Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa51b..06o&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SA51B-06
Physics
3332 Mesospheric Dynamics
Scientific paper
It is commonly believed that the seasonal variability in the tides is driven by seasonal variability in gravity wave effects on the tides. This study focuses on the nature of the three-way interaction of the tides, mean flow, and the gravity wave drag resulting from gravity wave breaking. First, the effects of the combined tide and mean flow on the characteristics of gravity wave propagation and breaking are examined using the gravity-wave drag parameterization of Alexander and Dunkerton. We characterize the vertical profile of gravity wave drag in terms of an complex effective Rayleigh friction coefficient (ERFC) that describes both the amplitude and phase of the gravity wave drag relative to the tidal oscillation of the winds. The ERFC depends on the gravity wave spectrum, the tidal profile structure and the mean wind. It is found that with weak mean winds, the gravity wave drag acts almost exactly out of phase with the tide, but the phase can be significantly modified by the presence of strong mean winds. Next, the effect of mean winds and damping with a compex Rayleigh friction on the global structure of the diurnal tide is examined. The tidal equations are solved in terms of generalized Hough functions. The pure imaginary component of the complex ERFC acts similar to a change in forcing frequency, and therefore affects both the latitudinal structure of the tide as well as the vertical wavelength (as reflected in Lamb's parameter). Mean winds also have a large effect on the structure of the tidal wind components. Although the Doppler shift produces only a minor change in the structure of the Hough function solution (i.e. the tidal temperature field), there are still significant changes in the polarization relations between the wind and temperature fields that can result from horizontal mean-wind shear. We conclude with a discussion of which of these aspects of the gravity wave/mean flow/tidal interaction are important for understanding the seasonal variability of the tides.
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