QBO Generated Inter-annual Variations of the Diurnal Tide in the Mesosphere

Details QBO Generated Inter-annual Variations of the Diurnal Tide in the Mesosphere QBO Generated Inter-annual Variations of the Diurnal Tide in the Mesosphere

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmsa41a1044m&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #SA41A-1044

Other

3332 Mesospheric Dynamics, 3334 Middle Atmosphere Dynamics (0341, 0342), 3337 Numerical Modeling And Data Assimilation, 3367 Theoretical Modeling, 3384 Waves And Tides

Scientific paper

In preparation for the measurements from the TIMED mission, we report results from a study with the Numerical Spectral Model (NSM), which produces in the diurnal tide significant inter-annual variations. Applying Hines' Doppler Spread Parameterization (DPS), small-scale gravity waves (GW) drive the Quasi-biennial Oscillation (QBO) and Semi-annual Oscillation (SAO). With a GW source that peaks at the equator and is taken to be isotropic and independent of season, the NSM generates a QBO with variable periods around 27 months and zonal wind amplitudes close to 20 m/s at 30 km. As reported earlier, the NSM reproduces the observed equinoctial maxima in the diurnal tide at altitudes around 95 km. In the present paper it is shown that the QBO modulates the tide such that the seasonal amplitude maxima can vary from one year to another by as much as 30%. Since the period of the QBO is variable, its phase relative to the seasonal cycle changes. The magnitude of the QBO modulation of the tide thus varies considerably as our long-term model simulation shows. To shed light on the underlying mechanisms, we discuss (a) the relative importance of the linearized advection terms that involve the meridional and vertical winds of the diurnal tide and (b) the effects of momentum deposition from GWs filtered by the QBO zonal winds.

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