Left. Baroclinic enstrophy growth with thermal relaxation, where a gas parcel returns to the initial temperature on a timescale τ. A stable entropy gradient can only be maintained between the extremes of too fast a relaxation (isothermal behavior) and too slow a relaxation (adiabatic behavior). Optimal growth occurs when τ is comparable to the dynamical time. Right. Baroclinic enstrophy growth with thermal diffusion, where heat diffuses over a scale height on a timescale τ. Optimal growth occurs on longer timescales when compared to the thermal relaxation case.