Monday, 23 January 2012
Non-Migrating Tides in the Thermosphere: In-Situ Versus Tropospheric Sources
Hall E (New Orleans Convention Center )
The importance of non-migrating (i.e., longitude-variable) tides to the dynamics and electrodynamics of the ionosphere-thermosphere system is now widely recognized. In many cases these tides propagate into the thermosphere from sources in the troposphere, but recent data interpretations suggest the existence of non-migrating tides excited in-situ as well. One source of such in-situ generated tides is non-linear tide-tide interactions. Another source not previously studied, and the focus of this investigation, is the generation of non-migrating tides through ion-neutral interactions moderated by the longitude-dependent ionosphere. We report on numerical experiments performed with the National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM), during both solar minimum (F10.7 = 75 solar flux units) and solar maximum (F10.7 = 200 solar flux units) conditions, with realistic magnetic field configuration, and an aligned-dipole configuration. We computed difference fields between simulations with a realistic magnetic field and aligned-dipole configurations to quantify the magnitude of the non-migrating tides excited through ion-neutral interactions. It is important to recognize that, in terms of tidal perturbations residing in the upper regions of the thermosphere (200-500 km), this dependence on solar cycle is opposite to that experienced by tides propagating upwards from the troposphere; therefore, the in-situ generated components could dominate some parts of the tidal spectrum at high levels of solar activity. Our computational results are considered in light of observational studies, which suggest that in-situ generated tides must exist in order to reconcile data-model differences.
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