CONDITIONAL CONVECTIVE HEATING IN A BAROCLINIC ATMOSPHERE - A MODEL OF CONVECTIVE FRONTOGENESIS

It is shown here that there exists a regime of balanced frontogenesis that is forced almost entirely by the diabatic heating due to convecti on at a front. This theory is explored in the context of the two-dimen sional semigeostrophic equations with an Eady basic state: convection is parameterized to be dependent on the low-level moisture convergence of the cross-frontal ageostrophic flow, in accordance with recent dia gnostic studies. The significant result is that the growth rate of the convective frontal system becomes independent of the total wavelength of the domain once the diabatic heating exceeds a relatively large th reshold magnitude. In this regime the frontal zone has a width and str ucture dependent on the heating magnitude but not on the wavelength. T he system is described as ''solitary'' or ''isolated'' since the dynam ics are self-contained and independent of the far field. The energetic s of the system have a diabatic conversion that is an order of magnitu de greater than that due to the large-scale alongfront temperature gra dient. The large-scale forcing is, however, necessary as a catalyst in maintaining a weak ageostrophic convergence that allows the convectiv e heating to be triggered. The constraint of alongfront geostrophic ba lance means that convective forcing alone cannot maintain frontogenesi s. It is suggested that the dynamics exhibited by the convectively dom inated front may also be important in the study of midlatitude squall lines. The propagation and dynamics of the front are interpreted in te rms of the notion of a ''diabatic Rossby wave.''