Time variations of solar UV irradiance as measured by the Solstice (UARS) instrument

An analysis is presented of solar ultraviolet irradiance measurements made by the SOLSTICE spectrometers on the Upper Atmosphere Research Satellite (UARS). Reported observations cover the wavelength interval 119–420 nm, and the analysis discussed here is for the time period 26 Nov 1991 to 31 Dec 1992, during which time solar activity decreased in intensity. At the time of peak activity, the average 27‐day variation had a relative amplitude of ∼8% at Ly‐α, tailing off to about 0.6% at 260 nm. It is shown that over the spectral interval 119–260 nm, the relative 27‐day harmonic was about a factor of two larger during the strongly disturbed as compared with the moderately disturbed period.