Using Plasma Wave Emissions to Measure Plasma Density and to Deduce Plasma 
Structure and Dynamics

Roger R. Anderson (1,2), Isamu Nagano (2), Satoshi Yagitani (2),
Hiroshi Matsumoto (3), Kozo Hashimoto (3), Hirotsugu Kojima (3),
Yasumasa Kasaba (4), Hironobu Takano (5),  Donald L. Carpenter (6),
James L. Green (7), and Scott Boardsen (7)

(1) The University of Iowa, Department of Physics and Astronomy,
Iowa City, IA  52242, USA
E-mail: roger-r-anderson@uiowa.edu, FAX: 319-335-1753

(2) Department of Information and Systems Engineering,
Faculty of Engineering, Kanazawa University, 2-40-20, Kodatsuno,
Kanazawa, Ishikawa 920-8667, JAPAN
E-mail: anderson@reg.is.t.kanazawa-u.ac.jp; nagano@reg.is.t.kanazawa-u.ac.jp;
	yagitani@reg.is.t.kanazawa-u.ac.jp

(3) Radio Science Center for Space and Atmosphere, Kyoto University,
Gokanosho, Uji, Kyoto 611-0011, JAPAN
E-mail: matsumot@kurasc.kyoto-u.ac.jp; kozo@kurasc.kyoto-u.ac.jp;
	kojima@kurasc.kyoto-u.ac.jp

(4) The Institute of Space and Astronautical Science,
3-1-1, Yoshinodai, Sagamihara, Kanagawa 229, JAPAN
E-mail: kasaba@stp.isas.ac.jp

(5) Toyama Prefectural University, Kosugi, Toyama 939-0398, JAPAN
E-mail: takano@pu-toyama.ac.jp

(6) Stanford University, STARLab, Stanford, CA 94305, USA
E-mail: dlc@nova.stanford.edu

(7) NASA Goddard Space Flight Center, Code 630, Greenbelt, MD 20771, USA
E-mail: green@mail630.gsfc.nasa.gov; boardsen@mail630.gsfc.nasa.gov

   Both in situ and remote Observations from the GEOTAIL and POLAR Plasma Wave
Instruments (PWI) of emissions related to the electron plasma frequency have
enabled us to measure the electron plasma density in the magnetosphere and
deduce its structure and dynamics.  On one pass in January 1993, GEOTAIL went
through the plasmasphere during orbit changing maneuvers.  In addition to
intense plasmaspheric hiss seen inside the plasmasphere and chorus seen outside,
the PWI also detected upper hybrid resonance (UHR) emissions that clearly
showed the structure and irregularities of the plasmasphere including ducts and
an increase in the density just before the plasmapause.  Similar UHR
observations were made by POLAR PWI in 1996 and 1997 during its perigee passes.
Remote measurements, although more challenging to interpret, have provided many
interesting observations.  Enhanced escaping terrestrial continuum radiation is
believed to be due to injected electrons from the plasmasheet during substorms
drifting around the earth eastward and impinging on the plasmapause and
magnetopause where steep density gradients occur.  Electrostatic emissions at
the local electron plasma frequency near harmonics of the electron cyclotron
frequency are mode converted to electromagnetic radiation that propagates out
unless or until it encounters a region denser than where it was generated.
Kilometric continuum radiation in the 100 kHz to 800 kHz frequency range (first
identified in the GEOTAIL PWI data) is believed to be due to a similar source
mechanism but from deeper within the plasmasphere.  These emissions contain much
narrowband filamentary and fine structure.  Occasionally narrowband filaments
lasting many hours have been observed.  Several instances of the escaping
terrestrial continuum radiation evolving into the kilometric continuum radiation
have been observed.  By comparing the appearance of these emissions from two or
more spacecraft we are able to deduce remotely the structure of the plasmasphere
and magnetosphere.  Some of the structure observed in both these emissions can
be explained by the bulges, ducts, and irregularities found in the plasmasphere.
Comparisons of wave data from GEOTAIL and wave and EUV imaging data
from IMAGE indicate that some kilometric continuum events have their source in
density notches deep within the plasmasphere.  Some of these notches have been
observed by the IMAGE/EUV to last for several days as had previously been
surmised from ISEE and CRRES PWI number density measurements.

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Presentation at the Yosemite Conference of Inner Magnetospheric Interactions, 
3 - 6 February 2004, Yosemite, California, USA