Change of Fog Frequency

Abstract

Data on fog occurrence from 26 Polish meteorological stations were analysed for the period 1966–2018. Annual and seasonal number of days with fog, number of days with fog of the duration <6 h, 6-12 h and >12 h, and number of days with dense, moderate and thin fog were studied in terms of spatial and temporal variability. In the high mountains, the fog frequency is the highest (about 300 days per year), no statistically significant multi-annual changes of most of the indices can be defined and the inter-annual variability is very low. At the seaside, the number of days with fog is the lowest (about 28 days per year on average) and the inter-annual variability is high. Therefore, no statistically significant trends can be determined for most of the indices. In the lowland areas of northern and central Poland, and in the uplands of southern Poland, high variability in fog occurrence and long-term trends can be observed in each region. For stations with the highest fog frequency, statistically significant increasing trends were obtained while for the others the trends were either decreasing or not significant statistically. As fog is a very localised phenomenon, downscaling methods of satellite image processing have to be developed in order to improve the spatial approach in long-term analyses.