1 / 14

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.

asabi
Download Presentation

Alfvén Wave Generation and Dissipation Leading to High-Latitude Aurora

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related