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Abstract:
The Magnetosphere-Ionosphere (MI) system is primarily driven by solar wind dynamics. The energy transfer from the solar wind to the Earth’s magnetosphere is most efficient under southward IMF Bz conditions. Generally, the southward IMF Bz drives the ring current which is measured by the Dst/SYM-H index. The geomagnetic storm during 21-22 January 2005 is considered to be anomalous as growth of the ring current is found to be under northward IMF Bz conditions. The SYM-H continues to grow for more than six hours, reaching a minimum value of -101 nT. The WINDMI model is utilised to estimate the growth of the ring current by using several coupling functions. However, none of these coupling functions could predict this unusual growth of the ring current under the northward IMF Bz conditions. A highly dense plasma sheet was observed during the anomalous period and incorporating this in the WINDMI model led to the successful reproduction of the observed disturbance. This investigation clearly shows the important role of the state of the magnetosphere in energizing the ring current. Therefore, it is suggested that the space weather models need to include both the conditions of solar wind and magnetosphere in order to get a better prediction of the strength of the ring current.
