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

Rayleighs 75 ILAT Jan 1998 Substorm Onsets Rankin & Gillam MPA UT, hours nm VIS Low-Resolution Camera, nm Lyons et al. ‘01

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

Goodrich et al. ‘98

1 0 “Fast Mode” Energy z z mp z z mp “Alfvénic” Energy x/z mp  Earthward Allan and Wright ‘00 t/  m p vzvz 10 Disturbance Time Step t = 6  mp Earthward Propagation of “Plasma Sheet” Disturbances Characteristics Parameters v Lobe = 2600 km/s z mp = 25 R E  mp = 1 min Fast-Alfvén mode coupling: k y = 1.3 Plasma  = 0 ! v A /v Lobe z z mp Alfvén Speed Profile

Coupling Efficiency Allan–Wright Simulation t/t mp 0.08 E AT /E FT Absorption Kivelson and Southwood ‘86 L y  15 R E L y  60 R E Coupling Parameter,

Phase Mixing, Dispersion and E || Dispersive Alfvén Waves  / e E || /E  >> 1 Kinetic << 1 Inertial Dispersion Lengths Phase mixing: L ph Ion gyroradius:  =  i (1+T e /T i ) Inertial Length: e = c/  pe Phase Mixing Length Altitude, R E  2 / e z/z mp L ph, R E PSBL LOBE Lysak and Carlson ‘81 Allen and Wright ‘98 x/z mp = 4, t/t mp = 6

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

E , mV/m Altitude, R E Low-Altitude Intensification Streltsov et al. ‘01

Reflection Coefficient J || = K  || J  =  P E  inc ref Wavelength, km 1 0 Reflection Coefficient Absorption, % Insulator Conductor v Am v Ai  d d 2 R E Vogt and Haerendel ’99 Lysak and Carlson ‘81

Alfvén Wave Absorption vs Wavelength Observed Width of Auroral Arcs Arc Width, km Knudsen et al. ‘01 Maggs and Davis ‘68 Number of Arcs Reflection Coefficient Absorption, % Wavelength, km ?

North-South Electric Field East-West Magnetic Field 2 mho5 mho M-I Interaction 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  P E 2 , ion outflow Reactive Ionosphere Lotko and Streltsov ‘99 Ionosphere Equator

Ponderomotive Ion Upwelling via Alfvén Waves a p|| = ¼  || (E  /B 0 ) 2 a p|| > a g at 1000 km altitude when E  > 200 mV/m Inertial M-I Coupling Strangeway et al. ‘00 Li and Temerin ’93

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 Theory Program