That is, the contour pattern reveals the "hills" and valleys" of the constant-pressure surface.

• Describe the topography of upper-air constant-pressure surfaces based on height contours, including the identification of Highs, Lows, ridges, and troughs.

Later models substituted the geometric coordinate with a pressure coordinate system, in which the geopotential heights of constant-pressure surfaces become dependent variables, greatly simplifying the primitive equations.

Ridges are topographic crests, usually pointing northward, and troughs are elongated depressions, usually pointing southward, on constant-pressure surfaces in the Northern Hemisphere.

In meteorology, a barotropic atmosphere is one in which the density depends only on pressure, so that isobaric surfaces (constant-pressure surfaces) are also isopycnic surfaces (constant-density surfaces).

This allowed for the validation of the assimilation algorithm without revisiting all the elements of the data pre-processing (such as radiosondes, surface reports, satellite temperature retrievals, etc.) The analysis was carried out on the 16 constant-pressure surfaces of the OI, with a similar representation of the short-range forecast error statistics.