The Earth as a radio source: The nonthermal continuum

TLDR: In this article, a weak nonthermal continuum, radiated by the earth from energetic electrons in the outer radiation zone, is studied and it is shown that the frequency spectrum of the continuum radiation consists of two components, a trapped component, which is permanently trapped within the magnetosphere at frequencies below the solar wind plasma frequency, and an escaping component which propagates freely away from the earth at frequencies above the plasma frequency.

Abstract: A weak nonthermal continuum, radiated by the earth from energetic electrons in the outer radiation zone, is studied. It is shown that the frequency spectrum of the continuum radiation consists of two components, a trapped component, which is permanently trapped within the magnetosphere at frequencies below the solar wind plasma frequency, and an escaping component which propagates freely away from the earth at frequencies above the solar wind plasma frequency. Direction finding measurements and measurements of the spatial distribution of intensity for both components indicated that the continuum radiation is generated (1) in a broad region which extends through the morning and early afternoon immediately beyond the plasmapause boundary, and (2) over a broad range of latitudes, including the magnetic equator. Possible mechanisms by which this radiation is generated, including gyro-synchrotron radiation from energetic electrons in the outer radiation zone, are discussed.

Full text

U.
of Iowa
74-39
(NASA-CR-142076)
THE
EARTH
AS
A
RADIO
N75-17022'
SOURCE:
THE
NON-THERMAL
CONTINUUM
Progress
Report
(Iowa
Univ.)
54 p
HC
$4.25
CSCL
04A
Unclas
G3/46
09835
.VERSITY
OA.
OUNDED
1
N
Department
of Physics
and
Astronomy
THE
UNIVERSITY
OF
IOWA
Iowa
City, Iowa
52242

U.
of
Iowa/74-39
The
Earth
as
a
Radio
Source:
The
Non-Thermal
Continuum
by
Donald
A.
Gurnett
December,
1974
Department
of
Physics
and
Astronomy
The
University
of
Iowa
Iowa
City,
Iowa 52242
This
work
was
supported.
in
part
by
the National
Aeronautics
and
Space
Administration
under contracts
NAS5-11074
and
NAS5-11431
and
Grants
NGL-16-O01-i43 and
NGL-16-001-002
and
by
the
Office
of
Naval
Research
under
Grant
N00014-68-A-0196-0009.

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74-3
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4.
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S.
TYPE
OF
REPORT
&
PERIOD
COVERED
THE
EARTH
AS
A
RADIO
SOURCE:
THE
NON-THERMAL
Progress,
December
1974
CONTINUUM
a.
PERFORMING
On
.
REPORT
NUMsER
7.
AUTHO(*)
I.
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OR
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NUMBE
V.)
Donald
A.
Gurnett
NOOO14-68-A-0196
-0009
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ADDRESS
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ELnENT.N
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Department
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Physics
and.
Astronomy
The
University
of
Iowa
Iowa
City,
Iowa
5
2
2
42
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December
1974
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SUPPLEMENTARY
NOTES
To
be
published
in
J.
Geophys.
Res.,
1975.
IS. KEY
WORDS
(Continue
on
rever
e
side
If
ne
else*r
Indiden
y
block
number)
Radio
Source
Non-Thermal
Continuum
20.
ABISTRACT
(Conlinue
on
reveree
slde
It
nceaery
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Identify
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umber)
[See
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2
ABSTRACT
In
addition
to
the
intense
and.
highly
variable
auroral
kilo-
metric
radiation
the
earth
also
radiates
a
weak
non-thermal
continuum
from
energetic
electrons
in
the
outer
radiation
zone.
The
intensity
of
this
continuum
radiation
decreases
with
increasing
frequency
and
is
usually
below
the
cosmic
noise
level
at
frequencies
above
100
kHz.
In
this
paper
we
show
that
the
frequency
spectrum
of
the
continuum
radiation
consists
of
two
components,
a
trapped
component,
which
is
permanently
trapped
within
the
magnetosphere
at
frequencies
below
the
solar
wind
plasma
frequency,
and
an
escaping
component
which
propagates
freely
away
from
the
earth
at
frequencies
above
the
solar
wind
plasma
frequency.
The
low
frequency
cutoff
of
the
continuum
radiation
spectrum
is
at
the
local
electron
plasma
frequency,
which
can
be
as
low
as
500
Hz
in
the
low
density
regions
of
the
distant
magnetotail.
Direction
finding
measurements
and
measurements
of
the
spatial
distribution
of
intensity
for
both
the
trapped
and
freely
escaping
components
are
used.
to
determine
the
region
in
which
the
continuum
radiation
is generated..
These
measurements
all
indicate
that
the
continuum
radiation
is
generated
in
a
broad
region
which
extends
through
the
morning
and
early
afternoon
from
about
4.0
hours
to
14.0
hours
local
time
immediately
beyond
the
plasmapause
boundary.
In
contrast

to
the
auroral kilcmetric
radiation,
which
is
generated in
the
high
latitude
auroral-zone
regions,
the continuum
radiation
appears
to
be
generated
over
a broad.
range
of
latitudes, including
the
magnetic
equator.
In
some
cases
the
continuum radiation
appears
to
be
closely
associated with
intense
bands
of
electrostatic
noise
which
are
ob-
served
near
the
electron
plasma
frequency
at
the
plasmapause.
Possi-
ble
mechanisms
by
which
this
radiation
could
be
generated,
including
gryo-synchrotron radiation
from
energetic
electrons
in
the outer
radiation
zone,
are
discussed.