Diameter and solar figure observations in the solar activity context with the astrolabe of Rio de Janeiro in 1998-2003

TL;DR

This study analyzes over 20,000 solar semidiameter observations from 1998-2003, examining their correlation with solar activity indicators and revealing phase shifts and latitude-dependent variations.

Contribution

It provides a detailed correction methodology for observational data and explores the relationship between solar semidiameter, irradiance, and activity cycles with phase shift analysis.

Findings

Strong correlations between semidiameter and solar activity indicators.

Identification of phase shifts indicating different regimes of solar response.

Latitude-dependent variations in solar semidiameter observed.

Abstract

From 1998 to 2003 the CCD Solar Astrolabe of the Observatorio Nacional in Rio de Janeiro made more than 20000 observations of the Solar Semidiameter. In the present work similar corrections for the observational results of 2002 and 2003 were determined. Initially, the values have been corrected in function of their mean quadratic offset to the local trend averages, therefore without modifying the measured variations. Finally, the values have been corrected for the bias, using coefficients obtained from the correlation between some observational parameters and the observational measures. Then the total series was compared with series of pointers of the solar activity. The hypothesis of variation of the semidiameter tied to the solar activity was examined through the correlations between the different pairs of pointers. Strong correlations between some pairs were obtained. Next, the same correlations were obtained now considering time delays of one series in relation to the other. Several pairs have shown an increase on the correlation, indicating the presence of a significant phase shift between them. For the pair solar semidiameter and irradiance the mode of the phase for maximum correlation was calculated for two distinct cases: either for the complete series of data, or leaving off the data relative to the epochs of the two summits of the solar activity cycle. The comparison shows that the solar semidiameter responds closely to variations of irradiance in the conditions where the peaks of activity are considered; inversely, it precedes the variations of irradiance, by at least one hundred days, when the peak values are discarded, thus indicating the existence of two distinct regimes. We also studied how the semidiameter of the Sun varies throughout its latitudes. It was noted that each band of latitude has a different response, even so there is a global variation in time.