An estimate for the size of cycle 23 based on near minimum conditions

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Abstract
The first occurrence of a high‐latitude, new cycle spot group for cycle 23 was in May 1996, in conjunction with a minimum in the smoothed monthly mean sunspot number. Since then, new cycle spot groups have become more predominant, and the smoothed monthly mean sunspot number has slowly risen. Such behavior indicates that new cycle 23 probably had its minimum annual average sunspot number, R(min), equal to 8.7, in 1996. Because this value is larger than the average for R(min), cycle 23 is expected to have a maximum amplitude, R(max), that, likewise, will be larger than average, suggesting further that it probably will be both fast rising (i.e., peaking before May 2000) and of shorter than average length (i.e., ending before May 2007). Another parameter well correlated with R(max) is the minimum amplitude of the aa geomagnetic index, aa(mm), which usually occurs either in the year of R(min) occurrence or, more often, in the following year. For 1996 the annual average of aa measured 18.6. Presuming this value to be aa(min) for cycle 23, we calculate cycle 23's R(max) to be about 171.0 ± 17.6 (i.e., the 90% prediction interval), based on the stronger (r = 0.98) bivariate fit of R(max) versus both R(min) and aa(min). Comparison of this estimate with others, using various combinations of parameters, yields an overlap in the prediction intervals for R(max) of about 168 ± 15, a range that is within the consensus recently reported by Joselyn et al. [1997] (= 160 ± 30). Thus this study supports the view that cycle 23 will have an R(max) that will be larger than average but smaller than was seen for cycle 19, the largest cycle on record with R(max) = 190.2.