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Ionospheric Sources of
Storm-time RC and
Plasmasheet Populations
R. B. Sheldon
The University of Alabama in Huntsville
The Ring Current Origin
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• 30’s/50’s Chapman-Ferraro / Alfven view from SW
• 60’s Radiation Belt “diffusion”
• 70’s Explorer 45, Hoffman “Nose events”
– Increased Convection E-field, brings plasmasheet ions
deep into the magnetosphere. The “notch filter” permits
only certain energy/PA’s deepest access. Partial RC
forms. Then cross-L transport circularizes the RC
• 80’s Spjeldvik, Sheldon, Kozyra, Fok, Jordanova, Chen...
• 90’s POLAR/IMAGE ENA satisfying confirmation
So where’s the beef?
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• Dessler-Parker-Sckopke doesn’t work like it should.
– despite ENA’s and Dst tracking each other well
• Great storms have 2 time-constant Dst recovery
• Models often have an unexplained 2X factor around
main phase (Fok, Jordanova, Chen)
• RC densities can surpass plasmasheet densities in
violation of Liouville’s theorem
• Average Energy drops during a big storm injection
• Composition Experiments don’t show plasmasheet
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Ionosphere Contribution to RC
• Before composition experiments we didn’t know
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O+,He+ are Iono, He++, C5+,O6+ are SW/Magneto
(1972) Shelley, Sharp: O+ exists in RC (E<30keV)
AMPTE (1984) Gloeckler: 50% Iono in RC (1<keV<300)
AMPTE (1986) Hamilton: O+ dominates
CRRES/MICS (1989) Grande: O+/H+ a Dst
• Somehow the ionosphere is getting involved in a
really major way. But how? (Joe vs. Robert)
– cleft ion fountain/auroral upflow not making RC energies
– plasmasphere just doesn’t have enough O+ to do it either
Some theories
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• Plasmasphere drains into LLBL, flows over pole and
makes a superdense plasmasheet, perfect for RC
– it takes a few days. Storms take < 1 hour from SSC.
• Storm heats atmosphere in auroral zone, sending
upflows of O+ into plasmasheet that convect to RC
– Daglis shows that RC O+ is very prompt, < 20 minutes
– Sheldon showed that O+ & He+ are nearly simultaneous
• Substorms preferentially heat O+
– Some storms have no substorms
– The O+ dominance is at lower energy than usual
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POLAR/CAMMICE Timing Study
• Cross-correlations
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Rosetta Stone, POLAR/CEPPAD
April 15, 1996 (Sheldon GRL 98)
3 Populations
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• The Ring Current is well understood. Radial
transport adiabatically heats the particles
• The 100 keV ions are probably “nose” ions
– pancake distribution, predominately H+,
“monoenergetic”, NOT adiabatically heated
• What is the lowest trace!!!???
– field-aligned, 40 keV, enriched in O+
– Energy stays nearly constant at 1/2 of “nose” ions!
• (Also seen March 21, 96; preferentially at equinox?)
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It’s the Ionosphere, Stupid
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What would have accelerated it to 40 keV?
Why is it strongly field-aligned?
Why does the energy track at 1/2 of nose ions?
How can it last from L=7 down to L=3?
Minimal Theory:
– Nose ions generate field-aligned potential at 1/2 of their
total kinetic energy which extract the ions from deep
within the ionosphere.
– Space Charge
Review the Physics
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• Injection of hot plasma into the dipolar
magnetosphere produces separation of charge
• When cold M’sph plasma is outnumbered, space
charge results. Consider the ions.
• Space charge expands the ions, mirror force
compresses the ions
• m DB = q DF ; D2F = 4pr
• so if Ba 1/r3, then r a 1/r5
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Some simple consequences
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The potential looks like the magnetic field
The electric field looks like derivative B
The density of ions looks like 2nd deriv B
Suppose field line is radial near the Earth
B = Br = 1 / r cos 
3
E = F  1 / r
n =  F 1/ r
2
6
5
Double Spikes
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mirror pt
mirror pt
n,F
S
Iono
Equator
Iono
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Double Layers & High Potential
• The separation of charge leads to voltages
proportional to the energy of the ions.
• Ionospheric electrons would neutralize the ions, but
for gradient B drifts.
• Energy is conserved, but this geometry acts as a
transformer, producing parallel fields
• It should work wherever gradient B drifts are large
enough (and gyroradii small)
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Can a Magnet act as a Capacitor?
• Standard Plasma books rarely do the dipole
– Krall-Trivelpiece (1986) deal only with homogeneous
magnetic fields.
• MHD is not valid wherever grad-B drifts are
important, e.g., inhomogeneous fields, hot plasma
• “Malmberg trap” for non-neutral plasmas
– Used to trap positrons, making anti-hydrogen
– A dipole B-field w/ ionosphere “looks like” Malmberg
• So is there any evidence for space charge in a dipole
magnetic field?
The UAH Spinning Terrella
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Bell
jar
High
Voltage
Low cost
Laboratory Space Plasma
Simple Physics
Cryo
pump
Sylvania Detectors
1 T Fe-B-Nd magnet
Mechanical feedthrough
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2K
3k
4k
Ion injection at 800 V
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B/W, lower resolution
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Higher Pressure He
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100 mTorr Helium
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400 mTorr Helium
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200 mTorr Helium, stationary
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200 mTorr Helium, spinning
Conclusions
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• Space charge can accumulate in a magnetic dipole
field, and discharges when it overcomes the
“insulator”. This produces a periodic “relaxation”
oscillator or discharge.
• These discharges are at some fixed fraction of the
injection energy. Simple theory (Whipple 77) argue
for E|| component of Etotal or pitchangle of injection
• At Earth, the “RC-time constant” is dynamic,
depending on (injection rate - neutralization rate)
– ri a ECON * nplasma
More Conclusions
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• Optimal Place for this discharge
– Low magnetospheric electron density - Plasmasphere
trough
– Low ionospheric conductivity- trough at night
• Equinoxes! (Check out the Russel-McPherron effect)
– High plasmasheet ion density - pre-midnight
• Optimal Time for this discharge
– High convection Electric field - storm injection
– High plasmasheet density - “primed” superdense PS
– After plasmasphere is removed (double-dip?)
Predictions
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• We should see keV precipitating electrons in a
highly localized region just before main phase of a
geomagnetic storm:
– PIXIE? (Schulz 98)
• We should see 2-beam instability generated waves
– Pc1 with gyrofrequency dropping to O+ at dusk (Mursula
98)
• We should see correlation between L-shell & O+
• Correlation between recovery rate and size
Astrophysical Jets
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