ABSTRACT
The least cloudy part of West Africa, the maps suggest, is not the Sahara but northern Nigeria, especially between Kano and Maiduguri. The graphs clearly show how less cloudy is the north than the south, yet how Bilma, the station furthest inland, is cloudier than F’Derik or Nouakchott at much the same latitude. But the diurnal change in cloud cover is more dramatic at Bilma than anywhere else in West Africa, Abong Mbang perhaps excepted. Judging from the lack of availability of visibility records it would seem that regular measurements are made at few stations in West Africa and there is a terrible lack of consistency in published data. The condensation of water vapour into droplets of water, probably about 18 to 30 μ in diameter, which will significantly impair visibility, will readily take place on hygroscopic particles, especially crystals of sea salt derived from evaporation.
