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 $10^{15}$ to $10^{17}$ 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&

Platelet ice, the Southern Ocean’s hidden ice: a review

Basal melt of ice shelves is not only an important part of Antarctica’s ice-sheet mass budget, but it is also the origin of one of the most peculiar types of sea ice found in the polar oceans: platelet ice. In many regions around coastal Antarctica, tiny ice crystals form and grow in supercooled plumes of Ice Shelf Water, releasing heat into the surrounding ocean. They usually rise towards the surface, eventually becoming trapped under an ice shelf as marine ice. Frequently, masses of those crystals are advected out of the ice-shelf cavity, and accumulate below a solid sea-ice cover to form a semiconsolidated layer. When the overlying sea ice grows into this so-called sub-ice platelet layer, the loose crystals are consolidated, adding additional thickness to the sea ice. These phenomena are generally referred to as platelet ice, although confusion about the terminology is widespread in the literature. The presence of platelet ice has a profound impact on sea-ice properties and processes in several regions of Antarctica, with numerous implications for the local polar marine biosphere. Most notably, sub-ice platelet layers provide a stable, sheltered, nutrient- and food-rich habitat which usually results in a highly productive and uniquely adapted ecosystem. It has also been hypothesised that platelet ice may be an indicator of the state of an ice shelf, although comprehensive time series are limited to the Ross Sea. This paper clears up the terminology by providing exact definitions of the relevant terms.We review platelet-ice formation, observational methods as well as geographical and seasonal occurrence. The physical properties and ecological implications are merged in a way understandable for physicists and biologists alike, to lay the foundation for the interdisciplinary research that is necessary to tackle the current knowledge gaps

Life history of an anticyclonic eddy in the Algerian basin from altimetry data, tracking algorithm and in situ observations

Frequently-forming long-life mesoscale eddies are observed in the Algerian Basin that influence the circulation of the wider Western Mediterranean Sea. Most of these structures store and transport water masses including associated physical and biological properties throughout the entire basin. In order to study the evolution of a long-life anticyclonic eddy, we use a multiplatform approach based on remote sensing data analysis and in situ measurements. We present a case study of an anticyclonic eddy that persisted for 17 months within the basin. The feature was identified through a hybrid method of eddy detection and tracking applied to altimetry data, and sampled twice during two different oceanographic cruises in autumn 2004 and late spring 2005. Transect observations of potential temperature, salinity, density and the dissolved oxygen concentration were utilised to infer water mass properties and eddy characteristics. In situ data show that water of Atlantic origin, initially trapped by the eddy during its formation, was modified during the eddy lifetime. The time evolution of radius, kinetic energy and vorticity suggests dividing the eddy lifetime into three phases: the eddy formation, an intermediate period of high variability and a final, lower energy phase. The track followed by the eddy confirms the hypothesis of an interaction with the North Balearic Front and a consequent change of the eddy's physical properties. Decomposing the eddy's kinetic energy into mean and fluctuating terms allows us to describe its interaction with the mean circulation of the basin. In particular during formation, the southern part of the eddy absorbs energy from the mean circulation, while it provides energy to the mean flow in its northern part. In the second phase, when the eddy is far from the coast, it receives energy from the mean flow. Combining in situ data analysis with the results of the satellite-imagery-based detection and tracking method has proven to be a very useful method in assessing the evolution of a mesoscale structure in the Algerian Basin and its interaction with the large scale ocean dynamics of the Western Mediterranean Sea

Taking research to members of the public

In 2006, with funding from the Engineering and Physical Sciences Research Council (£30k), 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 ‘police station’, 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 ‘bred’ together, to allow a composite to be ‘evolved’. The exhibit then presented a picture of the man’s face alongside the evolved composite, example composites created by previous visitors and an average (‘morphed’) composite from the last four visitors. The exhibit took about five minutes for a user to complete and was accompanied by a ‘Research Lab’, 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 Sun’s 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