Abstract
Context. Solar spectral irradiance (SSI) is the wavelength-dependent energy input to the top of the Earth’s atmosphere. Solar ultraviolet (UV) irradiance represents the primary forcing mechanism for the photochemistry, heating, and dynamics of the Earth’s atmosphere. Hence, both temporal and spectral variations in solar UV irradiance represent crucial inputs to the modeling and understanding of the behavior of the Earth’s atmosphere. Therefore, measuring the long-term solar UV irradiance variations over the 11-year solar activity cycle (and over longer timescales) is fundamental. Thus, each new solar spectral irradiance dataset based on long-term observations represents a major interest and can be used for further investigations of the long-term trend of solar activity and the construction of a homogeneous solar spectral irradiance record. Aims. The main objective of this article is to present a new solar spectral irradiance database (SOLAR-v) with the associated uncertainties. This dataset is based on solar UV irradiance observations (165−300 nm) of the SOLAR/SOLSPEC space-based instrument, which provides measurements of the full-disk SSI during solar cycle 24. Methods. SOLAR/SOLSPEC made solar acquisitions between April 5, 2008 and February 10, 2017. During this period, the instrument was affected by the harsh space environment that introduces instrumental trends (degradation) in the SSI measurements. A new method based on an adaptation of the Multiple Same-Irradiance-Level (MuSIL) technique was used to separate solar variability and any uncorrected instrumental trends in the SOLAR/SOLSPEC UV irradiance measurements. Results. A new method for correcting degradation has been applied to the SOLAR/SOLSPEC UV irradiance records to provide new solar cycle variability results during solar cycle 24. Irradiances are reported at a mean solar distance of 1 astronomical unit (AU). In the 165−242 nm spectral region, the SOLAR/SOLSPEC data agrees with the observations (SORCE/SOLSTICE) and models (SATIRE-S, NRLSSI 2) to within the 1-sigma error envelope. Between 242 and 300 nm, SOLAR/SOLSPEC agrees only with the models.
Highlights
Solar spectral irradiance (SSI) represents the dominant source of energy to the climate system (Kren et al 2017)
The modified Multiple Same-Irradiance-Level (MuSIL) technique was applied to the original SOLAR/SOLar SPECtrometer (SOLSPEC) irradiance time series to provide a corrected dataset of relative change in SSI
The selected scaled proxy and the original SOLAR/SOLSPEC irradiance dataset were smoothed over a 180-day boxcar to preserve only the solarcycle variation
Summary
Solar spectral irradiance (SSI) represents the dominant source of energy to the climate system (Kren et al 2017). Variations in SSI drive short-term changes in the middle atmosphere and influence the climate on long timescales (Floyd et al 2002; Gray et al 2010; Ermolli et al 2013; Solanki et al 2013; Shindell et al 2020). The visible and near-infrared solar irradiance plays a role in the global climate. All of the UV SSI at wavelengths between 150 and 300 nm are deposited in the middle atmosphere This energy plays an essential role in the chemistry, influence, and dynamics of this atmospheric layer. Solar irradiance at wavelengths (λ) of less than 300 nm is absorbed by the Earth’s atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space. During part of solar cycle 24 (December 2008 to late 2019), two independent sets of space-based instruments carried out continuous measurements of the solar spectrum over extended wavelength ranges. A second independent set consisting of the SOLar SPECtrometer (SOLSPEC) instrument (Thuillier et al 2009) of the SOLAR payload on board the International Space Station (ISS) performed
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