Multi-banded structure of chorus-like emission

Whistler-mode chorus emissions consist of individual wave packets exhibiting rising, falling tones or other spectral shapes (hooks or shapeless hiss) usually divided into two frequency bands separated by a gap at 1/2 of the electron cyclotron frequency (f_ce) close to the chorus source region. This configuration is often called banded chorus and it is correlated with the magnetic activity. Several theories have been published to explain how this specific configuration is generated. We present several tens of events of chorus emissions with more than two frequency bands and more than one gap that were found during more than 11 years of Cluster spacecraft measurements (from November 2000). Most of these “multi-banded emissions” were observed within 10° of geomagnetic latitude, i.e., inside or very close to the chorus source region. Most of studied events propagate with oblique wave normal angles and were detected under disturbed geomagnetic conditions.