It is well known that the atmospheric layers are coupled. However, such a coupling is difficult to identify except during strong coupling processes. The most prominent and impressive vertical coupling process in the middle atmosphere is the sudden stratospheric warming, caused by the interaction of planetary Rossby waves with the mean flow. Sudden stratospheric warmings are global events which are characterized by an explosive warming of the stratosphere (W) of up to 80K within a few days and a simultaneous cooling of the mesosphere (C) of up to 30K (see figure below). Additionally the zonal wind reverses and thus changes the propagation condition for all wave types during this event. Sudden Stratospheric warmings occur stronger and much more often in the northern than in the southern hemispheric winter. The cause for this property is the different distribution of sea and land in each hemisphere, causing planetary Rossby waves in the winter troposphere (0 – 10km).
These global phenomena as well as other coupling processes are studied using a combination of local radar wind measurements at mid and high latitudes, global satellite observations of temperatures and winds (e.g., MLS), and winds from assimilated model data (e.g., MERRA).
- P. Hoffmann, E. Becker, W. Singer und M. Placke, Seasonal variation of mesospheric waves at northern middle and high latitudes, J. Atmos. Solar-Terr. Phys., 72, 1068-1079, doi:10.1016/j.jastp.2010.07.002, 2010.
- V. Matthias, P. Hoffmann, M. Rapp und G. Baumgarten, Composite analysis of the temporal development of waves in the polar MLT region during stratospheric warmings, J. Atmos. Solar-Terr. Phys., doi:10.1016/j.jastp.2012.04.004, 2012.
- V. Matthias, P. Hoffmann, A. Manson, C. Meek, G. Stober, P. Brown und M. Rapp, The impact of planetary waves on the latitudinal displacement of sudden stratospheric warmings, Ann. Geophys., 31, 1397-1415, doi:10.5194/angeo-31-1397-2013, 2013.
- W. Singer, P. Hoffmann, G. Kishore Kumar, N. J. Mitchell und V. Matthias, Atmospheric coupling by gravity waves: Climatology of gravity wave activity, mesospheric turbulence and their relations to solar activity, in Climate And Weather of the Sun-Earth System (CAWSES): Highlights from a priority program, Springer, F.-J. Lübken, Dordrecht, The Netherlands, doi:10.1007/978-94-007-4348-9, 2012.
- N. M. Pedatella, H.-L. Liu, F. Sassi, J. Lei, J. L. Chau und X. Zhang, Ionosphere variability during the 2009 SSW: Influence of the lunar semidiurnal tide and mechanisms producing electron density variability, J. Geophys. Res., doi:10.1002/2014JA019849, 2014