The growth of ring current/SYM-H under northward IMF $B_z$ conditions
present during the 21-22 January 2005 geomagnetic storm
Abstract
The total energy transfer from the solar wind to the magnetosphere is
governed by the reconnection rate at the magnetosphere edges as the IMF
$B_z$ turns southward. The delayed response of the ring current to
solar wind driving can account for the anomalous growth of the SYM-H
under northward IMF $B_z$. The geomagnetic storm on 21-22 January
2005 is considered to be anomalous as the SYM-H index that signifies the
strength of ring current, grows and has a sustained peak value lasting
more than 6 hrs under northward IMF $B_z$ conditions. In this work,
first the standard WINDMI model is utilized to estimate the growth and
decay of various magnetospheric currents by using several solar
wind-magnetopsehre coupling functions. However, it is found that the
WINDMI model driven by any of these coupling functions is not fully able
to explain the enhancement of SYM-H under northward IMF $B_z$. The
SYM-H variations during the entire duration of the storm were only
reproduced when the effects of the dense plasma sheet were included in
the WINDMI model. The limitations of directly-driven models relying
purely on the solar wind parameters and not accounting for the state of
the magnetosphere are highlighted by this work.