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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, A04S90, doi:10.1029/2006JA012019, 2007

Analysis of the 3–7 October 2000 and 15–24 April 2002 geomagnetic storms with an optimized nonlinear dynamical model

E. Spencer

Center for Space Engineering, Utah State University, Logan, Utah, USA


W. Horton

Institute for Fusion Studies, University of Texas at Austin, Austin, Texas, USA


M. L. Mays

Institute for Fusion Studies, University of Texas at Austin, Austin, Texas, USA


I. Doxas

Center for Integrated Plasma Studies, University of Colorado, Boulder, Colorado, USA


J. Kozyra

Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan, USA


Abstract

A computationally optimized low-dimensional nonlinear dynamical model of the magnetosphere-ionosphere system called WINDMI is used to analyze two large geomagnetic storm events, 3–7 October 2000 and 15–24 April 2002. These two important storms share common features such as the passage of magnetic clouds, shock events from coronal mass ejections, triggered substorms, and intervals of sawtooth oscillations. The sawtooth oscillations resemble periodic substorms but occur in association with strong or building ring current populations and have injection regions that are unusually close to the Earth and unusually wide in magnetic local times (Henderson et al., 2006; Borovsky et al., 2007). The April 2002 event includes one of the best examples of sawtooth events ever observed. On 18 April 2002, sawtooth oscillations were clearly visible when solar wind conditions (IMF B z , density, pressure) were relatively steady with a slowly varying Dst. In this study, WINDMI is used to model the 3–7 October 2000 and 15–24 April 2002 geomagnetic activity. WINDMI results are evaluated focusing on the sawtooth intervals and the overall prediction of the westward auroral electrojet (AL) index and Dst index. The input to the model is the dynamo driving voltage derived from the fluctuating solar wind plasma and the interplanetary magnetic field measured by the ACE satellite. The output of the model is a field-aligned current proportional to the AL index and the energy stored in the ring current which is proportional to the Dst index. The model parameters are optimized using a genetic algorithm (GA) to obtain solutions that simultaneously have least mean square fit to the AL and Dst indices and also exhibit substorms of period 2–4 hours. The GA optimization results show that the model is able to predict the Dst index reliably and captures the timing and periodicity of the sawtooth signatures in the AL index reasonably well for both storm events.

Received 14 August 2006; accepted 7 December 2006; published 28 April 2007.

Keywords: WINDMI; magnetosphere; space weather.

Index Terms: 7954 Space Weather: Magnetic storms (2788); 7959 Space Weather: Models; 7924 Space Weather: Forecasting (2722); 7846 Space Plasma Physics: Plasma energization.

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Citation: Spencer, E., W. Horton, M. L. Mays, I. Doxas, and J. Kozyra (2007), Analysis of the 3–7 October 2000 and 15–24 April 2002 geomagnetic storms with an optimized nonlinear dynamical model, J. Geophys. Res., 112, A04S90, doi:10.1029/2006JA012019.