The spectral composition of TSI as measured by the SORCE SIM solar spectral radiometer

The SORCE (Solar Radiation and Climate Experiment) SIM (Spectral Irradiance Monitor) instrument is a satellite-borne prism spectrometer that measures the solar spectrum from 200-2700 nm with a cadence of at least 2 spectra per day and a wavelength dependent resolution of 1-33 nm. This instrument provides the temporal evolution of solar irradiance in the ultraviolet, visible, and infrared spectral regions. At some wavelengths in the ultraviolet, the SIM measurements exhibit variations similar to the Mg II core-to-wing ratio, and in the visible and IR they show similarities to the total solar irradiance (TSI) record, but with differing wavelength dependent amplitudes, phases, and shapes. Furthermore, the observed TSI variations can be examined in the context of the integral of the spectral irradiance over discrete spectral bands in the 200-1600 nm region showing the spectral contributions of solar active regions. Further insight into the solar variability observed by the SIM can be gained from analyzing the distribution of solar features as measured by the Precision Solar Photometric Telescope in conjunction with spectral decomposition (ApJ, 1999, 518, 480).