A microscopic and nanoscopic view of storm-time choruson 31 March 2001

O. Santolik (1, 2, 3) , D.A. Gurnett (1) , J.S. Pickett (1) , Michel Parrot (4) , N. Cornilleau-Wehrlin (5)

1 Department of Physics and Astronomy [Ames, Iowa]
2 Faculty of Mathematics and Physics [Praha/Prague]
3 IAP - Institute of Atmospheric Physics [Prague]
4 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
5 CETP - Centre d'étude des environnements terrestre et planétaires

We investigate intense whistler-mode chorus emissions which occurred during the geomagnetic storm on 31 March 2001. We use multipoint measurements obtained by the Cluster spacecraft in the premidnight equatorial region outside the plasmasphere at a radial distance of 4 Earth radii (L = 4.0 − 4.2). Observed spatio-temporal variations of the direction of the Poynting flux manifest a consistent pattern: the central position of the chorus source fluctuates at time scales of minutes within 1000–2000 km of the geomagnetic equator. We demonstrate that estimates of the electromagnetic planarity can be used to characterize the extent of the source, obtaining a range of 3000–5000 km. Discrete wave packets of chorus are observed to rise in frequency between 0.13 and 0.5 of the local electron cyclotron frequency, at a rate up to 20 kHz/s, having the maximum peak amplitudes of ∼20 mV/m. We observe a fine structure of subpackets with large amplitudes embedded in the interior of the wave packets. This fine structure has a typical delay of a few milliseconds between the two neighboring maxima of the wave amplitude. Longer delays occur with a decreasing probability density.

Domaines: Astrophysique [astro-ph]; Cosmologie et astrophysique extra-galactique [astro-ph.CO]

O. Santolik, D.A. Gurnett, J.S. Pickett, Michel Parrot, N. Cornilleau-Wehrlin. A microscopic and nanoscopic view of storm-time choruson 31 March 2001. Geophysical Research Letters, 2004, 31 (2), pp.L02801. ⟨10.1029/2003GL018757⟩. ⟨hal-00153125⟩