A straightforward estimation of the maximum sunspot number for cycle 23
Abstract. Using the annual number of geomagnetically quiet days (aa < 20 γ) for the year after the solar minimum, this precursor method predicts that the maximum sunspot number for cycle 23 will be 140 ± 32, indicating that cycle 23 will be similar to cycles 21 and 22.
Key words. Solar physics · astrophysics and astronomy (magnetic fields; general)