Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model |
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| Authors: | Bodil Karlsson Charles McLandress Theodore G Shepherd |
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| Institution: | 1. Department of Meteorology, Stockholm University, Svante Arrhenius väg 12, 106 91 Stockholm, Sweden;2. Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON, Canada M5S 1A7;1. University of Alaska, Fairbanks, USA;2. Virginia Polytechnic Institute and State University, Blacksburg, USA;3. University of Rostock, Kuehlungsborn, Germany;4. University of Rostock, Kuehlungsborn, Germany;5. University of Colorado, Boulder, USA;1. Institute of Physics, Ernst-Moritz-Arndt-University of Greifswald, Felix-Hausdorff-Str. 6, 17489 Greifswald, Germany;2. GATS Inc., Driggs, ID83422, USA;3. Formerly Institute of Physics, Ernst-Moritz-Arndt-University of Greifswald, Germany;1. Institute of Physics, Ernst-Moritz-Arndt-University of Greifswald, Felix-Hausdorff-Str. 6, 17489 Greifswald, Germany;2. Institute of Environmental Physics, University of Bremen, Bremen, Germany;1. GATS, Inc., Driggs, ID , USA;2. Space Science Division, Naval Research Laboratory, Washington, DCUSA;3. Virginia Polytechnic Institute, Blacksburg, VA, USA;4. Hampton University, Hampton, VA, USA |
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| Abstract: | Observations of noctilucent clouds have revealed a surprising coupling between the winter stratosphere and the summer polar mesopause region. In spite of the great distance involved, this inter-hemispheric link has been suggested to be the principal reason for both the year-to-year variability and the hemispheric differences in the frequency of occurrence of these high-altitude clouds. In this study, we investigate the dynamical influence of the winter stratosphere on the summer mesosphere using simulations from the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). We find that for both Northern and Southern Hemispheres, variability in the summer polar mesopause region from one year to another can be traced back to the planetary-wave flux entering the winter stratosphere. The teleconnection pattern is the same for both positive and negative wave-flux anomalies. Using a composite analysis to isolate the events, it is argued that the mechanism for inter-hemispheric coupling is a feedback between summer mesosphere gravity-wave drag (GWD) and zonal wind, which is induced by an anomaly in mesospheric cross-equatorial flow, the latter arising from the anomaly in winter hemisphere GWD induced by the anomaly in stratospheric conditions. |
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