Quasiperiodic Sunspot Oscillations on Timescales from Tens to Hundreds of Minutes: Groundbased Optical Observations (a Review)

Abstract

Over the last decade, a number of papers discussing long-period sunspot oscillations—with periods of tens and hundreds of minutes—have appeared. These studies are mainly based on the data of space probes. Despite the many possibilities in the time resolution and the absence of a distorting effect of the atmosphere, such studies face some artifacts connected with the pixel structure of an image (Nagovitsyn and Rybak, 2014); the existence of this phenomenon itself is still under discussion. On the other hand, starting already in the 1970s, long-period oscillations were studied by groundbased methods, including optical investigations after the mid-1980s. Since the papers containing the results of this research were mainly published in the Russian literature, which is not readily available for a wide range of specialists (mostly, in the Solnechnye Dannye bulletin or the proceedings of all-Russia conferences), they have been lost. The objective of this review is to recall these studies and their results and to combine the earlier findings with up-to-date ones.