Can Measurements of the Near‐Infrared Solar Spectral Irradiance be Reconciled? A New Ground‐Based Assessment Between 4,000 and 10,000 cm−1

• Published in: Geophysical research letters 2017-10, Vol.44 (19), p.10,071-10,080
• Main Authors: Elsey, Jonathan, Coleman, Marc D., Gardiner, Tom, Shine, Keith P.
• Format: Article
• Language: English
• Subjects: Atmosphere; Atmospheric sciences; Budgets; Carbon dioxide; Caviar; Climate; Climate change; Climate prediction; Computer simulation; Earth; Energy; Gases; ground‐based spectroscopy; I.R. radiation; Irradiance; Monte Carlo simulation; Near infrared radiation; Radiation; Radiation budget; radiative transfer; Solar irradiance; Solar spectra; Solar spectral irradiance; Spectra; Statistical methods; Sun; Ultraviolet radiation; Water vapor; Water vapour; Wavelengths; Weather forecasting
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL073902

The near‐infrared solar spectral irradiance (SSI) is of vital importance for understanding the Earth's radiation budget, and in Earth observation applications. Differences between previously published solar spectra (including the commonly used ATLAS3 spectrum) reach up to 10% at the low wavenumber end of the 4,000–10,000 cm−1 (2.5–1 μm) spectral region. The implications for the atmospheric sciences are significant, since this spectral region contains 25% of the incoming total solar irradiance. This work details an updated analysis of the CAVIAR SSI, featuring additional analysis techniques and an updated uncertainty budget using a Monte Carlo method. We report good consistency with ATLAS3 in the 7,000–10,000 cm−1 region where there is confidence in these results due to agreement with other spectra, but ~7% lower in the 4,000–7,000 cm−1 region, in general agreement with several other analyses. Key Points In light of continuing disagreement in observations of near‐infrared solar spectral irradiance (SSI), we present a new SSI with full uncertainty evaluation This SSI shows good agreement with the commonly‐used ATLAS3 SSI at shorter wavelengths but is ~7% lower at longer wavelengths This discrepancy is significant since the near‐infrared contains several strong water vapor bands, which influence the atmospheric energy budget Plain Language Summary The total energy arriving to Earth from the Sun is well known, but how much of this is visible; ultraviolet or infrared light is also important. This paper presents measurements of the Sun's infrared energy that reaches Earth. This infrared energy heats up the atmosphere as it is absorbed by the surface and by gases such as carbon dioxide and water vapor. Knowing how much of this infrared energy reaches us is important for weather prediction and for simulations of climate change (which depends on the amount of energy arriving at and leaving the atmosphere). Previous measurements of the Sun's infrared energy from both the ground and from satelites show significant disagreement. Our measurements help resolve this disagreement, and will enable more accurate representation of the Sun's infrared energy in weather and climate predictions.