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Thin current sheets in the Earth and Venus magnetotails
- Space Research Institute of RAS, Russia
- Skobeltsyn Institute of Nuclear Physics, Russia
- Lomonosov Moscow State University, Department of Physics, Russia
The Earth magnetotail, the region on the night side with the field lines
stretched in the Sun-Earth direction, forms due to the interaction between
the Earth dipole field and the solar wind flow. On the other hand, Venus
has no intrinsic magnetic field. The mechanism of the formation of the
Venus magnetotail is similar to the mechanism, proposed by Alfven for the
formation of comet tails. The Venus magnetotail is formed by the solar
wind flux tubes mass-loaded by the ionosphere ions (basically oxygen ions
O+). In spite of the different mechanisms the topologies of Earth
and Venus tails are generally similar. In both cases these are
magneto-plasma configurations with stretched field lines reminiscent of
the stretched slingshot.
The fundamental element of the magnetotail is the current sheet (CS). The
equilibrium CS structure and CS instabilities basically govern the
magnetotail dynamics. The data of multispacecraft Cluster mission and
single spacecraft Venus Express mission have allowed to obtain the
information about the equilibrium structure of CSs in the Earth and Venus
tails. It turns out that CSs in the Earth and Venus tails have a lot in
common. The equilibrium structure of these CSs can be described in the
frame of multicomponent anisotropic thin CS model (ATCS model). In ATCS
model ions (protons and oxygen ions) are described in the quasiadiabatic
approximation, while electrons are described in the frame of MHD. ATCS
model allows explaining a lot of observed properties of CSs in the Earth
and Venus tails: CS thickness, multiscale structure, embedding, bifurcated
structure, CS stability.
Although the transverse structure of CSs in the Earth and Venus tails is
similar, the magnetotail structure in the Sun-Planet direction is
nevertheless different. In particular the characteristic length of the
Earth magnetotail ( ~ 100÷200 RE ) is determined by the
dayside magnetopause reconnection and by the convection of open field
lines to the night side. On the other hand, the length of the Venus
magnetotail (~ 40 RV) and the tail structure in the Sun-Venus
direction is determined by the so-called ''magnetic slingshot'' effect -
the tension of magnetic field lines causes the evolution of the
mass-loaded flux tubes and results in their gradual straightening.