Properties of QBO and SAO generated by gravity waves |
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| Institution: | 1. NASA Goddard Space Flight Center, Atmospheric Chemistry and Dynamics Branch, Mail Code 910.4, Greenbelt, MD 20771, USA;2. SM & A Corporation, Vienna, VA, USA;3. 212 Thia Court, Coatsville, PA, USA;4. Hong Kong University of Science and Technology, Hong Kong, China;5. Furman University, Greenville, SC, USA;1. Deutsches Zentrum für Luft- und Raumfahrt, Deutsches Fernerkundungsdatenzentrum, Oberpfaffenhofen, Germany;2. Umweltforschungsstation Schneefernerhaus, Zugspitze, Germany;3. Universität Augsburg, Institut für Physik, Augsburg, Germany;4. Applied Physics Laboratory, The Johns Hopkins University, Laurel, MD, USA;5. NASA Langley Research Center, Hampton, USA;6. Center for Atmospheric Sciences, Hampton, USA;1. Institut für Astro- und Teilchenphysik, Universität Innsbruck, Technikerstr. 25/8, 6020, Innsbruck, Austria;2. Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos, 0610, Antofagasta, Chile;3. Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077, Göttingen, Germany;4. Department of Astrophysics, University of Vienna, Türkenschanzstr. 17, 1180, Vienna, Austria;5. Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85748, Garching, Germany;1. Space Science Division, Naval Research Laboratory, Washington, DC, USA;2. Computational Physics, Inc., Springfield, VA, USA;3. Remote Sensing Division, Naval Research Laboratory, Washington, DC, USA;4. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA;1. Instituto de Astrofísica de Andalucía, CSIC, P.O. Box 3004, E-18080, Granada, Spain;2. Centre for Research in Earth and Space Science, York University, 4700 Keele St., Toronto, Ontario, M3J 1P3, Canada;1. National Atmospheric Research Laboratory, Gadanki, 517 112, Pakala Mandal, Chittoor District, India;2. Department of Meteorology and Oceanography, Andhra University, Visakhapatnam, 530003, India;1. Institute for Meteorology, Universität Leipzig, Stephanstr.3, 04103, Leipzig, Germany;2. Institute for Experimental Meteorology, Obninsk, Russia |
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| Abstract: | In this paper we present an extension for the 2D (zonal mean) version of our numerical spectral mode (NSM) that incorporates Hines’ Doppler spread parameterization (DSP) for small-scale gravity waves (GW). This model is applied to describe the seasonal variations and the semi-annual and quasi-biennial oscillations (SAO and QBO). Our earlier model reproduced the salient features of the mean zonal circulation in the middle atmosphere, including the QBO extension into the upper mesosphere inferred from UARS measurements. The model is extended to reproduce the upwelling at equatorial latitudes that is associated with the Brewer–Dobson circulation — which affects significantly the dynamics of the stratosphere as Dunkerton had pointed out. In the presence of GW, this upwelling is produced in our model with tropospheric heating, which generates also zonal jets outside the tropics similar to those observed. The resulting upward vertical winds increase the period of the QBO. To compensate for that, one needs to increase the eddy diffusivity and the GW momentum flux, bringing the latter closer to values recommended in the DSP. The QBO period in the model is 30 months (mo), which is conducive to synchronize this oscillation with the seasonal cycle of solar forcing. Associated with this QBO are interannual and interseasonal variations that become increasingly more important at higher altitudes — and this variability is interpreted in terms of GW filtering that effectively couples the dynamical components of the mesosphere. The computed temperature amplitudes for the SAO and QBO are in substantial agreement with observations at equatorial and extra-tropical latitudes. At high latitudes, however, the observed QBO amplitudes are significantly larger, which may be a signature of propagating planetary waves not included in the present model. The assumption of hydrostatic equilibrium not being imposed, we find that the effects from the vertical Coriolis force associated with the equatorial oscillations are large for the vertical winds and significant for the temperature variations even outside the tropics, but the effects are small for the zonal winds. |
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