Baroclinic instability in an inviscid fluid with parabolic potential temperature profiles is investigated. Unlike the classical Eady model, there is no short wave cutoff. In addtion to the longwave disturbances, which are similar to the Eady waves, shortwave disturbances can also develop in the lower atmosphere, where the stratification is weaker. The growth rate of the short waves increases with increasing stratification aloft. The results show that shortwave disturbances can penetrate into the upper stable layer. The growth rate and disturbances of those waves may be associated with an effective Burger number, which is defined as where h* is the height of the maximum vertical heat ux (w101) and A is the horizontal wavelength.
Numerical simulations obtained from a nonlinear mesoscale model in Part II also con rm that the short waves can develop into a sur­ ce front within a few days. Those short waves may correspond to the medium-scale disturbances observed over the AMTEX (Air Mass Transformation EXperiment) regio.