Migrating thermospheric tides

Abstract

The capabilities of the global‐scale wave model (GSWM) [Hagan et al., 1995, 1999] are extended to include migrating thermospheric solar tides. The GSWM thermospheric tidal forcing parameterization is based on neutral gas heating calculated from first principles in the National Center for Atmospheric Research (NCAR) thermosphere/ionosphere electrodynamics general circulation model (TIE‐GCM). This is the first time that a physics‐based thermospheric forcing scheme has been used in a model like GSWM. Previous two‐dimensional steady state linear tidal models used exospheric temperature measurements to calibrate upper atmospheric tidal forcing. New GSWM results illustrate thermospheric tidal responses that are largely consistent with tides in the TIE‐GCM. Diurnal temperature amplitudes increase with increasing solar activity, but there is no analogous diurnal wind response. The thermospheric semidiurnal tide is much weaker than the diurnal tide. Semidiurnal temperature perturbations peak in the lower thermosphere where the semidiurnal forcing maximizes. The new in situ results must be combined with the GSWM upward propagating tide in the lower thermosphere, because the upward propagating components dominate the semidiurnal response throughout the region and the diurnal response below ∼130 km. In situ forcing accounts for most of the diurnal response aloft. Our preliminary evaluation of the GSWM thermospheric predictions is inconclusive. More extensive evaluations are necessary to make a firm assessment of whether the model captures the salient features of the seasonal and solar cycle variability of thermospheric tides.