 |
| Titel |
Martian oxygen escape rate as a function of upstream solar wind density: results from a hybrid model |
| VerfasserIn |
Xiao-Dong Wang, Mats Holmstroem |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107166
|
| Publikation (Nr.) |
 EGU/EGU2015-6857.pdf |
|
|
|
|
|
| Zusammenfassung |
| We investigate the dependence of oxygen escape rate at Mars on the proton density of
the upstream solar wind using a parallel hybrid model. The model handles ions as
particles and electrons as a massless, neutralizing fluid. The model currently contains
three ion species: protons and alpha particles from the solar wind, and a heavy
ion species from Martian ionosphere, which is atomic oxygen ion in this study.
The interplanetary magnetic field is set to follow the typical Parker spiral at Mars
with an intensity of 3 nT. The upstream solar wind velocity is 400 km/s, along the
-x axis. We vary the upstream proton density from np =0.2 cm-3 to np =25
cm-3 while keeping all other parameters fixed. The oxygen escape rate Q shows a
negative correlation with np within the range 0.5 < np < 3.5 cm-3. The ratio
between the maximum and the minimum escape rates is ~3. Outside this density
range the correlation is positive. This anticorrelation between Q and np within the
most probable range of the upstream proton density, and the relative variation of Q
are consistent with the latest experimental investigations on the same topic using
the ion data from MEX/ASPERA-3 [Ramstad et al., 2014]. We also investigated
cases under 500 km/s upstream velocity and CO2+ ions, the results are qualitatively
consistent.
The modeled magnetospheric morphology reveals two competing escape channels that
depend differently on the upstream density. The channel including the pickup ions and the
plasma sheet intensifies with increasing upstream density. The channel including the lobe
region and the boundary layer intensifies with decreasing upstream density due to a more
expanded induced magnetosphere. The latter dominates the ion escape when the density is
lower than ~2.5 cm-3. We also investigate the momentum transfer from the shocked solar
wind to the induced magnetosphere.
References: R. Ramstad, S. Barabash, Y. Futaana, H. Nilsson, M. Holmstroem [2014]:
The Martian escape rate as a function of upstream solar conditions, AGU Fall Meeting 2014,
P51B-3941, San Fransisco. |
|
|
|
|
|
|