Ionospheric Sources of Storm-time RC and Plasmasheet Populations

1. Ionospheric Sources of Storm-time RC and Plasmasheet Populations R. B. Sheldon The University of Alabama in Huntsville

2. 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

3. 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

4. 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

5. 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

6. POLAR/CAMMICE Timing Study • Cross-correlations

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

8. 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?)

9. 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

10. 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

11. 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

12. Double Spikes mirror pt mirror pt n,F S Iono Iono Equator

13. 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)

14. 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?

15. The UAH Spinning Terrella Bell jar High Voltage Low cost Laboratory Space Plasma Simple Physics Sylvania Detectors 1 T Fe-B-Nd magnet Mechanical feedthrough Cryopump

18. 2K 3k 4k

19. Ion injection at 800 V

20. B/W, lower resolution

21. Higher Pressure He

22. 100 mTorr Helium

23. 400 mTorr Helium

24. 200 mTorr Helium, stationary

25. 200 mTorr Helium, spinning

26. 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) • ria ECON * nplasma • rna ne & niono & 1/L

27. 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?)

28. 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

29. Astrophysical Jets