Cluster observations of beam-plasma instabilities above the polar cap by northward IMF.

A. Teste (1) , D. Fontaine (1) , P. Canu (1) , Pierrette Décréau (2) , A. Fazakerley

1 CETP - Centre d'étude des environnements terrestre et planétaires
2 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

During periods of northward IMF, at 5 to 8 Re altitude above the polar cap, Cluster spacecraft detect narrow and intense electron beams outflowing from the polar iono-sphere, very collimated along magnetic field lines. From a careful analysis of PEACE data, we can separate the beam distribution function from the ambient plasma contribution and estimate their characteristics. We show that these beams are accelerated to a few tens of eV and also heated. Moreover, these beams are extremely well correlated to broadband electrostatic emissions. We investigate the plasma-beam interactions and solve the linear wave dispersion relation to determine the instabilities likely to be triggered in this environment. Finally, we discuss the results by comparison with the observations.

Domaines: Planète et Univers [physics]

A. Teste, D. Fontaine, P. Canu, Pierrette Décréau, A. Fazakerley. Cluster observations of beam-plasma instabilities above the polar cap by northward IMF.. EGU, 2007, Vienna, Austria. ⟨hal-00154636⟩