Articles | Volume 21, issue 18
Atmos. Chem. Phys., 21, 13763–13795, 2021
https://doi.org/10.5194/acp-21-13763-2021
Atmos. Chem. Phys., 21, 13763–13795, 2021
https://doi.org/10.5194/acp-21-13763-2021

Research article 16 Sep 2021

Research article | 16 Sep 2021

The semiannual oscillation (SAO) in the tropical middle atmosphere and its gravity wave driving in reanalyses and satellite observations

Manfred Ern et al.

Data sets

The MLS Level 2 geopotential height product (version 4.2) NASA GES DISC https://acdisc.gesdisc.eosdis.nasa.gov/data/Aura_MLS_Level2/ML2GPH.004/

The MLS Level 2 temperature product (version 4.2) NASA GES DISC https://acdisc.gesdisc.eosdis.nasa.gov/data/Aura_MLS_Level2/ML2T.004/

The TIDI vector wind product (version 03.07a) NCAR HAO http://download.hao.ucar.edu/archive/tidi/data/vec0307a/

Operational global reanalysis: progress, future directions and synergies with NWP (https://apps.ecmwf.int/data-catalogues/era5/?class=ea) Hans Hersbach, Patricia de Rosnay, Bill Bell, Dinand Schepers, Adrian Simmons, Cornel Soci, Saleh Abdalla, Magdalena Alonso-Balmaseda, Gianpaolo Balsamo, Peter Bechtold, P. Berrisford, Jean-Raymond Bidlot, E. de Boisséson, Massimo Bonavita, P. Browne, Roberto Buizza, Per Dahlgren, Dick Dee, Rossana Dragani, Michail Diamantakis, Johannes Flemming, Richard Forbes, Alan J. Geer, Thomas Haiden, Elias Hólm, L. Haimberger, Robin Hogan, Andras Horányi, M. Janiskova, Patrick Laloyaux, Philippe Lopez, J. Munoz-Sabater, C. Peubey, Raluca Radu, David Richardson, Jean-Noël Thépaut, Frédéric Vitart, X. Yang, Ervin Zsótér, and Hao Zuo https://doi.org/10.21957/tkic6g3wm

The ERA-Interim reanalysis: configuration and performance of the data assimilation system (https://apps.ecmwf.int/archive-catalogue/?class=ei) D. P. Dee, S. M. Uppala, A. J. Simmons, P. Berrisford, P. Poli, S. Kobayashi, U. Andrae, M. A. Balmaseda, G. Balsamo, P. Bauer, P. Bechtold, A. C. M. Beljaars, L. van de Berg, J. Bidlot, N. Bormann, C. Delsol, R. Dragani, M. Fuentes, A. J. Geer, L. Haimberger, S. B. Healy, H. Hersbach, E. V. Hólm, L. Isaksen, P. Kållberg, M. Köhler, M. Matricardi, A. P. McNally, B. M. Monge-Sanz, J.-J. Morcrette, B.-K. Park, C. Peubey, P. de Rosnay, C. Tavolato, J.-N. Thépaut, and F. Vitart https://doi.org/10.1002/qj.828

MERRA-2 inst3_3d_asm_Nv: 3d, 3-Hourly, Instantaneous, Model-Level, Assimilation, Assimilated Meteorological Fields V5.12.4 Global Modeling and Assimilation Office (GMAO): https://doi.org/10.5067/WWQSXQ8IVFW8

MERRA-2 tavg3_3d_udt_Np: 3d, 3-Hourly, Time-Averaged, Pressure-Level, Assimilation, Wind Tendencies V5.12.4 Global Modeling and Assimilation Office (GMAO) https://doi.org/10.5067/CWV0G3PPPWFW

JRA-55: Japanese 55-year Reanalysis, Daily 3-Hourly and 6-Hourly Data Japan Meteorological Agency (JMA) https://doi.org/10.5065/D6HH6H41

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Short summary
Details of the driving of the semiannual oscillation (SAO) of the tropical winds in the middle atmosphere are still not known. We investigate the SAO and its driving by small-scale gravity waves (GWs) using satellite data and different reanalyses. In a large altitude range, GWs mainly drive the SAO westerlies, but in the upper mesosphere GWs seem to drive both SAO easterlies and westerlies. Reanalyses reproduce some features of the SAO but are limited by model-inherent damping at upper levels.
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