Global observations of 2day wave coupling to the diurnal tide in a high-altitude forecast-assimilation system

We examine wave components in a high-altitude forecast-assimilation system that arise from nonlinear interaction between the diurnal tide and the westward traveling quasi 2day wave. The process yields a westward traveling sum wave with zonal wave number 4 and a period of 16h, and an eastward traveling difference wave with zonal wave number 2 and a period of 2days. While the eastward 2day wave has been reported in satellite temperatures, the westward 16h wave lies outside the Nyquist limits of resolution of twice daily local time satellite sampling. Hourly output from a high-altitude forecast-assimilation model is used to diagnose the nonlinear quadriad. A steady state primitive equation model forced by tide-2day wave advection is used to intepret the nonlinear wave products. The westward 16h wave maximizes in the midlatitude winter mesosphere and behaves like an inertia-gravity wave. The nonlinearly generated component of the eastward 2day wave maximizes at high latitudes in the lower thermosphere, and only weakly penetrates to low latitudes. The 16h and the eastward 2day waves are of comparable amplitude and alias to the same apparent frequency when viewed from a satellite perspective.