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Radio atmospheric


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A frequency vs. time plot (spectrogram ) showing several whistler signals
amidst a background of sferics as received at Palmer Station , Antarctica
on August 24, 2005.

A *Radio Atmospheric signal* or *Sferic* (sometimes also spelled
"Spheric") is a broadband electromagnetic impulse that occurs as a result
of natural atmospheric lightning discharges. Sferics may propagate from
their lightning source without major attenuation in the Earth-Ionosphere
waveguide , and can be received thousands of kilometers from their source.
On a time-domain plot, a sferic may appear as a single high-amplitude
spike in the time-domain data. On a spectrogram , a sferic appears as a
vertical stripe (reflecting its broadband and impulsive nature) that may
extend from a few kHz to several tens of kHz, depending on atmospheric
conditions.

Sferics received from about two thousand kilometres distance or greater
have their frequencies slightly offset in time, producing /tweeks/.

When the electromagnetic energy from a sferic escapes the Earth-Ionosphere
waveguide and enters the magnetosphere , it becomes dispersed by the
near-earth plasma , forming a whistler signal. Because the source of the
whistler is an impulse (i.e., the sferic), a whistler may be interpreted
as the impulse response of the magnetosphere (for the conditions at that
particular instant).


[edit ] See also

* Lightning 
* 1955 Great Plains tornado outbreak
[1]

* Whistler (radio) 

[hide ]
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Atmospheric electricity 
General 	
Geophysics  *·* Atmospheric sciences
*·* Atmospheric physics
*·* Atmospheric dynamics
*·* Atmospheric chemistry
*·* Earth's magnetic field

Electromagnetism 	
ELF/VLF Electromagnetic emissions
	
Radio atmospherics  *·* Whistlers
*·* Chorus
*·* Hiss

Optical emissions
	
Transient luminous events  *·*
Upper-atmospheric lightning  *·*
Sprites  *·* St. Elmo's fire
*·* Ball lightning 

Sources 	
Solar radiation  *·* Lightning
*·* Equatorial electrojet 
Applications 	
Electrodynamic tethers  *·*
Magnetotellurics 
People 	
Egon Schweidler  *·* Nikola Tesla


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