Indices for the epochs of the solar activity minima

V. I. Makarov
Pulkovo Astronomical Observatory, St. Petersburg, Russia

Abstract

[1]  New solar activity indices for the sunspot cycle minima were obtained from the Ha synoptic charts for 1887-2005, Ca II K observational data of the solar disk at Kodaikanal for 1907-1995. The Apz index determines the area of the polar zone occupied by the magnetic field of one polarity, and A(t) is the sum of squares of dipole and octupole magnetic moments. The L(t) index is the total length of magnetic neutral lines on the Ha synoptic chart, and K(t) characterizes the complexity of the topology pattern of the general magnetic field of the Sun. It is determined by the inverse number of crossings of neutral lines with the meridian net on the Ha chart. The R(t) index characterizes the correlation factor of the magnetic field polarities in the latitude zones 40^o. The solar rotation index SSPD(t) is determined by the sum of the spectral density of the power of the magnetic field sector structures. The area of the Ca II K bright points at high latitudes is the S_K(t) index. It has been shown that the 11-year cycles of Apz(t), A(t), L(t), K(t), R(t), SSPD(t), and S_K(t) have maxima at the sunspot activity minimum and that they are ahead of the cycles of Wolf numbers, W(t), by 5-6 years.

Received 28 March 2006; revised 18 December 2006; accepted 20 February 2007; published 25 July 2007.

Keywords: sunspot cycle; new activity indices; solar magnetic field.

Index Terms: 7536 Solar Physics, Astrophysics, and Astronomy: Solar activity cycle; 7524 Solar Physics, Astrophysics, and Astronomy: Magnetic fields; 7538 Solar Physics, Astrophysics, and Astronomy: Solar irradiance.