An eastward propagating two-day wave: Evidence for nonlinear planetary wave and tidal coupling in the mesosphere and lower thermosphere

Temperature observations from the SABER instrument on the TIMED spacecraft are used to investigate the structure and evolution of an eastward propagating zonal wavenumber 2 disturbance with a period near two days. This oscillation obtains a maximum amplitude of nearly 10 K in the southern hemisphere mid-latitudes during late January. The timing and location of this planetary wave is coincident with the regular quasi two-day wave intensification that occurs annually in late January. The period, wavenumber and spatial structure of the eastward propagating two-day wave are consistent with a wave that results from a nonlinear interaction between the quasi two-day wave and the migrating diurnal tide. The existence of an eastward propagating wave with a period near two days coincident with the westward propagating two day wave will have an impact on the interpretation of ground based observations. Analysis of the SABER temperature observations are utilized to determine the structure and evolution of both this eastward propagating two-day wave and the classic westward propagating zonal wavenumber 3 quasi two-day wave during January 2005.