The role of tropical waves in the dynamics of the mesosphere

High resolution data of rainfall rate and infrared cloud top brightness temperature derived from TRMM and ISCCP have been used to construct estimates of latent heating and cloud top height every 3 hours on a .25 x .25 longitude-latitude grid. This heating is used to force a global timed-dependent model that includes the mesosphere and lower thermosphere, from which we study the spectrum of wave motion produced in response to the heating. Although the spectrum is rich with Rossby, Kelvin and inertia gravity waves throughout the stratosphere, the main component of the wave spectrum that remains in the mesosphere are of diurnal frequency – the nonmigrating tides – and a broad background of high frequency waves.

We will compare the nonmigrating tides generated by our model to tide observations made by the TIDI and SABER instruments aboard the TIMED satellite. Diurnal tide components in satellite data are aliased with stationary waves and waves with frequencies that are multiples of the diurnal. The model simulations can be used to interpret which wave components contribute to the observations, and to help distinguish between tides generated by latent heating and tides generated from other sources.

The high frequency wave background also interacts significantly in our model with the mean flow and with the migrating diurnal tide. We find, however, that this interaction does not produce the strong seasonal and interannual variation in the amplitude of the migrating tide that is found in observation data. The migrating tide component forced by latent heating is quite weak and it also does not contribute significantly to the seasonal variation.