Cloud detection in the Tropics - a suitable tool for climate-ecological studies in the high mountains of Ecuador

The detection of clouds and the analysis of cloud frequency play an important role for operational weather prediction as well as for climate-ecological studies. A threshold technique for cloud detection in the tropical Mountainous area of Ecuador is presented which is based on National Oceanic and Atmospheric Administration Advanced Very High Resolution Radiometer (NOAA-AVHRR) data. Cloud classification is performed for both day and night overpasses by applying several threshold tests which also include ancillary terrain information. From a set of 155 images, maps of relative cloud frequency are calculated for Ecuador and adjacent areas as well as the central study area of an ecological project in southern Ecuador (Loja). Results show a clear relation between topography, main airflow and cloudiness due to barrage and lee-effects. The spatial extension of high mountain ecosystems such as the Ecuadorian Paramo has been proven to be significantly influenced by the spatial pattern of cloud frequency.