How is the Sun’s atmosphere heated to multi-million degrees Kelvin? Despite its long history, this question still remains to be addressed. While the ultimate energy source is undoubtedly due to mechanical motions in the convection zone, there is no consensus as to how this energy is channeled to and then deposited in the solar atmosphere. With the availability of high-cadence, high-spatial-resolution instruments such as Hinode/SOT, SDO/AIA and IRIS, there has arisen an idea that magnetohydrodynamic (MHD) waves are the sought-after energy carrier, and solar atmospheric heating is then a result of their energy being transformed into heat. Indeed, observations indicate that the energy flux density carried by various waves is sufficient from the energy budget perspective.
The applicability of a wave-heating scenario hinges on a number of things. First, their energy-carrying capability is sensitive to the physical parameters of magnetized structures hosting these waves. These parameters are, however, not easy to directly measure. Second, different wave modes need to be dissipated in different ways. A pre-requisite is then to identify the nature of waves in various structures on the Sun. For this purpose, theories of MHD waves accounting for the highly inhomogeneous nature of the Sun’s atmosphere are needed but are far from complete.
Our group adopts the following approaches to address the issue of solar atmospheric heating.
l We develop MHD wave theories that incorporate such effects as transverse and longitudinal structuring. This is then followed by applications of wave theories to the inference of solar atmospheric parameters.
l We conduct analytical and numerical studies on MHD waves in the highly structured solar atmosphere to examine their generation, propagation and dissipation.
With the solar corona reaching temperatures over a million Kelvin, the solar atmosphere in open magnetic field regions cannot stay static but will expand. This coronal expansion, or more precisely the solar wind, is actually a result of solar atmospheric heating. Nonetheless, the solar wind itself is also an important subject to work on, given their rich measurements made both in situ and from remote-sensing. A popular idea is that while propagating outwards, MHD waves somehow become turbulent, and their energy is then picked up by solar wind species.
Our group has developed, in collaboration with others, a multi-fluid MHD code for the solar corona and solar wind. We treat different species on an equal footing by solving their transport equations. The methodology is that, with a given description for turbulence, we can then ask whether our model output can reproduce solar wind measurements. In this sense, the multi-fluid code can be seen as a quantitative testbed of turbulence theory.
Head: Prof. Dr. Bo Li (https://space.wh.sdu.edu.cn/info/1065/2073.htm , where you can find an always up-to-date list of Bo’s publications)
Faculty members: Dr. Shaoxia Chen, Dr. Hui Yu
Postdoctoral Scientists: Dr. Chong Huang
Graduate students: Haixia Xia, Mingzhe Guo, Zhipeng Wangguan
Current Research Grants
Properties and heating efficiencies of fast kink waves in spicules in solar coronal holes, National Science Foundation of China (NSFC), about CNY 800k, 2017.01-2020.12
Reliability of seismological tools for deducing solar coronal parameters using damped transverse waves, NSFC, CNY 900k, 2015.01-2018.12
A multifluid Magnetohydrodynamic approach for modeling the thermodynamics of coronal mass ejections, NSFC, CNY 800k, 2013.01-2016.12