anabatic wind

A local upslope wind which develops best in a valley. During the day the air in contact with the valley sides is heated to a greater degree than air at the same elevation but above the valley floor. This leads to convectional rising of the heated air, and a circulation pattern of upslope airflow from valley floor to ridge, to replace rising air. Windspeeds of 10–15 m/32–50 ft per second can occur.

An anabatic wind, from the Greek anabatos, verbal of anabainein meaning moving upward, is a wind which blows up a steep slope or mountain side. Air at a similar altitude over an adjacent valley or plain does not get warmed so much because of the greater distance to the ground below it.

The air over the hill top is now warmer than the air at a similar altitude around it and will rise through convection. This creates a lower pressure region into which the air at the bottom of the slope flows, causing the wind. It is common for the air rising from the tops of large mountains to reach a height where it cools adiabatically to below its dew point and forms cumulus clouds.

Katabatic winds are down-slope winds, frequently produced at night by the opposite effect, the air near to the ground losing heat to it faster than air at a similar altitude over adjacent low-lying land.