Thin current sheets in the Earth and Venus magnetotails

Zelenyi L.M.1, Artemyev A.V.1, Petrukovich A.A.1, Vasko I.Y.1, Malova H.V.1, 2, Popov V.Y.1, 3
  1. Space Research Institute of RAS, Russia
  2. Skobeltsyn Institute of Nuclear Physics, Russia
  3. 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.