HR: 14:40h
AN: SM22C-05    [PDF]
TI: Separating spatial and temporal variations in auroral electric and magnetic fields by Cluster multipoint measurements
AU: * Karlsson, T
EM: tkarlsson@plasma.kth.se
AF: Alfv\'{e}n Laboratory, Department of Plasma Physics, KTH, Stockholm, SE-10044 Sweden
AU: Marklund, G T
EM: marklund@plasma.kth.se
AF: Alfv\'{e}n Laboratory, Department of Plasma Physics, KTH, Stockholm, SE-10044 Sweden
AU: Figueiredo, S
EM: figueiredo@plasma.kth.se
AF: Alfv\'{e}n Laboratory, Department of Plasma Physics, KTH, Stockholm, SE-10044 Sweden
AU: Johansson, T
EM: tjohansson@plasma.kth.se
AF: Alfv\'{e}n Laboratory, Department of Plasma Physics, KTH, Stockholm, SE-10044 Sweden
AU: Buchert, S
EM: scb@irfu.se
AF: Swedish Institute of Space Physics, Box 537, Uppsala, SE-75121 Sweden
AB: Cluster multipoint measurements of the electric and magnetic field on auroral field lines at an altitude of 4 RE are used to show that it is possible to resolve the ambiguity of temporal versus spatial variations in the fields. We show that the largest electric fields (of the order of several hundreds of mV/m when mapped down to the ionosphere) are of a quasi-static nature, associated with upward electron beams, stable on a time scale of at least half a minute, and located in regions of downward current, and we conclude that they are the high-altitude analogues of the intense return current/black auroral electric field structures observed at lower altitudes by Freja and FAST. Outside of these structures there are temporal fluctuations, which are shown to likely be downward traveling Alfv\'{e}n waves. The periods of these waves are 20 - 40 s, which is not consistent with periods associated with either the Alfv\'{e}nic ionospheric resonator or field line resonances. The multipoint measurements enable us to estimate a lower limit to the perpendicular wavelength of the Alfv\'{e}n waves.
DE: 2704 Auroral phenomena (2407)
DE: 2708 Current systems (2409)
DE: 2712 Electric fields (2411)
DE: 2736 Magnetosphere/ionosphere interactions
DE: 2794 Instruments and techniques
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting