Observations of auroral broadband emissions by CLUSTER

J.-E. Wahlund (1) , A. Yilmaz (2) , M. Backrud (1) , D. Sundkvist (1) , A. Vaivads (1) , D. Winningham (3) , M. André (1) , A. Balogh (4) , J. Bonnell (5) , S. Buchert (1) , T. Carozzi (1) , Nicole Cornilleau (6) , M. Dunlop (7) , A. I. Eriksson (1) , A. Fazakerley (8) , G. Gustafsson (1) , Michel Parrot (9) , P. Robert (6) , A. Tjulin (1)

1 IRF - Swedish Institute of Space Physics [Uppsala / Kiruna]
2 COMU - Çanakkale Onsekiz Mart University
3 SwRI - Southwest Research Institute [San Antonio]
4 Space and Atmospheric Physics Group [London]
5 SSL - Space Sciences Laboratory [Berkeley]
6 CETP - Centre d'étude des environnements terrestre et planétaires
7 Blackett Laboratory
8 MSSL - Mullard Space Science Laboratory
9 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace

We present the results of a study based on several events of broadband ULF/ELF emissions observed in the auroral region by the CLUSTER multi-spacecraft at distances around 4-5 R_E. These emissions, observed below the ion plasma frequency, are similar to the broadband emissions observed at lower altitudes (800-4000 km) by rockets (e.g. AMICIST) and satellites (e.g. FREJA and FAST). As successive passages of the four CLUSTER satellites through nearly the same regions show, the intensity of the emissions depend on the thermal properties of the plasma and gradients thereof. The total Poynting flux is downward and is comparable to energy fluxes observed at lower altitudes. We believe the broadband emissions are the result of dispersed Alfvén waves (DAW), which propagates down the magnetic field lines, and emits higher frequency ion plasma wave modes.

Domaines: Géophysique [physics.geo-ph]

J.-E. Wahlund, A. Yilmaz, M. Backrud, D. Sundkvist, A. Vaivads, et al.. Observations of auroral broadband emissions by CLUSTER. Geophysical Research Letters, 2003, 30 (11), pp.1563. ⟨10.1029/2002GL016335⟩. ⟨insu-01410060⟩