Fog and low cloud detection over northern parts of the Northern Territory using geostationary satellite data, June to September 2004

An investigation of large-scale fog and low-cloud events over the northern part of the Northern Territory, Australia, during the dry season of 2004 was performed using a variety of Geostationary Operational Environmental Satellite (GOES) 9 imagery. In the course of this an evaluation of an Enhanced Dual Channel Infrared Difference method is conducted. The method has been developed within the Australian Bureau of Meteorology to assist in the detection of night-time fog and low cloud. This analysis was conducted on a large scale over the whole domain, and on a smaller scale in the vicinity of selected meteorological stations. Results indicate that on a large scale the method detects developing fog and low cloud well, however on the smaller scale it is limited by its finite resolution, giving good results only for some of the selected stations. Favourable geographical locations for fog and low cloud are identified for each month, and for the full four months of data. Analysis of the total area occupied by the fog and low cloud for each day over the duration of the study shows that the events cluster into episodes. Both the episodes and the geographical distribution of the fog and low cloud appear to be related to the synoptic-scale wind flow over the domain. Characteristics of the night-time formation and daytime dissipation of the fog and low cloud are presented for each month and for the full four months, and critical times and periods are identified. It was found that during the night the evolution of the fog and low cloud was influenced by linear disturbances moving through favoured locations, whilst during the day the dissipation of the signal is much slower over maritime areas than over land. The local sea-breeze is postulated to stimulate the dissipation over the southern Gulf of Carpentaria.