The New Version 3 of the Operational NOAA/NCEI Solar Irradiance Climate Data Record

The incoming solar irradiance is a fundamental quantity for studying Earth’s climate as it establishes Earth’s surface and atmospheric temperature, and drives coupled radiative, dynamical, and chemical processes that produce myriad land, ocean, and atmospheric interactions. The Sun’s irradiance is spectrally dependent, as is its variability, and this dependence must be reliably specified on time scales from days to centuries and longer. Space-borne observations have been essential for informing the magnitude and variability of solar irradiance forcing and in developing solar irradiance variability models. The models are essential in extrapolating and extending solar forcing estimates to broader time scales and spectral coverage than the direct observations provide.

Version 3 of the operational NOAA/NCEI Solar Irradiance Climate Data Record (CDR) is prescribed by Version 1 of the NASA NOAA LASP (NNL) solar variability models for total solar irradiance (TSI) and solar spectral irradiance (SSI). The NNLTSI1 and NNLSSI1 models hold heritage from the Naval Research Laboratory (NRL) models. These data-based models specify the change in solar irradiance, driven by changes in solar magnetic activity, through multiple linear regression relations that equate SSI and TSI change to visible features (faculae and sunspots) of magnetic activity.

The CDR V3 was transitioned to operations in August 2024 and provides improved estimates of daily-, monthly-, and yearly- averaged TSI and SSI from 1610 through present day than the previous CDR V2. Specific advances include: revised model coefficients informed by higher quality Total and Spectral Solar Irradiance Sensor (TSIS-1) SSI observations and a longer record of TSI and SSI; a new absolute irradiance scale based on TSIS-1 observations; a broader spectral coverage spanning the extreme ultraviolet through the far-infrared (~0 to 200,000 nm) to support research efforts of both the space weather and climate modeling communities; revised reconstructions of historical solar irradiance based on new, improved, magnetic flux transport calculations; a new, high spectral resolution SSI product to support atmospheric chemistry and dynamics studies; and new projections of annually-averaged solar irradiance to the year 2100.

The CDR V3 prescribes the solar forcing dataset of the 7^th Coupled Model Intercomparison Project.

In this work, we discuss the CDR V3 formulation, new capabilities, and present irradiance variability results on rotational, solar-cycle, and century time scales. Since the CDR V3 prescribes the solar forcing dataset of CMIP7, we will present our results in context with the previous CMIP6 solar forcing dataset.