Glossary Terms
- Solar Flare
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A space weather term for a sudden eruption of energy in the solar atmosphere lasting from minutes to hours from which radiation and particles are emitted. Flares are officially measured and classified based on peak X-ray flux from 1-minute-averaged GOES X-ray Sensor (XRS) observations in the 1–8-angstrom passband.
- Wave Cyclone
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(Also called wave depression.) A cyclone that forms and moves along a front.
The circulation about the cyclone center tends to produce a wavelike deformation of the front. The wave cyclone is the most frequent form of extratropical cyclone (or low). It was the purpose of the wave theory of cyclones to explain its life cycle.
- Alexander's dark band
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The dark region of the sky seen between the primary and secondary rainbows.
It is named after Alexander of Alphrodisias, the first person known to have commented upon it. He was the head of the Lyceum from 198 to 211 A.D.
- Megaflash
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A continuous mesoscale lightning flash with a horizontal path length of approximately 100 km or greater. The tremendous distances covered by megaflashes necessitate long flash durations as well, typically 5 s or greater.
- Cloudburst
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(Also called rain gush, rain gust.) In popular terminology, any sudden and heavy fall of rain, almost always of the shower type.
An unofficial criterion sometimes used specifies a rate of fall equal to or greater than 100 mm (3.94 inches) per hour.