Abstract
Abstract. The near-infrared (NIR) part of the solar spectrum is of prime importance for solar physics and climatology, directly intervening in the Earth's radiation budget. Despite its major role, available solar spectral irradiance (SSI) NIR datasets, space-borne or ground-based, present discrepancies caused by instrumental or methodological reasons. We present new results obtained from the PYR-ILIOS SSI NIR ground-based campaign, which is a replication of the previous IRSPERAD campaign which took place in 2011 at the Izaña Atmospheric Observatory (IZO). We used the same instrument and primary calibration source of spectral irradiance. A new site was chosen for PYR-ILIOS: the Mauna Loa Observatory (MLO) in Hawaii (3397 m a.s.l.), approximately 1000 m higher than IZO. Relatively to IRSPERAD, the methodology of monitoring the traceability to the primary calibration source was improved. The results as well as a detailed error budget are presented. We demonstrate that the most recent results, from PYR-ILIOS and other space-borne and ground-based experiments, show an NIR SSI lower than the previous reference spectrum, ATLAS3, for wavelengths above 1.6 µm.
Highlights
An accurate knowledge of solar spectral irradiance (SSI) remains central to the study of the climate on Earth
The mismatch between the PYR-ILIOS and IRSPERAD dataset varies between 2 % and 4.5 % in the central wavelength range between 1.0 and 1.8 μm, attaining 5 % in the 2.1 μm window and peaking to a maximum of 6 % in the 1.5 and 2.2 μm windows
The difference observed between IRSPERAD and PYRILIOS is not explained by the uncertainties of both datasets
Summary
An accurate knowledge of solar spectral irradiance (SSI) remains central to the study of the climate on Earth. The variability in the ultraviolet (UV) part of the spectrum and its influence on climate via the mechanisms of solar–terrestrial interactions, simulated by chemistry–climate models (Gray et al, 2010; Ermolli et al, 2013), constitutes most of the research in SSI measurements. The determination of its absolute level remains challenging (Meftah et al, 2017): the measurement of the topof-atmosphere (TOA) SSI started nearly 50 years ago and evolved both with ground-based and space-borne instruments, and a consensus on the absolute level in the NIR part is still to be achieved (Bolsée et al, 2014; Hilbig et al, 2018). Aircraft-borne instrumentation at an altitude of 12 km provided the first TOA SSI measurement dataset in 1969 (Arvesen et al, 1969) with an on-board standard of spectral irradiance.
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