Freezing fog formation in a supercooled boundary layer solving the winter fog forcasting challenge for Elmendorf Air Force Base, Alaska

摘要

We have examined four complex freezing fog events at Elmendorf Air Force Base, Alaska, to determine the root cause of the fog. These events have drastically impacted operations in the region for years, and are still a mystery to forecasters. The primary goal was to provide a detailed analysis of conditions within the boundary layer that contributed to freezing fog formation within the supercooled liquid water boundary layer. The data sets used to accomplish this goal were surface observations, upper air soundings, satellite images and water level data. In the end, the fog was identified to be the result of moisture flux at the surface during high tide, which interacts with cold air from valleys northeast of the base. The interaction causes spontaneous condensation, and fog drains towards the base due to thermal gradients established from differential cooling from diurnal radiative properties. A correlation exists between water levels and moisture flux, which is strong enough that forecasters should focus on water level data and wind speed and direction. Armed with this knowledge, the Air Force and the Department of Defense will reap the benefits of much more timely and accurate fog forecasts.