The behavior of sunspot contrast during cycle 23

Results are presented from a study of various sunspot contrast parameters in broadband red (672.3 nm) Cartesian full-disk digital images taken at the San Fernando Observatory (SFO) over eight years, 1997-2004, of the twenty-third sunspot cycle. A subset of over 2700 red sunspots was analyzed and values of average and maximum sunspot contrast as well as maximum umbral contrast were compared to various sunspot parameters. Average and maximum sunspot contrasts were found to be significantly correlated with sunspot area (r(s) = -0.623 and r(s) = -0.714, respectively). Maximum umbral contrast was found to be significantly correlated with umbral area (r(s) = -0.535). These results are in agreement with the works of numerous other authors. No significant dependence was detected between average contrast, maximum contrast, or maximum umbral contrast during the rising phase of the solar cycle (r(s) = 0.024, r(s) = 0.033, and r(s) = 0.064, respectively). During the decay phase, no significant correlation was found between average contrast or maximum contrast and time (r(s) = -0.057 and r(s) = 0.009, respectively), with a weak dependence seen between maximum umbral contrast and cycle (r(s) = 0.102).