Examination of Microphysical Relationships and Corresponding Microphysical Processes in Warm Fogs

In this paper, the microphysical relationships of 8 dense fog events collected from a comprehensive fog observation campaign carried out at Pancheng（32.2 N, 118.7 E） in the Nanjing area, China in the winter of 2007 are investigated. Positive correlations are found among key microphysical properties（cloud droplet number concentration, droplet size, spectral standard deviation, and liquid water content） in each case, suggesting that the dominant processes in these fog events are likely droplet nucleation with subsequent condensational growth and/or droplet deactivation via complete evaporation of some droplets. The abrupt broadening of the fog droplet spectra indicates the occurrence of the collision-coalescence processes as well, although not dominating. The combined efects of the dominant processes and collision-coalescence on microphysical relationships are further analyzed by dividing the dataset according to visibility or autoconversion threshold in each case. The result shows that the specific relationships of number concentration to volume-mean radius and spectral standard deviation depend on the competition between the compensation of small droplets due to nucleation-condensation and the loss of small droplets due to collision-coalescence. Generally, positive correlations are found for diferent visibility or autoconversion threshold ranges in most cases, although negative correlations sometimes appear with lower visibility or larger autoconversion threshold. Therefore, the compensation of small droplets is generally stronger than the loss, which is likely related to the sufcient fog condensation nuclei in this polluted area.     

Microphysical characteristics of sea fog over the east coast of Leizhou Peninsula, China

Microphysical properties of sea fog and correlations of these properties were analyzed based on the measurements from a comprehensive field campaign carried out from 15 March to 18 April 2010 on Donghai Island (21°35’’N, 110°32’5’’E) in Zhanjiang, Guangdong Province, China. There were four types of circula- tion pattern in favor of sea fog events in this area identified, and the synoptic weather pattern was found to influence the microphysical properties of the sea fogs. Those influenced by a warm sector in front of a cold front or the anterior part of low pressure were found to usually have a much longer duration, lower visibility, greater liquid water content, and bigger fog droplet sizes. A fog droplet number concentration of N≥1 cm-3 and liquid water content of L≥0.001 g m-3 can be used to define sea fogs in this area. The type of fog droplet size distribution of the sea fog events was mostly monotonically-decreasing, with the spectrum width always being >20 μm. The significant temporal variation of N was due in large part to the number concentration variation of fog droplets with radius <3 μm. A strong collection process appeared when droplet spectrum width was >10 μm, which subsequently led to the sudden increase of droplet spectrum width. The dominant physical process during the sea fog events was activation with subsequent condensational growth or reversible evaporation processes, but turbulent mixing also played an important role. The collection process occurred, but was not vital.     

2016年厦门机场一次爆发性浓雾的天气条件分析

浓雾不仅严重威胁着航空运行安全,而且导致的航班延误和取消亦给航空公司和社会经济效益带来巨大损失,因此开展机场爆发性浓雾的研究具有重要的科学意义和应用价值。利用常规气象观测资料、ECMWF细网格精细化数值预报产品(简称EC)和NCEP全球再分析资料,对2016年4月16日21:03—17日8:13(北京时)发生在厦门机场的一次爆发性浓雾天气过程进行分析,结果表明:海风和地面长波辐射为本次浓雾爆发性形成提供主要热力冷却条件。雾前10 min海风风速的突增使空气过饱和度增大,促使了雾的生成和爆发性增长。潮湿土壤的蒸发提供了充足水汽,也是雾第二次爆发性增长的直接原因。850 hPa以下显著增温增湿和700 hPa下沉运动维持了贴地强逆温,为雾爆发性形成提供了极稳定的层结条件。EC对此次浓雾形成的重要因子预报能力差异较大,虽然能准确预报海风的形成和机场入夜后云量的骤减,但对于海风预报的稳定性有待提高。      

济南爆发性增强冬季雾的物理特征分析

利用宏、微观观测资料,分析了济南4次出现爆发性增强冬季雾过程的类型以及形成、发展、减弱和消散的主要机制,研究了形成、发展、成熟和减弱阶段,以及爆发性增强期间的微物理演变特征,探讨了爆发性增强的触发机制。结果表明：1）夜间地面长波辐射及弱冷空气入侵造成的气温下降是济南冬季雾形成和发展的主要因素,干冷空气入侵或日出后太阳辐射加热升温,近地层相对湿度下降是雾消散或减弱的主要机制。2）形成阶段,核化和凝结增长过程启动但并不活跃,碰并强度很弱,以未碰并和偶发碰并为主;发展阶段,核化和凝结增长等微物理过程开始活跃,碰并过程启动,大滴开始增多;成熟阶段,核化、凝结和碰并增长非常活跃,各微物理量均达到最大值,谱最宽;减弱阶段,核化、凝结过程减弱,碰并过程减弱并消失,雾滴蒸发,能见度增大。3）爆发性增强的宏观物理特征主要表现为极大风速增大、气温下降、相对湿度增大、水汽压下降;微观物理特征主要表现为数浓度、液态含水量等微物理量出现跃增,以及谱型由“单峰”结构突变为“多峰”结构。4）相对湿度增大主要与气温下降有关,水汽压下降则与异常活跃的凝结增长有关;气温下降是济南冬季雾爆发性增强的直接原因,弱水汽输送产生的增湿作用对爆发性增强具有一定的促进意义。     

