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it (Acuña et al.
1998
). Actually, it is a magnetic barrier, which diverts the bulk
of solar wind shock around the planet. There exists a sharp boundary (ionopause)
between the magnetised magnetosheath and the ionosphere, as shown in Fig.
7.9
.
The location of the magnetosheath and ionopause can change with the solar wind
dynamic pressure. Thermal pressure balances magnetic pressure at the ionopause
boundary. Mass loading of the magnetosheath does effect the flow behind the shock
such that the pickup of neutrals ionised outside the ionopause (i.e. pick up ions)
contribute to further stagnation of this flow and to the growth of the magnetic barrier.
Consequently, this contributes to the development of the magnetotail.
MGS has observed a magnetosheath at about 435 km on the sunlit hemisphere
of Mars during quiet conditions (Mitchell et al.
2000
). In the magnetosheath the
planetary neutrals are mainly H atoms of the hydrogen corona. Fast hydrogen atoms
are produced by charge exchange between solar wind protons and hydrogen corona
in this region. These energetic proton-hydrogen atoms have the same energies as the
solar wind protons and move in the same direction as that of the fast protons just
before the collisions (Haider et al.
2002
). In this way the magnetosheath of Mars can
be compressed similar to that observed in the Earth's magnetosphere (Dandouras
et al.
2007
) and the accelerated solar wind protons get turned into fast hydrogen
atoms at lower altitudes. To verify that the flare of 13 May 2005 has an effect on
the magnetosheath of Mars, Haider et al. (
2012
) analysed the magnetic field data
obtained from MGS at altitudes
420 and
430 km from 12 to 18 May 2005.
The variation of magnetic field measured in the magnetosheath region of Mars is
shown in Fig.
7.10
. There are two broad peaks in the magnetic field at an altitude
of
420 km on 15 and 17 May with the values
50 nT and 40 nT at 21:50 UT
and 02:52 UT, respectively. These values are larger than that the magnetic field
normally observed at altitude
430 km by a factor of
2.5. Before and after these
times, the magnetic field does not change significantly between these two altitudes.
This suggests that the CME arrived at Mars on 15 May at about 21:50 UT and
compressed its magnetosheath by about 10-15 km.
Haider et al. (
2012
) also ran a three-dimensional kinetic solar wind model
(Hakamada-Akasofu-Fry version 2/HAFv.2) to confirm the arrival of CME at Mars
following the solar flare of 13 May 2005. This model does not provide any way
to distinguish between the effects on the ionosphere of magnetic storm from the
CME shocks and the energetic particles from that shock. Figure
7.11a-h
shows
simulated ecliptic plane profile of IMF (about to 2 AU) from 15 to 18 May 2005.
The simulation confirmed that the CME reached Mars on 15 May 2005 after its
Fig. 7.8
(
a
) Measured TEC (
blue colour
) and predicted TEC (
red colour
)intheEregion
ionosphere of Mars for the period 29 May to 3 June 2003. (
b
) Measured TEC (
blue colour
)and
predicted TEC (
red colour
) in the E region ionosphere of Mars for the period 15-20 January 2005.
(
c
) Measured TEC (
blue colour
) and predicted TEC (
red colour
) in the E region ionosphere of
Mars for the period 12-18 May 2005. CME arrival and its effect on 30-31 May 2003, 2-3 June
2003 and 16-17 May 2005 are marked by an
arrow line
(Reproduced from Haider et al. (
2012
)by
permission of John Wiley & Sons Ltd.)
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