Solar Spectral Variability as measured by the SORCE SIM Instrument

The Spectral Irradiance Monitor (SIM) on-board the Solar Radiation and Climate Experiment (SORCE) satellite provides the first comprehensive measurements of solar spectral irradiance (SSI) variability from 200-2400 nm, accounting for about 97 percent of the total solar irradiance (TSI) incident at the top of the Earth's atmosphere. SIM observations indicate that, in addition to modulation due to active region passage, the SSI values for wavelengths with a brightness temperature greater than 5770 K show a brightening with decreasing solar activity, whereas below this value there is a dimming. These results demonstrate that different parts of the solar atmosphere contribute differently to the TSI with the behavior in the deep photospheric layers giving an opposing and nearly compensating solar cycle trend to that in the upper photospheric and lower chromospheric layers that produce the ultraviolet contributions. We will show these results over the last 4.5 years of the mission during the descending phase of Solar Cycle 23 that includes the solar minimum time period of the Whole Heliosphere Interval (WHI).