Painegradienttivoima

Painegradienttivoima (pressure gradient force) is the force exerted on air by spatial variations in atmospheric pressure. It acts horizontally, from regions of higher pressure toward regions of lower pressure, causing an air parcel to accelerate as it moves down the pressure gradient.

Mathematically, for a gas with density ρ, the horizontal acceleration due to this force is a = -(1/ρ) ∇p_h, where ∇p_h is the horizontal pressure gradient. The strength grows with the pressure change over distance: a ≈ -(Δp)/(ρ Δx). On weather maps, closely spaced isobars indicate a large horizontal pressure gradient and a strong Painegradienttivoima, while widely spaced isobars indicate a weak one.

In the free atmosphere, the Painegradienttivoima is typically balanced by the Coriolis force, leading to geostrophic wind, described conceptually by f k × v_g ≈ (1/ρ) ∇p. The result is wind that tends to flow parallel to isobars. Near the Earth's surface, friction reduces the atmospheric rotation and causes winds to cross isobars, accelerating toward lower pressure.

Painegradienttivoima arises from spatial variations in atmospheric pressure caused by temperature contrasts, humidity, fronts, and topography, among other factors. It is a fundamental component of the momentum equation in meteorology and, together with other forces, drives much of the large-scale and regional wind patterns observed in the atmosphere.