Variation of solar oscillation frequencies in solar cycle 23 and their relation to sunspot area and number

¹ School of Mathematics and Statistics, The University of Sheffield, S3 7RH, UK
e-mail: R.Jain@sheffield.ac.uk
² National Solar Observatory, Tucson, Arizona 85712, USA
³ School of Physics and Astronomy, SUPA, University of Glasgow, G12 8QQ, UK

Received: 22 June 2012
Accepted: 15 August 2012

Abstract

Aims. Studying the long term evolution of the solar acoustic oscillations is necessary for understanding how the large-scale solar dynamo operates. In particular, an understanding of the solar cycle variation in the frequencies of solar oscillations can provide a powerful diagnostic tool for constraining various dynamo models. In this work, we report the temporal evolution of solar oscillations for the solar cycle 23, and correlate with solar magnetic activity indices.

Methods. We use solar oscillation frequencies obtained from the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, correlate them with the sunspot number provided by the international sunspot number, R_I, and compare them with the sunspot number calculated with the Sunspot Tracking And Recognition Algorithm (STARA).

Results. We find that the mean frequency shifts correlate very well with the sunspot numbers obtained from two different datasets. We also find a hysteresis-type behaviour for the STARA sunspot area and mean magnetic field strength for the different phases of the solar cycle. The increase in solar oscillation frequencies precedes slightly the increase in total sunspot area and the mean magnetic field strength for the solar cycle 23. We briefly discuss the cyclic behaviour in the context of p-mode frequencies.