 |
| Titel |
Comparing the contributions of ionospheric outflow and high-altitude production to O+ loss at Mars |
| VerfasserIn |
Michael Liemohn, Shannon Curry, Xiaohua Fang, Blake Johnson, Markus Fraenz, Yingjuan Ma |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083535
|
|
|
|
|
|
| Zusammenfassung |
| The Mars total O+ escape rate is highly dependent on both the ionospheric and high-altitude
source terms. Because of their different source locations, they appear in velocity
space distributions as distinct populations. The Mars Test Particle model is used
(with background parameters from the BATS-R-US magnetohydrodynamic code)
to simulate the transport of ions in the near-Mars space environment. Because it
is a collisionless model, the MTP’s inner boundary is placed at 300 km altitude
for this study. The MHD values at this altitude are used to define an ionospheric
outflow source of ions for the MTP. The resulting loss distributions (in both real and
velocity space) from this ionospheric source term are compared against those from
high-altitude ionization mechanisms, in particular photoionization, charge exchange, and
electron impact ionization, each of which have their own (albeit overlapping) source
regions. In subsequent simulations, the MHD values defining the ionospheric outflow
are systematically varied to parametrically explore possible ionospheric outflow
scenarios. For the nominal MHD ionospheric outflow settings, this source contributes
only 10% to the total O+ loss rate, nearly all via the central tail region. There is
very little dependence of this percentage on the initial temperature, but a change in
the initial density or bulk velocity directly alters this loss through the central tail.
However, a density or bulk velocity increase of a factor of 10 makes the ionospheric
outflow loss comparable in magnitude to the loss from the combined high-altitude
sources. The spatial and velocity space distributions of escaping O+ are examined and
compared for the various source terms, identifying features specific to each ion source
mechanism. These results are applied to a specific Mars Express orbit and used to
interpret high-altitude observations from the ion mass analyzer onboard MEX. |
|
|
|
|
|
|