Katabatic wind

Katabatic comes from a Greek word meaning descending. In meteorology it generally refers to air flowing downhill because cooling near a slope makes it denser than air at the same height farther away. Gravity then drives the denser air downslope, with local terrain guiding its path. This mechanism differs from anabatic flow, in which sun-warmed air rises along a slope. Meteorological literature has sometimes used katabatic broadly for any downslope wind, so precise usage identifies the cooling and density contrast involved.

Over many land regions, slopes cool after sunset. Air in contact with the chilled surface becomes colder than air above the nearby valley and drains downslope, often collecting in low areas. Such flows are commonly nocturnal and generally modest in speed, although terrain and weather conditions vary. The Royal Meteorological Society's educational resource notes that snow- or ice-covered terrain can support katabatic winds at other times as well, and narrow valleys may intensify flow through channeling.

Antarctica provides a large-scale setting for katabatic flow. The elevated ice-sheet interior cools the air near its surface; cold, dense air can drain down the ice slopes toward the coast. The continent's topography strongly organizes low-level wind directions, and valleys or other terrain features can concentrate flow. At coastal sites, however, observed winds may combine katabatic forcing with larger-scale pressure systems. Researchers caution that wind direction or a surface temperature change alone may not reliably identify a katabatic episode.

By transporting cold air downslope, katabatic winds influence local weather and the exchange of air between high ground and valleys or coasts. They can redistribute loose snow and affect where snow accumulates; USGS describes accounting for such wind effects in studies of snowfall in Antarctica's McMurdo Dry Valleys. Their strength and impacts depend on the slope, cooling, surface conditions, atmospheric structure and channeling, so a single speed or daily pattern does not apply everywhere.