3.06 Annual and monthly frequency of fog and low cloud in the Namib Desert11
Fog defines much of the Namib Desert's climate. It occurs during all months of the year in a band along the coast that may extend more than 100 kilometres inland. The maps here, derived from satellite and ground data, illustrate the average frequency of fog and low cloud along the entire Namibian coast over the year and from month to month. Inland fog or low cloud occurs most frequently in the spring and summer months between September and March. Seasonal changes in airflow (figure 3.01) likely drive this pattern.
The central area of the coast experiences the highest frequency of fog, with a third of the days in each year having some fog. Ground-based measurements at the coast suggest that, here, fog peaks in winter, between April and August.12
While the satellites detect the presence of all low cloud, the distinction between fog and cloud is often difficult. The height of the cloud base increases between August and March, and much of the cloud at the coast at this time (which is evident in the maps) would not be recorded as fog at ground level.
Photo: J Henschel
Photo: MODIS Terra, NASA