Letter to the Editor

Predictions of strengths of long-term variations in sunspot activity

Indian Institute of Astrophysics, Bangalore – 560 034, India

Corresponding author: jj@iiap.ernet.in

Received: 13 November 2002
Accepted: 24 February 2003

Abstract

Recently, using Greenwich data (1879–1976) and SOON/NOAA data (1977–2002) on sunspot groups we found a big or a moderate drop in the solar equatorial rotation rate, A, occurred after every four solar cycles suggesting the existence of “double Hale cycle (DHC)" and “Gleissberg cycle (GC)" in A. We also found the existence of “Hale cycle (HC)" and GC in the latitude gradient of the rotation, B (Javaraiah [CITE]). Using these results here we made forecasts for the following: (i) epochs of the forthcoming big and moderate drops in A; (ii) the epoch of maximum  during the current GC of B; (iii) the strengths of DHCs and HCs of sunspot activity which follow the big and the moderate drops in A; (iv) violation of the Gnevyshev & Ohl rule during the current HC 11 which consists of cycles 22 and 23; and (v) deduced the near complete absence of sunspot activity during the deep Maunder minimum.