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AGU: Journal of Geophysical Research, Space Physics

 
Abstract
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Abstract

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 106, NO. A12, PP. 30,253-30,269, 2001
doi:10.1029/2001JA900114

Wave normal and Poynting vector calculations using the Cassini radio and plasma wave instrument

G. B. Hospodarsky

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA

T. F. Averkamp

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA

W. S. Kurth

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA

D. A. Gurnett

Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa, USA

M. Dougherty

Imperial College, Blackett Laboratory, London, England

Umran Inan

Department of Electrical Engineering, Stanford University, Stanford, California, USA

Troy Wood

Department of Electrical Engineering, Stanford University, Stanford, California, USA

Wave normal and Poynting vector measurements from the Cassini radio and plasma wave instrument (RPWS) are used to examine the propagation characteristics of various plasma waves during the Earth flyby on August 18, 1999. Using the five-channel waveform receiver (WFR), the wave normal vector is determined using the Means method for a lightning-induced whistler, equatorial chorus, and a series of low-frequency emissions observed while Cassini was in the magnetosheath. The Poynting vector for these emissions is also calculated from the five components measured by the WFR. The propagation characteristics of the lightning-induced whistler were found to be consistent with the whistler wave mode of propagation, with propagation antiparallel to the magnetic field (southward) at Cassini. The sferic associated with this whistler was observed by both Cassini and the Stanford VLF group at the Palmer Station in Antarctica. Analysis of the arrival direction of the sferic at the Palmer Station suggests that the lightning stroke is in the same sector as Cassini. Chorus was observed very close (within a few degrees) to the magnetic equator during the flyby. The chorus was found to propagate primarily away from the magnetic equator and was observed to change direction as Cassini crossed the magnetic equator. This suggests that the source region of the chorus is very near the magnetic equator. The low-frequency emission in the magnetosheath has many of the characteristics of lion roars. The average value of the angle between the wave normal vector and the local magnetic field was found to be 16°, and the emissions ranged in frequency from 0.19 to 0.75 ƒ ce , where ƒ ce is the electron cyclotron frequency. The wave normal vectors of these waves were primarily in one direction for each individual burst (either parallel or antiparallel to the local field) but varied in direction throughout the magnetosheath. This suggests that the sources of the emissions are far from the spacecraft and that there are multiple source regions.

Received 11 November 2000; accepted 24 July 2001; .

Citation: Hospodarsky, G. B., T. F. Averkamp, W. S. Kurth, D. A. Gurnett, M. Dougherty, U. Inan, and T. Wood (2001), Wave normal and Poynting vector calculations using the Cassini radio and plasma wave instrument, J. Geophys. Res., 106, 30,253–30,269, doi:10.1029/2001JA900114.

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