SOLAR UV SPECTRAL IRRADIANCE VARIATIONS

Recent measurements of the relative temporal variations of solar UV radiation are reviewed. The long-term increase in solar UV irradiance during the rise of solar cycle 22 through April 1990 is comparable to the decrease from the solar cycle 21 peak in late 1981 to the 1986 minimum. Although several marked differences occur in the short-term or solar-rotational variations of the UV and Ottawa 10.7 cm radio flux (F10), the shape of the long-term solar-cycle increase of F10 is quite similar to that of UV enhancements.