Waves and Instabilities of the Midlatitude Atmosphere: An Observational Analysis using Potential Vorticity

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9313785 Emanuel One and two day forecasts of weather in the midlatitudes at the synoptic-scale and greater are highly accurate, and longer- range forecasts simulate the general behavior, if not the details, of the atmosphere. Despite this, the dynamics of synoptic-scale waves and instabilities are not altogether well understood. Moreover, synoptic-scale waves and instabilities are yet to be parameterized as in terms of planetary-scale processes, even though there is evidence that these waves are in a state of statistical quasi-equilibrium with the planetary waves on time scales longer than a few weeks. This research effort involves two related objectives which are directed at improving our understanding of the dynamical processes involved in baroclinic situations. The first is to deduce a mathematical expression of an effective refractive index for Rossby waves using balance approximations of order higher than quasi- geostrophy. The second is to develop and apply a methodology for calculating climatological distributions of this effective refractive index (a function of potential vorticity) from observations, not a straight-forward task given the extremely inhomogeneous distributions potential vorticity in the real atmosphere. Once these are determined, the PIs can better understand the wave propagation characteristics in the atmosphere. Their intention is to apply their results to the study of atmospheric blocking events and low-frequency variability. ***