Source location of chorus emissions observed by Cluster
- 1LPCE/CNRS, 3A Avenue de la Recherche, Orléans, 45071 France
- 2Charles University, V Holesovickach 2, Praha 8, 18000 Czech Republic
- 3CETP/UVSQ, 10/12 Avenue de l’Europe, Velizy, 78140 France
- 4LESIA, Place Jules Janssen, Meudon, 92195 France
- 5CESR, 9 Av. Colonel Roche, Toulouse, 31029 France
Abstract. One of the objectives of the Cluster mission is to study sources of various electromagnetic waves using the four satellites. This paper describes the methods we have applied to data recorded from the STAFF spectrum analyser. This instrument provides the cross spectral matrix of three magnetic and two electric field components. This spectral matrix is analysed to determine, for each satellite, the direction of the wave normal relative to the Earth’s magnetic field as a function of frequency and of time. Due to the Cluster orbit, chorus emissions are often observed close to perigee, and the data analysis determines the direction of these waves. Three events observed during different levels of magnetic activity are reported. It is shown that the component of the Poynting vector parallel to the magnetic field changes its sense when the satellites cross the magnetic equator, which indicates that the chorus waves propagate away from the equator. Detailed analysis indicates that the source is located in close vicinity of the plane of the geomagnetic equator.
Key words. Magnetospheric physics (plasma waves and instabilities; storms and substorms); Space plasma physics (waves and instabilities)