NOAA 11 Solar Backscattered Ultraviolet, model 2 (SBUV/2) instrument solar spectral irradiance measurements in 1989-1994 - 1. Observations and long-term calibration

Measurements of solar ultraviolet (UV) irradiance are a valuable diagnostic of physical processes in the solar atmosphere and a key component in characterizing the external forcing of the Earth's atmosphere. However, the deleterious effects of solar UV radiation on satellite instrument components have complicated efforts to determine the magnitude of long-term solar variations for almost 30 years. The NOAA 11 Solar Backscatter Ultraviolet, model 2 (SBUV/2) instrument, primarily designed to measure stratospheric ozone, also made daily spectral scan measurements of solar UV irradiance in the 160-405 nm region from February 1989 to October 1994. An onboard calibration system and comparisons with coincident Shuttle SBUV (SSBUV) measurements were used to correct for long-term NOAA 11 instrument sensitivity changes. Time series of the NOAA 1 1 solar irradiance data indicate a long-term accuracy of approximately +/-0.9-2.3% (2 sigma) over the 5.5-year data record. Long-term solar irradiance changes of approximately -3% are observed between 215 and 250 nm, increasing in magnitude to approximately -7% at 200-205 nm. Additional discussion of solar variations observed by NOAA 11 SBUV/2 are presented by DeLand and Cebula [this issue].