Laboratory for
Climatology and Remote Sensing

Abstract:

A European fog climatology of fog frequency and fog properties which is based on a 10-years time series of NOAA-AVHRR data is under preparation. In this paper, preliminary results are presented. A fog map for 63 days provides a clear distinction of fog frequency in Europe: The pre-alpine basins reveal the highest fog frequency, a secondary maximum is observed for the river valleys of the lower mountain ranges and the fog minimum is located in the transition zone between the maritime coastal fog of the North Sea and the area of continental valley fog of the river valleys. The potential of VIS and MIR data for the calculation of fog optical and microphysical properties are discussed in the scope of a case study.

Abstract:

A 10-year fog climatology of Germany and adjacent areas, based on NOAA-Advanced Very High-Resolution Radiometer (AVHRR) data, is presented. Maximum fog frequency is obtained for the Lake Constance area; minimum fog occurrence, accounting for basins and river valleys, is located in the Lower Rhine area. This is a transition zone between coastal advection fog and the more continental radiation fog of the lower mountain range. Fog persistence is estimated by a comparison of night and day maps. Using the bispectral approach of Nakajima and Nakajima [J. Atmos. Sci. 52, (1995) 4043], the potential of weather satellite data for climatologies of fog’s optical and microphysical properties is examined. Maps of fog optical depth, effective radius and liquid water path (LWP) are computed from well-illuminated noon images and the resulting data set is statistically evaluated. Typical features of advection fog are obtained for the coastal areas of the North and Baltic Seas, while the fog of the pre-Alpine basins reveals characteristics of continental radiation fog. The results are in general accordance with field observations of various sources.