Lessons from TIMED for Modeling the Wave Driven Equatorial Oscillations in the Middle Atmosphere

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3300 Atmospheric Processes, 3334 Middle Atmosphere Dynamics (0341, 0342), 3367 Theoretical Modeling, 3389 Tides And Planetary Waves

Scientific paper

By applying Hines' Doppler Spread Parameterization (DSP) for small-scale gravity waves (GW), the 3D Numerical Spectral Model (NSM) generates in the zonal mean (wave number m = 0) the quasi-biennial oscillation (QBO) and semi-annual oscillation (SAO), which dominate the zonal circulation at equatorial latitudes. As observed, the NSM reproduces these equatorial oscillations extending from the lower stratosphere into the upper mesosphere. Recent measurements with the SABER instrument on TIMED, analyzed to delineate the tides and variations in the zonal mean (Huang et al., Spring AGU 2005), produce temperature variations for the SAO that are significantly different from those predicted. While the modeled phase variations with altitude and latitude agree reasonably well with the observations, the NSM underestimates the amplitudes significantly. The model predictions were generated with a GW source independent of season and to a lesser extent with the planetary waves that are produced by instabilities. Numerical experiments show that the altitude for the GW source and its latitude dependence affect the SAO and QBO significantly. It is well known that, in principle, eastward propagating Kelvin waves and westward propagating Rossby gravity waves, due to convection at low latitudes, can generate the stratospheric QBO and SAO. The TIMED measurements are now teaching us that we must include these waves in the NSM to supplement the GWs that propagate in the east/west directions. Huang et al. produce for the zonal mean also the intra-seasonal temperature variations with periods between 2 to 4 months, and their characteristics and amplitudes are essentially reproduced in the NSM with the GWs that propagate in the north/south directions.

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