A katabatic wind is a type of drainage wind that carries high-density air from an elevated area down a slope toward a lower elevation. This atmospheric movement is driven by gravity acting on a cold, heavy air mass. Temperature differences are the primary cause of this meteorological phenomenon.
The Mechanism of Formation
The formation of a katabatic wind begins with the cooling of air over a high-elevation surface, such as a plateau or mountain slope. This cooling often occurs through radiative cooling, a process where the ground rapidly loses heat to the atmosphere, especially at night under clear skies. The air immediately in contact with this chilled surface also cools, causing it to become significantly denser than the surrounding atmosphere at the same altitude.
This cold, dense air is heavier than the warmer air below it and the surrounding air column. Gravity then pulls this heavy air mass downslope, causing it to flow down the gradient of the topography. This gravity-driven flow characterizes a true katabatic wind, distinguishing it from winds caused by large-scale pressure systems.
The speed of the resulting wind is influenced by the steepness of the slope and the magnitude of the temperature difference between the air mass and the surrounding environment. As the air flows downward, it can accelerate, and the flow is often concentrated and funneled by valleys or narrow canyons. This pooling of cold air can also lead to the formation of a temperature inversion in the valley below, where temperature increases with height instead of decreasing.
Geographic Settings and Global Occurrence
Katabatic winds occur where there is elevated terrain and conditions for significant cooling. The two most prominent settings for these winds are large, high-altitude ice sheets and deep alpine valleys. Over massive ice sheets, like those found in Greenland and Antarctica, the winds are strong and persistent.
The high-elevation ice plateau of Antarctica provides a constant source of intensely cold air. The gravitational potential energy stored in this cold, dense air drives sustained winds from the interior toward the coast. When this airflow is channeled through coastal gaps or valleys, the winds can reach hurricane-force speeds, sometimes exceeding 180 miles per hour.
In mountainous regions, such as the Alps or the Rocky Mountains, katabatic flows are typically part of a diurnal cycle known as a mountain breeze. The cold air drains down the slopes and accumulates in the valley bottoms after sunset. While generally gentler than polar flows, these nightly drainage winds are responsible for creating pockets of frost and significantly lowering temperatures in low-lying areas.
Differentiating Katabatic Winds from Other Downslope Flows
The direct opposite of a katabatic wind is an anabatic wind, which is an upslope flow of air. Anabatic winds form during the day when solar radiation warms the mountain slopes. This warming causes the air in contact with the slopes to become buoyant and flow upward.
Winds such as the Foehn or the Chinook are also downslope flows, but their driving mechanism is different. These winds are driven by large-scale pressure gradients, not solely by local cold-air drainage. As Foehn-type winds descend, they undergo adiabatic warming, arriving at the valley floor warm and often dry.
In contrast, katabatic winds, like the Bora in the Adriatic or the Mistral in France, are fundamentally cold when they reach the lower elevations. The Bora is a strong, cold wind descending from the mountains onto the Adriatic Sea. The Mistral blows down the Rhône Valley to the Mediterranean, driven by cold, dense air being pulled downslope by gravity.