Visibility versus precipitation rate and relative humidity

The purpose of this work is to summarize the relationships between visibility versus hydrometer types and relative humidity from measurements that were collected during the Alliance Icing Research Study (AIRS 2) which was conducted in the Ottawa-Mirabel area from 3 November 2003 to 12 February 2004. The main observations were precipitation rates for rain and snow from the hot plates and Precipitation Occurrence Sensor System (POSS), ice and liquid particle characteristics from in-situ data, visibility from the Belfort visibility meter, relative humidity and temperature. Presently, visibility parameterizations related to hydrometeor type in models are not adequate. Some previous works have shown that particle type is an important factor in visibility calculation but usually it is ignored. The results show that significant differences exist among the various parameterizations of visibility and that their application within models should be carefully addressed. Comparisons of previous parameterizations to the new visibility relationships indicate that simulated visibility values could be improved significantly.