Quasi-Static Alfvén Wave Dynamics and Scale-Dependent Energy Deposition

Theory Program Quasi-Static Alfvén Wave Dynamics and Scale-Dependent Energy Deposition in Magnetosphere-Ionosphere Coupling W. Lotko, A. Streltsov Dartmouth College R. Lysak University of Minnesota • What is a quasi-static Alfvén wave? • Consequences for m-i coupling • Low-altitude energy deposition • Observational features SM 71B-05

Quasi-static Alfvén Wave: Conditions • 0PvA() >> 1 •  < 1 / 0P (low altitude) •  f < 14 mHz (Freja) • e.g., P = 5 S f < 6 mHz (FAST) • f < 1 mHz (Polar, Cluster) , f wave frequency  field-aligned distance above E region P Pedersen conductance vA() local Alfvén speed

P = 10 S Rankin et al. ‘00 2 200 1.5 150 hB , nT– m B , nT 1 100 0.5 50 0.6 0.5 0.7 0.8 0.9 1.0 equator ionosphere /i Shear Alfvén Wavefunction

E> J|| = K || d B0ê E< i J =PE  Quasi-static Alfvén Wave: Fields Vogt & Haerendel ‘98 Knudsen et al. ‘92 Transverse Length Scale for Chiu-Cornwall-Lyons ‘80 Weimer et al. ‘85

ref inc J|| = K || 100 1 Insulator Reflection Coefficient Absorption, % 0 ~d Conductor -1 0 10 0.1 1 100 1000 J =PE  Wavelength, km Reflection and Absorption vAm 2 RE vAi Lysak and Carlson ‘81 Vogt and Haerendel‘98

constant current P = 10 S constant voltage Dissipation Layer Energy Deposition: Length-Scale Dependence Streltsov and Lotko ‘02

E> J|| = K || d E< Collisionless absorption Inferred Quantity i Poynting Fluxes J =PE 

equator 125 s 220 s ENS ionosphere 235 s 141 s E LayerJ  J  Ne + – Ne2 + – P + – E –+ Stable?yesno 251 s 157 s 266 s 173 s 281 s 188 s 297 s 204 s L = 7.25 8.25 670 mV/m Feedback Instability Ionospheric Alfvén Resonator Streltsov and Lotko ‘02

0 equator BEW -50 ENS 600 nT mV/m -100 -150 670 mV/m 400 ENS ionosphere -200 200 distance, km 0 BEW PE 0 50 100 150 200 5 150 (mV/m)2 km (nT)2 km 270 nT 4 PB 100 3 2 j 50 k, km-1 1 0 0 0 0.05 0.10 0.15 0.20 0.25 80 A/m2 Time Step = 297 s “Satellite” Measurements Streltsov and Lotko ‘02

Alfvén waves  quasi-static at low altitude ( < 10 mHz ) • MI Coupling • Lower magnetosphere: vA() >>  High “rigidity” • Jump in E at  (Haerendel - “fracture”) • Observational Features • Impedance: • S  electron energy flux • Feedback  low-altitude structure SUMMARY

Quasi-Static Alfvén Wave Dynamics and Scale-Dependent Energy Deposition