An Improved Solar Spectral Irradiance Composite Record

Abstract:

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. Analyses of the past observations of the SSI data sets have identified some irradiance offsets and some small residual instrumental trends. These corrections are applied and then combined with the previous SSI composite, called the GSFC SSI2 composite, to provide a new SSI composite, called the LASP GSFC SSI #3 (LGSSI3). This improved composite extends the wavelength coverage down to 0.5 nm and up to 1600 nm and the time coverage up to 2020. The new LGSSI3 solar variability results and comparisons with SSI models are presented.