Modeling the Response of the Thermosphere and Ionosphere to Extreme Space Weather Events

Abstract:

If a Carrington-type CME event of 1859 or the solar wind conditions experienced by STEREO-A on July 23rd, 2012 hit Earth, how might the thermosphere, ionosphere, and plasmasphere respond? To start with, the response would be dependent on how the magnetosphere reacts and channels the energy into the upper atmosphere. For now we can assume the magnetospheric convection and auroral precipitation inputs would look similar to a 2003 Halloween storm but stronger and more expanded to mid-latitude, much like what the Weimer empirical model predicts if the solar wind Bz and velocity were -60nT and 1500km/s respectively. For a Halloween-level geomagnetic storm event, the sequence of physical process in the thermosphere and ionosphere are thought to be well understood, but physical models still struggle to capture the magnitude of the response. For an extreme solar storm, it is unclear if the response would be a natural linear extrapolation of the response or if non-linear processes would begin to dominate. Numerical simulations have been performed with a coupled thermosphere ionosphere model to quantify the likely response to an extreme space weather event. The simulation predict the neutral atmosphere would experience horizontal winds of 1.5 to 2.0 to km/s, vertical winds exceeding 150m/s, and the “top” of the thermosphere well above 1000km. Predicting the ionosphere response is somewhat more challenging because there is significant uncertainty in quantifying some of the other driver-response relationships such as the magnitude and shielding time-scale of the penetration electric field, the possible feedback to the magnetosphere, and the amount of nitric oxide production. Within the limits of uncertainty of the drivers, attempts are being made to try to quantify the magnitude of the neutral and plasma response, and if non-linear responses are predicted.