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:

The formation, dynamics and spatial distribution of heavy precipitation during the 1991/92 El Nin˜o in Ecuador and northern Peru were examined by means of Meteosat-3 imagery, NOAA-AVHRR-based multichannel sea surface temperatures (MCSST) and additional meteorological observations. The Convective and Stratiform Technique (CST) was used for rain retrieval by means of Meteosat IR data and a cross-correlation approach was applied to Meteosat image sequences to derive cloud motion winds (CMW) which are essential for the analysis of circulation patterns leading to severe precipitation. From an analysis of 45 days with severe precipitation it is proven that three mechanisms were responsible for the formation of heavy rains. Each mechanism reveals a speci? c localized impact. (1) The most frequent mechanism (frequency of ~61%) represents an extended land–sea breeze system. During such weather conditions, predominantly locally con? ned precipitation patterns occured. Areas a? ected by the sea wind front during the day were the coastal plains up to the 1000m contour line on the western Andean slope. Local maxima in the frequency of cloudiness leading to precipitation could be found at isolated peaks of a lower coastal cordillera. At night the highest frequency of precipitation was found over the warm water surface of the Gulf of Guayaquil, mainly due to its coastal shape which signi? cantly favours convergence of the nocturnal land breeze. (2) Convection, initiated in the coastal plain and on the western Andean slopes during the afternoon, was signi? cantly intensi? ed by an entrainment of remainders of cirrus shields from the Amazon basin. These cloud fragments spilled over the Andes with well-developed trades in the mid/upper troposphere which blew in the opposite direction to the daily sea/up-slope breeze. The spill over points were characterized by areas of deep convection on the western Andean slopes and were frequently valley axes perpendicular to the mountain chain as well as the Andean depression in southern Ecuador. (3) During the main El Nin˜o phase (March– April ), heavy and persistent precipitation was extended over wide areas of the coastal plain showing neither a distinct diurnal cycle nor preferential areas. Deep convection was frequently organized in mesoscale convective complexes (MCC) and was spatially correlated with MCSST > 27ß . The extensive instability of the troposphere during these weather conditions was marked by convective cloud streets and an intensi? cation of the meridional Hadley circulation o? the coast of southern Ecuador and Peru.

Abstract:

The development of a 4D GIS application for the realistic rendering of fog clearance is presented. The system comprises of a 2D raster GIS, a 3D volume rendering technique and a 4D animation procedure. The application extensively uses NOAA-AVHRR data to provide a realistic view of fog coverage and fog optical properties.