Fog over water, often seen as a misty layer clinging to the surface, primarily occurs due to a temperature difference between the air and the water.
How Steam Fog Forms
Steam fog, a common type of water fog, forms when cold air moves over warmer water. This process is explained simply:
- Warm water: The water body, such as a lake or ocean, retains heat, especially if the surrounding air is significantly cooler.
- Cold air: A mass of colder air moves across the warmer water.
- Evaporation and mixing: The warmer water evaporates, adding moisture to the air immediately above it. This moist air mixes with the colder air above.
- Cooling and condensation: The mixing process cools the moist air. When the air cools enough, its capacity to hold water vapor decreases, and the excess moisture condenses into tiny water droplets.
- Fog formation: These countless tiny water droplets scatter visible light, creating the appearance of fog. This fog often looks like wisps of smoke rising from the water's surface.
This process is particularly noticeable in autumn and early winter when cold air masses encounter relatively warmer bodies of water. The fog is often most dense near the water's surface, gradually thinning as it rises and mixes with the drier, less saturated air above.
