Counterstreaming Beams and Flat-Top Electron Distributions Observed with Langmuir, Whistler, and Compressional Alfvén Waves in Earth’s Magnetic Tail

Abstract

Relevant new clues to wave-particle interactions have been obtained in Earth's plasma sheet (PS). The plasma measurements made on Cluster spacecraft show that broadband (approximately 2-6 kHz) electrostatic emissions, in the PS boundary layer, are associated with cold counterstreaming electrons flowing at 5-12x10(3) km s(-1) through hot Maxwellian plasma. In the current sheet (CS), electromagnetic whistler mode waves (approximately 10-80 Hz) and compressional Alfvén waves (<2 Hz) are detected with flat-topped electron distributions whose cutoff speeds are approximately 15-17x10(3) km s(-1). These waves are damped in the central CS where |B|<or=1.5 nT, plasma beta approximately 100, and electron distributions isotropic. Three mechanisms are at work: the beta-dependent lower hybrid drift instability (LHDI), acceleration of electrons along the B field by the LHD waves and whistler mode emissions triggered by the cyclotron resonance instability.