Synoptic scale meteorology

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A schematic showing a synoptic-scale mid-latitude depression over the United States.

The synoptic scale in meteorology (also known as large scale or cyclonic scale) is a horizontal length scale of the order of 1000 kilometres (about 620 miles) or more [1]. This corresponds to a horizontal scale typical of mid-latitude depressions. Most high and low pressure areas seen on weather maps are synoptic-scale systems. The word synoptic is derived from the Greek word sunoptikos meaning seen together.

The Navier-Stokes equations applied to atmospheric motion can be simplified by scale analysis in the synoptic scale. It can be shown that main terms in horizontal equations are Coriolis force and pressure gradient terms; therefore, one can use geostrophic approximation. In vertical coordinate momentum equation simplifies to hydrostatic equilibrium equation.