Geostrophic wind scale

From Glossary of Meteorology



geostrophic wind scale

A graphical device used for the determination of the speed of the geostrophic wind from the isobar or contour-line spacing on a synoptic chart.

It is a nomogram representing solutions of the geostrophic wind equation:
ams2001glos-Ge31
where geopotential height is the vertical coordinate; or
ams2001glos-Ge32
where atmospheric pressure is the vertical coordinate. In the above equations, Vg is the speed of the geostrophic wind, ρ the density of the air, f the Coriolis parameter, p the pressure at a fixed geopotential height, z the height of a constant-pressure surface, and n horizontal distance measured normal to the flow. The n axis is directed to the right of the flow in the Northern Hemisphere and to the left of the flow in the Southern Hemisphere. In the nomogram, standard values of ρ or g are usually adopted. The gradient of pressure or height is approximated by the finite difference ratio, Δpn or Δzn, in which a standard difference in pressure or height is adopted; Δn then represents the normal distance between isobars or contour lines drawn. The nomogram often utilizes Δn as the abscissa and the latitude as ordinate, so that the speed of the geostrophic wind may be read from a family of lines of the graph.


Copyright 2024 American Meteorological Society (AMS). For permission to reuse any portion of this work, please contact permissions@ametsoc.org. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act (17 U.S. Code § 107) or that satisfies the conditions specified in Section 108 of the U.S.Copyright Act (17 USC § 108) does not require AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a website or in a searchable database, or other uses of this material, except as exempted by the above statement, require written permission or a license from AMS. Additional details are provided in the AMS Copyright Policy statement.