A Mechanism for the Local Production of Faculae

We offer a new viewpoint that can explain some of the recently obtained high-resolution observations of granules and faculae. Examining the data of Scharmer, Gudiksen, Kiselman et al. (2002) we observe many granules undergo an evolution that results in faculae emerging from within their boundaries, and moving towards and into intergranular lanes. These faculae have a characteristic hairpin substructure. The evolving morphology can be closely described by a fluid dynamic instability we call the “vortex/shear layer” (VSL) interaction. It occurs in all granules whose underlying structure has vorticity when they emerge into the photosphere through the sub-photospheric turbulent boundary layer (SPTBL). The VSL results in the creation of vortices from the distributed vorticity of the SPTBL. The subsequent stretching of these vortices results in high amplification of vorticity, and the concurrent high amplification of the background magnetic field. Magnetic field lines spiral around the vortices, as well as being stretched along their axis. Thus, the VSL is also the origin of a coherent local dynamo. The spiral sheathing of high magnetic flux results in a simple explanation for the “hot wall” effect. The VSL also creates the “dark lanes” observed by Lites, Scharmer, Berger et al. (2004) and groupings of bright hairpins/vortex sheet ensembles, which look like the ribbon faculae (Berger, Rouppe van der Voort, Lofdahl et al., 2004). The SPTBL results in emerging tilted granules, which when combined with the VSL create the three-dimensionality which Lites, Scharmer, Berger et al. (2004), also observed. Both the VSL and the SPTBL result, on average, in a west side bias of hairpin faculae and granular three-dimensionality. An erratum to this article is available at .     

Relationship between sediment distribution and Posidonia oceanica seagrass

Relationships between sedimentary features and the distribution and structure of Posidonia oceanica meadows were investigated in the Gulf of Oristano (Sardinia) in a study site stretching from the mouth of the Tirso River in a more sheltered, inner sector of the gulf to an outer, more exposed sector near the rocky Cape San Marco. The results demonstrate that gradients in sediment texture and composition can be related to meadow distribution and areal coverage. We suggest that this involves the mechanical trapping of fine particles by the plants, enhanced mud deposition due to dampening of wave action in the meadows, and the admixture of bioclastic sediments linked to increased production by epiphytes and invertebrates. Independent evidence of seagrass erosion was recorded in an unvegetated breach in the meadow. The mass of fine sediment which would be resuspended in the wake of meadow destruction was estimated at 30–90 × 10³ tonnes km⁻², an amount which could substantially influence water quality and ecosystem stability in the gulf. Received: 27 May 1999 / Revision accepted: 2 February 2000     

Structural damage in the cities of Reggiolo and Carpi after the earthquake on May 2012 in Emilia Romagna

This paper addresses the structural damage to the main buildings of the cities of Reggiolo and Carpi after the primary earthquake shocks on May 20th and 29th, 2012, in Emilia Romagna. The damage survey, performed via form-based methods, highlights the different seismic behaviour of several types of buildings, especially those having historical features, and the consequences of the damage in terms of costs. Moreover, an analysis of some failure mechanisms activated in Reggiolo enables the evaluation of the local peak ground acceleration, due to the soil amplification.     

Relationships between multibeam backscatter,sediment grain size and Posidonia oceanica seagrass distribution

The use of data, including bathymetry, backscatter intensity and the angular response of backscatter intensity, collected using multibeam sonar (MBS) systems to recognise seabed types was evaluated in the inner shelf of central western Sardinia (western Mediterranean sea), a site characterised by a complex seabed including sandy and gravelly sediments, Posidonia oceanica seagrass beds growing on hardgrounds (i.e. biogenic carbonates) and sedimentary substrates.     

Sediment characteristics and macrofauna distribution along a human-modified inlet in the Gulf of Oristano (Sardinia, Italy)

We studied the spatial variability and within-year temporal changes in hydrological features, grain size composition and chemical characteristics of sediments, as well as macrofaunal assemblages, along a heavily modified inlet in the Gulf of Oristano (western Sardinia, Italy). The inlet connects the Cabras lagoon to the gulf through a series of convoluted creeks and man-made structures, including a dam and fish barriers built in the last three decades. Sediments were muddy and mainly composed of the "non-sortable" fraction (i.e., <8 microm particle size) in all four areas investigated: Lagoon, Creeks, Channel and Seaward. Along the inlet, however, the ratio between the <8 microm and the 8-64 microm fractions was highest in Creeks and Channel, between the fish barriers and the dam, suggesting impaired hydrodynamics. Consistently, steep gradients in water salinity, temperature and dissolved oxygen concentrations were found in proximity to the fish barriers. The whole inlet was characterized by a major organic enrichment of sediments, with up to an annual mean of 33.6% of organic matter and 11.7% of total organic carbon in Seaward due to the presence of seagrass leaf litter. Acid-volatile sulphide and chromium-reduced sulphur concentrations were highest throughout the year in Seaward and Lagoon, respectively, with a peak in summer. Consistently, the whole inlet supported low structured macrofaunal assemblages dominated by few opportunist species, with a relatively lower diversity in Lagoon throughout the year and the highest abundances in Seaward in summer. We infer that the presence of artificial structures along the inlet, such as fish barriers and the dam, impair the lagoon-gulf hydrodynamics, sediment exchange and animal recruitment and colonization. We suggest that the removal of these structures would favour water renewal in the Cabras lagoon, but would also increase the outflow of organic C-bonding fine particles into the gulf with serious consequences for Posidonia oceanica and Cymodocea nodosa seagrass meadows. We conclude that all possible consequences of such initiatives should be carefully considered before any action is taken.