Sea smoke, also known as steam fog or arctic sea smoke, occurs when a mass of extremely cold, dry air moves over a body of significantly warmer water. The visual effect is a low-lying, wispy layer of mist that appears to rise from the surface like smoke or steam. The formation of this unique fog is a direct result of the intense temperature gradient between the water and the overlaying atmosphere.
The Science of Formation
The process of sea smoke creation begins with the evaporation of water from the relatively warm surface. Because the water is much warmer than the air above it, a thin layer of air immediately above the surface becomes heated and rapidly saturated with water vapor.
This warm, highly saturated air then rises and mixes turbulently with the frigid, dry air mass that is moving across the water. The cold air has a much lower capacity to hold water vapor than the air at the surface. When the two air masses mix, the combined temperature instantly drops below the dew point of the mixture.
This rapid cooling causes the excess water vapor to condense into countless tiny liquid droplets. The resulting fog is confined to the shallow layer of air near the water, often looking like the “steam” rising from a hot drink. The water itself is the source of the moisture that forms the fog.
Necessary Conditions and Geography
A large temperature differential between the air and the water is the primary requirement for sea smoke to develop. For a noticeable fog to form, the air temperature needs to be at least 10°C to 15°C colder than the water’s surface temperature. During extreme cold snaps, this difference can easily exceed 20°C, leading to a denser display.
This phenomenon is most common in high-latitude regions, such as the Arctic and Antarctic, where very cold air masses regularly sweep over unfrozen ocean patches. However, it can also be seen in temperate climates during severe cold outbreaks, notably over the Great Lakes, the Gulf of Maine, and the St. Lawrence Seaway. The resulting fog typically forms as shallow, vertical columns that rarely rise more than a few meters above the water surface.
Sea Smoke Versus Other Fog Types
Sea smoke belongs to a category known as evaporation fog or steam fog, which distinguishes it from the two most common types of fog: advection fog and radiation fog. The main difference lies in the source of cooling that leads to condensation. Sea smoke forms because the air is cooled from the bottom up by mixing with the frigid air above it, and moisture is added from the warm water below.
Advection Fog
Advection fog forms when warm, moist air moves horizontally over a cold surface, such as cold ocean currents or snow-covered ground. The air itself is cooled to its dew point by the cold surface beneath it, causing condensation.
Radiation Fog
Radiation fog typically forms over land on clear, calm nights. It is created when the ground cools the air from the bottom down through the emission of infrared energy.
Sea smoke requires the water to be warmer than the air, rather than the air cooling down over a cold surface. The atmospheric instability created by warm air rising into cold air causes the characteristic turbulent, wispy appearance of sea smoke. This is in contrast to advection fog, which often involves a more stable atmosphere.