OCCULT PRECIPITATION - SAMPLING, CHEMICAL-ANALYSIS AND PROCESS MODELING IN THE SUMAVA MTS (CZECH-REPUBLIC) AND IN THE TAUNUS MTS (GERMANY)

This paper deals with occult precipitation as a process affecting the water balance and chemistry. The methods used in assessing the fog-water amount are discussed. A micrometeorological mathematical resistance model predicted annual gross deposition of cloudwater of 81 mm year(-1) in the Sumava Mts. (South Bohemia); the net deposition was 47 mm year(-1). Chemical analyses of occult precipitation (fog- and cloud-water, rime-water) both in the Sumava Mts. (Czech Republic) and in the Taunus Mts. (Germany) were made. Cloud- and fog-water samples were collected using active cloud-water collectors installed on the tops of the Sumava and the Taunus Mts. Altogether, 54 samples of cloud- and fog-water and 45 samples of rime-water were collected and analysed. Concentrations of the major ions were significantly higher in occult precipitation than in rain-water. Enrichment factors for cloud vs. rain varied from two to 32. In the Sumava Mts. the estimated. wet deposition for NH4+, NO3- and SO42- via cloud droplet impaction and sedimentation represents 1410 kg km(-2) year(-1), 2650 kg km(-2) year(-1) and 2508 kg km(-2) year(-1), respectively.