Fog at New Zealand Airports

Abstract

Fog has a significant impact on the aviation industry in New Zealand, and many other parts of the world. In spite of its importance, there are few studies on fog in New Zealand. This thesis studies the occurrence and causes of fog at twelve New Zealand aerodromes. Firstly, a comprehensive and detailed climatological study of fog at the aerodromes was made. This investigated the similarities and differences between fog occurrence at each aerodrome. The climatological study also highlighted the important influence synoptic weather systems have on fog. The results showed fog usually occurs when an anticyclone is centred either directly over, east or north-east of New Zealand. Night time radiative heat fluxes at the surface were investigated in a later section of the thesis, because of the important roles they have in the formation of radiation fog. A radiative transfer model was used to quantify the influence different cloud types have on the radiative transfer model was used to quantify the influence different cloud types have on the radiative fluxes, and ultimately fog occurrence. Low stratus has the largest influence of any cloud type on the surface radiation flux. Higher clouds have a lesser effect. An interesting result was that cirrus often has a significant influence on the heat flux, and can not be ignored in radiative models, despite its great height. Finally several fog prediction models, including neural networks, Markov chains (described by Renwick, 1989) and climatology were tested on data from Christchurch airport. It was found Markov chains are the most accurate model for forecasts up to four hours. Thereafter neural networks are potentially more accurate, provided accurate dew-point depression forecasts are available.