Reflected Solar Wind in the foreshock region of Venus observed by Venus Express M. Yamauchi1, Y. Futaana1, R. Lundin1, S. Barabash1, M. Wieser1, A. Fedorov2, J.-A. Sauvaud2, T.L. Zhang3, W. Baumjohann3, J.D. Winningham4, R.A. Frahm4, E. Dubinin5, and M. Fraenz5. (1) Swedish Institude of Space Physics, Kiruna, Sweden, (2) Centre d’Etude Spatiale des Rayonnements, Toulouse, France, (3) Space Research Institute, Graz, Austria (4) Southwest Research Institute, San Antonio, Texas, USA (5) Max-Planck-Institut fur Sonnensystemforschung, Katlenburg-Lindau, Germany Characteristics of ions flowing upstream along IMF from the Venus bow shock (BS): Comparison to Earth and Mars

Summary Venus Express / ASPERA-4 often observes nearly field-aligned beam-like protons (FAB) in the foreshock region of Venus (Fig. 1, Fig. 2) : (1) They travel away from the quasi-parallel bow shock of Venus, nearly along the interplanetary magnetic field (Fig. 2, Fig. 3). (2) About 2~6 times energy of the solar wind proton energy (Fig. 1). (3) The protons are classified into two beams: (a) field-aligned beam in the SW frame of reference, and (b) field-aligned beam in Venus frame of reference which gyrates in the SW frame (Fig. 3). The combination forms a pancake-like distribution. They are similar to those at the terrestrial foreshock region (Fig. 4). On the other hand, Mars Express, with the same instrumentation a Venus Express, does not observe the FAB in the Martian foreshock region. We instead observe effective perpendicular acceleration (Fig. 4) along the shock surface. The difference must come from the different gyroradii of the ions.

Fig 1: , ∑ 3-min scan SW SW SW SW BS BS BS BS Scan=-45°~45° e- (top) & H+ (rest) at different angle

B B B B 2006-6-18 connected to BS 2008-10-28 connected to BS Fig 2: Beam = foreshock Sometimes no beam in foreshock Fig 2: Top: VEX trajectory (both approaching Venus) and projected IMF, Middle: three components of IMF, Bottom: H+ spectrogram at sectors where FAB is observed (cf Fig. 1)

Fig 3: pitch angle distribution SW SW SW Fig 3: pitch angle distribution FAB in the SW frame FAB in the Venus frame SW

Mars ≠ Venus, but both // and  accel. are clear Fig 4: other planets Earth ≈ Venus, but f ≈ Maxwellian SW SW V// V// cluster-3 cluster-1 V V (Cao et al., 2008)

Fig 4b

Fig 3b

Fig 2b Y Z X X BX, BY, BZ 2006-6-20 not connected to BS