STUDY ON METHODS TO CALCULATE VISIBILITY ON BLOWING SNOW

Information on the occurrence of blowing snow is useful in enabling drivers to select safer and more appropriate routes. Visibility meters have been used to measure the intensity of blowing snow on roads. However, the area covered by the presently installed visibility meters is too limited to obtain region-wide information on blowing snow. This led us to seek methods of estimating the intensity of blowing snow using wind velocity, snowfall intensity and other parameters, all of which are obtained relatively easily. First, based on past studies on mass flux of snow (Mf) and visibility (Vis), we established that log(Vis) =-0.773 log(Mf) + 2.845 for visibility up to 3000 m. Considering that mass flux of snow is snow concentration multiplied by wind velocity, we then attempted to establish methods to estimate snow concentration. For this, two conditions were examined to estimate snow concentration using wind velocity and snowfall intensity. In one condition, the wind velocity at 10 m above the ground was 8.5 m/s or greater and the temperature was less than-2 ℃; in the other condition, the wind velocity at 10 m above the ground was less than 8.5 m/s or the temperature was-2 ℃ or higher. The visibility estimated using related equations agreed closely with the measured visibility, which indicates that our visibility estimation methods can be applied to region-wide monitoring of blowing snow on roads.