Making of a solar spectral irradiance dataset I: observations, uncertainties, and methods

Abstract

Context. Changes in the spectral solar irradiance (SSI) are a key driver of the variability of the Earth's environment, strongly affecting the upper atmosphere, but also impacting climate. However, its measurements have been sparse and of different quality. The ''First European Comprehensive Solar Irradiance Data Exploitation project'' (SOLID) aims at merging the complete set of European irradiance data, complemented by archive data that include data from non-European missions. Aims. As part of SOLID, we present all available space-based SSI measurements, reference spectra, and relevant proxies in a unified format with regular temporal re-gridding, interpolation, gap-filling as well as associated uncertainty estimations. Methods. We apply a coherent methodology to all available SSI datasets. Our pipeline approach consists of the pre-processing of the data, the interpolation of missing data by utilizing the spectral coherency of SSI, the temporal re-gridding of the data, an instrumental outlier detection routine, and a proxy-based interpolation for missing and flagged values. In particular, to detect instrumental outliers, we combine an autoregressive model with proxy data. We independently estimate the precision and stability of each individual dataset and flag all changes due to processing in an accompanying quality mask.Results. We present a unified database of solar activity records with accompanying meta-data and uncertainties. Conclusions. This dataset can be used for further investigations of the long-term trend of solar activity and the construction of a homogeneous SSI record.

Solar forcing for CMIP6 (v3.2)

“…Furthermore, the short-term and long-term uncertainties of the SSI time series are determined. These steps are detailed in Schöll et al (2016).…”

Revised historical solar irradiance forcing

“…Ly α line is important for the proper simulation of terrestrial atmospheric temperature and chemistry. Schöll et al (2016) analysed the results of the radiative transfer code COSI and reported that both the absolute value and variability of the reconstructed Ly α flux are strongly underestimated. The disagreement with the absolute value has been resolved by using NESSY, the new version of the radiative transfer code, which is able to properly simulate solar irradiance below 130 nm (see Tagirov et al (2017) for details).…”

The high-resolution extraterrestrial solar spectrum (QASUMEFTS) determined from ground-based solar irradiance measurements

“…As recent studies have demonstrated (e.g. Schöll et al, 2016), the solar spectra measured from satellite platforms can differ significantly between each other, due in part to instrument degradation issues arising from the harsh space environment and the difficulties in accounting for possible instrument changes between the preflight calibration and its operation in space. In a strict metrological sense, such measurements cannot be considered traceable to SI (International System of Units) since metrological traceability inherently requires the repeated demonstration of the uninterrupted traceability to primary standards, which is currently not available to instruments located in space (https://www.nist.gov/traceability/ supplementary-materials-nist-policy-review#internal_map).…”