Dynamics of Magnetic Bright Points

The dynamics of the Sun are governed by its magnetic fields. The most striking feature of these magnetic fields is the large scale magnetic field configuration seen by sunspots which vary in a well known eleven years cycle. But it is also known that there is a whole range of different kind of magnetic fields scaling down to the yet detected less extended (< 200 km diameter) magnetic fields which appear in the form of single isolated flux tubes. All of these fields interact with the solar atmosphere and are the driving energy sources for features like flares and CMEs. A still not completely understood keystone problem of solar physics is the coronal heating problem. This problem is made up by the observational fact that the outermost layer of the solar atmosphere - the Corona - is hotter than the layers beneath it. This state is in strong contrast to thermodynamics and can be only sustained by continuous heating. One of the supposed heat sources can be the dynamic of small scale magnetic fields. It is expected that disturbances in the photosphere (e.g. the interaction with the granulation) can lead to waves along the magnetic flux tubes that are partly reflected and absorbed in the higher atmosphere and can therefore heat this layer. In this proposal we want to extend the knowledge about the smallest kind of magnetic fields, seen as Magnetic Bright Points (MBPs), in regard of this heating problem. For this task we want to use data from the Japanese Hinode satellite mission. This satellite caries among other instruments the yet largest ever in space flown optical telescope for such studies (SOT, solar optical telescope; 50 cm aperture). The used data will mainly consist of filtergrams taken in the G-band (a magnetic field sensitive spectral range). For the identification of the MBPs we will use already existing and tested programmes and algorithms which will be further extended. The goals of our proposal would be to gain a better understanding of important parameters describing the dynamics of these small scale magnetic fields (velocity-, lifetime-, magnetic field strength-, brightness- distribution). On the other hand we want to study the chromospheric response of the underlying photospheric dynamics too. This can be done by a second kind of filtergram taken in the Ca II-H line, which is magnetic field sensitive and formed in the chromosphere. By analysing co-temporal and co-spatial filtergrams of both types we want to identify wave processes and brightness changes (indicating heating) in both layers. The third aim consists of building up a collaboration with the Indian Institute of Astronomy situated in Bangalore. This institute hosts - under its director Siraj Hasan - a well known group that uses simulations for investigations of wave propagation and wave heating processes in the solar atmosphere. We want to work in a close cooperation with this group and exchange our found observational facts with their found simulational findings.

The dynamics of the Sun are strongly associated with space weather and Coronal mass ejections that can damage satellite systems of lead to large-scale electrical power outages. The understanding of the conditions in the Sun, especially the magnetic fields, are of special interest. Sunspots are large magnetic field concentrations, visible on the surface of the Sun, the Photosphere and are linked to the 11-yr solar activity cycle. The smallest magnetic phenomena that are visible with high resolution solar telescopes are magnetic bright points (MBPs), which have diameters less than 200 km and expand vertically into the Chromosphere. Their dynamics are strongly influenced by convective plasma motions, the granulation. The analysis of observations and computer simulations possibly provide information about the heating of the chromosphere which may be induced by disturbances of magnetic flux tubes. Hence, automated segmentation and tracking algorithms for detecting MBPs and granules were developed. A new population of small granules (< 800 km) was detected in data from observations and simulations. These small granules are situated between regular granules and are difficult to detect due to their dark appearance. Their evolution is disturbed by turbulent plasma motions and they show a lifetime of less than 2 minutes (regular granules: 15-20 min). Their dynamics differ in regard to their diameter, intensity and velocity evolution compared to the population of regular granules. Long-time analysis of MBPs in observations shows that the number of MBPs correlates with the solar activity cycle but is shifted by 2.5 months. The study of the temporal evolution reveals a complex dynamic for MBPs, which are mostly associated with strong downflows. The analysis of the evolution of MBPs requires information of the magnetic field strength, which can be measured indirectly via the degree of polarization. A commonly used tool for this application is the SIR code. This code was optimized using parallelization techniques to considerably enhance the runtime performance. A speed enhancement for analyzing a dataset was improved from 4 years to 1 week. The tool was made available for the scientific community to assure an easier and faster analysis.In the duration of the project, a new innovative simulation code was started being developed in order to analyze the dynamics of the MBPs in the Chromosphere and their effects on the Chromospheric heating. The code is based on the newest studies in the field of numerics and uses different parallelization methods that guarantee a fast runtime performance. First successfully completed test were already compared to different renowned computer simulations and showed confident results.