martian pick-up ions (and foreshock): solar-cycle and seasonal variation m. yamauchi(1); t. hara(2);...
TRANSCRIPT
Martian Pick-up Ions (and foreshock): Solar-Cycle and
Seasonal Variation
M. Yamauchi(1); T. Hara(2); R. Lundin(3); E. Dubinin(4); A. Fedorov(5); R.A. Frahm(6); Y. Futaana(1); R. Ramstad(1); H. Nilsson(1); M. Holmstrom(1); S. Barabash(1)
(1) Swedish Institute of Space Physics (IRF), Kiruna, Sweden; (2) Space Sciences Laboratory, University of California, Berkeley, USA; (3) IRF, Umea, Sweden; (4) Max-Planck-Institut fur Sonnensystemforschung, Germany; (5) Institut de Recherche en Astrophysique et Planetologie (IRAP), CNRS/Universite de Toulouse, France; (6) Southwest Research Institute, USA
RS: Bow-shock radius (~ 5000 km for Martian Subsolar)
MA: Alfvén Mach number
rg: Gyroradius ( ~ 1000 km for 2 keV H+ under 6 nT)
c/pi: Inertia length (100 km for 5/cm3 H+)
RS MA c/piRS rg/RS cold H+ at BS foreshock
Earth 5 ~ 1.2 ~ 0.3 ~ 0.4 no yes
Venus 1 1 1 1 very little yes
Mars ~ 0.5 ~ 1.4 ~ 5 ~ 8 some less
Comet ? 1~2 large large massive ?
Venus-Mars-Comet differencePlanetary Size & Gravity Standoff distance & Exospheric Size
Cold ion inside Solar Wind / Bow Shock
Actual observation (scan over )
pickup ions
BS BS
SW SW
foreshock
No clear pickup ionSW reflection occurs but no foreshock at X>0
SW reflection
Cold ion density outside Bow Shock varies with exospheric extent (visible~UV) and ion production rate (UV).
Next: Solar Cycle dependence
Season: Sun-Mars distance changes 20% (radiation flux 45%)
Observation Probability
note: automated method is far from perfect (e.g., including reflected ions near bow shock), but statistics is clear
(using automated method to identify ring)
2005.6–8 2007.7–9 2009.3–7 2011.3–6 2013.1–4
Southern Summer (tilt angle) ≈ short distance
2004.6–10 2008.4–9 2010.3–8 2012.2–6
Southern Winter (tilt angle) = long distance 100%
50%
0%
No Hemispheric differenceNorth Summer (distant)South Summer (close)
S hemisphere
N hemisphere
S hemisphere
N hemisphere
100%
50%
0%
It looks like
1. Season >> Solar cycle (clear)
2. Not only UV level (need to confirm)
Statistic by Manual Method(examine 2005-2012 data by eye)
Summer during Solar Minimum (bow shock is longer distance!) produces more pick-up ions than Winter during Solar Maximum
Reflected ions also forms "ring" "probability" is high near bow shock
Manual (eye) examination statistics
2-month averaged result
Compared with UV level
Summer during Solar Minimum (bow shock is longer distance!) >> Winter during Solar Maximum
Probability of clear pick-up ions
(1) Intensity of the ring ions varies by at least one order of magnitude by variable Sun-Mars distance.
(2) For the same UV flux level, Summer during Solar Minimum produces more pick-up ions in the solar wind than Winter during Solar Maximum not only UV
(3) Ring ions is strong close to bow shock (inside regions full of reflected ions) not only UV
(4a) Ring ions sometime appear less than one day during Winter, and (4b) disappear for some period during Summer (difficult to attribute this to IMF variability). not only UV
Summary
Implication
• Electron impact ionization?
• Exosphere breeds?
• Alfven's critical ionization process? (foreshock creates ring?)
Production of pick-up ions is very variable in the independent way from solar radiation.
Related to pick-up ions
(1) Fate of pick-up ions: Comet-like diffusion
(2) O+ sneaking out event to upstream
(3) Relation to Foreshock
(1) Diffusion of pick-up ions
Similar to comet!X≈+1 RM
X≈1.5 RM
(2) Oxygen outside bow shock
No O+ pick-up from O-corona, but can be picked up
(3) Foreshock
2005: almost none
2007: sometimes2008: sometimes
2009: rare2010: sometimes2011: rare
Foreshock vs pick-up ions
Except 2007 June-September (Martian summer), foreshock during Martian summer (out of phase from pick-up ion. Solar cycle (UV) might play some role in this cases
foreshocks foreshocksforeshocks
NoteAlthough anti-phase, we do observe co-existence of Foreshock with pick-up ions (rare event)
Conclusion
Martian upstream is a real plasma laboratory that the Earth cannot provide. Just related to the pick-up phenomenon, many unknown physics exist.
Martian pick-up ion physics is a good reference for Comet pick-up ion physics
Thank you
we need to classify all “non-solar wind” ions because the Martian upstream is full of reflected ions, pickup ions, and thermalized form of these ions.
For sold probability work,
In 2011 paper, we reported that we could not find foreshock in 2005 data (we used highest post-acc data).
(comet-like) scattered pick-up ions
Foreshock
Reflected (and accelerated) at bow shock
Detached Bow shock
ring distribution in SW2005: rare 2005.1 - 2005.5 & 2005.9 – 2005.10 / often 2005.7 & 2005.11
2007: rare 2007.1 – 2007.4 / some 2007.9 – 12 often 2007.6 - 2007.8
2008: rare 2008.1 –12
2009: rare 2009.1 – 3 & 2009.11 – 12 / some 2009.4 – 10 often 2009.8
2010: rare 2010.1 –10 / some 2010.11 – 12
2011: rare 2011.8 –12 / some 2011.1 – 2 often 2011.3 - 2011.6
2012: rare 2012.1 –7 & 2012.9 –10 / some 2012.8 & 2012.11 –12
2013 rare 2012.8 / some 2012.9 often 2012.2 – 2012.3
pick-up ions (ring distribution)
bow
sho
ck
upstream pick-up
downstream pickup = comet-like scatter
comet-like scatter
pick-up + reflected
Reflected with pick-up ions
Reflected without pick-up ions
Reflected ⇒Foreshock
foreshock boundary
detached bow shock
(1) Gravity: Venus > Mars < comet
(2) Exosphere: Venus < Mars < comet
(3) newly born H+ in Solar Wind: Venus < Mars < comet
(4) Bow shock: Venus ≠ Mars ≠ comet
Venus-Mars-Comet difference: cold H+