[1] A Whole Atmosphere Model (WAM) has been used to explore the possible physical connection between a sudden stratospheric warming (SSW) and the dynamics and electrodynamics of the lower thermosphere. WAM produces SSWs naturally without the need for external forcing. The classical signatures of an SSW appear in the model with a warming of the winter polar stratosphere, a reversal of the temperature gradient, and a breakdown of the stratospheric polar vortex. Substantial changes in the amplitude of stationary planetary wave numbers 1, 2, and 3 occur as the zonal mean zonal wind evolves. The simulations also show a cooling in the mesosphere and a warming in the lower thermosphere consistent with observations. The magnitude of this particular SSW is modest, belonging to the category of minor warming. In the lower thermosphere the amplitude of diurnal, semidiurnal, and terdiurnal, eastward and westward propagating tidal modes change substantially during the event. Since the magnitude of the warming is minor and the tidal interactions with the mean flow and planetary waves are complex, the one-to-one correspondence between tidal amplitudes in the lower thermosphere and the zonal mean and stationary waves in the stratosphere is not entirely obvious. The increase in the magnitude of the terdiurnal tide (TW3) in the lower thermosphere has the clearest correlation with the SSW, although the timing appears delayed by about three days. The fast group velocity of the long vertical wavelength TW3 tide would suggest a faster onset for the direct propagation of the tide from the lower atmosphere. It is possible that changes in the magnitude of the diurnal and semidiurnal tides, with their slower vertical propagation, may interact in the lower thermosphere to introduce a terdiurnal tide with a longer delay. An increase in TW3 in the lower thermosphere would be expected to alter the local time variation of the electrodynamic response. The day-to-day changes in the lower thermosphere winds from WAM are shown to introduce variability in the magnitude of dayside low latitude electric fields, with a tendency during the warming for the dayside vertical drift to be larger and occur earlier, and for the afternoon minimum to be smaller. The numerical simulations suggest that it is quite feasible that a major SSW, with a magnitude seen in January 2009, could cause large changes in lower thermosphere electrodynamics and hence in total electron content.Citation: Fuller-Rowell, T., F. Wu, R. Akmaev, T.-W. Fang, and E. Araujo-Pradere (2010), A whole atmosphere model simulation of the impact of a sudden stratospheric warming on thermosphere dynamics and electrodynamics,
[1] Using data from 75 ionosonde stations and 43 storms, and based on the knowledge gained from simulations from a physically based model, we have developed an empirical ionospheric storm-time correction model. The model is designed to scale the quiet time F region critical frequency (foF2) to account for storm-time changes in the ionosphere. The model is driven by a new index based on the integral of the a p index over the previous 33 hours weighted by a filter obtained by the method of singular value decomposition. Ionospheric data were sorted as a function of season and latitude and by the intensity of the storm, to obtain the corresponding dependencies. The good fit to the data at midlatitudes for storms during summer and equinox enable a reliable correction, but during winter and near the equator, the model does not improve significantly on the quiet time International Reference Ionosphere predictions. This model is now included in the international recommended standard IRI2000 [Bilitza, 2001] as a correction factor for perturbed conditions.
This paper first describes the technique that has been developed to obtain realistic, daytime, vertical ExB drift velocities in the equatorial ionosphere using two ground‐based magnetometers, one on the magnetic equator and the other located ±6°–9° away in latitude. This technique is then employed to study the unique ExB drift signatures associated with sudden stratospheric warming events (SSW) in both the Peruvian and Philippine longitude sectors, occurring in January 2003 and January 2004. It is found that the semidiurnal shaped signature first appears in the Peruvian sector and 3 days later appears in the Philippine sector. In both sectors, the ExB drift signature lasts for approximately 5 days.
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