Abstract
Inclusion of surface drag produces an additional growth rate peak at Lx ≈ 1000 km, even if the curvature (d2ū/dZ2) of the basic zonal wind profile is not favorable and diabatic heating due to the liberation of latent heat not allowed for. The growth rate of this most unstable intermediate-scale wave increases with surface drag and decreases with internal friction. This wave has amplitude maxima near the surface and at about 1.5 km. A uniform friction at all depths does not produce a second growth rate peak, but it reduces the growth rate of the Eady-Charney mode.
