ar095.wang_j01 Posted: 09-Aug-96 Updated: Events specified: AR 7420, etc.
J.Wang, K.Shibata, N.Nitta, G.Slater, H.Hudson, S.Savy and Y.Ogawara
It has been recognized since 1960's that the X-ray brightness in the corona is correlated to the surface magnetic fields. We see bright X-ray emission when the gradient of line-of-sight magnetic fields increases and the magnetic configuration becomes more complicated. The high spatial and temporal resolution available from Yohkoh SXT observations opened a new page in solar research. A few very important discoveries revealed essential aspects of coronal heating and dynamics, such as the X-ray jets, cusp formation, transient brightening of X-ray loops, and continual expansion of active corona, and so on. They are clearly magnetically- driven phenomena. Study of their associations with the surface magnetic field evolution becomes extremely important. Many projects in this aspect have been proposed and produced fruitful results.
We intended to focus on the dynamics of large-scale loops in active regions, and its association with the surface magnetic field activity. By magnetic field activity we mean the changes in flux (emergence and cancellation), non-potentiality development (shear, current), and some eruptive energy release in surges, flares including microflares observed in optical waveranges. Huairou high resolution vector magnetograms will play a major role in this study. Co-alignment of vector magnetograms with SXT images, deprojection of the images, and 3-d extrapolation of the magnetic field should be the key procedures of the study. We will work primarily on the observations close to the disk center for clear identification of loop footpoints, and the underlying magnetic structure and evolution. Thermal properties will be diagnosed for coronal loops using Yohkoh SXT and other observations.
This is an observational study, and we will mainly concern the causal relation between the surface magnettic activity and large-scale loop dynamics. So far, we have completed a piece of work on the shrinkage of large-scale non-flare loops in the southern part of AR 7420. Those loops brightened suddenly by footpoint ejection from separatrix between a satellite bipole and the main bipole, and then cooled and contracted in size. The long silence of magnetic activity in the south of the region seems to be well correlated with the cooling and the shrinking. Further efforts to understand the 3-d structure, the south-north asymmetry in loop dynamics, the ejections at footpoints are undertaken. Other regions are also surveyed as further targets to investigate. Possible numerical simulations are under consideration.