Mesoscale Dynamical Regimes in the Midlatitudes

The atmospheric mesoscales are characterized by a complex variety of meteorological phenomena that defy simple classification. Here a full space‐time spectral analysis is carried out, based on a 7 day convection‐permitting simulation of springtime midlatitude weather on a large domain. The kinetic energy is largest at synoptic scales, and on the mesoscale it is largely confined to an “advective band” where space and time scales are related by a constant of proportionality which corresponds to a velocity scale of about 10 m s−1. Computing the relative magnitude of different terms in the governing equations allows the identification of five dynamical regimes. These are tentatively identified as quasi‐geostrophic flow, propagating gravity waves, stationary gravity waves related to orography, acoustic modes, and a weak temperature gradient regime, where vertical motions are forced by diabatic heating. Key Points The space and time scales of atmospheric mesoscale motions are related by an advective scaling Five dynamical regimes are identified, based on dominant physical processes Vertical motions can be roughly approximated using a weak temperature gradient balance