Upper Ionosphere of Mars During Solar Quiet and Disturbed Conditions - Planetary Exploration and Science: Recent Results and Advances - page 116

consider ionisation by solar radiation (Winchester and Rees 1995 ), explain the total
electron concentration obtained by the radio occultation experiments. The nightside
ionospheric models considering the precipitation of solar wind electrons agree with
the Viking radio observations rather than other models (Haider et al. 2002 ). In spite
of the relatively large number of measurements and models, the effect of coronal
mass ejection (CME), magnetic storms, aurorae and solar flares are not understood
in detail in the upper ionosphere of Mars. This chapter describes observations on
the upper ionosphere of Mars during quiet and disturbed conditions. The modelling
of the upper ionosphere is also described in this chapter.

7.2 Martian Ionosphere and Source

UV and X-ray radiations are the major ionising sources in the upper atmosphere
of Mars. The photons of these frequencies contain sufficient energy to dislodge an
electron from a neutral gas upon absorption. The reverse process to ionisation is
recombination in which a free electron is captured by a positive ion. At Mars the
main reaction in the ionosphere is the dissociative recombination of O 2 C and the
energy is carried away in the form of kinetic energy by two resulting O atoms. The
ionisation depends primarily on the sun and its activity. The amount of ionisation
in the Martian ionosphere varies greatly with the amount of radiation received
from the sun. Thus, there is a diurnal and seasonal effect on Mars. During the
northern winter/northern summer, Mars is away/close to the sun. Thus, it will
receive less solar UV radiation during winter than summer. The activity of the sun
is also associated with the sunspot cycle, with more radiation occurring with more
sunspots. Although Mars has a strong magnetic field originating in the crust, these
fields are not global and therefore do not deflect solar wind particles which can
ionise the upper atmosphere of Mars. However, the interaction of solar wind with
inhomogeneous crustal fields is a major cause of spatial and temporal variations and
thus in the ionospheric chemistry, dynamics and energetic (Nagy et al. 2004 ;Brain
2006 ; Withers 2009 ; Mendillo et al. 2011 ). The upper ionosphere of Mars is divided
into E and F region. These two regions are described in the following sections.

7.2.1 E Region Ionosphere

Mars ionospheric E layer, which has its peak density at about 115 km, is produced
by X-ray radiation in the daytime ionosphere at wavelength range 10-90 Å (Haider
et al. 2002 ; Rishbeth and Mendillo 2004 ;Haideretal. 2009a , b ). At night the E
layer disappears because the primary source of ionisation is no longer present. The
vertical structure of the E layer is primarily determined by the competing effects of
ionisation and recombination. The ion composition calculation shows that O 2 C and
NO C are the major ions in the E region with N 2 C and O C as minor ions (Haider et al.
2012 ). Figure 7.1 shows production rate (photoionisation C photoelectron impact