IMAGE/HENA: NOT ONLY PRETTY PICTURES

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IMAGE/HENANOT ONLY PRETTY PICTURES

• Pontus Cson Brandt, D. G. Mitchell, S. Ohtani,
  E. C. Roelof, R. Demajistre, B. Anderson
  JHUAPL, MD
• Acknowledgements R. A. Wolf (Rice, TX), M. C.
  Fok and N. Tsyganenko (NASA GSFC, MD), LANL-team

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OUTLINE

1. IMAGE mission
2. Why ENA imaging?
3. MI-coupling at work
4. Global substorms?
5. Next step multi-point observations
6. What else?
7. Conclusions

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B. R. Sandel, Univ. of Arizona Lead Investigator
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THE IMAGE MISSION

• Lifetime 2000-2005
• 800 x 8 Re solar inertial orbit (more later on
  orbit)
• LENA 50 eV-10 keV
• MENA 1-50 keV
• HENA 10-200 keV (hydrogen) 50-180 keV (oxygen)
• FUV auroral imager (proton and electron aurora)
• EUV plasmaspheric imager. Images light
  resonantly scattered sunlight scattered on He.

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Charge Exchange
A magnetically trapped ion captures an electron
from a neutral hydrogen atom...
creating an energetic neutral atom (ENA) that is
no longer trapped.
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High-Energy Neutral Atom (HENA) Imager
Lead Investigator D. Mitchell, Applied Physics
Lab
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STORM AS SEEN BY HENA March 31 2001 (60-119 keV
protons)
-40 nT
21 nT
26 nT
0730 UT
0830 UT
0930 UT
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WHY ENA IMAGING?

• The only way to image proton plasma.
• The hot plasma (ring current/plasma sheet) in the
  Terrestrial magnetosphere has proven to be more
  dynamic than anticipated.
• Need to measure global pressure on timescales lt
  10-20 min.
• All of the region 2 and probably a large portion
  of the nightside region 1 current system is
  PRESSURE DRIVEN.

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MEASURED/COMPUTED QUANTITIES
SCIENTIFIC UNDERSTANDING
ENA
STORM, SUBSTORM DYNAMICS
PRESSURE
CURRENTS
MI-COUPLING
B-FIELD TOPOLOGY
DB (Biot-Savarts)
ADIABATIC EFFECTS ON RADIATION BELTS
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Drawback when using PAD components currently the
same PAD everywhere in space.
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Dipole validity
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IONS ? CURRENT
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Field aligned currents (FAC)(Region 2 system)
HENA
IRIDIUM (Courtesy Dr. B. Anderson, JHUAPL)
Micro A/m2
-0.91
-0.1
0.1
0.91
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WHAT HAVE WE LEARNED SO FAR?

• The morphology of the storm-time ring current
  depends heavily on the ionospheric conductivity.
• Storm main phase ring current peaks around
  midnight.
• Storm-time substorm injections can have an
  extreme local time extent (to noon).
• Heavy ions (O) are energized dramatically during
  storm-time substorms.
• Storm-substorm relationship confirming the
  convection dominated storm picture.

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MI COUPLING AT WORK (Storm main phase modeling
by M. C. Fok et al., JGR, 2001)
NEW PICTURE
OLD PICTURE
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MI COUPLING AT WORK
The Comprehensive Ring Current Model (CRCM) Fok
et al., 2001 computes the E-field
self-consistently via the closure through the
ionosphere. Matches HENA observations.
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MI-COUPLING AT WORK

• Old picture storm-time ring current peaks at
  dusk, because thats where the Alfven layer comes
  closest to the Earth in a dawn-dusk E-field.
• New picture Wolf, 1980 Fok et al., 2001
  storm-time ring current peaks at midnight.
  Consistent with IMAGE results Cson Brandt et
  al., 2002.
• Mechanism
• The convectional E-field (dawn-dusk) try to force
  Hall currents to flow across the terminators
  (conductivity jump)?positive charge
  build-up?skewing of potential pattern.
• Probably some additional intricate effects.

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SubAuroral Polarization Stream (SAPS) (Foster et
al., EOS and JGR, 2002)
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GLOBAL SUBSTORMS?

• Substorms during extended storm main-phases
  appears to have an extremely wide injection front
  that can wrap around the Earth.
• Are we dealing with an azimuthal current sheet
  rather than a cross-tail current?

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0903 MLT
1110 MLT
1714 MLT
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1940 MLT
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2304 MLT
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NOT PARTICLE TRANSPORT!

• LANL, 75-113 keV. Propagation speed 11.4
  deg/min
• Proton drift speed at L6.6, E100 keV is 22
  deg/min
• GOES B-field. Propagation speed 8.5 deg/min
• A survey of events have shown that dipolarization
  and particle injections go together. The most
  extreme injection/dipolarization at noon,
  midnight and dawn!
• Dipolarization at extended local times?
• Propagating dipolarization in the B-field, or,
• An azimuthally propagating current sheet
  disruption?
• HENA give insight in the local time extent.

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MULTI-POINT OBSERVATIONS

• One single image cannot resolve the PAD (to any
  good accuracy)!
• Chinese mission with Irish/Swedish ENA imager
  will launch in mid 2004.
• IMAGE will then be close to Equator and on its
  way to south-pole apogee.?
• one polar vantage point and on at the equator can
  resolve large-scale pitch-angle distributions
  (PAD) for the first time!
• Specifically is there a high-energy (100 keV)
  component of trapped ions during storm main
  phase?
• Perigee passes with IMAGE and simultaneous apogee
  passes with DSP will give essential information
  on upper atmosphere interactions during different
  phases of the storm/substorm.
• Note tomography requires far more vantage points
  than just a couple.

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CONJUNCTIONS
JAN 2001
JAN 2002
JAN 2003
JAN 2004 Mostly equatorial vantage point
JAN 2005 Mostly polar
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PAD AND VANTAGE POINTS60-119 keV hydrogen ENA
EQUATORIAL VANTAGE POINT Dst-54 nT
POLAR VANTAGE POINT Dst-71 nT
Note a factor of 2 stronger flux for equatorial
vantage point?Anisotropy2.
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MULTI POINT OBSERVATIONPRE-LAUNCH STUDIES

• Simulate DSP ENA images with instrumental
  response
• Apply and improve APL inversion technique on
  simulated DSP images and observed HENA images.
  Individually and as multipoint data.
• Develop intercalibration techniques by using
  e.g. Cluster/CIS data
• Important develop a method for including a
  spatially varying PAD.

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WHAT ELSE?

• Storm-substorm relationship computing DENA
  (equivalent Dst through DSP-relation)
• Plasmasheet studies during substorms
• O and substorms
• Upper bounds on ENAs from the heliospheric
  termination shock much weaker than expected.
• Characterization of storm ring current to improve
  Tsyganenko magnetic field model.

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CONCLUSIONS
REPRINTS AVAILABLE

• sd-www.jhuapl.edu/IMAGE

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