RELATION BETWEEN THE RING CURRENT AND SUB-AURORAL ELECTRIC FIELDS

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RELATION BETWEEN THE RING CURRENT AND SUB-AURORAL
ELECTRIC FIELDS

• P. Cson Brandt, J. Goldstein, J. C. Foster , M.
  C. Fok, E. C. Roelof, R. DeMajistre

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SUB-AURORAL POLARIZATION STREAM (SAPS)
Enhanced electron density in the DUSK sector
during storm mainphases.
J. C. Foster et al., GRL, 2003.
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PLASMASPHERE
The PLASMASPHERE is the cold plasma inside the
ring current. Its transport is only governed by
electric fields. Hence, it is an excellent
tell-tale of the E-field of the inner
magnetosphere.
Grebowsky et al., JGR, 1970.
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MAGNETOSPHERIC E-FIELD
The poleward ionospheric SAPS E-field maps to a
radially outward E-field in the equatorial
magnetosphere.
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MAGNETOSPHERIC E-FIELD
Enhanced E-fields at dusk have been observed by
CRRES.
Rowland, thesis, 2000.
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MAGNETOSPHERIC E-FIELD
GOLDSTEIN TUESDAY 1440
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RING CURRENT RELATION
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RING CURRENT RELATION

• SAPS appears to enhance simultaneous with ring
  current.
• What is the relation?

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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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RING CURRENT RELATION

• We know from HENA that the Region 2 FACs
  intensify.
• Dr. Mei-Ching Foks CRCM can predict the SAPS,
  so lets ask it.

Cson Brandt et al., JGR, 2002. Roelof et al.,
and Cson Brandt et al., Adv. Space Res., 2003.
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MODEL RESULTS(Comprehensive Ring Current Model
CRCM)
M. C. Fok et al., JGR, 2001.
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MODEL RESULTS(Comprehensive Ring Current Model
CRCM)

• The CRCM predicts two requirements for SAPS
  formation
• Enhanced R2 FAC.
• High conductivity in the auroral region.
• Wellcan these be seen?

M. C. Fok et al., JGR, 2001.
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FAC (Iridium)
0400 0500 UT
0200 0300 UT
Iridium magnetometer data provides FAC (courtesy
of B. Anderson). Red is upward. Blue is downward.
R1-R2 pair increases around dusk. Consistent with
first requirement.
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AURORAL CONDUCTIVTY?
FUV observations at 0400 UT on 2 June 2001.
Auroral emissions enhanced around dusk. Likely
higher conductivity in the region. Consistent
with the second theoretical requirement.
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SUMMARY

• SAPS fields and flows observations
• GPS receivers see enhanced TEC
• Millstone Hill see enhanced sunward flow
• DMSP see enhanced ion flow velocities
• SAPS forms in assocation with increased partial
  ring current during mainphases.
• SAPS affect the plasmapause.
• Enhanced R2 FAC and high R1 conductivity is
  required for SAPS to form.

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WORK IN PROGRESS

• More exact timing studies with HENA, EUV, TEC,
  DMSP and Millstone data.
• Specify requirements more quantitatively for SAPS
  formation in the CRCM and survey all cases.
• Assimilate FACs and conductivity into model.

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• Correlation best with SOLAR WIND SPEED and IMF
  By
• More storms needed
• Inversion maturing. Validations continue. Focus
  on higher energies.
• Eastward rotation due to strong equatorward
  Pedersen currents (R1 to R2) around dawn
  according to models.

Cson Brandt et al., GRL, 2002.
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STATISTICAL PRESSURES

• 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

Ebihara et al., GRL, 2002.
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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