Geoscience Reference
In-Depth Information
OBSERVATIONAL FEATURES OF THE SECONDARY
LAYER OF THE MARTIAN IONOSPHERE
HAI-REN LIAO
†,¶
, JING-SONG WANG
†,‡,∗
, HONG ZOU
†
and XIAO-DONG WANG
†
†
School of Earth and Space Sciences, Peking University, Beijing, China
‡
China Meteorological Administration, Beijing, China
∗
wangjs@cma.gov.cn
¶
wjs@pku.edu.cn
The behaviors of both the density and height of the peak of the primary Mar-
tian ionospheric layer have been intensively investigated. On the contrary, the
study on the secondary layer is mainly focused qualitatively on the photo-
chemistry processes leading to this layer. The observational behaviors of the
secondary peak, i.e., that of the peak height and the peak density, are seldom
emphasized. In this paper, the Martian ionospheric profiles obtained by the
Mars Global Surveyor (MGS) Radio Science (RS) experiments during two con-
tinuous periods are investigated. For 1,678 of the available 3,377 ionospheric
electron density profiles, the secondary peak can be easily distinguished. Both
the solar zenith angle dependence and the solar activity dependence of the sec-
ondary peak are investigated. E10.7, the integrated extreme ultraviolet (EUV)
energy flux at the top of the atmosphere reported in units of 10.7 cm radio flux,
is used as the proxy of solar radiation in this study. However, the main pho-
toionization source for the secondary layer is not mainly EUV but soft X-ray.
This shortcoming should be improved by using X-ray flux measurements; how-
ever, this is beyond the scope of this study.
1. Introduction
The observed electron density profiles of the Martian ionosphere always
present a primary or upper layer, and a trend of a secondary or lower layer,
which could behave as a peak, a ledge or a shoulder, but sometimes even
not present.
1
,
2
A third layer is also noticed by authors (e.g., Refs. 3 and 4).
The behaviors of both the height and density of the primary peak have
been intensively studied,
5
-
11
while the study on the secondary layer has
been mainly focused on the photochemistry processes.
3
,
12
,
13
It is believed
that the secondary layer is produced by the ionization due to the solar soft
X-ray radiation and impact of photo- and secondary electrons.
The Radio Science (RS) experiment aboard Mars Global Surveyor
(MGS)
18
has obtained many electron density profiles of the Martian
135
