Exploring the atmospheric and weather conditions for hoar frost formation at OR Tambo International Airport: A case study of ground aircraft icing events for the period 2017-2023.

<p>Ground aircraft icing has an adverse effect on the aerodynamic performance of aircrafts as well as the efficient operations of airlines and airports. The South African Weather Service (SAWS) Aviation Weather Centre (AWC) issues forecasts and warnings for the aviation community, which include aerodrome warnings for hoar frost accumulation. The infrequent and notable temporal occurrence of this weather phenomena renders it a rare aviation hazard to warn for, therefore understanding the weather and atmospheric conditions conducive for its formation is important for accurate forecasting. This study analyses 28 incidents of ground aircraft icing events at OR Tambo International Airport, South Africa, for the period 2017 to 2023. The study analysed the weather conditions during these events, and the dominant synoptic-scale systems during 8 ground aircraft icing events where multiple aircrafts and airlines were affected by long delays. The results indicated that ground aircraft icing occurred less than seven times per annum during the study period, and predominantly during the winter months. The analysis of observational data determined the thresholds of various weather variables that are considered for hoar frost forecasting, which considered ambient temperature, relative humidity, pressure and present weather conditions. The analysis of the synoptic-scale systems during ground aircraft icing events revealed that the overland ridging of the South Atlantic Ocean High Pressure system was dominant at the surface with an upper air high pressure system, preceded by the passage of a cold front and associated upper trough system. These results contribute to the guiding information for hoar frost/ice forecasting and warning in the Standard Operating Procedure for AWC and regional forecasters at the SAWS.</p>