8 research outputs found
Link between the chromospheric network and magnetic structures of the corona
Recent work suggested that the traditional picture of the corona above the
quiet Sun being rooted in the magnetic concentrations of the chromospheric
network alone is strongly questionable. Building on that previous study we
explore the impact of magnetic configurations in the photosphere and the low
corona on the magnetic connectivity from the network to the corona.
Observational studies of this connectivity are often utilizing magnetic field
extrapolations. However, it is open to which extent such extrapolations really
represent the connectivity found on the Sun, as observations are not able to
resolve all fine scale magnetic structures. The present numerical experiments
aim at contributing to this question. We investigated random
salt-and-pepper-type distributions of kilo-Gauss internetwork flux elements
carrying some to Mx, which are hardly distinguishable by
current observational techniques. These photospheric distributions are then
extrapolated into the corona using different sets of boundary conditions at the
bottom and the top. This allows us to investigate the fraction of network flux
which is connected to the corona, as well as the locations of those coronal
regions which are connected to the network patches. We find that with current
instrumentation one cannot really determine from observations, which regions on
the quiet Sun surface, i.e. in the network and internetwork, are connected to
which parts of the corona through extrapolation techniques. Future
spectro-polarimetric instruments, such as with Solar B or GREGOR, will provide
a higher sensitivity, and studies like the present one could help to estimate
to which extent one can then pinpoint the connection from the chromosphere to
the corona.Comment: 8 pages, 5 figures, acceped for publication in A&
Modeling the (upper) solar atmosphere including the magnetic field
The atmosphere of the Sun is highly structured and dynamic in nature. From
the photosphere and chromosphere into the transition region and the corona
plasma- changes from above to below one, i.e. while in the lower
atmosphere the energy density of the plasma dominates, in the upper atmosphere
the magnetic field plays the governing role -- one might speak of a ``magnetic
transition''. Therefore the dynamics of the overshooting convection in the
photosphere, the granulation, is shuffling the magnetic field around in the
photosphere. This leads not only to a (re-)structuring of the magnetic field in
the upper atmosphere, but induces also the dynamic reaction of the coronal
plasma e.g. due to reconnection events. Therefore the (complex) structure and
the interaction of various magnetic patches is crucial to understand the
structure, dynamics and heating of coronal plasma as well as its acceleration
into the solar wind.
The present article will emphasize the need for three-dimensional modeling
accounting for the complexity of the solar atmosphere to understand these
processes. Some advances on 3D modeling of the upper solar atmosphere in
magnetically closed as well as open regions will be presented together with
diagnostic tools to compare these models to observations. This highlights the
recent success of these models which in many respects closely match the
observations.Comment: 14 pages, 7 figures, accepted for publication in Adv. Space Re
Taking research to members of the public
In 2006, with funding from the Engineering and Physical Sciences Research Council (ÂŁ30k), we built a themed exhibit with the Sensation Science Centre in Dundee. In the main part of the exhibit, which was kitted out as a âpolice stationâ, a visitor would see a video of a man pretending to commit a crime and construct a composite of his face using a simplified version of our EvoFIT facial-composite system. Visitors were asked, using written and spoken prompts, to select faces from an array of alternatives, with selected items being âbredâ together, to allow a composite to be âevolvedâ. The exhibit then presented a picture of the manâs face alongside the evolved composite, example composites created by previous visitors and an average (âmorphedâ) composite from the last four visitors. The exhibit took about five minutes for a user to complete and was accompanied by a âResearch Labâ, a station which explained more of the underlying science: themes around evolution, computer-based generation of faces, forensic use of composites, etc. We expected the exhibit to last five years but, partly due to the robustness of the hardware, it remains today and is still popular
Evolution of the Fine Structure of Magnetic Fields in the Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sunâs atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun