What are Whistlers?

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What are Whistlers?
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A whistler is an electromagnetic radio wave that
when converted to sound is usually experienced as
a descending tone.
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Although a whistler is an EM wave, it is a very
low frequency wave, much lower than what we
normally think of for a radio wave. It is so low
that little more than a long wire and audio
amplifier is needed to pick it up.
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Legitimized Observations!
1894
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World War I
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L. R. Owen Storey first worked out the origin of
whistlers in 1952 for his PhD thesis at Cavendish
Laboratory University of Cambridge
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Owens Quite Unpopular Answer
Ionosphere can typically only produce D 2
s1/2 while dispersions of D 60 s1/2 are
measured.
WORSE H. J. A. Ratcliffe, Owens thesis adviser,
presents his results at the 1952 URSI meeting in
Sydney, but notes Owens theoretical
interpretation is probably wrong.
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mid 1950s
Seattle, WA
Unalaska, AK
Stanford, CA
Byrd Station, Antarctica
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Donald Carpenter, 1963
Discovers the Plasmapause from ground whistlers
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Konstantin Gringauz, 1959
Makes the first in-space measurements of the
plasmasphere from Luna 2
URSI 1963
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Whistlers Can Last For 10s of Seconds How is
That Possible?
Since EM whistlers waves travel very great
distances, you would expect their strength to
fall rapidly as the waves spread out. That does
not happen, because small irregularities in the
density of ionized gas (plasma) guides and
confines the energy to narrow channels that
maintain the strength of the wave until some is
passed into the opposite hemisphere and some is
reflected back.
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So What is Frequency Dispersion?
You may know that the speed sound travels is
different for different types of medium and state
of matter or phase.
vsolids gt vliquids gt vgases
In Air v 331 m/s (0.6 m/s/C)T (at 20oC it
is 343 m/s)
In Water at 20oC it is 1483 m/s, while in
structural steel is it 4512 m/s
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So What is Frequency Dispersion?
In a dispersive medium waves of different
frequency have different wavelengths and
consequently move with different speeds.
For Whistler Electromagnetic Waves the dispersion
equation is
(Or just check out the slinky)
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Whistler Propagation Theory
Dispersion effect weighted toward equatorial
densities
Carpenter Smith 1964
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What Possible Reason Could I Have Had to Inflict
the Last Two Slides on You?
Well Really just to make one point. A whistler
sounds the way it does, because of how things are
in space near the Earth. Anyone can pick up
whistlers with a low frequency radio receiver.
You know how a sound is different when you hear
it outside as compared to in a small room or in a
large auditorium. To hear the sound is to also
experience the environment where you hear it.
Hearing whistlers allows us to experience a small
part of space near Earth that is also like that
near Jupiter, Saturn, and elsewhere in the
universe. It is beautiful to hear and a tool for
exploring the universe.
Space is Accessible!
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Burton and Boardman Introduced the Sound
Spectrograph in 1930
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Frequency Dispersion
Trace D T0
1 186 -0.5
2 117 11.8
3 53 20.2
4 83 20.4
5 150 20.7
6 75 28.2
7 228 28.2
8 377 28.3
9 532 28.4
10 675 28.5
11 808 28.9
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1
3
5
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1
5
4
2
3
10
11
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8
6
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How Can Whistlers Be Used in the Classroom?

• To teach the history of discovery and the
  hardship of changing peoples minds
• To inspire youth to imagine they can study the
  universe the universe holds secrets revealed by
  measurements accessible to them
• To teach the application of mathematics,
  graphing, and skills of scientific interpretation
• To teach critical thinking how weather on Earth
  and in space is connected through whistlers how
  other measures of space weather can be used to
  interpret their observations
• To teach about the Earths magnetic field, how it
  reaches into space (not just on the surface) and
  how it is changing over time now and in the past
• To teach about how sound and other waves move
  through matter
• What else?