Solar%20Wind-Magnetosphere%20Interactions%20via%20Low%20Energy%20Neutral%20Atom%20Imaging

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Solar Wind-Magnetosphere Interactionsvia Low
Energy Neutral Atom Imaging

• T E Moore1, M R Collier1, M-C Fok1, S A
  Fuselier2, D. G. Simpson1, G. R. Wilson3,
  M. O. Chandler4
• 1. NASAs Goddard Space Flight Center,
  Interplanetary Physics Branch, Code 692,
  Greenbelt, MD 20771
• 2. Lockheed Martin Advanced Technology Center,
  Dept. H1-11, Bldg. 255, Palo Alto, CA 94304
• 3. Mission Research Corporation, 589 W. Hollis
  St., Suite 201, Nashua, NH 03062
• 4. National Space Science and Technology Center,
  NASA MSFC SD50, Huntsville AL 35805
• LENA was motivated by need for time-resolved
  ionospheric outflow observations.
• Also responds to neutral atoms with energies up
  to a few keV (from sputtering).
• As a result, we have been able to
• Show that ionospheric outflow responds to solar
  wind dynamic pressure variations.
• Observe that the response is prompt.
• Infer a heating source below 1000 km altitude for
  the larger flux events.
• Use neutral atom emissions to reveal the
  magnetosheath, with cusp-related structures.
• Infer dayside structure in the geocorona. .
• Measured the annual variation of the neutral
  solar wind.
• Probe the interstellar gas and dust in the inner
  solar system.
• Directly observe the interstellar neutral atom
  focusing cone at 1 AU.
• LENA imaging has thus proven to be a promising
  new tool for studying the interplanetary medium
  and its interaction with the magnetosphere, even
  from inside the magnetosphere.

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Low Energy Neutral Atoms (LENA) CME/Storm Onset
and Response
Hr Before Hr After Snap Perigee

• Solar Wind LENA increase marks CME arrival at
  0915 hrs.
• Earth sector LENA respond within travel time of
  35eV O0.

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Comparison with Ion Outflows
LENA H/O/Total Images
TIDE Polar Ion Outflows
Neutral Fraction vs Source Altitude

• Preliminary comparisons
• Some spatial correspondence (day - night here)
• Flux comparison indicates low altitude source
  region
• Best correspondence w/ auroral oval from
  transverse views (not shown)
• Posters AGUsm01 SM72A-14 (Coffey et al.),
  -15(Wilson et al.)

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Simulated LENA Emissions
Auroral zone emissions
Uniform polar emissions
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Sources of Indirect SW-LENA
Collier et al. Nov JGR p.24,893
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Solar LENA flux profile
Strong similarity to ram pressure profile
observed at WIND.
Tracking observed at some time scales, not others.
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Simulation of Indirect LENAs

• Simulations performed by M.-C. Fok using MHD
  magnetosheath.
• Analogous to ring current ENA simulations, using
  an CCMC (BatsRUS) MHD model of the magnetosheath,
  and looking out.
• LOS integration from 8 to 50 RE, excepting
  antisunward 90 cone. Images collapsed in polar
  angle, for IMAGE.
• No true solar LENAs assumed to arrive in solar
  wind here.

200 eV
4000 eV
Dawn-Dusk Orbit
Dawn-Dusk Orbit
Noon-Midnight Orbit
Noon-Midnight Orbit
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• Solar wind flux or dynamic pressure increases
  produce a big reaction in LENA.
• A brightening is seen especially between the sun
  pulse and the Earth (white line here).
• Is this the expected relation between solar wind
  intensity and ENA emission from this region?

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We expect a very strong dependence because so
many factors are affected by solar wind flux (and
Pd).
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Simulation of Magnetosheath CE

• CCMC Simulations based on BatsRUS Code
• LOS integration from IMAGE spacecraft by M-C Fok.
  
• Consider periods of enhanced Pd solar wind for
  compressed magnetopause.
• Remote sensing of cusp and cleft possible with
  sufficient sensitivity and-or Pd.

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Seeing Magnetosheath Structure

• CCMC (BatsRUS) MHD simulation of the 31 March
  2001 event, showing magnetosheath density
  distribution along LENA lines of sight at about
  0450 UT

• LENA spin modulation near the peak of the 31
  March 2001 event at about 0450UT

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Remote-Sensing the Magnetosheath
Simulations indicate features of the
magnetosheath should be visible and are visible
from inside the magnetosphere.
Sun
MS
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Evidence for Geocoronal Erosion?
Data LENA background adjusted flux gt 30 eV
Deflectors
5-50 RE
5-12 RE
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Short term, storm variations reflect solar wind
intensity variations, CMEs, and distribution of
the geocorona.
Long term, seasonal variations reflect solar
system distribution of neutral gas (interstellar
and other sources)
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SW ENA Model of Bzowski et al.Icarus 1996
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Limit on Inner Solar System Dust
Collier et al., AGU SM2001
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Predicted Direct ISN Observations
Fuselier, 1997
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Direct ISNs, Interpreted?
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3D Interstellar Neutral Trajectories
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ISN Flux
12/1
1/1
2/1
3/1
12/1
1/1
2/1
3/1
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Conclusions

• We have been able to
• Validate earlier statistical inferences that
  ionospheric heating responds to solar wind
  dynamic pressure variations.
• Observe that the response is prompt, as fast as
  hydromagnetic wave propagation speeds.
• Infer that the heating source must lie lower than
  1000 km altitude for the larger flux events.
• Use neutral atom emissions to reveal the
  magnetosheath, with cusp-related structures.
• Infer dayside structure in the geocorona, owing
  to solar wind erosion by charge exchange.
• Measure the annual variation of the neutral solar
  wind.
• Interpret annual variation in terms of
  interstellar neutral gas and dust in the inner
  solar system.
• Directly observe the interstellar neutral atom
  focusing cone at 1 AU.

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Comparison with Dayside Aurora
8 June 2000 CME Arrival

• See Fuselier et al., GRL 15 March 2001.
• Before/After images of dayside aurora.
• IMF Bz generally Northward.
• Similar in many ways to 24 Sept 98 CME, with
  resultant Ionospheric Mass Ejection Moore et
  al., GRL, 1999

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Direct ISNs, Observed
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