The research results of the Fuxian-Lake Solar Observatory of Yunnan Observatories have been published in The Astrophysical Journal recently. They found that the corona of the upper solar atmosphere rotates faster than the underlying photosphere (which is statistically significant).

The solar “energy” contained in the sunlight comes from the nuclear reaction inside the Sun. According to the Second Law of Thermodynamics, the temperature of the solar atmosphere must gradually decrease from inside to outside. However, observations show that the coronal temperature of the upper solar atmosphere is hundreds of times higher than that of the underlying photosphere. This is the so-called mystery of anomalous coronal heating.

Currently, the heating of the upper atmosphere of the Sun is a far-unsolved problem. Current theoretical models and observational studies tend to support that small-scale magnetic activity heats the corona, but they address the issue only through heating methods and channels, and there are many controversies among them. Observational studies show that small-scale magnetic activity rotates faster than large-scale magnetic activity. The corona rotates abnormally faster than the underlying photosphere, and such a rotation feature indicates that the corona is heated by small-scale magnetic activity.

They have analyzed the periodicity of different colors of sunlight and found that for far-ultraviolet sunlight, the rotation period is about 26.3 ± 0.13 days, and for near-infrared sunlight, the rotation period is about 27.5 ± 0.06 days. The solar transitional region and corona emit X-ray and far-ultraviolet light; the upper layer (or higher) of the solar chromosphere emits ultraviolet and near-ultraviolet light; the chromosphere and the high photosphere emit 400-800-nm visible light; and the bottom of the photosphere emits 900-1600-nm infrared light.

A series of studies at the Fuxian-Lake Solar Observatory of Yunnan Observatories show that the upper atmosphere of the Sun is affected mainly by small-scale magnetic activity, and resultantly temperature is abnormally higher in the upper atmosphere than that in the lower atmosphere, and the upper atmosphere rotates abnormally faster than the lower layer. Meanwhile, the studies also show that the change of solar irradiance (solar constant) is due to small-scale magnetic activity.

The research is supported by the National Natural Science Foundation of China.

Contact:

LI Kejun

lkj@ynao.ac.cn

Yunnan Observatories