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TEMPORAL STABILITY OF SUNSPOT UMBRAL INTENSITIES: 1986-2012
We examine the relative intensity of sunspot umbrae during the period from 1986 to 2012 using photometric images from the San Fernando Observatory. 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 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. These findings do not indicate that sunspots have become less dark during cycles 23 and 24.