Geoscience Reference
In-Depth Information
Without any treatment in advance, among all of the 3,377 profiles, 2,667
can be catalogued to type 1, i.e., with a distinct secondary layer. However,
to avoid “pseudo-peak” caused by observation noises, a 5-point running
average is applied to all the 2,667 profiles and 1,678 profiles of them can
be still treated as type 1. Therefore, these 1,678 profiles have convincing
secondary layer and are left for further investigation. The density and height
of the peak are easily read from each profile.
The dependence on the solar zenith angle and the solar radiation of
both the peak density and peak height of the secondary layer are investi-
gated here. The flux of solar extreme ultraviolet (EUV) radiation near Mars
is not available, but it can be derived from the E10.7 at the Earth orbit
with distance and direction correction. E10.7 is the integrated EUV energy
flux at the top of the atmosphere reported in units of 10.7 cm radio flux
(F10.7)
15
,
16
and is available at http://SpaceWx.com. Actually the 10.7 cm
radio flux (presented by F10.7) is has no physical connection with the atmo-
spheric processes, while the EUV radiation (presented by E10.7) is the main
ionizing source for ionosphere, so E10.7 is a better proxy than F10.7 for ion-
izing flux. In this paper, the daily averaged E10.7 index is used as a proxy
of the solar EUV flux.
15
,
19
3.
Results
The occultation location on the Mars surface varies with time during the
MGS/RS measurement and about every 12 continuous orbits of MGS
around Mars corresponds to a period of the longitude variation of the
occultation location.
18
Since planetary scale waves in the neutral atmo-
sphere can appear as longitudinal variations in the Martian ionosphere,
1
a
daily running average is applying to the dataset to reduce the effects of the
longitudinal variation.
Figure 2 shows the dependence of the daily averaged secondary peak
density,
N
m
, and height,
z
m
, upon the solar zenith angle (SZA, denoted as
χ
). The left panel is for period I, the right panel is for period II. Analogous to
the description of the SZA dependence of the Martian ionospheric primary
peak, i.e.,
N
m
=
N
m0
cos
k
χ,
(1)
z
m
=
z
m0
+
H
ln sec
χ,
(2)
where
N
m0
and
z
m0
are the sub-solar (
χ
= 0) peak density and height,
respectively,
k
is a parameter that depends on the photochemical process,
6
