Long-period oscillations of millimeter emission above sunspots

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.