Long-period oscillations of millimeter emission above sunspots

¹ University of Turku, 20014 Turku, Finland
e-mail: vvsvid@rambler.ru
² Sobolev Astronomical Institute, Saint Petersburg State University, Universitetsky pr.28, St. Petergof 198504, Russia
³ Bauman Moscow State Technical University, 2 Bauman street 5, Moscow 105005, Russia
⁴ Aalto University, Metsähovi Radio Observatory, Kylmälä, Finland

Received: 15 June 2011
Accepted: 1 September 2011

Abstract

Aims. The investigation of long quasi-periodic oscillations in sunspots/active regions based on millimeter radio data was the main goal of this work.

Methods. Data from simultaneous monitoring observations of solar active regions at 37 GHz and 93 GHz at two different ground-based radio telescopes were obtained. We analyzed them with the methods of wavelet (Morlet) and global wavelet spectrum analysis.

Results. Two main ranges (10−60 and 80−130 min) of long quasi-periodic oscillations were found. We compared them with 17 GHz Nobeyama Radioheliograph (NoRH) data and obtained the same ranges for the long-period oscillations. The long-period oscillations found in this study are relatively stable and could be interpreted as a radial mode of sunspot oscillations.