Lightning detector

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A lightning detector is a device that detects lightning produced by thunderstorms. There are three primary types of detectors: ground-based systems using multiple antennas, mobile systems using a direction and a sense antenna in the same location (often aboard an aircraft), and space-based systems.

Ground-based and mobile detectors calculate the direction and severity of lightning from the current location using radio direction-finding techniques together with an analysis of the characteristic frequencies emitted by lighting. Ground-based systems use triangulation from multiple locations to determine distance, while mobile systems estimate distance using signal frequency and attenuation. Space-based lighting detectors, on artificial satellites, can locate range, bearing and intensities by direct observation.

Ground-based lightning detector networks are used by meteorological services like the National Weather Service in United States and the Meteorological Service of Canada, and by other organizations like electrical utilities and forest fire prevention services.

Contents

1 Limitations
2 Lightning detectors vs. weather radar
3 Aviation use
4 References
5 External links

Limitations

Each system used for lightning detection have its own limitations. Lets mention:

A ground-based lightning network must be able to detect a strike with at least three antennas to locate it within an acceptable margin of error. This often leads to rejection of cloud-to-cloud lightning as one antenna might note the position of the strike on the starting cloud and the other antenna on the receiving one. As a result, ground-based networks have a tendency to underestimate the number of strikes, especially at the beginning of the storms where cloud-to-cloud lightning is prevalent.

Since they use attenuation rather than triangulation, mobile detectors can sometimes mistakenly indicate a weak lightning strike nearby as a strong one further away, or vice-versa.

Space-based lightning networks suffer from neither of these limitations, but the information provided by them is often several minutes old by the time it is widely available, making it of limited use for real-time applications like air navigation.

Lightning detectors vs. weather radar

A thunderstorm life cycle and associated reflectivities from a weather radar

Distribution of electric charges and lighning strikes in and around a thunderstorm

Lightning detectors and weather radar are complementary to detect storms: lightning detectors indicate electrical activity, while weather radar indicates precipitation. Both phenomena are associated with thunderstorms and can help to indicate the storm strength.

The first image on the right shows the life cycle of a thunderstorm:

Air is moving upward due to instablility.
Condensation occurs and radar can pick up echos above ground (colored areas).
Eventually the mass of rain drops is too large to be sustained by the updraft and drop toward the ground.

The cloud has to develop to a certain vertical extent before lightning is produced, so generally a weather radar will indicate a developing storm before a lightning detector does; however, it is not always clear from early returns whether a shower cloud will develop into a thunderstorm, and weather radar also sometimes suffers from a masking effect by attenuation, where precipitation close to the radar can hide (perhaps more intense) precipitation further away. Lightning detectors do not suffer from a masking effect and can provide confirmation of when a shower cloud has turned into a thunderstorm.

Lightning may be also located outside the precipitation recorded by radar — the second images shows that this happens when strikes originate in the anvil of the thundercloud (top part blown ahead of the cumulonimbus cloud by upper winds) or on the outside edge of the rain shaft. In both cases, there is still an area of radar echoes somewhere nearby.

Aviation use

Large airliners are more likely to use weather radar than lightning detectors, since weather radar can detect smaller storms that also cause turbulence; however, modern avionics systems often include lightning detection as well, for additional safety.

For smaller aircraft, especially in general aviation, there are two main brands of lightning detectors (often referred to as sferics, short for atmospherics): Stormscope, produced originally by Ryan (later B.F. Goodrich) and currently by L3, and the Strikefinder, produced by Insight. Lighting detectors are inexpensive and lightweight, making them attractive to owners of light aircraft (particularly of single-engine aircraft, where the aircraft nose is not available for installation of a radome).

References

External links

[Recent North American lightning activity] from Environment Canada
[Lightning detection guide] (PDF) from the U.S. NOAA
[Lightning origin and research on detection from space from NASA]
[Blog posting] about lightning detection and air traffic control
[Archived e-mail thread comparing the Stormscope and Strikefinder]
[Stormscope product page]
[Strikefinder product page]

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