We propose to establish, with greater certainty than now available, the magnitude and temporal structure of the sun s irradiance variability at ultraviolet, visible and infrared wavelengths over…

This federal contract award from the National Aeronautics and Space Administration (NASA) was granted to the University of Colorado, a U.S. state government entity and institution of higher learning. The $239,975.76 grant is for the University to establish the magnitude and temporal structure of the Sun's irradiance variability across ultraviolet, visible, and infrared wavelengths over time scales from months to decades. The goal is to consolidate this data into an improved proxy model of spectral irradiance variability with associated uncertainties, to benefit climate and atmospheric science communities. The University will systematically quantify irradiance variations and relationships to solar activity indicators, with a focus on reanalyzing the SME solar UV irradiance database. This work will provide the first quantitative uncertainties in knowledge of solar spectral irradiance variations over multiple time scales. The University will also provide leadership for the Solar Irradiance Science Team. No set-aside designation is mentioned for this grant award.

We propose to establish, with greater certainty than now available, the magnitude and temporal structure of the sun s irradiance variability at ultraviolet, visible and infrared wavelengths over time scales from months to multiple decades, and to consolidate this new information into an improved proxy model of spectral irradiance variability with associated uncertainties, in a format readily accessible to climate and atmospheric communities. The approach is a methodical investigation to establish separately in each available solar spectral and total irradiance database, those variations that are unequivocally of solar origin, their associations with solar activity indicators, and plausible instrumental changes. Each database will be analyzed on three, increasingly longer time scales to specify and understand irradiance changes: 1) monthly, arising from solar rotational modulation, when instrumental changes are smaller than solar changes and relationships with proxy indicators can be well established, 2) during the solar cycle when instrumental changes can exceed real solar changes, causing ambiguity in proxy relationships and in scaling the rotational associations, and 3) over multiple decades for which solar observations in the 2008-2009 prolonged minimum of solar activity, relative to the prior 1996 minimum, afford a unique, unprecedented opportunity for detection. Firstly, we will systematically quantify commonality of irradiance variations on monthly time scales in individual databases and relationships to sunspot and facular proxies, deducing quantifiable uncertainties in measurements and understanding. For specifying solar cycle irradiance variations a key aspect of the proposed work is reanalysis of the SME solar UV irradiance database with improved wavelength calibration. With limited solar exposure and in-flight diffuser sensitivity monitoring, the SME observations potentially provide one of the most stable databases for establishing true solar cycle irradiance variability. Using the reanalyzed SME database we will quantify how solar rotational variations, and their relationships to sunspot and facular proxies, scale to solar cycle changes. Total solar irradiances observations will be similarly analyzed, after first removing the sunspot darkening component. Constraining the solar UV spectral irradiance and total irradiance changes over the solar cycle by necessity then constrains the total energy changes in the visible and infrared spectrum. To assess possible longer-term changes, we will investigate the extent to which multiple solar observations demonstrate the needed stability to determine real solar changes between the 1996 and 2008 solar minima, assess the most stable and applicable proxies of irradiance variability, and provide new estimates and models of long-term irradiance changes. The significance of our proposed work is that in addition to systematically investigating key assumptions in solar irradiance variability models that rotational modulation scales to solar cycle variability and that the facular component of total and spectral irradiance are temporally similar we will provide, for the first time, uncertainties in knowledge of solar spectral irradiance variations on multiple time scales reflecting those inherent in the extant databases. The overall product will be a new version of the nrlssi spectral irradiance variability model that is consistent with the extant databases and with simultaneous total irradiance database, taking into account uncertainties. Provision of quantitative uncertainties in solar irradiance variability will aid in reconciling issues about sunclimate interactions arising from the SIM observations. We propose as well to provide team leadership for the sist, with DR. J. Lean undertaking the primary responsibility in consultation with DRS gary rottman and peter pilewskie, and with the assistant of vanessa george in organizing telecons and team meetings.