Large-scale atmospheric waves observed by TIMED/SABER

Large-scale atmospheric waves, including forced and free oscillations, have been the subject of theoretical and observational studies for many years. In particular, tropospheric observations have revealed the presence of several Rossby normal modes, most notably the first and second symmetric normal modes, the 5- and 16-day waves. Above the tropopause, and especially above the middle stratosphere, there has not existed until recently a set of observations that could provide a global, synoptic view of large-scale waves(which nonetheless are known to be of fundamental importance to the dynamics of the region). The SABER instrument, an infrared limb radiometer onboard NASA's TIMED satellite, has been making nearly continuous observations, with effective time resolution of ~12 hours, from 2002 until the present time. Here we use Salby's fast Fourier synoptic mapping(FFSM) method to calculate synoptic spectra of the SABER data and provide a true synoptic climatology of large-scale traveling waves in the stratosphere, mesosphere and lower thermosphere (MLT) spanning the period 2002-2008. The results show the presence of various wave modes, including forced Kelvin and Rossby–gravity waves, eastward-propagating diurnal oscillations (“non-sun-synchronous tides”), and a set of oscillations associated with the so-called "2-day wave." Several Rossby normal modes, including the 16-, 10- and 5-day waves are also apparent in the observations. The seasonal and interannual variability of these waves is documented, as are some aspects of their relationship to the zonal mean state, e.g., the tropical QBO and sudden stratospheric warmings in the northern winter hemisphere.