Russian Researchers Obtain New Data on Solar Magnetic Field Asymmetry
Researchers from the Institute of Earthquake Prediction Theory and Mathematical Geophysics (Russian Academy of Science) and HSE University have proven that asymmetry between meridional flows in the northern and southern hemispheres of the Sun depends on the anomalies of the solar magnetic field. Research undertaken by Elena Blanter and Mikhail Snirman reveals new aspects of the importance of solar magnetic field asymmetry for predicting the anomalies of the Sun’s activity. The article has been published in Solar Physics.
Researchers from the Institute of Earthquake Prediction Theory and Mathematical Geophysics (Russian Academy of Science) and HSE University have proven that asymmetry between meridional flows in the northern and southern hemispheres of the Sun depends on the anomalies of the solar magnetic field. Research undertaken by Elena Blanter and Mikhail Snirman reveals new aspects of the importance of solar magnetic field asymmetry for predicting the anomalies of the Sun’s activity. The article has been published in Solar Physics.
The Sun’s magnetic field plays a pivotal role in human life. Forecasting magnetic storms is essential for aviation, protection of ground technical systems, space flight missions and launches of research and commercial satellites. The mechanisms of the solar magnetic field have yet to be fully explored due to the complexity of processes inside the Sun and the impossibility of performing direct measurements.
The solar magnetic field forms under the dynamo mechanism in the Sun’s convection zone. Figure 1 shows that the convection zone is a little less than one-third of the Sun’s radius and is located at the surface of this star. Above the convection zone is the Sun’s corona, which can be seen during a solar eclipse. The dynamo theory provides an explanation for the 11-year cycles of solar magnetic activity, which can be observed due to changes in the number and location of sunspots on the Sun. A large meridional flow in the convection zone affects that dynamo mechanism.
The meridional flow can be represented as two giant circulation cells, one cell for each hemisphere. At the Sun’s surface, the flow is directed from the equator to the poles, while inside the convection zone, plasma circulates back to the equator. The research shows that the meridional flow appears to be a much more complex process—a single flow can be a sum of smaller circulation cells, just like a system of coupled gears.
The research uses the Kuramoto model, named after the Japanese physicist Yoshiki Kuramoto, to describe the system of such coupled circulation cells in the Sun’s physics. The classic model describes synchronization of coupled oscillatory systems consisting of several cells to determine the conditions under which the circulation cell system may be regarded as a single whole and when it falls into independent unrelated motions.
The authors of the article have previously studied the long-term evolution of meridional flows in the Sun’s northern and southern hemispheres by using systems of two coupled circulation cells. The present paper, however, focuses on the four-cell system, which provides a more accurate picture of the complex structure of the Sun’s meridional flow.
This latest approach allowed the researchers to describe changes of the solar plasma circulation intensity at the Sun’s different latitudes. The authors managed to relate the asymmetry of magnetic fields, observed in Solar Cycles 19-20 and 23-24, to the asymmetry of meridional flows in the northern and southern hemispheres.
In fact, it was assumed that each oscillator is coupled with only one other oscillator. Therefore, a system of four oscillators can be either a chain model or a ring model (see Figure 2). Solving the Kuramoto equations and studying the parameters of each oscillator helped identify the conditions under which they are synchronized and participate in massive transmissions of plasma flows as a single whole.
The research shows that the asymmetry between meridional oscillations in the Sun’s northern and southern hemispheres reveals itself for a long time and may be ascribed to the anomalies of the Sun’s magnetic field.
The researchers believe that in the solar dynamo model the role played by the meridional circulation in anomalous solar activity has not been sufficiently studied and deserves closer attention in the future.
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