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Alfvén Wave Generation and Dissipation Leading to High-Latitude Aurora

Alfvén Wave Generation and Dissipation Leading to High-Latitude Aurora. W. Lotko Dartmouth College. A. Streltsov, M. Wiltberger Dartmouth College. Genesis Fate Impact. SM 52B-08. Substorm Onsets. 557.7 nm. 30 Jan 1998. Rankin & Gillam MPA. Rayleighs. 4999. 75. 1657. 549.

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Alfvén Wave Generation and Dissipation Leading to High-Latitude Aurora

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  1. Alfvén Wave Generation and Dissipation Leading to High-Latitude Aurora W. Lotko Dartmouth College A. Streltsov, M. Wiltberger Dartmouth College • Genesis • Fate • Impact SM 52B-08

  2. Substorm Onsets 557.7 nm 30 Jan 1998 Rankin & Gillam MPA Rayleighs 4999 75 1657 549 ILAT 70 182 60 65 20 1 3 5 7 9 11 13 UT, hours VIS Low-Resolution Camera, 557.7 nm Lyons et al. ‘01

  3. 10 Jan 1997 Equatorial Noon-Midnight Ex Ex Power at 1.3 mHz in electric field Ex (GSM) from LFM global MHD. Fourier transforms are computed from time interval 0900-1200 UT. Wiltberger et al. ‘02

  4. Goodrich et al. ‘98

  5. 1 Alfvén Speed Profile Disturbance vz t/mp 0 1 z zmp 1 0 0 0.5 1 vA/vLobe z zmp “Fast Mode” Energy 0 1 z zmp “Alfvénic” Energy 0 6 5 4 3 2 1 0 x/zmp  Earthward Earthward Propagation of “Plasma Sheet” Disturbances Fast-Alfvén mode coupling: ky = 1.3 Plasma  = 0 ! Characteristics Parameters vLobe = 2600 km/s zmp = 25 RE mp = 1 min Time Step t = 6 mp Allan and Wright ‘00

  6. Kivelson and Southwood ‘86 0.5 Absorption 0 0 1 2 Coupling Parameter, .08 EAT/EFT Ly 15 RE Ly 60 RE 0 0 2 4 6 8 10 t/tmp Coupling Efficiency Allan–Wright Simulation

  7. 100 100 1 2/e2 Lph, RE LOBE PSBL .001 0.1 0 5 0 10 1 z/zmp Altitude, RE Phase Mixing, Dispersion and E|| Dispersion Lengths Phase mixing: Lph Ion gyroradius:  = i(1+Te/Ti) Inertial Length: e = c/pe Dispersive Alfvén Waves /e E||/E >> 1 Kinetic Phase Mixing Length << 1 Inertial x/zmp = 4, t/tmp = 6 Lysak and Carlson ‘81 Allen and Wright ‘98

  8.  = 0.4ci (1 – vc/|v||e|), |v||e| > 0 Low-Altitude Dissipation  = 0 Lysak and Dum ‘83 Streltsov et al. ‘01

  9. 100 E, mV/m 10 0 5 10 15 Altitude, RE Low-Altitude Intensification Streltsov et al. ‘01

  10. ref inc J|| = K || 100 1 Insulator Reflection Coefficient Absorption, % 0 Conductor  d -1 0 10 0.1 1 100 1000 J =PE  Wavelength, km Reflection Coefficient vAm 2 RE vAi Lysak and Carlson ‘81 Vogt and Haerendel ’99

  11. 100 1 Reflection Coefficient Absorption, % 0 -1 0 10 0.1 1 100 1000 Wavelength, km Knudsen et al. ‘01 Maggs and Davis ‘68 Number of Arcs 100 0.1 1 10 Arc Width, km Alfvén Wave Absorption vs Wavelength Observed Width of Auroral Arcs ?

  12. M-I Interaction North-South Electric Field • Alfvén wave FAC • exceeds current- • carrying capacity • of lower m’sphere • E|| is induced to boost • electron parallel flux • Accelerated electrons • nonuniformly ionize • E-layer • Gradients in  induce • quasi-electrostatic, • inertial Alfvén waves • at low altitude • Ionospheric Alfvénic • fluctuations enhance • Joule heating PE2, • ion outflow 2 mho Reactive Ionosphere 5 mho Equator Ionosphere East-West Magnetic Field Lotkoand Streltsov ‘99

  13. Inertial M-I Coupling Ponderomotive Ion Upwelling via Alfvén Waves ap|| = ¼||(E/B0)2 ap|| > ag at 1000 km altitude when E > 200 mV/m Li and Temerin ’93 Strangeway et al. ‘00

  14. Theory Program SUMMARY • Genesis (magnetotail) • CPS compressional disturbances  shear Alfvén waves in PSBL • Phase mixing in PSBL gradient creates smaller scale structure • Fate (low-altitude magnetosphere) • Small k  Ionospheric penetration, reflection • Moderate k  Strong absorption in collisionless E|| layer • Large k  Reflection at E|| layer, momentum transfer to electrons • Impact (ionosphere/thermosphere) • Enhanced Joule heating • Electron acceleration, 10-km scale auroral arcs • Ionospheric activation  Small-scale resonator Alfvén waves • Ponderomotive lifting of ionospheric ions

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