Whistler (radio)

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A frequency versus time graph ( spectrogram ) showing multiple Whistler signals received at Palmer Station , Antarctica on August 24, 2005.

A whistler is a low-frequency electromagnetic signal that can be generated, for example, by thunderstorms . The frequencies of a Whistler are between 1 and 30 kHz, usually with a maximum between 3 and 5 kHz. In terms of frequency, they are within the human hearing range and can be converted directly into acoustic signals with a suitable receiver.

They are caused by lightning strikes in which the impulse wanders away from the earth and returns to the earth along the magnetic field lines. Due to the lower speed of propagation ( dispersion ) of the lower frequencies in the plasma of the ionosphere and magnetosphere , they are perceived as a descending tone that can last for several seconds. Whistlers are divided into Pure Note Whistlers , Diffuse , 2-hop and Echo Train .

Whistler were also received by Jupiter , which proves the existence of thunderstorms there.

Designations

The propagation of a signal in the earth-ionosphere waveguide is called sferic . If the signal originated in the ionosphere and is able to propagate through the magnetosphere, it becomes a jumping propagation in which it is reflected back and forth on opposite sides of the planet until it has completely weakened. To make it clear in which part of this jump pattern the signal is located, it is assigned a number. On his first upward path it is considered 0 + respectively. After it has passed the magnetic equator , it is named 1 - . The + or - sign indicates the upward or downward spread. The number represents the current half jump number. The re-reflected signal is then referred to as 1+ until it passes the geomagnetic equator again; then it says 2 - etc.

literature

  • Robert A. Helliwell: Whistlers and Related Ionospheric Phenomena . Dover Publications, 2006, ISBN 0-486-44572-0 . Originally published by Stanford University Press, Stanford, California (1965). See also Whistlers and VLF Emissions by the same author.
  • R. Romero: Radio Nature . Radio Society of Great Britain , Potters Bar 2008, ISBN 978-1-905086-38-2 .

Web links

Individual evidence

  1. ^ RL Smith, JJ Angerami: Magnetospheric Properties Deduced from OGO 1 Observations of Ducted and Conducted Whistlers. In: Journal of Geophysical Research. vol 73, no January 1, 1968.