The Solar Irradiance Spectrum at Solar Activity Minimum Between Solar Cycles 23 and 24

Abstract

International audienceOn 7 February 2008, the SOLAR payload was placed onboard the International Space Station. It is composed of three instruments, two spectrometers and a radiometer. The two spectrometers allow us to cover the 16 - 2900 nm spectral range. In this article, we first briefly present the instrumentation, its calibration and its performance in orbit. Second, the solar spectrum measured during the transition between Solar Cycles 23 to 24 at the time of the minimum is shown and compared with other data sets. Its accuracy is estimated as a function of wavelength and the solar atmosphere brightness-temperature is calculated and compared with those derived from two theoretical models

The Infrared Solar Spectrum Measured by the SOLSPEC Spectrometer Onboard the International Space Station

“…The corresponding irradiance was found to be lower than ATLAS 3 ( Figure 1). This was reported at the MOCA meeting "Our Warming Planet" (Montreal, Canada, 2008), and has recently been published by Thuillier et al (2014). Figure 1c shows that the SOLAR 2 IR SSI is smaller than ATLAS 3 and differs by as much as 7 % at 1 700 nm (see also Figure 9 in Thuillier et al, 2014).…”

“…This was reported at the MOCA meeting "Our Warming Planet" (Montreal, Canada, 2008), and has recently been published by Thuillier et al (2014). Figure 1c shows that the SOLAR 2 IR SSI is smaller than ATLAS 3 and differs by as much as 7 % at 1 700 nm (see also Figure 9 in Thuillier et al, 2014). In light of this disagreement, a reference spectrum identified as SOLAR 1 was constructed with the SOLAR 2 spectrum, but it substitutes the 1 100 -2 400 nm range with measurements from ATLAS 3 (Thuillier et al, 2014).…”

“…SOLSPEC data have been used to produce a composite spectrum that extends over the spectral domain of the previous spectra and is representative of the lowest solar minimum of the modern era. It is referred to as the SOLAR 2 composite (Thuillier et al, 2014). Bolsée et al (2014) recently proposed that the solar irradiance in the infrared (IR) domain is significantly lower than given by the ATLAS 3 reference solar spectrum, for example by about 7 % at 1 700 nm.…”

The role of the Fraunhofer lines in solar brightness variability

“…We note, however, that the exact behaviour of the continuum variability strongly depends on the temperature structures of the quiet Sun and magnetic features in the deepest photospheric layers. These layers provide a very small contribution to the emergent line spectra, so that it is difficult to reliably constrain their temperature structures in 1D semi-empirical modelling, especially taking intro account the uncertainties in the measurements of the IR solar irradiance which emanates from the deep photospheric layers (Thuillier et al 2014;Bolsée et al 2014;Thuillier et al 2015). Consequently our model does not allow us to unambiguously rule out an in-phase continuum variability.…”

Metrology of the Solar Spectral Irradiance at the Top Of Atmosphere in the Near Infrared Measured at Mauna Loa Observatory: The PYR-ILIOS campaign

“…An upgraded version (SOLAR/SOLSPEC), including a fully refurbished NIR channel, readout electronics and extended wave-20 length range up to 3.2 µm of SOLSPEC flew from 2008-2017 on board the International Space Station (ISS) (Thuillier et al (2009)), releasing the SOLAR 2 (Thuillier et al (2013)), SOLAR/SOLSPEC (Bolsée (2012)) and SOLAR-ISS(IR) (Meftah et al (2017)); it is nowadays the instrument that measured farther the SSI in the NIR. The instrument providing the longest time series of SSI measurements in the NIR is the SIM (Spectral Irradiance Monitor) prism spectrometer on SORCE (Solar Radiation and Climate Experiment) launched in 2003 (Harder et al (2000a), Harder et al (2005)) and still on orbit but with 25 scarce operational time, due to the end of battery life.…”