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15 January 2009: Lake Champlain Sea Smoke, Steam Devils, and Waterspouts
Exotic Whirls in Arctic Air
Overview | Images | Definitions | Weather Conditions | Historical Arctic Waterspouts
III. Definitions

Arctic Sea Smoke or Steam Fog develops when very cold (arctic) air moves across relatively warm, open water. Strong upward fluxes of latent heat from the water surface result in water vapor quickly condensing as it is mixed and cooled with the adjacent cold air. Since the air adjacent to the water surface is also convectively unstable, the arctic sea smoke or steam fog will be seen rising in turbulent plumes associated with shallow convective overturning of the very unstable air over the water (Lake Champlain in this case). Upon further upward mixing, the fog will eventually evaporate and dissipate in the dry arctic air, on the order of 10 meters above the water surface. As such, arctic sea smoke is a relatively shallow phenomenon.

waterspout NOAA file photo A waterspout (Figure III-1) is a narrow, rotating column of air that forms over water, and appears as a condensation funnel which extends from the water surface to a cumuliform cloud above. Formation typical requires a surface convergence line over the water, with some source of low-level rotation along the line that can be stretched vertically and strengthened by the convective cloud updraft itself. Waterspouts are generally of lesser intensity than a tornado, and similar to the strength of a dust devil. The formation mechanism is also thought to be similar to a class of weaker tornadoes observed over land referred to as landspouts. Waterspouts are most common in tropical environs (e.g., near the Florida Keys), but have been documented in arctic air masses. Unlike tornadoes - which typically develop with supercell thunderstorms - waterspouts are commonly observed from just modest lines of cumulus congestus clouds, as occurred over Lake Champlain on 15 January 2009.
Figure III-1. A mature tropical waterspout near the Florida Keys on 10 September 1969 (from the NOAA Photo Library).

A steam devil is similar in nature to a waterspout in arctic air. However, we might differentiate between a steam devil and waterspout by whether or not the condensation funnel is deep and strong enough to be attached to a convective cloud above. Deeper convective motions and vertical stretching extending from the water surface to the convective cloud base would generally result in a stronger, longer-lived feature (waterspout) as compared with a shallower, shorter-lived feature (steam devil). We might expect the vertical depth of a waterspout to be on the order of hundreds of meters, while the vertical extent of a steam devil is on the order of tens of meters.
Overview | Images | Definitions | Weather Conditions | Historical Arctic Waterspouts
Figure III-1. A mature tropical waterspout near the Florida Keys on 10 September 1969. (from the NOAA Photo Library).


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