# Presentation: 725844

## Ionospheric Sources of Storm-time RC and Plasmasheet Populations

- R. B. Sheldon
*The University of Alabama in Huntsville*

## The Ring Current Origin

- 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?

- 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

## Ionosphere Contribution to RC

- Before composition experiments we didn’t know
- 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

- 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

## POLAR/CAMMICE Timing Study

- Cross-correlations

## Rosetta Stone, POLAR/CEPPAD April 15, 1996  (Sheldon GRL 98)

## 3 Populations

- 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?)

## It’s the Ionosphere, Stupid

- 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

- 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

## Some simple consequences

- 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

## Double Spikes

- Equator

- n,F

- Iono

- Iono

- S

- mirror pt

- mirror pt

## 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)

## 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

- Bell jar

- Cryopump

- High Voltage

- Low cost
- Laboratory Space Plasma
- Simple Physics
- Sylvania Detectors
- 1 T Fe-B-Nd magnet
- Mechanical feedthrough

## Slide 16

## Slide 17

## 2K

-         3k
- 4k

## Ion injection at 800 V

## B/W, lower resolution

## Higher Pressure He

## 100 mTorr Helium

## 400 mTorr Helium

## 200 mTorr Helium, stationary

## 200 mTorr Helium, spinning

## Conclusions

- 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
- rn a ne & niono & 1/L

## More Conclusions

- 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

- 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