Generation of intense quasistatic fields at high altitudes by the Ionospheric Alfvén Resonator

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. Ionospheric Alfvén Resonator Field Line Resonator Multiple resonant cavities Standing Alfvén waves confined by gradients and conducting boundaries • 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. Ionospheric Alfvén Resonator Field Line Resonator M-I Alfvén Resonator Multiple resonant cavities Standing Alfvén waves confined by gradients and conducting boundaries • 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

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

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

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

7. Active Ionization and Depletion Upward current Downward current

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

9. polar cap plasmasheet down up 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 M-I Alfvén resonator? Johansson et al.‘04

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

11. Resonator “keyogram”

12. Resonator keyogram − zoom view

13. Resonator keyogram − zoom view

14. Variation with altitude

17. High VA 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) Conclusions