Researchers at the Fuxian Lake Solar Observation Base of Yunnan Observatories, Chinese Academy of Sciences (CAS) have made important progress in the field of long-term evolution of the overall behavior of solar activity/variation ("macro" sun). The research results were published in Scientific Reports.
Sunspots are the most significant and the longest observed activity phenomena on the solar photosphere (i.e. the sun seen by the naked eye). The sunspots’ butterfly diagram is one of the most symbolic achievements in solar observations. Based on long-term multi-waveband observations of the photosphere, the chromosphere, and the corona, it is found that the atmosphere above the magnetic butterfly diagram that is colder than the photosphere background, is shown as a butterfly body, which is hotter than the background, thus expanding the concept of the butterfly diagram proposed more than a century ago to the "butterfly body" (see Figure 1). This is also a significant global evidence of the magnetic-field heating of the upper atmosphere (the heating of the upper atmosphere is global, and the butterfly body is the most significant evidence of the global heating of the solar atmosphere).
Fig.1 Illustration of the 3-dimensional solar butterfly body throughout the solar atmosphere from the photosphere to the corona. The x-axis roughly indicates time-unit years in the 11-year solar cycle, the y-axis indicates latitudes within 40 ° (N: the northern hemisphere, and S: the southern), and the z-axis indicates height from above the bottom of the photosphere.
Looking at long-term evolution of the solar poles, the brightening of the polar region is one of the most significant features. Early observations found that the brightening in the polar region of the photosphere and chromosphere, was statistically in anti-phase with the solar cycle. The latest space and ground long-term multi-waveband observations show that the polar brightening in the coronal layer is in phase with the solar cycle. Therefore, based on the long-term observations of the atmosphere in the polar region, the concept of "polar layered temporally-staggered brightening " is proposed, and it is speculated that the polar brightening is attributed to the magnetic fields of different categories.
The anomalous heating of the corona is one of the eight key problems in contemporary astronomy. Similarly, the chromospheric abnormal heating is also a problem that has puzzled the solar physics community for a long time. The chromospheric and coronal (i.e. upper atmosphere) heating are listed as two topics among 10,000 scientific problems (astronomy volume) in China. The butterfly body clearly indicates that the upper active atmosphere is heated by the magnetic fields distributed as the butterfly diagram. The long-term evolution of the background chromospheric atmosphere (quiet atmosphere) after deducting the active atmosphere is in anti- phase with the solar cycle, which must be caused by the magnetic fields with similar evolutionary characteristics. The phenomenon of "polar layered temporally-staggered brightening" indicates that the background quiet corona atmosphere is probably heated by the magnetic fields with the same evolutionary characteristics as the brightening phenomenon. The viewpoint that different categories of the magnetic fields act at different heights in the atmosphere is put forward, and the statistical explanation of the abnormal heating of the upper atmosphere is given. On the contrary, if we do not start from the perspective of different categories of the magnetic fields, we may not have a comprehensive understanding to the abnormal heating.
Researchers from National Astronomical Observatories, CAS found that the magnetic fields in the solar atmosphere can be divided into five categories according to the long-term evolution and spatial distribution of different magnetic fluxes. The current research of solar physics mainly focuses on the observational analysis and theoretical interpretation of magnetic activities. The solar atmosphere is magnetic. From the perspective of categories of the magnetic fields, researchers at the Fuxian Lake Solar Observation Base have made progress in the above aspects, and thus built a basic framework for the role of different categories of the magnetic fields. The origin of the magnetic fields in the solar interior is speculated based on the above results, the research results of helioseismology, and the rotation characteristics of magnetic structures.
This work is supported by the National Natural Science Foundation of China, Yunnan Provincial Talent Training and Support Plan (Yunling Scholar Program and Innovation Group Program), and Yunnan Natural Science Foundation.
Contact:
LI Kejun
Yunnan Observatories, CAS
Email: lkj@ynao.ac.cn
