Abstract
Many chorus emissions were observed in the frequency range from 200 Hz to 1 kHz when the GEOTAIL spacecraft was skimming inside the dayside magnetopause. The Wave Form Capture (WFC) onboard GEOTAIL obtained simultaneous wave forms of two electric and three magnetic components of the emissions. Spectral structures of the chorus emissions observed by the WFC are roughly classified into four types: rising tone, falling tone, hook, and structureless. In this paper, as a preliminary report, the wave normal directions for each type of the emissions except for the structureless are derived by the Means' method around the geomagnetic field line to know their propagation characteristics. In addition, Poynting directions of the chorus emissions are derived by using their five electromagnetic components. Derived propagation directions of the chorus emissions along a GEOTAIL orbit indicate that they are generated around the dayside geomagnetic equator, which is consistent with the well-known model of chorus generation through cyclotron resonance in the dayside outer magnetosphere.
