Max Planck Institute for Solar System Research | 2020 Jun 25
In the convection zone of the star, the plasma currents make a huge turnover that lasts about 22 years
Solar activity fluctuates in a rhythm of about eleven years, which is reflected among other things in the frequency of sunspots. A complete magnetic period lasts 22 years. Scientists have long been puzzling over what causes this cycle. It must be related to the conditions beneath the "skin" of our star: A layer of hot plasma - electrically-conductive gas - extends from the surface to 200,000 kilometers below. The plasma within this convection zone is constantly in motion. A team of scientists ... has now succeeded in drawing the most comprehensive picture of the plasma flows in north-south-direction to date. The researchers have found a remarkably simple flow geometry: the plasma describes a single turnover in each solar hemisphere, which lasts for about 22 years. In addition, the flow in the direction of the equator at the bottom of the convection zone causes spots to form closer and closer to the equator during the solar cycle.The meridional flow, visualized here by moving corks, sets the period of the Sun’s
magnetic cycle by transporting the magnetic field around the convection in 22 years,
i.e. one magnetic sunspot cycle. © MPS / Z.-C. Liang
The number of sunspots on the visible solar surface varies; sometimes there are more, sometimes fewer. The distance between two sunspot maxima is about eleven years, after 22 years the sunspots are again magnetically polarized in the same way. During the maximum not only large sunspots appear, but also active regions. In addition, impressive arcs of hot plasma reach far into the solar atmosphere, particles and radiation are hurled into space in violent eruptions. At the activity minimum, however, the sun calms down noticeably. ...
Meridional Flow in the Sun’s Convection Zone Is a Single Cell in Each Hemisphere ~ Laurent Gizon et al
- Science 368(6498):1469 (26 Jun 2020) DOI: 10.1126/science.aaz7119