Sunspot Group Area Index and the Waldmeier Rule

We consider the applicability of the classical Waldmeier rule or effect, i. e. , the relationship between the amplitude of the 11-year solar cycle and the length of its rising branch (rise time), to a series of total sunspot areas. We show that the absence of a correlation revealed by some authors is associated with the influence of quasi-biennial oscillations and the choice of a smoothing method. We propose a new proxy series of yearly mean sunspot group area that is free from the quasi-biennial component and Gnevyshev gaps. For this series we have estimated the correlation coefficient between the solar cycle amplitude and the length of the rising branch, R 0. 8, confirming the universality of the Waldmeier rule. Values of R up to 0. 99 have been reached in the modified formulations that relate the amplitude to the maximum and mean activity growth rates, making them promising for an early prediction of the solar cycle amplitude.