1. Generation of intense quasistatic fields at high altitudes by the Ionospheric Alfvén Resonator Bill Lotko, Jon Watts, Anatoly Streltsov Thayer School of Engineering Dartmouth College

2. Multiple resonant cavities Standing Alfvén waves confined by gradients and conducting boundaries Ionospheric Alfvén Resonator Field Line Resonator IAR ~ 1- 10 sec (Polyakov ‘76; Trakhtengerts, Feldstein ’81; Belyaev et al ’87; Lysak ‘88) FLR ~ 1 – 10 min (Samson ‘72; Southwood ‘74; Chen, Hasegawa, ‘74)

3. Multiple resonant cavities IAR ~ 1- 10 sec (Polyakov ‘76; Trakhtengerts, Feldstein ’81; Belyaev et al ’87; Lysak ‘88) FLR ~ 1 – 10 min (Samson ‘72; Southwood ‘74; Chen, Hasegawa, ‘74) MIAR ~ 1 min Standing Alfvén waves confined by gradients and conducting boundaries Ionospheric Alfvén Resonator M-I Alfvén Resonator Field Line Resonator

4. Atkinson ’70, Sato ’78, Lysak ’91, Trakhtengerts and Feldstein ’91 Feedback-gain in an active ionosphere: Resonator

5. Atkinson ’70, Sato ’78, Lysak ’91, Trakhtengerts and Feldstein ’91

6. Alfvén resonator frequency (fundamental) Constructive interference Ion mobility Alfvén Resonance Condition (for an “insulating” reflector) f = 1 / 4  = V A / 4L  = V  4  = 4L (V  / V A ) V  = M i E  M i = ion mobility insulator conductor

7. Active Ionization and Depletion Upward current Ionization  Conductance  Electric field  Downward current Ionization  Conductance  Electric field 

9. Observations from low-altitude satellites (FAST) Paschmann et al. ‘03 polar cap

10. Observations at higher altitude Intense electromagnetic activity in the “PSBL” ~ 1-min oscillations Oscillations confined mainly to downward current channel Integrated Poynting flux is upward Johansson et al. ‘04 polar cap plasmasheet down up M-I Alfvén resonator?

11. Opgenoorth et al. ‘02 Aikio et al. ‘04 Active Ionization and Depletion

12. Two-fluid Alfvénic Response of the Magnetosphere Electron parallel momentum Density continuity Current continuity v ||e - electron parallel speed; IC - electron collision frequency; AR - effective collision frequency representing wave-particle interactions. ρ i - ion Larmour radius. 0

13. Coupling to Ionospheric Conducting layer Density Continuity Equation n = n 0 + n 1 E-region plasma number density; S 1 =  n 0 2 ionization source maintaining equilibrium n 0 j || field-aligned current;  recombination coefficient. Current Continuity Equation  P,  H height-integrated Pedersen and Hall conductances. 0 0

14. Modeling Region − Plasmasheet boundary layer Computational Domain − Dipole + Rectangle − Nonuniform grid in altitude NUMERICAL SIMULATIONS Streltsov et al., 2002

15. Density, Alfven speed / refractive index IAR MIAR

16. Resonator “keyogram”

17. Resonator keyogram − zoom view

19. Variation with altitude

20. Simple Layered Model

21. Resonator stability properties How does the growth rate change with cavity size? Longer cavities  − larger || AND  − unstable at higher  P − lower frequency − lower growth rate k  cutoffs regulated by: high-k  − parallel resistivity low-k  − recombination

24. Conclusions High V A region  lossy Alfvén resonator cavity Fundamental period ~ 1 minute Feedback unstable resonator modes in  currents – Onset near current maximum – Decelerating propagation toward  current channel – Mode decays when it enters  current channel Strong coupling ion sound- IAR mode coupling – Pondermotive force creates ionospheric upwelling –  n/n ~ 1 holes (bottomside) and patches (topside)