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Ann. Geophys., 21, 1931-1938, 2003
www.ann-geophys.net/21/1931/2003/
© European Geosciences Union 2003
Cellular automata model of magnetospheric-ionospheric coupling
B. V. Kozelov and T. V. Kozelova
Polar Geophysical Institute, Apatity, Murmansk Region, 184209, Russia
Abstract. We propose a cellular
automata model (CAM) to describe the substorm activity of the
magnetospheric-ionospheric system. The state of each cell in the model is
described by two numbers that correspond to the energy content in a region of
the current sheet in the magnetospheric tail and to the conductivity of the
ionospheric domain that is magnetically connected with this region. The driving
force of the system is supposed to be provided by the solar wind that is
convected along the two boundaries of the system. The energy flux inside is
ensured by the penetration of the energy from the solar wind into the array of
cells (magnetospheric tail) with a finite velocity. The third boundary (near to
the Earth) is closed and the fourth boundary is opened, thereby modeling the
flux far away from the tail. The energy dissipation in the system is quite
similar to other CAM models, when the energy in a particular cell exceeds some
pre-defined threshold, and the part of the energy excess is redistributed
between the neighbouring cells. The second number attributed to each cell
mimics ionospheric conductivity that can allow for a part of the energy to be
shed on field-aligned currents. The feedback between "ionosphere" and
"magnetospheric tail" is provided by the change in a part of the
energy, which is redistributed in the tail when the threshold is surpassed. The
control parameter of the model is the z-component of the interplanetary
magnetic field (Bz IMF), "frozen" into the solar wind. To study the
internal dynamics of the system at the beginning, this control parameter is
taken to be constant. The dynamics of the system undergoes several
bifurcations, when the constant varies from - 0.6 to - 6.0. The Bz IMF input
results in the periodic transients (activation regions) and the inter-transient
period decreases with the decrease of Bz. At the same time the onset of
activations in the array shifts towards the "Earth". When the modulus
of the Bz IMF exceeds some threshold value, the transition takes place from
periodic to chaotic dynamics. In the second part of the work we have chosen as
the source the real values of the z-component of the interplanetary magnetic
field taken from satellite observations. We have shown that in this case the
statistical properties of the transients reproduce the characteristic features
observed by Lui et al. (2000).
Key words. Magnetospheric physics
(magnetosphere-ionosphere interactions) – Space plasma physics (nonlinear
phenomena)
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