From the QBO to Rieger-type periods: Explaining extreme solar events by tidally triggered magneto-Rossby waves

Abstract

It has recently been demonstrated that the occurrence of extreme solar events is governed by a phase-stable period close to 1.723 years (629.29 days). According to our previously developed tidally-synchronized solar dynamo model, this is one of the periods resulting from two-planet spring tides exerted by the tidally dominant planets Venus, Earth and Jupiter, which trigger magneto-Rossby waves in the solar tachocline. Overall, the squared sum of these three waves incorporates nine periods ranging from 59 to 629 days. Using a standard Rayleigh test, we demonstrate that all nine of these periods can be identified in the data on extreme solar events. For the latter, we use a combination of 72 ground-level enhancement (GLE) events with various X-flare data, the number of which increases when the threshold is successively lowered from X10 to X1. To identify the spectral peaks, it is necessary to analyze the sidebands that emerge due to the modulation with the longer-term periods such as the 11-year Schwabe cycle and the third harmonics of the Hale cycle. In this framework, the seminal Rieger period of 154 days is re-interpreted as the lower sideband of 146 days which is the quarter of the synodic period of Venus and Earth.