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What are Whistlers?

What are Whistlers?. A whistler is an electromagnetic radio wave that when converted to sound is usually experienced as a descending tone.

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What are Whistlers?

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  1. What are Whistlers?

  2. A whistler is an electromagnetic radio wave that when converted to sound is usually experienced as a descending tone.

  3. 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.

  4. Llanfair Lowestoft Haverfordwest Legitimized Observations! 1894

  5. Amplifier World War I

  6. L. R. Owen Storey first worked out the origin of whistlers in 1952 for his PhD thesis at Cavendish Laboratory University of Cambridge

  7. Whistlers with Atmospherics Whistlers without Atmospherics

  8. Whistler pairs Multiple-flash Triple-D Overlapping

  9. 400 cm-3 Owen’s 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, Owen’s thesis adviser, presents his results at the 1952 URSI meeting in Sydney, but notes Owen’s theoretical interpretation is probably wrong.

  10. Robert Helliwell “The Father of Whistler Research” mid – 1950’s Seattle, WA Unalaska, AK Stanford, CA Byrd Station, Antarctica

  11. Donald Carpenter, 1963 Discovers the Plasmapause from ground whistlers

  12. Konstantin Gringauz, 1959 Makes the first in-space measurements of the plasmasphere from Luna 2 URSI 1963

  13. Whistlers Can Last For 10’s 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.

  14. 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 > vliquids > 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

  15. 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)

  16. normalized Whistler Propagation Theory Dispersion effect weighted toward equatorial densities Carpenter & Smith 1964

  17. 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!

  18. Frequency Time Burton and Boardman Introduced the Sound Spectrograph in 1930

  19. Frequency Dispersion 1 3 1 3 5 7 9 11 1 5 4 2 3 10 11 9 8 7 6

  20. How Can Whistlers Be Used in the Classroom? • To teach the history of discovery and the hardship of changing people’s 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 Earth’s 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?

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