Magnetospheric Dynamics and the Effects of Ion Composition on the Ring Current Strength and Recovery Rate During Extreme Storm of November 2003

The extreme geomagnetic storm of November 20-21, 2003 was created by an ICME interacting with the Earth's magnetosphere and the Dst index dropped below -420 nT (World Geomagnetism Data Center, Kyoto). This superstorm has a "classic" Dst profile with a well-defined main phase (~18h) and an exponential recovery phase (~2d). The storm is an important event to study because 1) the simplicity of the Dst profile; 2) good coverage of magnetospheric inputs (availability of IMF data) and observations; 3) an excellent candidate to understand the response of the magnetosphere and ring current to extreme driving conditions.

We carried out studies of this extreme storm of November 2003 with a coupled global model (MHD BATSRUS - ring current CIMI), by varying the ion composition in the inner magnetosphere. In particular, two runs were carried out, one with H+ dominant ring current, and one with O+ dominant ring current. It was shown that the dynamics of the main phase Dst is reproduced reasonably well for both runs although the run with H+ dominant ring current shows a stronger Dst response. However, the recovery rates for both runs turned out to be much slower than that in the observed Dst. To understand the results, we also performed simulations of the same event with a stand-alone version of the CIMI model, also varying the ion composition. Both tests demonstrated similar main phase dynamics, but the rate of recovery of the O+ dominant ring current was found to be faster. We explain the difference in recovery rate by a faster charge exchange loss for the O+ dominant ring current. We attribute the difference between the results of the global coupled model and the results of the stand-alone model by temperature condition at the boundary of the ring current. We discuss the validation of the results by comparison with measurements of energetic neutral atoms (ENA) by the IMAGE s/c made during this event. The application of the results in geomagnetic storm predication will be discussed as well.