Application of Numerical Models in Visibility Forecasting for Airports over Taiwan

Visibility is an important safety factor for aircraft takeoff and landing, and the most common phenomena causing hazardous low visibility in Taiwan are fog and haze. This study analyzed the characteristics of low-visibility events in Taiwan’s airports and found that fog is much more common than haze in causing low-visibility events. Further efforts were then targeted on the predictability of low-visibility events that associated with fog by numerical model. The model used in this study is the Weather Research and Forecasting Model coupled with a two-moment cloud microphysics scheme with aerosol-cloud interactive capability. Detailed microphysical properties such as the number and mass concentrations of cloud/fog droplets were simulated, and the information was used to diagnose the effect radius of cloud/fog droplets for calculating visibility. Such physics-based calculation was compared with those derived from popular empirical formulas to show the importance of using more detailed microphysics scheme for better visibility predictions.