Statistics on low cloud occurrence per month along the South-Western African coast at 7:00 and 14:00 UTC, 2004 to 2009

The spatial and temporal patterns of fog and low clouds along the South-Western African coast are characterized based on an evaluation of Meteosat SEVIRI satellite data. A technique for the detection of fog/low clouds in the region is introduced, and validated using 1 year of CALIOP cloud lidar products, showing reliable performance. The frequency of fog and low cloud in the study area is analyzed by systematic application of the technique to all available Meteosat SEVIRI scenes from 2004 to 2009, for 7:00 UTC and 14:00 UTC. The highest frequencies are encountered in the area around Walvis Bay, with a peak in the summer months. Fog and low clouds clear by 14:00 UTC almost everywhere over land.

本研究通过评估Meteosat SEVIRI卫星数据，对非洲西南沿海雾与低层云的时空分布特征进行了系统表征。本研究提出了一种适用于该区域的雾/低层云检测方法，并采用1年的CALIOP云激光雷达产品对该方法开展验证，结果表明其性能可靠。通过将该检测方法系统性应用于2004至2009年间所有可获取的Meteosat SEVIRI卫星影像，本研究针对世界协调时（UTC）7:00与14:00两个时段，分析了研究区域内雾与低层云的发生频率。雾与低层云的高发区集中在鲸湾（Walvis Bay）周边区域，且在夏季月份达到频次峰值。几乎所有陆地区域的雾与低层云均会在世界协调时14:00前消散。