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TYPE I, II, III, IV
See RADIO EMISSION
A fast radio burst spectrum of a FLARE. It has a U-shaped appear- ance in an intensity-vs.-frequency plot.
ULTRA HIGH FREQUENCY (UHF)
Those radio frequencies exceeding 300 MHz.
The dark core or cores (umbrae) in a SUNSPOT with PENUMBRA, or a sunspot lacking penumbra.
UNIVERSAL TIME (UT)
See COORDINATED UNIVERSAL TIME.
With regard to geomagnetic levels, a descriptive word speci- fically meaning that 8 is less than or equal to the Ap INDEX which is less than or equal to15.
VERY HIGH FREQUENCY (VHF)
That portion of the radio frequency spectrum from 30 to 300 MHz.
VERY LOW FREQUENCY (VLF)
That portion of the radio frequency spectrum from 3 to 30 kHz.
WHITE LIGHT (WL)
Sunlight integrated over the visible portion of the spec- trum (4000 - 7000 angstroms) so that all colors are blended to appear white to the eye.
WHITE LIGHT FLARE
A major FLARE in which small parts become visible in white light. Such flares are usually strong X-ray, radio, and particle emitters.
An historic term for SUNSPOT NUMBER. In 1849, R. Wolf of Zurich originated the general procedure for computing the sunspot number.
A daily average background X-ray flux in the 1 to 8 angstrom range. It is a midday minimum designed to reduce the effects of FLAREs.
A temporary enhancement of the X-ray emission of the sun. The time-intensity profile of soft X-ray bursts is similar to that of the H-ALPHA profile of an associated FLARE.
ZURICH SUNSPOT CLASSIFICATION
A sunspot classification system that has been modified for SESC use.