Analysis of the 2007 year CIR Events using the WINDMI Model: Energy Distribution and Ring Current Evolution

In the present solar minimum there were multiple low latitude coronal holes present on the solar surface ejecting streams of fast solar wind. We examine recurring CIR events in the year 2007 that cause Dst decreases of less than -40 nT and compare results with CME events in the years 2000 and 2002. We use a low dimensional model of the nightside magnetosphere called WINDMI to perform the analysis. The solar wind driving voltage input to the model is calculated from ACE solar wind parameter data using different magnetosphere-ionosphere coupling functions. The outputs of the model are the westward Auroral Electrojet current and the energy stored in the Earth's ring current which can be used to predict the AL and Dst indices. In order to investigate the differences in ring current growth and energization, the global energy components of the WINDMI model are compared separately under CME and CIR forcing. The twenty two physical parameters of the model are optimized for each event under different driving conditions using a genetic algorithm by matching the predicted indices against AL and (pressure) corrected Dst indices provided by the WDC Kyoto. The role of substorm injection in ring current build up and extended decay times during CIR events is discussed. Contributions from ohmic losses and particle injection towards ring current energization is compared between CIR and CME events.