A set of numerical simulations of the full Boussinesq equations including system rotation is carried out, in order to fully solve the problem of the origin of the k-5/3 mesoscale wave number energy spectra measured in the free atmosphere. In a companion paper (E. Lindborg, The energy cascade in a strongly stratified fluid, submitted to Journal of Fluid Mechanics, 2005, hereinafter referred to as Lindborg, submitted manuscript, 2005) it is shown that such a spectrum can arise as a result of a special type of forward energy cascade seen in the limit of strong stratification. In this letter we study the effect of rotation on such an energy cascade and show that it can prevail in the presence of system rotation as long as the Rossby number is above a critical value, which is determined to Rocrit ≈ 0.1.