Articles | Volume 28, issue 7
Ann. Geophys., 28, 1463–1466, 2010
https://doi.org/10.5194/angeo-28-1463-2010
Ann. Geophys., 28, 1463–1466, 2010
https://doi.org/10.5194/angeo-28-1463-2010

  16 Jul 2010

16 Jul 2010

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

R. P. Kane R. P. Kane
  • Instituto Nacional de Pesquisas Espacias, INPE C.P. 515, 12201-970 São Jose dos Campos, SP, Brazil

Abstract. 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 Rz(max)) of the next cycle. For solar cycle 24, Kane (2007a) used aa(min)=15.5 (12-month running mean), which occurred during March–May of 2006 and made a preliminary estimate Rz(max)=124±26 (12-month running mean). However, in the next few months, the aa 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 Rz(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 aa(min)=8.7, the latest prediction is, Rz(max)=58.0±25.0.