The Role of Unbalanced Motion in the Upper Troposphere and Stratosphere

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9903514Dunkerton, NWRA"The Role of Unbalanced Motion in the Upper Troposphere and Stratosphere" The unbalanced component of motion - consisting of gravity waves, inertial instabilities and forced circulations - is essential to the evolution of large-scale balanced flow in the atmosphere. The principal investigator and colleagues will examine several aspects of unbalanced dynamics relevant to the tropical troposphere, stratosphere, and mesosphere as well as the extratropical upper troposphere and stratosphere in an attempt to understand how these unbalanced motions are produced. The PI will examine:(1) the stability of the near-equatorial Rossby-wave critical layer to unbalanced flow instabilities, including inertial and divergent barotropic instability. Local instabilities occur as planetary Rossby waves from midlatitudes draw anomalous potential vorticity (PV) into the winter hemisphere while setting up a reversed meridional gradient of PV. The structure and growth rate of local instabilities will be explored for realistic distributions of potential vorticity.(2) the role of gravity waves in the quasi-biennial and semiannual oscillations. The PI will use a new parameterization for gravity wave induced force for this study, and a diagnostic measure of gravity wave momentum flux in mean vertical shear will be extended to equatorially trapped modes. (3) the effect of body forces on the Hadley circulations. (4) the excitation of inertia-gravity waves (IGWs) in an idealized baroclinic lifecycle using a numerical model in which type of baroclinic instability is varied over a wider range of lifecycles. (5) the nature of observed shallow disturbances near the jetstream. Observations from the Middle and Upper Atmosphere (MU) radar and Japanese rawinsonde observations of velocity layers will be analyzed in a collaborative study with Dr. Kaoru Sato of Kyoto University. (6) the role of inertia-gravity waves in transport near the tropopause. This also will be done in collaboration with Dr. Sato and will use simulations from a high-resolution general circulation model.