Purpose:

to discover the underlying causes of super dense fog/smoke. Super-fog is a serious hazard to transportation.

Introduction

Forest and agricultural burning release chemical compounds and particulate matter into the atmosphere. Although most of this material contributes to visibility reductions through haze and provides chemical constituents available for reactions with other atmospheric pollutants, there are occasions when smoke is entrapped locally and combines with water vapor to produce zero visibility smoke/fog or super-fog. Super-fog threatens transportation when it drifts over roadways - a problem in the South, especially at night.

Solution

Simulating smoke movement at night is a complex, time-dependent problem. Wind shifts transport smoke to different locations at various times during the same night. Land management personnel charged with alerting the appropriate authorities of pending transportation hazards must know where and when smoke will arrive. Wind observations from nearby weather stations are often unreliable because of the local nature of night winds. Numerical modeling constraints imposed by forest managers are stringent. The models have to fit on laptop PC computers and run in faster-than-real-time, yet be able to model smoke on the terrain scales that the smoke "sees". Smoke can move through shallow gaps in ridges and down road and stream cuts. Therefore, the mesh size for the model can be as small as 30 meters, the minimum resolved grid distance in the digital elevation models (DEM) provided by the U.S. Geological Survey. The speed requirements for this very fine mesh model are atteined by minimizing the number of computations. The mathematics must be simple and the physical terms describing complex processes must be simplified or replaced with empirical terms.