2017-11-15安徽颍上团雾天气特征分析及气象服务探讨

团雾是一种严重威胁公路交通安全的恶劣天气,因其具有较强的局地性、突发性特点,也是目前公路交通气象预报服务的难点之一。针对2017年11月15日发生在安徽阜阳滁新高速颍上段的团雾交通事故,利用颍上交通气象站、焦岗湖交通气象站与颍上气象站的逐10 min气温、相对湿度、风速、能见度监测数据,结合欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts)的分析场资料,分析了安徽颍上团雾交通事故发生地的局地环境特征和当日的天气特征及成因,探讨了高速公路团雾预报服务的不足和未来工作展望,为进一步做好团雾天气交通气象服务提供借鉴和参考。主要结论如下:此次团雾发生在辐射雾的天气形势背景下,夜间辐射降温幅度达5℃以上,为团雾发生提供了低温条件;团雾发生地地势低洼且临近水系,水汽输送通道流畅,水汽充足,黎明后底层空气湿度维持在85%以上,是团雾发生的诱因之一;日出后风力保持静风状态,空气流动性差,造成近地面层水汽聚集,是团雾发生的重要原因。     

遥感影像目标检测的轻量化密集连接网络北大核心CSCD

针对无人机遥感影像中可能出现的多个密集的小目标,在检测时会出现误检、漏检的难点问题,本文提出了一种基于YOLO v4的具有密集连接网络模块的遥感影像轻量化目标检测算法,实现了对无人机遥感影像中车辆小目标的高精度识别。首先,对YOLO v4主干网络CSP Darknet53的卷积层采用密集连接、稀疏连接两种处理方式,加强特征的提取和重复使用,以缓解梯度消失问题;然后,对此模块进行模型剪裁,减少网络层数并定义为新的密集连接网络模块;最后,在NWPU-VHR-10数据集和笔者所在课题组制作的Vehicle-850无人机影像数据集上进行了对比试验并取得了较好的效果。本文改进后的网络结构在提高遥感影像目标检测准确率的同时,缩短了网络模型的收敛时间,减少了模型占用的内存空间,提高了遥感影像中目标检测的速度。     

江西田村圩地区遥感地质信息提取及找矿预测

开展江西田村圩地区遥感地质解译,提取区域地质构造、侵入岩体、地层及蚀变信息,初步剖析测区典型矿床矿化遥感蚀变信息特征;提取研究区遥感成矿、控矿条件,开展区域成矿远景研究。依据离子吸附性稀土矿的成矿规律,综合遥感地貌解译和风化特征矿物异常信息提取结果,圈定5处稀土矿遥感找矿预测区。尝试建立石英脉型钨矿的遥感找矿预测模型,圈定钨矿找矿远景区4处,为区域地质调查工作提供找矿线索。     

A THREE-DIMENSIONAL NUMERICAL STUDY ON DENSE FOG OVER MOUNTAINOUS AREAS

Using the non-hydrostatic meso-scale model MM5v3, dense fog that occurred from March 7 to March 8, 2001 over the Mts. Nanling area was studied. With integrated field experiments and observations, the occurrence, development and lift mechanism of fog were analyzed. The results indicate that before the coming of stratiform clouds, southerly warm and wet air ascended along mountainside and cooling condensation formed mountain fog. Then fog was formed by the stratiform on cloud-contacting mountaintop. A front inversion layer accelerated the development and extended the duration of the lower cloud and fog. The intensity, occurrence time, mass content and the variation of temperature and relative humidity of the fog agreed with those of the observation. It showed that the meso-scale model has the potential to forecast mountain fog.     

两种陆面方案对陆雾与海雾模拟效果的对比研究

利用WRF(Weather Research and Forecasting)模式,针对1次陆雾与1次同时包含近海雾区与开阔海域雾区的海雾个例,开展了2种陆面方案——SLAB(five-layer thermal diffusion scheme)方案与Noah(Noah land surface scheme)方案—...     

2021年春季海洋天气评述

2021年春季(3—5月)的大气环流特征为:北半球极涡为偶极型分布,极涡较常年平均值偏强,中高纬度西风带呈现4波型。3月,南下冷空气活动偏弱,月内海雾过程频发。4月,北部海域受高压影响,低层形势场稳定,冷空气活动减弱。5月,我国近海受温带气旋影响出现大风天气。春季我国近海出现了5次8级以上大风过程,其中冷空气大风过程2次,冷空气和温带气旋共同影响的大风过程1次,温带气旋影响的大风过程2次。春季共有8次海雾过程,3月3次,4月2次,5月3次。近海浪高在2 m以上的海浪过程有8次,大浪日数偏少。西北太平洋和南海共生成2个台风。我国近海的海面温度整体呈上升趋势,东部和南部海域升温明显,南部和北部海域海面温度梯度增加。