Fog forecasting at Cape Town International Airport : a climatological approach

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. CopyrightDissertation (MSc)--University of Pretoria, 2011.Geography, Geoinformatics and Meteorologyunrestricte

Climatological characteristics of fog at Cape Town International Airport

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.http://www.ametsoc.org/pubs/journals/waf/index.htmlam201

A climatology of drylines in the interior of subtropical Southern Africa

DATA AVAILABILITY STATEMENT : The ERA5 data (Hersbach. et al. 2018) used were downloaded from the Copernicus Climate Change Service (C3S) Climate Data Store. Satellite imagery was downloaded from EUMETSAT Data Store. Station data in this study are available on request from the South AfricanWeather Service (SAWS) (http://www.weathersa. co.za). Other surface observation data were downloaded from online (www.ogimet.com), as were monthly ERSSTv5 data for the Ni ˜no-3.4 region (Huang et al. 2017) (https://climexp. knmi.nl/).A climatology of synoptic drylines on the subtropical southern African interior plateau (SAP) is developed using ERA5 reanalysis specific humidity and surface temperature gradients and an objective detection algorithm. Drylines are found to occur regularly during spring and summer (September–March), and almost daily during December of that period, but rarely in winter. A westward shift in peak dryline frequency takes place through the summer. Drylines peak first over the eastern parts of the SAP during November with a mean of 10 drylines and then over the central (mean of 12) and western SAP (mean of 20) in December. During midsummer, drylines over the eastern SAP are negatively correlated with drylines in the west. Between 1980 and 2020, a significant correlation exists between ENSO and dryline days over the eastern (r = 0.44; p value = 0.004) and central (r = 0.41; p value = 0.008) SAP with fewer drylines (up to 10) occurring during years with increased surface moisture and more drylines (up to 45) occurring during years with decreased surface moisture. Drylines forming over the eastern parts of the SAP were more likely to move westward than drylines over the central and western parts. Onset times across the SAP show that drylines have a tendency to form during either the late morning to early afternoon (1100 and 1400 LST) or during the early evening hours (1700 and 2000 LST), suggesting that the surface heat trough (Kalahari heat low) and westward moisture transport mechanisms, such as the Limpopo low-level jet and ridging highs, are responsible for the formation of most drylines across the SAP.South African National Research Foundation (NRF) ACSyS Programme and the FLAIR programme, a partnership between the African Academy of Sciences and the Royal Society funded by the U.K. Government’s Global Challenges Research Fund.https://journals.ametsoc.org/view/journals/clim/clim-overview.xmlam2023Geography, Geoinformatics and MeteorologySDG-13:Climate actio

Climatological Characteristics of Fog at Cape Town International Airport

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.http://www.ametsoc.org/pubs/journals/waf/index.htmlam201