APPLICATION OF BRETHERTONS INTERPRETATION OF BAROCLINIC INSTABILITY IN THE PRESENCE OF HORIZONTAL SHEAR AND COMPRESSIBILITY

The stability of a non-Boussinesq-Eady model [Eady, E.T., 1949. Long w aves and cyclone waves, Tellus 1, 33-52.] with constant horizontal mer idional shear in a middle latitude channel is considered. The effects of compressibility and meridional shear can be interpreted in terms of sloping north-south boundaries in an otherwise Boussinesq-Eady proble m. The focus is on the physical interpretation of these effects in a h ighly truncated two meridional mode solution, It is found that near th e short-wave cutoff of Eady, the compressibility and the meridional sh ear contribute to an effective channel depth which reduces the penetra tion depth required for instability and these mechanisms therefore ten d to destabilize the flow. Yet, compressibility provides a stabilizati on by attenuating the edge wave's phase speeds which disrupts the phas e relationships required to maintain instability. The implications of these mechanisms for deep non-Boussinesq planetary atmospheres are dis cussed. (C) 1997 Elsevier Science B.V.