Minor Ion Manifestations In The Earth's Magnetotail: Analysis of Waves Observed During Cassini's Earth Flyby
Abstract
The waves observed by the magnetic field experiment on Cassini in theEarth magneto- tail during its swingby manoeuvre are analysed. We show that they belong roughly to two classes. The first one is comprised of transverse waves in the ion cyclotron range which can be uniquely identified as bi-ion cyclotron waves on the He++ resonance branch. In the Earth's magnetotail at distances between 30 and 65 Re such waves are observed for the first time. A statistical study of their polarisation, frequency distri- bution and propagation direction properties produces a picture which is in very good agreement with theoretical predictions for low frequency waves in a bi-ion plasma with energetic proton component of anisotropic velocity distribution. We interpret the piling up of the waves about half the proton cyclotron frequency in terms of bi-ion cyclotron wave excitation at the gyrofrequency of a heavy ion constituent and as a proof for the presence in this region of a low concentration of double charged He-ions of solar wind origin. The second type of waves are highly compressional and we at- tempt to explain them as a manifestation of mirror mode structures. We discuss this hypothesis and analyse the possible origin scenarios and the relation of these waves to deep magnetotail mirror mode observations reported previously.
- Publication:
-
EGS General Assembly Conference Abstracts
- Pub Date:
- 2002
- Bibcode:
- 2002EGSGA..27.3625B