Spatio-temporal structure of storm-time chorus

0176532 - UFA-U 20030020 RIV US eng J - Článek v odborném periodiku
Santolík, Ondřej - Gurnett, D. A. - Pickett, J. S. - M. Parrot, M. - Cornilleau-Wehrlin, N.
Spatio-temporal structure of storm-time chorus.
Journal of Geophysical Research. Roč. 108, A7 (2003), s. 7-1-7-14, doi:10.1029/2002JA009791, 2003. ISSN 0148-0227
Grant CEP: GA ČR GA202/03/0832; GA MŠMT ME 650
Grant ostatní: NASA(US) NAG5-9974
Výzkumný záměr: CEZ:AV0Z3042911; CEZ:MSM 113200004
Klíčová slova: storm-time chorus emissions * whistler mode * propagation analysis
Kód oboru RIV: BL - Fyzika plazmatu a výboje v plynech
Impakt faktor: 2.992, rok: 2003

We discuss chorus emissions measured by the four Cluster spacecraft at close separations during a geomagnetically disturbed period on 18 April 2002. We analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 EarthŽs radii, within a 2000 km long source region located close to the equator. The characteristic wave vector directions in this region are nearly parallel to the field lines and the multipoint measurement demonstrates the dynamic character of the chorus source region, changing the Poynting flux direction at time scales shorter than a few seconds. The electric field waveforms of the chorus wave packets (forming separate chorus elements on power spectrograms) show a fine structure consisting of subpackets with a maximum amplitude above 30 mV/m. To study this fine structure we have used a sine-wave parametric model with a variable amplitude. The subpackets typically start with an exponential growth phase, and after reaching the saturation amplitude they often show an exponential decay phase. The duration of subpackets is variable from a few milliseconds to a few tens of milliseconds, and they appear in the waveform randomly, with no clear periodicity. The obtained growth rate (ratio of the imaginary part to the real part of the wave frequency) is highly variable from case to case with values obtained between a few thousandths and a few hundredths.
Trvalý link: http://hdl.handle.net/11104/0073508