Abstract.Results are presented of measured variations of the photospheric solar diameter, as concurrently observed at three sites of the R2S3 (Réseau de Suivi au Sol du Rayon Solaire) consortium in 2001. Important solar flux variations appeared in that year, just after the maximum of solar activity cycle 23, make that time stretch particularly promising for a comparison of the multi-site results. The sites are those in Turkey, France and Brasil. All observations are made with similar CCD solar astrolabes, and at nearby effective wavelengths. The data reductions share algorithms, that are alike, the outcomes of which are here treated after applying a normalization correction using the Fried parameter. Since the sites are geographically quite far, atmospheric conditions are dismissed as possible causes of the large common trend found. Owing to particularities of each site, the common continuous observational period extends from April to September. The standard deviation for the daily averages is close to 0. 47 for the three sites. Accordingly, the three series are smoothed by a low-pass-band Fourier filter of 150 observations (typically one month). The main common features found are a declining linear trend, of the order of 0.7 mas/day, and a relative maximum, around MJD 2120, of the order of 100 mas. Standard statistical tests endorse the correlation of the three series.

We study the correlation between geomagnetic and solar semi-diameter measurements made at two of our ground stations (Vassouras and Rio de Janeiro, Brazil). The study comprises the period from March 1998 to November 2003, for which daily means were compared. Both series describe correlated, but different, phenomena and, consequently, before a correlation study, an individual analysis of each data set was necessary. One of the motivations of the present work was to further explore the correlation with lags found between the solar semi-diameter and some solar activity estimators, which supports the probabilistic forecasting of the solar activity and hence, of the solar driven geomagnetic variations

Abstract. Here we derive a formulation connecting the observed variations of the solar diameter to the heliophysics of the photosphere, in particular in connection to the granulation pattern and morphology. The results from the measurements are next used to correlate the variations of the semi-diameter and of estimators of the solar activity along the solar cycle 23. The values obtained strongly support a broader physical description of the photosphere, intertwining the diameter variations with the irradiance, the sunspots, the 10.7 cm radio emission, and to a lesser degree with the integrated magnetic field and with the flares count.Keywords. Sun: fundamental parameters, granulation, flares, activity, radio radiation Searching for long time behavior of solar granulationWe have obtained the images of the full solar disc from the Big Bear Solar Observatory. These images cover the beginning, the peak, and the post-peak of the solar cycle 23. They are densely distributed between 2000 to 2006. The images are all of 1364 × 1035 pxs. The same telescope, the same camera and the same orientation were used. The exposition time varies from 50 to 80 ms. We have examined two kinds of images: Fl imagessubtracted from dark and from flat field (1261 images), and Fr images -subtracted from limb darkening (1341 images)To avoid limb darkening influences, we took only the central part of the images. Thus, we considered only the central part from each original image up to 0, 35 of the solar radius. In this way only 2% of intensity variation remains even for Fl images. The central portion of the Sun was next divided in 10 × 10 collateral sectors. Each sector has 30 × 30 pxs. In each sector the statistics described below have been independently applied, and sectors deviating from the average by 3σ or more were removed from all the final analyses. This strategy seeks to discard the presence of sunspots from the solar granulation description.Three estimators are here used as first assessment to the granulation state. For each estimator the average of the sectors is calculated (after removing the deviating ones).(a) standard deviation of counts (S) as probe of the grains' mean size. (b) difference between the uppermost and lowest counts tenths (Q) as probe of the grains' brightness.(c) degree of the better adjusted polynomial along lines and columns (N) as probe of the grains' number.The model then assumes a patch of grains formed by bright centers and dark intergrain contours. Through large number statistics the balance between the two structures along the solar cycle is assessed. After all Fl and Fr images have been treated, and the three statistics obtained for each one, a final filter was applied removing within each year the 72 at https://www.cambridge.org/core/terms. https://doi

Abstract. 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.