Abstract
The stability analysis of a hyperbolic tangent velocity profile in an isothermal atmosphere In the presence of the ground is presented. It is shown that such a system has a number of modes in addition to the one studied by Drazin and that unstable waves can he excited, for finite values of some minimum Richardson number of the flow, even in the limit of horizontal wavelengths going to infinity. Some of the unstable waves belonging to these new modes are able to propagate energy and momentum away from the shear zone and may therefore play an important role in microscale flow dynamics and in coupling of small-scale phenomena to mesoscale flow motions.
