Model comparison of oxygen ion loss at Mars
Shannon Curry1, Michael Liemohn1, Xiaohua Fang2, Yingjuan Ma3, David Brain2
1Department
of Atmospheric, Oceanic & Space Sciences, University of Michigan
The Mars pick-­‐up ion transport model has been developed to study the rela3ve role of kine3c processes on ion transport through near-­‐Mars space. Mars does not have a strong, intrinsic dipole magne3c field and consequently the solar wind directly interacts with the dayside upper atmosphere causing par3cles to be stripped away from the atmosphere. The main objec3ve of this work is in conjunc3on with the Mars-­‐solar wind Interna3onal Space Science Ins3tute (ISSI) to conduct comparisons of codes for iden3cal simula3on scenarios. By facilita3ng a number of groups to collec3vely define run configura3ons, exactly comparable model results of the Mars space environment can be been generated. The three cases for comparison are: A = solar min, no exosphere B = solar min, with exosphere C = solar max with exosphere Figure 1
§  The equatorial view of the production rate shows the
three sources of ionization from 300 km to 3 RM.
§  The dayside dominance in production is evident in all
three sources, but the nightside production varies
much more so.
§  For ions produced as a result of photoionization, the
optical shadow behind the planet has essentially no
ion production while the dayside shows production as
a function of altitude. SZAis not accounted for.
§ 
Both charge exchange and electron impact ion
production illustrate the magnetosheath bias where
the solar wind protons bombard the neutral
atmosphere inside of the induced magnetosheath.
of Colorado, Boulder
3University
of California. Los Angeles
Mars pick-­‐up ion model Mo#va#on PRODUCTION
2University
Case
A
Case
B
Case
C
The test par3cle simula3on is a parallelized 3-­‐D Monte Carlo model that describes how Mars pickup oxygen ions are transported and accelerated [Fang et al., 2008]. The pick-­‐up ions are created through : 1) photoioniza3on, 2) charge exchange with solar wind protons, 3) impact ioniza3on by solar wind electrons Global mars-­‐solar wind MHD model The background electric and magne3c fields which the ions above follow are calculated by the Mars BATS-­‐R-­‐US model. The simula3on is a 3-­‐D mul3species model [Ma et al., 2004] which solves the conserva3ve form of the MHD equa3ons LOSS
Figure 3
§  The escape rates to the right illustrate an
annulus (see insert, right) of loss in the
Case
northern hemisphere around a 3 RM shell,
A
in units of # O+ / cm3 for the three ISSI
cases (note different scales!)
§  All three ionization source mechanisms are plotted against the
total in order to highlight both the change in dominance at each
spatial location as well as the particularly high loss in the
northern pole
Figure 4
§  The escape rates are as a function of solar cycle case and
Case
3
ionization
source
mechanism,
in
units
of
#
O+
/
cm
B
§  Additionally, the percentage of the total loss that each ionization
mechanism contributes to is plotted for all three cases.
VELOCITY SPACE DISTRIBUTIONS
Figure 2
§  VSDs explain where and in what direction
the loss is occurring for a given energy
range.
§  Θ is the polar angle where 0° < Θ°< 90°
represents the expected upward velocity
§  φ is the azimuthal angle where 90°< ϕ <
270° represents expected tailward motion.
§ 
The figure shows the virtual detector
places downtail
§  Note the low energy ranges, particularly
between 0-10 eV, which are below the
MEX and MAVEN ion energy thresholds
[Lundin et al. , 2011]
§ 
§ 
§ 
§ 
Figure 1: Equatorial cut of producCon rates Case B
Case C
Case
C
Figure 3: Annulus of O+ escape at 3 RM Figure 4: Escape rates and percentages Figure 2: Downtail Velocity Space Conclusions Kine3cs are important for understanding O+ transport through near-­‐Mars space Ioniza3on mechanisms play a significant role in determining transport and escape Inclusion of the hot corona significantly alters the escape rates of O+ The low energy loss is cri3cal to include in total escape rate calcula3ons Future Work §  Future work in this area will directly support the the interests of the NASA Mars Explora3on Program, which includes the MAVEN mission as the next Mars Scout. §  This proposed study will quan3fy Mars' upper atmospheric loss and also examine the usage of high-­‐
al3tude ion measurements to determine the source mechanism and loca3on of the pick-­‐up ions. 1.  Fang, X., M. W. Liemohn, A. F. Nagy, J. G. Luhmann, and Y. Ma, On the effect of the Martian crustal magnetic field on atmospheric erosion, Icarus, 206, 130-138, 2010.
2. Lundin, R., Barabash, S., Yamauchi, M., Nilsson, H., Brain, D. On the relation between plasma escape the Martian crustal field , Geophysical Research Letters ), 38, 2011
3. Ma, Y., A. F. Nagy, I. V. Sokolov, and K. C. Hansen, Three-dimensional, multispecies, high spatial resolution MHD studies of the solar wind interaction with Mars, Journal of Geophysical Research (Space Physics), 109, 7211+, 2004. D