First fully diurnal fog and low cloud satellite detection reveals life cycle in the Namib

摘要

Fog and low clouds (FLCs) are a typical feature along the southwestern Africancoast, especially in the central Namib, where fog constitutes a valuableresource of water for many ecosystems. In this study, a novel algorithm is presented todetect FLCs over land from geostationary satellite data using only infraredobservations. The algorithm is the first of its kind as it isstationary in time and thus able to reveal a detailed view of the diurnaland spatial patterns of FLCs in the Namib region. A validation against netradiation measurements from a station network in the central Namib reveals ahigh overall accuracy with a probability of detection of 94 %, a false-alarm rate of 12 % and an overall correctness of classification of 97 %.The average timing and persistence of FLCs seem to depend on the distance tothe coast, suggesting that the region is dominated by advection-driven FLCs.While the algorithm is applied to study Namib-region fog and low clouds, itis designed to be transferable to other regions and can be used to retrievelong-term data sets.