Fog water flux at a canopy top: Direct measurement versus one-dimensional model

A one-dimensional model [Lovett, 1984. Rates and mechanisms of cloud water deposition to a subalpine balsam fir forest. Atmospheric Environment 18, 361–371] to quantify fog water deposition was compared with results of long term (13 months) measurements of turbulent exchange with the eddy covariance method at a mountainous site in Central Europe. Turbulent exchange is mainly deposition and dominates over sedimentation at that site, therefore eddy covariance is a suitable tool in quantifying fog water deposition. The model can be operated with use of the measured droplet size distribution (DSD), with a DSD as parameterized from liquid water content (LWC) data, or with the measured visibility (VIS) as a quantitative indicator for fog. The latter is the easier measurement and therefore preferable for long-term applications. We compared the fog water deposition on a monthly basis. If VIS data are used as model input, the overall underestimate of the measurement is −23% as compared to the measurements. Using LWC and the parameterized DSD as input, the deviation is +37%. All deviations are highly significant.