HAL will be down for maintenance from Friday, June 10 at 4pm through Monday, June 13 at 9am. More information
Skip to Main content Skip to Navigation
Journal articles

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

Abstract : 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.
Complete list of metadata

Cited literature [28 references]  Display  Hide  Download

https://hal.archives-ouvertes.fr/hal-01068755
Contributor : Catherine Cardon Connect in order to contact the contributor
Submitted on : Friday, September 26, 2014 - 11:46:42 AM
Last modification on : Thursday, February 10, 2022 - 11:20:03 AM
Long-term archiving on: : Saturday, December 27, 2014 - 11:00:12 AM

File

PICARD_SOL_-_meftah_et_al_-_20...
Publisher files allowed on an open archive

Identifiers

Citation

Mustapha Meftah, T. Corbard, Abdanour Irbah, R. Ikhlef, F. Morand, et al.. Ground-based measurements of the solar diameter during the rising phase of solar cycle 24. Astronomy and Astrophysics - A&A, EDP Sciences, 2014, 569, A60 (15p.). ⟨10.1051/0004-6361/201423598⟩. ⟨hal-01068755⟩

Share

Metrics

Record views

780

Files downloads

118