Long-term evolution of magnetospheric current systems during storms
Ganushkina, N. Yu.
Pulkkinen, T. I.
Kubyshkina, M. V.
Singer, H. J.
Russell, C. T.
arxiv: Physics::Space Physics
We present a method to model the storm-time magnetospheric
magnetic field using representations of the magnetic field arising
from the various magnetospheric current systems. We incorporate
the effects of magnetotail changes during substorms by introducing
an additional localized thin current sheet into the Tsyganenko T89
model. To represent the storm-time ring current the T89 ring
current is replaced by a bean-shaped current system, which has a
cross section that is close to the observed distribution of
trapped particles in the inner magnetosphere and has an eastward
flowing inner and westward flowing outer components. In addition
to the symmetric ring current, an asymmetric partial ring current
is taken into account with closing Region 2 sense field-aligned
currents. Magnetopause currents are varied in accordance with
solar wind dynamic pressure variations. Three moderate geomagnetic
storms when <i>D<sub>st</sub></i> reached about –150 nT and one big storm
with <i>D<sub>st</sub></i> about –250 nT are modelled. The model free
parameters are specified for each time step separately using
observations from GOES 8 and 9, Polar, Interball and Geotail
satellites and <i>D<sub>st</sub></i> measurements. The model gives a high
time-resolution field representation of the large-scale magnetic
field, and a very good reproduction of the <i>D<sub>st</sub></i> index. It is
shown that the ring current is most important during intense
storms, whereas the near-Earth tail currents contribute more to
the <i>D<sub>st</sub></i> index than the ring current during moderate storms.<br><br>
<b>Key words.</b> Magnetospheric physics (Current systems;
Magnetospheric configuration and dynamics; Storms and