Waldmeier law for sunspot cycles: Statistical significance and implications for dynamo

Waldmeier law for the relation between the rise phase duration and amplitude of solar cycles is an indicator for strength of nonlinearity in the solar dynamo. The paper compares the Waldmeier law parameters for sunspot number and area in solar cycles 12–25. Uncertainty in dates of cycles’ maxima and minima is fixed by smoothing with the Gaussian filter. The ratio of sunspot number to area is shown to differ significantly between rise and decline phases of solar activity. The high correlation for Waldmeier law in sunspot number is an artifact of the Wolf number definition and does not imply any strong nonlinearity in the dynamo mechanism. The relative low correlation and significance level of about 70 % in Waldmeier law for sunspot area indicates a weak nonlinearity in the solar dynamo and agrees with evidences from observations of stellar rotation.