Period persistence of long period oscillations in sunspots

¹ Centre for Fusion, Space and Astrophysics, Physics DepartmentUniversity of Warwick, Coventry CV4 7AL, UK
e-mail: n.d.y.chorley@warwick.ac.uk
² Central Astronomical Observatory of RAS at Pulkovo, 196140 St Petersburg, Russia
³ Nobeyama Solar Radio Observatory/NAOJ, 384-1305 Nagano, Japan

Received: 15 February 2011
Accepted: 24 March 2011

Abstract

Long period oscillations in the microwave radiation intensity generated over the sunspot of NOAA AR 10330 are studied with the Nobeyama Radioheliograph as the sunspot passes over the solar disk, over the course of 9 days (06−15 April 2003). Periodogram, Fourier and global wavelet analyses reveal the presence of a significant oscillatory component in the range P ≈  50−120 min over the course of the observations. The spectral amplitudes of five significant Fourier components in the range P = 50−150 min are also seen to be stable over the observations, when the data are not affected by changes in magnetic configuration in the region. The ground-based nature of the instrument naturally introduces long data gaps in such long duration observations and the presence of the gaps does not allow any conclusion as to the stability of the phases of the oscillations. As a model to explain the persistence of the dominant long periods, a simple oscillator with a nonlinear driving term is proposed. The spectral difference between distinct peaks within, e.g. the 3 min spectral band, is expected to be able to resonate with the long period one hour oscillations.