Abstract:
The character of fog at Cape Town International Airport (CTIA), South Africa, is investigated, using 13 yr
of historical hourly data during the period 1997–2010. Hourly surface observations are used to identify fog
types that most frequently affect CTIA, by using an objective fog-type classification method that classifies fog
events according to their primary formation mechanisms. Fog-type characteristics, such as the minimum
visibility, duration, and time of onset and dissipation, are determined. Self-organizing maps (SOMs) are used
to determine the dominant synoptic circulation types associated with fog at CTIA. Results show that radiative
processes are the most common cause of fog, with an enhanced likelihood of radiation fog in winter. Cloudbase-
lowering fog and advection fog events are more likely at the start of the fog season. As the fog season
(March–August) progresses, synoptic circulations associated with fog change from a dominant low pressure
pattern along the west coast in March and April to a dominant interior high pressure pattern toward July and
August. The techniques presented may be used to provide aviation forecasters with a detailed description of
the types of fog that frequently occur, their characteristics, and the synoptic circulation associated therewith.
