In mountain meteorology, an upslope wind driven by heating (usually daytime insolation) at the slope surface under fair-weather conditions. The mechanism of the anabatic wind can be described as follows. The warm surface heats a vertical column of the atmosphere starting at the slope surface and reaching up to a few hundred meters deep. This column is warmer than the column at the same levels over the valley or plain, resulting in hydrostatic low pressure over the slope relative to over the valley or plain. The horizontal pressure gradient, maximized at the slope surface, drives an acceleration directed toward the slope, or up the slope. Although the pressure-gradient forcing is at its maximum at the slope, surface friction causes the peak in the anabatic wind speeds to occur above the surface, often by several tens of meters; if the surface heating is strong, however, the momentum will tend to be vertically mixed. Speeds in the mountain–valley anabatic flow layer are often 3–5 m s−1. Because heating at the surface promotes deeper mixing than cooling does, the heated layer, often occurring as a convective or mixed layer, is generally deeper than a cooled or katabatic layer. Slopes occur on many scales, and consequently anabatic flows also occur on many scales. At local scales anabatic winds are an along-slope component of mountain–valley wind systems. At scales ranging from the slopes of individual hills and mountains to the slopes of mountain ranges and massifs, anabatic flows represent the daytime component of mountain–plains wind systems. In general usage, this term does not suffer from the multiplicity of meanings that katabatic wind does.