The Shape of the Solar Limb: Models and Observations

Thuillier, G.; Claudel, Jennyfer; Djafer, Djelloul; Haberreiter, M.; Mein, N.; Melo, S. M. L.; Schmutz, W.; Шапиро, А. И.; Short, C. Ian; Sofia, S.

doi:10.1007/s11207-010-9664-7

Cited by 28 publications

(35 citation statements)

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“…Rutten and Kostik, 1982;Shchukina and Trujillo Bueno, 2001). The spectrum of the quiet Sun calculated with COSI is in good agreement with the solar spectrum measured by SOLSTICE (up to 320 nm) and SIM (above 320 nm) onboard the SORCE satellite during the 2008 solar minimum, and with the SOLSPEC measurements during the ATLAS 3 mission in 1994 (Thuillier et al, 2011). Shapiro et al (2013a) showed that COSI can accurately reproduce the center-to-limb variation of solar brightness in the Herzberg continuum retrieved from the analysis of solar eclipses observed by LYRA/PROBA2 (Large Yield RAdiometer/PRoject for On-Board Autonomy).…”

Section: Cosisupporting

confidence: 76%

Recent variability of the solar spectral irradiance and its impact on climate modelling

et al. 2013

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The lack of long and reliable time series of solar spectral irradiance (SSI) measurements makes an accurate quantification of solar contributions to recent climate change difficult. Whereas earlier SSI observations and models provided a qualitatively consistent picture of the SSI variability, recent measurements by the SORCE (SOlar Radiation and Climate Experiment) satellite suggest a significantly stronger variability in the ultraviolet (UV) spectral range and changes in the visible and near-infrared (NIR) bands in anti-phase with the solar cycle. A number of recent chemistry-climate model (CCM) simulations have shown that this might have significant implications on the Earth's atmosphere. Motivated by these results, we summarize here our current knowledge of SSI variability and its impact on Earth's climate.

We present a detailed overview of existing SSI measurements and provide thorough comparison of models available to date. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. We investigate these direct and indirect effects using several state-of-the art CCM simulations forced with measured and modelled SSI changes. A unique asset of this study is the use of a common comprehensive approach for an issue that is usually addressed separately by different communities.

We show that the SORCE measurements are difficult to reconcile with earlier observations and with SSI models. Of the five SSI models discussed here, specifically NRLSSI (Naval Research Laboratory Solar Spectral Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar Radiation Physical Modelling), and OAR (Osservatorio Astronomico di Roma), only one shows a behaviour of the UV and visible irradiance qualitatively resembling that of the recent SORCE measurements. However, the integral of the SSI computed with this model over the entire spectral range does not reproduce the measured cyclical changes of the total solar irradiance, which is an essential requisite for realistic evaluations of solar effects on the Earth's climate in CCMs.

We show that within the range provided by the recent SSI observations and semi-empirical models discussed here, the NRLSSI model and SORCE observations represent the lower and upper limits in the magnitude of the SSI solar cycle variation.

The results of the CCM simulations, forced with the SSI solar cycle variations estimated from the NRLSSI model and from SORCE measurements, show that the direct solar response in the stratosphere is larger for the SORCE than for the NRLSSI data. Correspondingly, larger UV forcing also leads to a larger surface response.

Finally, we discuss the reliability of the available data and we propose additional coordinated work, first to build composite SSI data sets out of scattered observations and to r...

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Section: Cosisupporting

confidence: 76%

Recent variability of the solar spectral irradiance and its impact on climate modelling

et al. 2013

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“…A study of the shape of the solar limb (models and observations) was carried out by Thuillier et al (2011). Several kinds of solar atmosphere models were compared.…”

Section: Spectral Dependence Of Solar Continuum Radiusmentioning

confidence: 99%

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

Meftah

Corbard

Irbah

et al. 2014

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Context. For the past thirty years, modern ground-based time-series of the solar radius have shown different apparent variations according to different instruments. The origins of these variations may result from the observer, the instrument, the atmosphere, or the Sun. Solar radius measurements have been made for a very long time and in different ways. Yet we see inconsistencies in the measurements. Numerous studies of solar radius variation appear in the literature, but with conflicting results. These measurement differences are certainly related to instrumental effects or atmospheric effects. Use of different methods (determination of the solar radius), instruments, and effects of Earth's atmosphere could explain the lack of consistency on the past measurements. A survey of the solar radius has been initiated in 1975 by Francis Laclare, at the Calern site of the Observatoire de la Côte d'Azur (OCA). Several efforts are currently made from space missions to obtain accurate solar astrometric measurements, for example, to probe the long-term variations of solar radius, their link with solar irradiance variations, and their influence on the Earth climate. Aims. The Picard program includes a ground-based observatory consisting of different instruments based at the Calern site (OCA, France). This set of instruments has been named "Picard Sol" and consists of a Ritchey-Chrétien telescope providing full-disk images of the Sun in five narrow-wavelength bandpasses (centered on 393.37, 535.7, 607.1, 782.2, and 1025.0 nm), a Sun-photometer that measures the properties of atmospheric aerosol, a pyranometer for estimating a global sky-quality index, a wide-field camera that detects the location of clouds, and a generalized daytime seeing monitor allowing us to measure the spatio-temporal parameters of the local turbulence. Picard Sol is meant to perpetuate valuable historical series of the solar radius and to initiate new time-series, in particular during solar cycle 24. Methods. We defined the solar radius by the inflection-point position of the solar-limb profiles taken at different angular positions of the image. Our results were corrected for the effects of refraction and turbulence by numerical methods. Results. From a dataset of more than 20 000 observations carried out between 2011 and 2013, we find a solar radius of 959.78 ± 0.19 arcsec (696 113 ± 138 km) at 535.7 nm after making all necessary corrections. For the other wavelengths in the solar continuum, we derive very similar results. The solar radius observed with the Solar Diameter Imager and Surface Mapper II during the period 2011-2013 shows variations shorter than 50 milli-arcsec that are out of phase with solar activity.

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“…According to solar astrolabe measurement, the variation of the solar radius with solar activity is about 200 mas , and, according to physical solar models, the dependency to wavelength is about 20-30 mas (Thuillier et al 2011). Therefore, to validate these dependencies, especially the dependency to wavelength, one of the requirements is to have results without the effect of the processing method.…”

Section: Resultsmentioning

confidence: 99%

Processing Method Effect on Sun Diameter Measurement With CCD Solar Astrolabe

Djafer

Irbah

2012

ApJ

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Photometric Sun diameter measurement is based on the calculation of the inflection point of the solar limb. In ground measurement, this point is located at a position on the solar limb where the signal-to-noise ratio is very high, which necessitates the appropriate filtering techniques to eliminate the noise while preserving its position. In this paper, we compare the filtering method currently in use to process the CCD solar astrolabe data, the FFTD method widely used, with a different method that we propose. Using the acquired data from the CCD astrolabe at Calern, France during 1997, we can obtain a mean difference of 130 mas in the measured radii.

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The Shape of the Solar Limb: Models and Observations

Cited by 28 publications

References 28 publications

Recent variability of the solar spectral irradiance and its impact on climate modelling

Recent variability of the solar spectral irradiance and its impact on climate modelling

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

Processing Method Effect on Sun Diameter Measurement With CCD Solar Astrolabe

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