Upper Ionosphere of Mars During Solar Quiet and Disturbed Conditions - Planetary Exploration and Science: Recent Results and Advances - page 131

Therefore, electron density decreases exponentially with height in this model.
The photochemical equilibrium model includes photoionisation process, chemical
reactions and their production and loss processes under steady state condition.
There is a reasonable agreement between two model calculations in the absence of
photoionisation. Before MARSIS observations, Leblanc et al. ( 2002 ) had simulated
the vertical profile of energy deposition rate in the Martian ionosphere for the SEP
event of 20 October 1995. However, they did not study the ionospheric effects of
this SEP event at Mars. Their results are comparable with Sheel et al. ( 2012 )inthe
vicinity of ionisation peaks produced by this SEP event.

7.4 Auroral Ionosphere

Aurorae are often seen in the upper atmosphere of Earth at high latitudes following
the occurrence of solar flares and CMEs. Since Mars has no strong remnant of
an ancient intrinsic magnetic field in the northern hemisphere (Acuña et al. 1998 ),
Fox ( 1992 ) argued that Mars should have Venus-like diffuse aurora in this region.
However, auroral events are not observed in the northern hemisphere, but effects
of magnetic storms have been detected in the ionosphere of Mars (Haider et al.
2009b , 2012 ). Bertaux et al. ( 2005 ) have discovered southern aurora in the night-
time atmosphere (solar zenith angle 117.5 ı ) of Mars using the 'Spectroscopy for
the Investigation of the Characteristic of the Atmosphere of Mars' (SPICAM)
experiment onboard MEX. Figure 7.13a shows the limb observations carried for
450-750 s at wavelength range of 100-350 Å in the night-time atmosphere.
HLyman-' (121.6 nm) and NO bands (181-298 nm) are clearly visible in this
figure. Figure 7.13b represents an auroral spectrum integrated over the wavelength
range of the NO bands (181-298 nm) as a function of time for the five spatial
bins. There is a strong peak in all the bins. These spectra were observed at a
tangent altitude of 19 km. Local time was 21:00 h and longitude and latitude were
198.4 ı and 46.3 ı , respectively. These measurements were carried out using nadir
looking direction in the strong crustal magnetic field region where the field lines are
nearly open (Lundin et al. 2006 ; Mitchell et al. 2007 ;Haideretal. 2010 ). Leblanc
et al. ( 2008 ) found a good correlation among the measured auroral emission by
SPICAM, the measured downward/or upward flux of electrons by ASPERA-3 and
the TEC recorded by MARSIS. They found that TEC increased when there was a
precipitation of high flux auroral electrons into the atmosphere of Mars. During the

Fig. 7.11 Ecliptic plane simulations out to 2 AU of IMF and solar wind disturbances predicted by
the HAFv.2 model during 15-18 May 2005 at selected time: ( a ) 15 May at 0.00 UT, ( b ) 15 May at
8:00 UT, ( c ) 15 May at 16:00 UT, ( d ) 16 May at 0:00 UT, ( e ) 16 May at 12:00 UT, ( f ) 17 May at
0:00 UT, ( g ) 17 May at 16:00 UT and ( h ) 18 May at 0:00 UT. IMF lines are shown in red (away
sectors) and in blue (towards sectors). The locations of the Earth and Mars are indicated by black
dots (Reproduced from Haider et al. ( 2012 ) by permission of John Wiley & Sons Ltd.)