FAA Aircraft Dispatcher (ADX)MeteorologyHard
A dispatcher reviewing conditions over an open bay near a cold airport observes wisps of fog rising directly off the water surface on a clear, calm, very cold morning. The water temperature is much warmer than the overlying air. This type of fog is best classified as:
- ARadiation fog
- BSteam fog (evaporation fog)
- CUpslope fog
- DAdvection fog
Show answer & explanationAnswer & explanation
Correct answer: B. Steam fog (evaporation fog)
Steam fog, also called evaporation fog or arctic sea smoke, forms when cold air moves over much warmer water, causing rapid evaporation that quickly saturates the cold air directly above the surface, producing rising wisps of fog.
Why the other options are wrong
- A. Radiation fog forms over land from nighttime radiational cooling, not over open water.
- C. Upslope fog forms from moist stable air being forced up rising terrain, unrelated to this water-based process.
- D. Advection fog forms from warm moist air moving horizontally over a colder surface, the reverse temperature relationship.
Steam Fog (Arctic Sea Smoke)
Fog formed when cold air moves over significantly warmer water, causing evaporation that saturates the air directly above the surface and produces visible rising wisps.
- Requires cold air over much warmer water
- Common in polar and high-latitude regions in fall/winter
- Can contribute to icing and low-level instability near the surface
Memory trick: Steam fog: warm water 'sweats' into cold air like a hot cup of coffee.