The variability of the mean-flow of the equatorial middle atmosphere is dominated by the quasi-biennial and semiannual oscillations (QBO and SAO). Dr. Dunkerton will continue his investigation of the dynamics of these oscillations, emphasizing the theory of nonlinear mean meridional circulations in the middle atmosphere, their effect on the east and west phases of SAO and QBO, the effect of localized aerosol heating in the tropics (e.g., the circulation changes which result from volcanic eruptions like Mt. Pinatubo) and mechanisms of coupling the QBO to the high- latitude polar vortex. The stability of equatorial Rossby-wave critical layers will be investigated, focussing on the role of equatorial inertial instabilities on a nonparallel basic state distorted by Rossby waves from midlatitudes. Excitation and propagation of equatorial waves in the tropical troposphere will also be addressed. This research is important not only for basic understanding of the structure and dynamics of the middle atmosphere, but also for understanding short-term climate variability.
