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Available sunspot models and the theory of mixing length indicate that the observed changes in the umbral/penumbral (U/P) ratio may be equivalent to changes in the solar constant. These data from observations of sunspot activity cover the period 1875 through 1981 reconstructions are possible back to 1832. [National Center for Atmospheric Research, Boulder, CO (United States) Solar Records: The Wolf Sunspot Index and Umbral/Penumbral Ratio These findings do not indicatemore » that sunspots have become less dark during cycles 23 and 24.« less We looked for a possible time variation in the sunspot umbral contrast during the 27 yr covering cycles 22, 23, and the rise of cycle 24, and we did not find a significant change. We confirm the presence of a relationship between the mean umbral core intensity and the mean sunspot area, as found in previous studies, and do not find a notable change in this relationship between cycles 22 and 23. We examine the relative intensity of sunspot umbrae during the period from 1986 to 2012 using photometric images from the San Fernando Observatory. TEMPORAL STABILITY OF SUNSPOT UMBRAL INTENSITIES: 1986-2012ĭe Toma, G. As an illustration, this extrapolation is used to calculate a very simple model for the reradiation necessary to balance the flux deficit. A model is shown for extrapolating visible-hemisphere spot areas to the invisible hemisphere. Attention is given to a photometric sunspot index, a global measure of spot flux deficit, and models for the compensating flux excess. Approaches are discussed for obtaining a crude estimate of the irradiance deficit produced by sunspots and of the total luminosity reduction for the whole global population of sunspots. It is pointed out that the darkness of a sunspot on the visible hemisphere of the sun will reduce the solar irradiance on the earth. The effects of sunspots on solar irradiance The CFDT sunspot deficits suggest a substantial irradiance contribution from faculae and active region plage.
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Data from this Cartesian full disk telescope (CFDT) are analyzed with attention given to the period between June 4 and Jbecause of the availability of overlapping sunspot area and irradiance deficit data from high-resolution digital spectroheliograms made with the San Fernando Observatory 28 cm vacuum solar telescope and spectroheliograph. S.Ī photometric telescope constructed to obtain photometric sunspot areas and deficits on a daily basis is described. Photometric measurements of solar irradiance variations due to sunspotsĬhapman, G. This may partly be explained by a change in the ratio between the areas of the spots and the surrounding faculae. This unexpected result cannot be interpreted by a change of the contrast relative to the quiet Sun (as it is normally defined and determined by direct photometry) but rather as a change of the contrast between the spots and their surrounding as seen in total irradiance (integrated over the solar disk). The factor changes with time from about 0.6 in 1980 to 1.1 in 1990. The results can be used as a `calibration' of PSI in terms of gain, the factor by which PSI has to be multiplied to yield the observed irradiance change. The correlation between the newly calculated PSI and total solar irradiance is studied for different phases of the solar cycles 21 and 22 using bi-variate spectral analysis. A detailed description of the method is provided.
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Moreover, the observations are screened for outliers which improves the homogeneity of the data set substantially, at least for the period after December 1981 when NOAA started to report data from a few instead of one to two stations.
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An improved PSI calculation is presented it takes into account the area dependence of the contrast and calculates `true' daily means for each observation using the differential rotation of the spots. It has been shown that the former PSI models overestimate the effect of dark sunspots on solar irradiance furthermore results of direct sunspot photometry indicate that the contrast of spots depends on their area. It is calculated from the sunspot data published in the Solar-Geophysical Data catalog. The photometric sunspot index (PSI) was developed to study the effects of sunspots on solar irradiance. Improvement of the photometric sunspot index and changes of the disk-integrated sunspot contrast with timeįroehlich, Claus Pap, Judit M.