HORIZONTAL BUOYANCY FLUX OF INTERNAL GRAVITY-WAVES IN VERTICAL SHEAR

The equations of motion describing two-dimensional internal gravity wa ves were analyzed to derive an expression for the horizontal buoyancy flux-i.e., the correlation between buoyancy (or temperature) and horiz ontal velocity-in various cases involving vertical shear. It is shown that, although this correlation vanishes at zeroth order for a single wave, its first order contribution is nonzero due to shear, even for s teady, conservative, incompressible waves. Departures from steady, con servative motion or quasi-compressibility also cause a nonzero correla tion. Several cases were analyzed and some numerical results obtained for waves approaching a critical layer of reduced intrinsic phase spee d. With weak shear, the buoyancy flux is small relative to vertical mo mentum flux, as expected from the perturbation theory. Strong vertical shear enhances the buoyancy flux within the shear zone and causes par tial reflection beneath, producing a nonzero correlation (at zeroth or der) in this region. These effects may explain recent observations of zonal wind and temperature cospectra in the equatorial lower stratosph ere.