Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa33a0269m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SA33A-0269
Physics
3332 Mesospheric Dynamics, 3334 Middle Atmosphere Dynamics (0341, 0342), 3367 Theoretical Modeling, 3384 Acoustic-Gravity Waves, 3389 Tides And Planetary Waves
Scientific paper
An empirical analysis of temperature measurements from the SABER instrument on the TIMED spacecraft, which delineates the zonal mean and diurnal variations, reveals a pronounced QBO extending from the stratosphere into the upper mesosphere [Huang et al., Ann. Geophys. 2006]. In the equatorial stratosphere the QBO propagates downward with a velocity of about 1.3 km/months, consistent with the observed zonal wind oscillations. In the mesosphere rapid phase reversals occur similar to those characteristic of the SAO. The QBO and SAO temperature variations peak near the equator, but then increase again towards mid latitudes. By applying Hines' Doppler Spread Parameterization for small-scale gravity waves (GW), the Numerical Spectral Model (NSM) can describe the QBO and SAO in the middle atmosphere. Along with the SAO, a mesospheric QBO was predicted with the 2D version of the NSM [Mengel et al., GRL, 1995] and was observed in the UARS wind measurements [Burrage et al., JGR, 1996]. A comparison between the TIMED measurements and the 3D version of the NSM however shows that the model cannot adequately simulate the observations. In the stratosphere, the QBO and SAO amplitudes are not much smaller than those observed, and the rate of downward propagation around the equator is reproduced. In the mesosphere, however, the modeled amplitudes are significantly smaller. Modeling experiments show that, compared with the 2D version, the 3D amplitudes for the QBO and SAO decrease at higher altitudes in the mesosphere. The waves that force the oscillations share the momentum in 3D with tides and planetary waves whose amplitudes grow with height. Compared to 2D, less wave momentum is thus available in 3D to generate the zonal-mean oscillations at higher altitudes. We are now have supplementing the GW source in the NSM with observed eastward propagating Kelvin waves and westward propagating Rossby gravity waves, which were originally invoked to generate the stratospheric QBO [Lindzen and Holton, 1968]. Several studies [e.g., Hamilton et al., JAS, 1995] found that these planetary waves alone cannot generate the stratospheric QBO. Our modeling experiments, however, show that even a modest GW source, isotropic to first order, can coax the planetary waves into generating the QBO. With the additional wave forcing we expect that the model can be improved sufficiently to simulate also the mesospheric QBO and SAO. With larger wave forcing in the stratosphere, the GW filtering will become more pronounced to produce the rapid phase reversals observed in the mesosphere. Our results show that in the mesosphere, generated in part by the meridional circulation, the temperature variations for the QBO and SAO extend with enhanced amplitudes to the poles. QBO-related temperature variations up to 10 K could be generated around 85 km altitude and thus produce inter-annual variations in the Polar Mesospheric Clouds (PMC) that will be studied with the forthcoming Aeronomy of Ice in the Mesosphere (AIM) mission.
Huang Fang
Mayr Hans
Mengel J. J.
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