Day-to-day migrating and nonmigrating tidal variability due to the six-day planetary wave

The 20E2 wave is produced by the nonlinear interaction between the DE3 and the six-day planetary wave, and its large amplitude indicates the importance of including the realistic spectra of nonmigrating tides in numerical simulations of planetary waves. The GSWM simulations reveal that the DW1 is not significantly influenced by the changes in the zonal mean winds. We thus conclude that the DW1 changes are driven by a combination of changes due to nonlinear interaction with the six-day planetary wave as well as changes due to zonal asymmetries that result from the six-day planetary wave.

The six-day planetary wave induced changes in zonal mean zonal winds lead to a general reduction in the amplitude of DE2 and DE3, and introduce a slight periodic behavior in these tides. The effect of changing zonal mean zonal winds appears to be the primary driver of the changes in the DE2. However, for DE3, although the changes that can be attributed to zonal mean zonal wind variability are not insignificant, the primary driver of the DE3 perturbations appears to be the nonlinear interaction with the six-day planetary wave.

Last, we demonstrate that the day-to-day changes in the DE3 introduce similar day-to-day changes in the daytime wave number-4 longitude structure in the low-latitude ionosphere. These results indicate that short-term variability in the low-latitude ionosphere is likely to be driven by similar short-term variability in nonmigrating tides in the MLT.