Fog forecasting at Cape Town International Airport : a climatological approach

Abstract

Cape Town International Airport (CTIA) is located along the extreme southern portion of the west coast of South Africa which has the highest frequency of fog in the country. Fog occurs more frequently at CTIA than at any other of the international airports in South Africa. Fog forecasting research in South Africa has largely been neglected and fog forecast verification results show the urgent need for improvement. Accurate fog forecasts are imperative for the aviation industry to prevent costly flight delays and diversions. The main aim of this research is to improve the forecasts of fog at CTIA. The first step towards realising this aim is to provide aviation forecasters with a comprehensive fog climatology that encompasses all aspects of fog: from the seasonal characteristics, to detail regarding the types of fog that frequently occur, synoptic circulations associated with fog and characteristics of the vertical profile of the lower troposphere and boundary layer in which fog forms. Fog types at CTIA are classified by means of an objective hierarchical classification method that takes the formation mechanisms of fog into consideration. Self Organising Maps (SOMs) are used as a synoptic typing method, to determine the synoptic circulations that are most frequently associated with fog at CTIA. Case studies are presented to illustrate the formation mechanisms of 5 different fog types by means of the synoptic circulation, surface observations, satellite imagery and atmospheric soundings. Conclusions drawn from these case studies can assist forecasters with the identification of potential fog events in advance. It is recommended that climatology and case study results be made available to aviation forecasters at CTIA and that similar studies be conducted for all international airports in South Africa that are frequently affected by fog. Copyright