The Influence of Meridionally Sloping Topography on Baroclinic Instability and Its Implications for Macroclimate

Abstract

The instability of two-level and two-layer quasi-geostrophic models containing zonally symmetric, meridionally sloping lower boundaries are discussed and compared. The influence of this topography is to reduce the eastward phase speed of the unstable waves and to lengthen the most unstable wave if the slope is upward toward the pole, and to increase the eastward phase speed of the unstable waves and to shorten the most unstable wave if the slope is upward toward the equator. The instability may be slightly enhanced or reduced for a very small slope depending on the model characteristics. For a sufficient slope, such as on the Antarctic Continent, the instability is curtailed. During the major ice ages in geological history, the ice field extended equatorward to the middle latitudes. Although the meridional temperature contrast (i.e., baroclinicity) is enhanced along the boundary of the ice field, the poleward slope of the ice field tends to diminish instability and the associated poleward transport of sensible heat is reduced or inhibited. However when the height of the mountains is a large portion of the total depth of the model, the winds at these places will be stronger. Hence the above conclusion should be viewed with caution.