# Inertial flow

From AMS Glossary

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## inertial flow

Flow in the absence of external forces; in meteorology, frictionless flow in a geopotential surface in which there is no pressure gradient.

The centrifugal and Coriolis accelerations must therefore be equal and opposite, and the constant inertial wind speed where

*V*_{i}is given by*f*is the Coriolis parameter and*R*the radius of curvature of the path. The inertial path is anticyclonic in both hemispheres, more strongly curved near the poles than near the equator, resembling a series of similar loops called inertial circles. The inertial frequency with which these loops are described by the parcel is approximately equal to*f*/2π = 2 sinφ per sidereal day, where φ is the latitude. All the loops are bounded on the north and south by the same parallels of latitude, but the parcel has a net longitudinal movement as it describes them. The inertial period (the reciprocal of inertial frequency) is just one-half pendulum day.