STORM PRESSURE DISTRIBUTIONS FROM IMAGE/HENA

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STORM PRESSURE DISTRIBUTIONS FROM IMAGE/HENA

• P. Cson Brandt, D. G. Mitchell, E. C. Roelof, R.
  Demajistre, A. T. Y. Lui
• The Johns Hopkins University Applied Physics
  University

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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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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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High-Energy Neutral Atom (HENA) Imager
Lead Investigator D. Mitchell, Applied Physics
Lab
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(No Transcript)
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CONSTRAINED LINEAR INVERSION
ENA-cts in pixel i
MEASUREMENT EQUATION
Ion flux in equatorial plane
Quadrature weights geometry, mapping, etc.
STANDARD CONSTRAINED LINEAR SOLUTION Twomey,
1977
Constraint matrix
Constraint strength
BAD (WEAK) g
GOOD g
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OPTIMIZING g
Simulated test ENA image
Test ion distribution
simulate
invert
Minimize difference
Minimize difference
simulate
Inverted ENA image
Simulated ENA image
g1e-10
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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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GLOBAL PROTON PRESSURESCson Brandt et al.,
2002
INVERSIONS
0900 UT 12 Aug 2000 10-198 keV
1800 UT 4 Oct 2000 10-198 keV (65 of total)
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OLD PICTURE

• Shouldnt the ring current peak at dusk?
• Particle drift in corotationconvection field

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OLD PICTURE

• and it is WELL-KNOWN that the magnetic
  depression on ground maximizes around dusk!

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OLD PICTURE GROUND MAGNETIC DEPRESSION(Courtesy
of R. Clauer)
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SOWHAT IS GOING ON?

• HENA shows lt20 min snapshots of the mainphase,
  which is hard to get resolve with statistical
  studies.
• The ground magnetic depression is caused mostly
  by ionospheric currents.

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GEOMAGNETIC DEPRESSION(Crooker et al. 1981)

• Observational and theoretical evidence for an
  overlap of the Region 1 and 2 currents around
  noon.?
• Net down going current around noon
• Net up going current around midnight
• Causes depression on ground.
• Poster1100 by Yamashita et al. and Nakano et
  al., this conference.

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STATISTICAL PRESSURES 1.Lui, DeMichelis

• Results from AMPTE/CCE CHEM and MEPA study does
  not agree fully Lui, DeMichelis et al.
• Probably due to too crude binning of data (Kpgt3
  for Lui AEgt100 nT for Demichelis)
• We will try to narrow down on main phases and
  re-examine the data sets.
• Shows how dynamic the ring current morphology is
  in the main phase - recovery phase transition
• IMAGE/HENA data indicates that the main phase
  ring current spreads westward and can reach noon
  in 1-2 hours. Geomagnetic indices are still high
  ? binning in geomagnetic indices will smear the
  ring current.

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NEW PICTURE(Wolf et al. already in the
70sRCM runs)
Enhanced pressure
No significant ring current pressure
Sub-Auroral Polarization Streams (SAPS)
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NEW PICTURE(Wolf et al. already in the 70s)

• 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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STATISTICAL PRESSURES 2.

• 1-200 keV protons from POLAR/MICS Ebihara et
  al., GRL, 2002
• Manually investigated 300 storms and picked
  mainphases (Dst steadily decreasing) when POLAR
  was close to equatorial plane

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MAINPHASE?RECOVERY(24 NOV 2001)
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CONCLUSIONS

• IMAGE/HENA observes main phase proton pressure
  distribution peaked around midnight.
• O pressure appears to be closer to pre-midnight
  sometimes, but not in the 18-21 MLT sector as
  ground magnetic depression suggests.
• Ground magnetic depression is probably due to FAC
  and not the partial ring current and can thus not
  be used to infer the location of the ring
  current.
• Self consistent models Wolf (RCM), Fok (CRCM)
  agree ? ionospheric conductivity gradient are
  essential.
• Recent statistical study by Ebihara et al. 2002
  agrees.
• Ring current morphology changes too quickly to
  allow the main phase to be binned by magnetic
  activity (indices are still high in early
  recovery phase, when ring current is spreading
  westward?smearing will result)