Objectives. The solar spectral irradiance (SSI) data set is a key record for studying and understanding the energetics and radiation balance in earth's environment. Understanding the long-term…

This is a $355,728.70 grant awarded by NASA to the University of Colorado's Office of Contracts and Grants Division to study long-term variations in solar spectral irradiance (SSI) over solar cycles 21 through 24. The objectives are to separate solar cycle variability from instrumental trends in past SSI satellite measurements, produce a more accurate composite SSI record, and combine it with new SSI measurements expected from the upcoming Total Solar Irradiance Sensor (TSIS) and Compact Spectral Irradiance Monitor (CSIM). The research will apply a new technique called Multiple Same-Irradiance-Level (MUSIL) analysis to public SSI records from several NASA and NOAA satellites dating back to the 1970s. This improved SSI composite record will benefit studies of Earth's radiation budget, atmospheric solar heating, and other sun-climate research efforts. The award is structured as a grant for research and does not have a set-aside designation.

Objectives. The solar spectral irradiance (SSI) data set is a key record for studying and understanding the energetics and radiation balance in earth's environment. Understanding the long-term variations of the SSI over time scales of the 11-year solar activity cycle and longer is critical for many sun-climate research topics. There are satellite measurements of the SSI since the 1970S that contribute to understanding the solar variability over solar cycles (SC) 21 to 24, with most of these SSI measurements in the ultraviolet and only recently in the visible and near infrared for SC 23 and 24. A limiting factor for the accuracy of the previous results is the uncertainties for the instrument degradation corrections, for which there are fairly large corrections relative to the amount of solar cycle variability at some wavelengths. The objectives of this study are (1) to separate out solar cycle variability and any residual uncorrected instrumental trends in the past SSI satellite measurements, (2) to produce a more accurate SSI composite record over solar cycles 21 to 24, and (3) to combine this improved SSI composite record with the new total spectral irradiance sensor (tsis) and compact spectral irradiance monitor (csim) measurements of SSI that are expected to start in 2018. Methodology. A new technique called the multiple same-irradiance-level (musil) analysis has been developed that examines a SSI time series at different levels of solar activity to provide long-term trends in a SSI record, and the most common result is a downward trend that is most likely from uncorrected instrument degradation. The SSI record is then updated with this residual instrumental trend to provide a more accurate solar cycle variability result. This technique applied to the highly accurate total solar irradiance (TSI) record indicates that this analysis can provide a relative uncertainty of about 5% of the true solar cycle variability. This technique will be applied to each wavelength in the public SSI records from the solar mesospheric explorer (SME: 1981-1989, SC 21-22), NOAA solar backscatter ultraviolet (sbuv: 1978-1997, SC 21-22), upper atmosphere research satellite (uars: 1991-2005, SC 22-23), timed solar extreme ultraviolet spectrometer (see: 2002-present, SC 23-24), solar radiation and climate experiment (sorce: 2003-present, SC 23-24), and ozone monitoring instrument (OMI: 2004-present, SC 23-24). These SSI observations cover the spectral range from 115 NM to 2400 NM with about 1 NM resolution at most wavelengths. Expected outcome. The musil analysis will provide new estimates for solar cycle variability for each wavelength for eight different SSI records over solar cycles 21 to 24. Consistency of analysis for the different SSI records will help to make a new multiinstrument SSI composite record. These results will be a valuable resource for earth scientists who are studying and modeling earth's radiation budget, solar heating effects in the atmosphere and at the surface, and any other sun-climate data analysis and modeling efforts. The new SSI composite record can also be a benefit to the other sist team members, especially so for those who may be developing models of solar variability or also developing other SSI records. This improved SSI record will then be compared to the new total spectral irradiance sensor (tsis) measurements, and those comparisons will help to further validate this new musil technique with the accurate tsis observations and to extend this new composite SSI record into the future. Sist team leader. This proposal includes the option for DR. TOM woods to be the sist team leader to provide leadership in developing new, improved TSI and SSI climate records. He will organize, in partnership with the HQ sist program scientist, the annual sist team meetings to discuss new results. He will also setup a sist team web sharing site at lasp.