Spatio‐temporal structure of storm‐time chorus

• DOI: 10.1029/2002ja009791
• Publication Date: 2003-07-11T06:37:15Z
• Authors: O. Santolík; D. A. Gurnett; J. S. Pickett; M. Parrot; N. Cornilleau‐Weh...
• Keywords: Chorus; Van Allen Probes; Field line

We discuss chorus emissions measured by the four Cluster spacecraft at close separations during a geomagnetically disturbed period on 18 April 2002. analyze lower band of below one half electron cyclotron frequency, radial distance 4.4 Earth's radii, within 2000 km long source region located to equator. The characteristic wave vector directions in this are nearly parallel field lines and multipoint measurement demonstrates dynamic character region, changing Poynting flux direction time scales shorter than few seconds. electric waveforms packets (forming separate elements power spectrograms) show fine structure consisting subpackets with maximum amplitude above 30 mV/m. To study we have used sine‐wave parametric model variable amplitude. typically start an exponential growth phase, after reaching saturation they often decay phase. duration is from milliseconds tens milliseconds, appear waveform randomly, no clear periodicity. obtained rate (ratio imaginary part real frequency) highly case values between thousandths hundredths. same simultaneously observed different closely separated internal subpacket structure. scale can thus be kilometers plane perpendicular line, or hundreds line (corresponding propagation entire packet). Using delays time‐frequency curves spacecraft, found as simultaneous calculations. roughly correspond whistler‐mode group velocity estimated cold plasma theory. also corresponding antiparallel for two neighboring packets, less 0.1 s apart.