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Reflected Solar Wind in the foreshock region of Venus
observed by Venus ExpressM. 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
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.
Summary
Scan
=-45
°~45
°
Fig 1:e- (top) & H+ (rest) at different angle
SWSW SW
SW
BS BS BSBS
, ∑ 3
-min
sca
n
2006-6-18 2008-10-28
B
connected to BS
B B B
Beam = foreshock
Fig 2:
connected to BSSometimes no beam in foreshock
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
SW
FAB in the SW frameFAB in the Venus frame
(Cao et al., 2008)
V// V//
V V
cluster-3 cluster-1
SW SW
Earth ≈ Venus, but f ≈ Maxwellian
Fig 4: other planets
Mars ≠ Venus, but both // and accel. are clear
Fig 4b
Fig 3b
2006-6-20
BX, BY, BZ
not connected to BS
Y
X X
ZFig 2b