WHISPER new observation - Narrow band observation - Harmonic form

1. nfce waves in the plasmasphere region : A new observation using WHISPER/CLUSTER instrument F. El-Lemdani Mazouz (1,2), P. M. E. Décréau (1), J. L. Rauch (1), J. G. Trotignon (1), X Vallières (1), S. Kougblenou (1), P. Canu (2), F. Darrouzet (3).(1)LPC2E, ( France), (2)LPP ( France), (3)IASB-BIRA, (BELGIUM). Email: mazouz@cnrs-orleans.fr B E Receptive antenna ZGSE e+ e+ e- Injection particules Particules injection sun XGSE Spin plan YGSE Modulation index θ Abstract:Whisper instrument on board CLUSTER spacecraft allows the detection of a new class of wave observation in the plasmasphere region. We present here, spectral and statistical properties of these observations observed at nfce, at frequencies higher than the local plasma frequency. We start via an event study to present spectral properties of these observations, frequency and intensity behaviour are determined. High values of the modulation index, and intensity dependence on the B field orientation indicates a linear polarization on the spin plan. We present also a statistical study, on the nfce events, using a data set covering the three years 2002-2004. Strong MLT dependence of these emissions is shown. The correlation between these observations and a particular form of the plasmasphere so called “Christmas tree form” is pointed out. Finally the study of the variation of the Ae index indicates an augmentation of this index one day before the events, indicating a correlation between injection of energetic particles and the observation of nfce emissions. A New class of wave observation: nfce emissions C4 20040317 60 80 SM coordinates 50 5 fce 60 40 dB above 10-7VrmsHz-1/2 30 40 Frequency (kHz) 20 20 10 2 0 0 20:50 4.60 -23.50 22.94 21:11 4.36 -11.12 23.09 21:32 4.43 2.38 23.25 21:53 4.11 15.62 23.42 22:14 4.13 31.05 23.63 UT R(Re) LATSM(°) MLT Position of the satellites at 21h10 Time frequency dependence M7 • WHISPER new observation • - Narrow band observation • - Harmonic form • - Northern and in the southern hemisphere • - Regular plasmasphere ; « Christmas Tree » • Method of the maxima of intensity: • - Exactly situated at nfce • - Successive observation on each band • - 3 harmonics in the NH : M7,M6,M5 • Predicted by Farrel (2001) M6 M5 Statistical properties Orientation / Magnetic Field Occurrence of nfce observation • 3 years of data: 2002-2004 : • 30 events (C3 observation) ~8 % • Strongly confined to the • premidnight sector 20040317 Equatorial L-MLT projection on Sm coordinates Variation of Θ (angle between electric and magnetif field) • High values of fp • Typical values of the • « Christmas Tree form » Linear polarisation observed in the spin plane • Modulation about 90% Equatorial values of the plasma frequency • Maximum of intensity for the higher harmonic M7 (3.10-4 Vrms.Hz-1/2 ) nfce observations • Maximum of intensity in the perpendicular direction /B • High values of the Ae index • 24 hours before the observation • Conclusion • WHISPER instrument allows the detection of a new class of wave phenomena at nfce, predicted by a maser synchrotron theory (Farrel, 2001). • nfce observation: rare phenomena strongly confined to premidnight sector • Statistical and events study shown the relationship between this observation and the plasmasphere “Christmas-tree” form. • MLT localization and AE index variation shown the correlation between nfce observation and particle injection. • Mode observation in the perpendicular direction / magnetic field • Particule injection t-24 t Noon 12 09 15 ALL perigee pass 2 3 4 5 6 L(RE) Dawn 06 Dusk 18 Plasmapause 03 21 nfce 00 Midnight t t-24 Variations of the AE index in the 24 hours preceding an observation