Observed variations of the solar photospheric diameter (original) (raw)

A comment on ?Regular structures of the solar photosphere

Astronomy and Astrophysics, 2002

A recent Letter to the Editor (Getling & Brandt 2002) suggests that solar granulation is not entirely random, instead showing large scale spatial and long term temporal coherence. The authors cite as evidence the persistence of bright granular size objects in images even after long term temporal averaging, the reoccurrence of bright granules in time series at locations of local maxima in the average image, and the presence of large scale regular structures in time-average images. This paper demonstrates that all three of these observations are consistent with a completely random and changing flow pattern and do not require self organization of the granular flows.

A solar cycle lengthwise series of solar diameter measurements

Proceedings of the International Astronomical Union, 2009

The measurements of the solar photospheric diameter rank among the most difficult astronomic observations. Reasons for this are the fuzzy definition of the limb, the SNR excess, and the adverse daytime seeing condition. As a consequence there are very few lengthy and consistent time series of such measurements. Using modern techniques, just the series from the IAG/USP and from Calern/OCA span more than one solar cycle. The Rio de Janeiro Group observations started in 1997, and therefore in 2008 one complete solar cycle time span can be analyzed. The series shares common principles of observation and analysis with the ones afore mentioned, and it is complementary on time to them. The distinctive features are the larger number of individual points and the improved precision. The series contains about 25,000 single observations, evenly distributed on a day-by-day basis. The typical error of a single observation is half an arc-second, enabling us to investigate variations at the expected level of tens of arc-second on a weekly basis. These features prompted to develop a new methodology for the investigation of the heliophysical scenarios leading to the observed variations, both on time and on heliolatitude. The algorithms rely on running averages and time shifts to derive the correlation and statistical incertitude for the comparison of the long term and major episodes variations of the solar diameter against activity markers. The results bring support to the correlation between the diameter variation and the solar activity, but evidentiating two different regimens for the long term trend and the major solar events.

On the Constancy of the Diameter of the Sun During the Rising Phase of Solar Cycle 24

The Astrophysical Journal, 2015

The potential relationship between solar activity and changes in solar diameter remains the subject of debate and requires both models and measurements with sufficient precision over long periods of time. Using the PICARD instruments, we carried out precise measurements of variations in solar diameter during the rising phase of solar cycle 24. From new correction methods we found changes in PICARD space telescope solar radius amplitudes that were less than ±20 mas (i.e. ±14.5 km) for the years 2010-2011. Moreover, PICARD ground-based telescope solar radius amplitudes are smaller than ±50 mas from 2011 to 2014. Our observations could not find any direct link between solar activity and significant fluctuations in solar radius, considering that the variations, if they exist, are included within this range of values. Further, the contribution of solar radius fluctuations is low with regard to variations in total solar irradiance. Indeed, we find a small variation of the solar radius from space measurements with a typical periodicity of 129.5 days, with ±6.5 mas variation.

The variation of the mean size of the photospheric granules close to and away from a sunspot

Solar Physics, 1989

We study the mean size of granules as a function of distance from the boundaries of the sunspot penumbra. We use for the determination of the mean size two different methods, a visual and a photometric. In all cases the mean diameter of the granules away from the spot was greater than the mean diameter of the granules in the neighbourhood of the penumbra. Our study is based on an excellent sequence of photos, taken at the Pic-du-Midi Observatory on May 11, 1979.

On the Constancy of the Solar Diameter

The Astrophysical Journal, 2000

Why does the solar luminosity vary and could it change on human timescales by enough to a †ect terrestrial climate ? As important as these questions are, we lack answers because we do not understand the physical mechanisms responsible for the solar irradiance cycle. Progress here depends on discovering how changes in the solar interior a †ect energy Ñow from the radiative and convection zones out through the photosphere. Measurements of small changes in the solar radius are a critical probe of the SunÏs interior stratiÐcation ; they can tell us how and where the solar luminosity is gated or stored. Here we report results from a sensitive 3 yr satellite experiment designed to detect solar diameter Ñuctuations.

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

Astronomy & Astrophysics, 2014

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 arc-seconds (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-arc-second that are out of phase with solar activity.

The Variation of the Mean Size of the Photospheric Granules Near and Far from a Sunspot

Springer eBooks, 1989

Heliospheric consequences of solar activity in geophysical and interplanetary phenomena

Geofísica Internacional, 2004

Hemos hecho un análisis de diversos fenómenos solares como el flujo magnético solar total, el área de los hoyos coronales polares y las manchas solares. Investigamos su evolución temporal a lo largo de varios ciclos solares y su posible relación con ondas de choque interplanetarias, comienzos repentinos de tormentas magnéticas en la Tierra y variaciones en la intensidad de rayos cósmicos. Nuestros resultados enfatizan la relación entre la emergencia de flujo magnético solar y la dinámica del medio interplanetario, en particular la importancia de la evolución de los hoyos coronales y la estructura de la heliosfera.

42 Years of Continuous Observations of the Solar Diameter from 1974 to 2015

arXiv: Solar and Stellar Astrophysics, 2015

Several group in the World followed the solar diameter with dedicated instruments, namely solar astrolabes, since 1974. Their data have been gathered in several observing stations connected in the R2S3 (Reseau de Suivi au Sol du Rayon Solaire) network and through reciprocal visits and exchanges: Nice/Calern Observatory, Rio de Janeiro Observatorio Nacional/Brazil, IAG/Universidade de Sao Paulo/Brazil, Antalya Observatory/Turkey, San Fernando/Spain. The tradition of these observational efforts is here briefly sketched with the aim to evidence the possibility to analyze against the solar activity all these 42 years data at once by overcoming the problem of the shift between the different series. Each instrument has its own density filter with a prismatic effect responsible of that shift. The overall change of the solar radius during the last century is evident by comparing the Auwers' radius of 959.63" (1891, present IAU standard) with 959.94" (2015, from eclipses and Ve...

Analysis of large-scale photospheric dynamics during the solar cycle 24

2018

The analysis of the movements of the solar photosphere has been used by several authors to study the dynamics of solar plasma at various spatial and temporal scales. This work, in particular, is focused on the study of vertical movements, in order to perform a statistical analysis of the flow maps to characterize some dynamic aspects of the photospheric plasma along the time evolution of the Sun. To carry out this analysis, we used a set of images obtained by the HMI instrument HMI (Helioseismic and Magnetic Imager) aboard the SDO mission (Solar Dynamics Observatory) to which local correlation tracking algorithms (LCT) were applied. they allow the identification of areas of convergence and divergence of the plasma at certain time intervals during the solar cycle 24, thus covering moments of high and low solar activity. The study gives us the reason for the meridional movements showing that in low latitudes the outgoing emergency flow occupied a higher percentage of area, while in th...

Observed variations of the solar photospheric diameter (original) (raw)

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