Convective and dynamical instabilities due to gravity wave motions in the lower and middle atmosphere: Theory and observations

Dynamical and convective instabilities are two mechanisms that contribute significantly to the dissipation of larger‐scale motions and the generation of turbulence in the middle atmosphere. The former are normally due to enhanced velocity shears and/or a local minimum of the static stability either in the mean flow or associated with low‐frequency wave motions. The most common dynamical instability is the Kelvin‐Helmholtz (KH) instability which is often manifested in the atmosphere as a series of KH billows. Convective instabilities occur where the lapse rate becomes superadiabatic through the action of gravity waves and appear to predominate for high‐frequency wave motions. This paper reviews the theory and the observational evidence for both types of instabilities in the lower and middle atmosphere.