Editorial Type:
Article
Article Type:
Research Article

Climatological Characteristics of Fog at Cape Town International Airport

Lynette van Schalkwyk Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, and eTV (Pty) Ltd., Cape Town, South Africa

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Liesl L. Dyson Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, South Africa

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Print Publication:
01 Jun 2013
DOI:
https://doi.org/10.1175/WAF-D-12-00028.1
Page(s):
631–646
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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. Cloud-base-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.

Corresponding author address: Lynette van Schalkwyk, Dept. of Geography, Geoinformatics and Meteorology, Private Bag X20, Hatfield 0028, South Africa. E-mail: lynvanschalkwyk@gmail.com

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. Cloud-base-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.

Corresponding author address: Lynette van Schalkwyk, Dept. of Geography, Geoinformatics and Meteorology, Private Bag X20, Hatfield 0028, South Africa. E-mail: lynvanschalkwyk@gmail.com
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