Modeling Studes of the Interannual Variability of Large- Scale Waves and Circulation

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Abstract ATM-9526136 Tung, Ka Kit University of Washington Title: Modeling Studies of the International Variability of Large-Scale Waves and Circulation Previous NSF projects by the PI were concerned with (a) internal variability of the large- scale planetary waves in the extra-tropics, and (b) year-to-year variability of the extra-tropical waves and circulation caused by the equatorial QBO. In the current proposed project, the PI will model the extra-tropical stratosphere in response to (i) specified, variable, observed planetary wave amplitude at the tropopause for a 12-year period and (ii) the changing phase of the equatorial QBO in zonal wind. The numerical model containing the needed ingredients and mechanisms has already been built and tested by Kinnersley and has produced realistic climatology in waves and circulation and realisitic time-dependent evolution for planetary waves one, two and three for the one-year period May 1980 to April 1981. In the proposed project, the model will be run with the observed tropopause planetary wave forcing from 1980 to 1992. A second cause of year-to-year variability in the extratropical stratosphere, which is perhaps the more important one as far as irreversible mixing of tracers and forcing of mean circulation are concerned, is the effect of the phase of equatorial QBO on the propagation and location of breaking of planetary waves in the extra-tropical wave-guide. The mechanism was first proposed by Holton and Tan involving the location of zero-wind lines. A modified mechanism was proposed by the PI involving the effect of the equatorial QBO on the extra-tropical wave-guide for stationary waves, and the effect of the wave-guide changes on the breaking and mixing of the planetary waves. These mechanisms will be tested in the proposed project. To validate the hypothesis, the simulated result will be compared with observation. The comparison will involve zonal mean temperature and zonal wind, planetary wave amplitud es, and meridional circulation as inferred from the distribution of tracers. This research is important because it seeks to advance the understanding of long-term variability of weather- and climate- related atmospheric circulation features.