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Ann. Geophys., 15, 1176-1186, 1997
www.ann-geophys.net/15/1176/1997/
© European Geosciences Union 1997
Diurnal tidal variability in the upper mesosphere and lower thermosphere
M. E. Hagan1, C. McLandress2, and J. M. Forbes3
1National Center for Atmospheric Research, High Altitude Observatory, Boulder, Colorado, USA
2Institute for Space and Terrestrial Science, North York, Ontario, Canada
3Department of Aerospace Engineering Sciences, University of Colorado, Boulder, USA
Abstract. We explore tropospheric latent heat release
as a source of variability of the diurnal tide in the mesosphere and lower
thermosphere (MLT) in two ways. First, we present analyses of the UARS WINDII
horizontal wind data, which reveal signatures of nonmigrating tidal effects as
large as 25 m/s during both vernal equinox and boreal winter. These effects are
of greater relative importance during the latter season. Complementary
global-scale wave model (GSWM) results which account for a tropospheric latent
heat source generally underestimate the observed nonmigrating tidal effects but
capture the seasonal variability that is observed. Second, we pursue a new
parameterization scheme to investigate seasonal variability of the migrating
diurnal tidal component of the latent heat source with GSWM. These results
confirm previously reported seasonal trends, but suggest that the MLT effects
may be as much as an order of magnitude larger than earlier predictions.
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