equal chance in April but the YSH occurrence drops to around one third and the CAC rises to around two third of chance in May.（3） The common feature in the two types of synoptic conditions is that surface divergence center is located over the Yellow Sea.（4） For the YSH type of fog, water vapor comes mainly from local evaporation with a well-defined dry layer present in the lower atmosphere; for the CAC type of fog, however, water vapor comes mainly from areas outside the Yellow Sea with a thick surface layer of high humidity.（5） With the differences in weather patterns and its associated vertical distribution of the humidity and the transportation of water vapor, there are two types of sea fogs. Most fogs of the CAC types are ＂warm＂ fog, while fogs of YSH type have nearly equal chance to be ＂warm＂ and ＂cold＂ fog.

一次高压型海雾中的液态含水量演变特征

2008年3月16—17日在粤西电白出现了一次在高压天气系统控制下的海雾过程。利用这次海雾的综合观测数据,分析了这一高压型海雾的液态含水量演变特征,讨论了液态含水量与雾滴平均直径和数密度以及气温、风速、湍流交换等的关系。结果显示:(1)海雾有发展-消散-再发展的准周期性变化特征;(2)海雾过程中的雾滴数有显著的变化,而雾滴平均直径的变化较小;雾滴数变化对海雾的发展、消散起主要作用;(3)在海雾生成和发展阶段,空气的冷却机制起主要作用;而在海雾的维持阶段冷却机制的作用并不明显;(4)在雾的生成阶段,弱湍流交换有利于雾的生成;而在雾的发展和维持阶段,湍流交换减弱,液态水增长,反之液态水减少。湍流交换的强、弱与海雾发展-消散-再发展的周期性变化有密切关系。

珠江口海雾天气气候特征及成因分析

利用设立于珠江口海域具有较高时间分辨率的自动气象站的观测资料,结合欧洲中期天气预报中心再分析逐日数据集ERA-Interim,对珠江口海雾的天气气候特征、环流场及相关的气象和水文因子进行分析研究。结果表明:海雾日数月际变化显著,海雾盛季为2—4月;日变化特征表现为海雾多生成于夜间—凌晨时段,多消散于早晨—上午时段。珠江口海雾发生的大尺度环流形势可分为冷锋型、均压场型、低压前部型和高压后部型4类,其中冷锋型海雾属于混合雾,其他均属于平流冷却雾。进一步的分析表明,层结稳定且适宜的相对湿度、风速、风向及海-气温差等气象和水文条件,有利于珠江口海雾过程的发生和发展,这对做好海雾过程的预报具有一定的指导意义。

德雷克海峡夏季海雾的分析研究

本文利用中国第三次南极考察的海上实测水文气象资料 ,以及智利南极弗雷气象中心和阿根廷所发布的每日高空和地面天气图 ,对海雾进行了天气学分析 ,指出了夏季影响德雷克海峡地区的海雾过程主要是平流冷却雾。通过分析这种海雾生消时的气压场和其它要素场特征 ,得出一些有益的结论 ,从而为本区海雾的预报提供了依据。

渤海中西部近海与沿岸海雾的特征分析

利用2004—2012年渤海湾埕北油田A平台的气象水文观测资料以及塘沽、秦皇岛、兴城和龙口4个环渤海沿岸观测站的常规观测资料进行统计分析,得出渤海中西部海雾的气候特征及影响因子,归纳了天气系统模型,并给出了相关气象要素的定量化指标。结果表明:渤海海雾年际变化明显,其中2005年出现频次最少,2007年最多,不同海区海雾月际变化特征有所差异,但都存在冬季高发期,且海雾高发期受到温度空间分布的影响,08时海雾出现频次最多,其日变化特征受太阳辐射和海陆差异影响;依据高低空环流形势和地面主要影响系统,将渤海海雾发生时的天气形势分为均压场型,倒槽冷锋型,低压场型和高压场型4种并分别给出概念模型,各海区均压场型出现概率最高,渤海湾和莱州湾海区倒槽冷锋型次之,辽东湾海区低压场型占比第二;渤海海雾在海气温差正负时皆可出现且差值多在2℃以内,总体盛行风向特征不显著,这些特征与黄海海雾预报差异较大;此外,沿岸相对湿度达到90%以上,近海相对湿度达到80%以上,风速在0—3级之间,低层大气存在逆温层时,有利于渤海海雾的生成和发展。

黄海海雾天气气候特征及其成因分析

利用2002—2008年的地面观测资料、青岛小浮标站资料、海洋大气综合资料、NCEP再分析资料和卫星云图等资料,对黄海海雾的天气气候特征、环流型和相关的水文、气象因子进行分析研究。结果表明,黄海海雾呈现逐年递增的年际变化,且集中发生在春夏季,自南向北雾季逐渐推迟,发生频数增多;一日中主要出现在夜间至早晨。黄海海雾可归纳为冷锋型、高压后部型和均压场型三种天气类型。海雾是流入黄海的黑潮暖流分支与沿岸的冷水流相遇,在适宜的海温、气海温差、大气稳定度和风场等水文、气象条件下形成的,这些条件可为海雾发生、发展的预报提供一些参考依据。

大气-海雾多层环境下的天空偏振模式

为研究复杂海洋环境下天空偏振模式分布情况,针对大气-海雾复杂海洋环境,研究垂直方向上大气-海雾多层介质的天空偏振分布模式。利用简化的大气、海雾双层结构模拟复杂海洋情况,分别采用Rayleigh及Mie散射方法求得大气、海雾均匀介质层的散射系数,采用基于矢量辐射传输方程的倍加累加方法计算两层介质间的辐射传输,得到全天空偏振分布情况,以太阳子午线上海雾层下行辐射为重点研究地面观测到的偏振特性变化趋势。研究结果表明:在太阳位置处可得到偏振度(DOP)的最小值,在太阳高度角与观测高度角夹角为90°时可得到DOP最大值;随着能见度下降,DOP逐渐增加,且观测高度角大于90°时DOP增大效果明显;对于可见光典型波长,当波长增大时DOP逐渐减小,且随着能见度的减小,波长对偏振特性的影响越来越小。