Size of the coming solar cycle 24 based on Ohl's Precursor Method, final estimate

• Main Author: R. P. Kane
• Format: Article
• Language: English
• Published: Copernicus Publications 2010-07-01
• Series: Annales Geophysicae
• Online Access: https://www.ann-geophys.net/28/1463/2010/angeo-28-1463-2010.pdf

In Ohl's Precursor Method (Ohl, 1966, 1976), the geomagnetic activity during the declining phase of a sunspot cycle is shown to be well correlated with the size (maximum sunspot number <I>Rz</I>(max)) of the next cycle. For solar cycle 24, Kane (2007a) used <I>aa</I>(min)=15.5 (12-month running mean), which occurred during March–May of 2006 and made a preliminary estimate <I>Rz</I>(max)=124±26 (12-month running mean). However, in the next few months, the <I>aa</I> index first increased and then decreased to a new low value of 14.8 in July 2007. With this new low value, the prediction was <I>Rz</I>(max)=117±26 (12-month running mean). However, even this proved a false signal. Since then, the aa values have decreased considerably and the last 12-monthly value is 8.7, centered at May 2009. For solar cycle 24, using <I>aa</I>(min)=8.7, the latest prediction is, <I>Rz</I>(max)=58.0±25.0.