Total solar irradiance (TSI) has been measured from space since 1978, providing the best data record of the net energy powering the earth's climate system. Variations in the TSI over long periods of…

This federal contract award to The Regents of the University of Colorado, doing business as the University of Colorado Office of Contracts and Grants Division, is a $354,506.34 grant for research to improve historical reconstructions of total solar irradiance (TSI) measurements. The work will update the sunspot record used in TSI models, re-compute flux-transport model results, and continue improving the existing TSI composite that provides a 40-year record of variability and uncertainties in the net energy driving the Earth's climate system. This will help climate studies distinguish natural solar variability from anthropogenic influences. The award was granted by the National Aeronautics and Space Administration (NASA) without a set-aside designation. The University of Colorado is an accredited public research university that has previously received federal contracts and grants for space weather modeling, AI decision support, air quality assessments, and other research and development across science, technology, engineering, and mathematics disciplines.

Total solar irradiance (TSI) has been measured from space since 1978, providing the best data record of the net energy powering the earth's climate system. Variations in the TSI over long periods of time can cause climate changes that must be distinguished from anthropogenic influences for understanding climate variability. Climate studies rely on modeled TSI reconstructions that extend the space-borne TSI measurements back thousands of years. The two most prominent TSI models are the nrltsi and the satire models. With the proposed efforts, we will improve the historical TSI reconstructions from both the nrltsi and satire models both forward in time and back to the year 1610 by incorporating three primary improvements to the models' inputs. In particular, via this proposal we will: 1. Update the 400-year sunspot record used in TSI models for historical reconstructions 2. RE-compute flux-transport results to improve historical solar-variability estimates 3. Improve the TSI-measurement composite, providing a reference for TSI models improve sunspot records: the TSI models rely on sunspot records, reevaluations of which thus affect historical TSI reconstructions. Preliminary such effects were described by kopp ET AL. [9] using the first release (v.2) of an updated sunspot record by the sunspot index and long-term solar observations (silso) project. Refinements to this record via several complementary or independent methods are being considered by an international space studies institute (issi) team with two meetings planned in 2018 to recommend updates to this record. PI kopp and collaborator dudok DE WIT are members of this issi team. Our team will help create a future version (v.3) of the silso sunspot records and estimate historical TSI reconstructions based on these new records. RE-compute flux-transport model results: flux-transport models help distinguish the amount of open VS. Closed magnetic fields on the sun. The latter more directly affect the TSI but the former better provide a long-term indicator of historical solar activity via solar modulation of galactic cosmic rays and thus cosmogenic-isotope records. We will use the improved sunspot record as source data in the advective flux transport model [22,23] to give better estimates of secular variability from those in the prior flux-transport-based version of the nrltsi model [24]. This newer state-of-the-art surface flux-transport model incorporates many advances made over the last decade. Continue TSI composite: an improved TSI composite is being created by a 2014 sist team led by PI kopp. That project utilizes a statistically-driven method for combining data from the 39-year record of space-borne instruments into a single time-series [5]. Specific improvements over prior composites include: the use of data from all available instruments, weighting each by its intrinsic noise based on a data-driven methodology; an unbiased, statistically-driven, scale-wise selection of instrument data; smoothing temporal transitions between instruments; systematic estimation of the time-dependent uncertainty associated with each TSI record and the final TSI composite. The resulting composite provides climate modelers and researchers studying solar variability a fourdecade record of variability and uncertainties in the net energy driving the earth's climate system. We will update and improve this TSI composite by incorporating new spacecraft data from upcoming instruments, such as NASA's tsis/TIM, and by implementing refinements to the composite-creation methodology. These three independent and complementary efforts will provide improved solar forcings and uncertainties for global-climate models. With these advances, we will compute the TSI reconstructions from the satire and the nrltsi models to estimate the variability in the long-term TSI record and the range of historical solar forcing, as needed for climate studies.