Modeling the thermospheric response to solar flares

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Physics and Astronomy


Measurements of the incoming solar extreme ultraviolet (EUV) irradiance now allow models to be driven at higher temporal resolution and with better accuracy than with proxy-based models. Using solar irradiance measurements from the Solar EUV Experiment (SEE) instrument to drive the Global Ionosphere-Thermosphere Model, the global thermospheric response to the 28 October 2003 and 6 November 2004 solar flares is presented. The model indicates that the thermospheric density at 400 km can increase by as much as 14.6% in under 2 hours because of the flare and takes 12 hours to settle to close to a nominal state. Intense dayside heating launches nightward propagating gravity waves that transport energy efficiently to the nightside at velocities near the local sound speed plus the bulk wind velocity. Measurements from the Champ satellite indicate that the simulated day to night propagation time is similar to the observed one. Substantial density enhancements occur near the midnight sector as the wave converges on itself. In some locations the nightside perturbations are as large as those on the dayside. The convergence of the wave also leads to significant adiabatic heating of the nightside thermosphere. Eventually, the wave is reflected back toward the dayside but is quickly damped.

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