How to Calculate the Geostrophic Wind Using ‘Real’ Data Geostrophic Wind Eqns. As you know from class, geostrophy represents an exact balance between the pressure gradient force (PGF) and the Coriolis force (f; units of 1/s). In equations (1), the PGF is represented by the horizontal partial derivative of the geopotential. (1) In practice, the horizontal partial derivates in (1) can be represented by the change in height (z) over the horizontal distance (latitude for y; longitude for x) on a constant pressure map. (2) Coriolis Force (f) ϕ = latitude and Ω is the angular velocity of the Earth’s rotation Useful #’s: 0.5 m/s = 1 knot; 1 degree of latitude = 111 km; g = gravity = 9.8 m/s2

Fig. 1: 500 hPa Heights, Wind Vectors (knots) B C

Fig. 2 700 hPa Heights 250hPa Heights X X X X