Abstract
Abstract. Chorus emissions are often observed by the STAFF spectrum analyser on board the 4 satellites of CLUSTER. This instrument provides the cross spectral matrix of three magnetic and two electric field components. Dedicated software processes this spectral matrix in order to determine the propagation characteristic of these chorus waves. Measurements of the parallel component of the Poynting vector around the magnetic equator indicate that the chorus waves propagate away from this region which is considered as the source area of these emissions. This is valid for the most intense waves observed on the magnetic and electric power spectrograms. But it has also been observed that lower intensity waves propagate toward the equator at the same frequency. Using the wave normal directions of these waves, a ray tracing study has shown that the waves have suffered a Lower Hybrid Resonance (LHR) reflection at low altitudes and now return to the equator at a different location with a lower intensity. The paper presents other similar events when WBD data are simultaneously recorded. The WBD experiment provides a much better time resolution and allows one to check the structure of the returning waves. It is observed that these waves have still a high degree of polarization, even if they started to lose the coherent structure of the chorus elements. They reach the equator with a small wave normal angle which is more efficient for a further amplification. It is explained that these emissions could be a source of hiss.
Highlights
Chorus waves are intense whistler-mode emissions consisting of a sequence of discrete elements
Parrot et al (2003b) have recently presented an event recorded on 29 October 2001, where magnetospherically reflected chorus waves are observed using ray tracing with the four CLUSTER satellites
As for the first event, a backward ray tracing has been performed between 15:25 and 15:49 UT, a time interval where SC1, SC2 and SC4 observe chorus waves which escape from the equator, and SC3 observes at the same frequency an emission which returns to the equator
Summary
Chorus waves are intense whistler-mode emissions consisting of a sequence of discrete elements. Parrot et al (2003b) have recently presented an event recorded on 29 October 2001, where magnetospherically reflected chorus waves are observed using ray tracing with the four CLUSTER satellites. STAFF-SA does not have enough time and frequency resolutions to verify the nature of the reflected waves, for example, to search for possible signs of discrete chorus elements. Another wave experiment WBD (Wideband) on board CLUSTER is used. A ray tracing program is operated to emulate the trajectories of the waves in the magnetosphere (Cerisier, 1970; Cairo and Lefeuvre, 1986; Muto and Hayakawa, 1987; Parrot et al, 2003b) This ray tracing software uses a diffusive equilibrium model for electron density.
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