Definition: Steam devil: A small, gentle whirling column of saturated air of varying height, with a small diameter and an approximately vertical axis, that forms when cold air is over a relatively much warmer body of water or saturated surface.
Steam devils are typically seen in association with steam fog (Arctic sea smoke). The vortices are of the order of a metre in diameter and several metres high. They form over relatively warm bodies of water (or exceptionally over a saturated land surface) when the air near the ground is very unstable due to much colder air above. A steam devil has been observed over a frosty grass surface when the Sun is heating the ground.