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h
n
h
n
h
n
h
n
CO
2
N
2
H
O
CO
2
e
-
+
CO,
O
CO
2
NO
n
O
h
O
2
O,O
2
CO
2
,
O
2
H
O
2
e
N
2
H
+
O
+
O
+
e
N,
N
n
h
O,O
O
NO
CO
2
NO
COH
+
NO, N
2
NO
+
NO, O
e
N,O
Fig. 7.4
Ionospheric chemical reaction scheme of Mars upper ionosphere (Reproduced from Chen
et al. (
1978
) by permission of John Wiley & Sons Ltd.)
between CO
2
C
and O is the dominant source of O
C
at heights below 190 km. Above
this altitude solar radiation is an important production mechanism for O
C
.Theion
N
2
C
is produced by photoionisation and is lost by reaction with CO
2
. The chemical
reaction scheme for the upper ionosphere of Mars is shown in Fig.
7.4
.
7.3.1
Effects of Solar Flares on the Upper Ionosphere
Several solar flares of classes M and X were registered on the sun during the
maximum phase of solar cycle 23. Responses to these flares in the Martian
ionosphere have been reported by several investigators. Using MARSIS data,
Nielsen et al. (
2006
) reported that the maximum electron density in the Martian
ionosphere suddenly increased from 1.8
10
5
to 2.4
10
5
cm
3
at 08:39 UT on 15
September 2005. This coincided closely in time with the increase in solar X-ray
fluxes measured from GOES 12 spacecraft at the Earth, as shown in Fig.
7.5
.
Mendillo et al. (
2006
) examined ionospheric data of MGS and reported two elevated
electron density profiles during the solar X-ray flares which occurred on 15 April
and 26 April 2001 at 13:50 UT and 13:10 UT, respectively. They found 200 %
enhancement in the electron density profiles during these flares, as shown in Fig.
7.6
.
Haider et al. (
2009b
) studied solar flare of 13 May 2005 and the following CMEs and
reported their effects in the E region ionosphere. Mahajan et al. (
2009
) surveyed all
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