On the methods to identify clustering properties in sequences of seismic time-occurrences

In recent years there has been deep development in the use of techniquesto analyse the statistical properties of point process time series. Furthermoremany efforts have been made to establish robust methods to identify timeclustering structures in the temporal distribution of seismic events. In thispaper we intend to give a systematic review of some common usedtechniques to characterise the temporal properties of an earthquakesequence; we also present new methods, commonly used in other scientificfields, to reveal time clustering structures in a seismic sequence and toclearly identify non-poissonian behaviours at different time scales. Anapplication of these methods has been performed on the seismicity ofIrpinia-Basilicata area (Southern Italy).     

Convective flows around sunspot-like objects

Results are given for calculations of convective flows around objects in the outer layers of the Sun that have similar characteristics to small sunspots. These objects are allowed to radiatively (diffusively) exchange heat with their surroundings, but convective motions and exchange are absent. This assumption is based on the simple presumption that a sunspot magnetic field maintains pressure equilibrium with the surrounding medium and prevents convective exchange with that medium.The flow structure around the object, and the question of the overall balance or redistribution of the emerging heat flux as suggested by earlier empirical models, are studied and discussed.After a period of adjustment, shortly after the sunspot-like object is placed into the domain, the layer readjusts itself so that most of the heat flux actually reappears at the surface, although some fraction of the flux is carried horizontally far from the object. There is no indication of long term storage of the heat flux that would normally appear in the place where the object resides. Finally, when the object is removed, the surrounding medium responds very quickly and soon returns to the undisturbed state before the object was in place.The present numerical treatment includes restrictions that may influence aspects of the heat redistribution, convective flows and time scales. In particular, the shape of the object and its size (somewhat smaller than a sunspot) are important, as is the number of spatial dimensions and the treatment of some boundary conditions. Since all of these issues require further investigation, some discussion is presented regarding the applicability of our results to real sunspots.     

Did multiple sediment-associated stressors contribute to the 1999 lobster mass mortality event in Western Long Island Sound, USA?

Near-bottom hypoxia during summer months has been a documented recurring phenomenon for decades in western Long Island Sound (WLIS); this temperate estuary has also supported, until 1999, a substantial American lobster (Homarus americanus) fishery. In response to a dramatic mass die-off of lobsters that began in WLIS in the late summer of 1999, a benthic habitat survey using a sediment-profile imaging (SPI) camera was conducted in October 1999. Follow-up surveys involving SPI and simultaneous measurements of dissolved oxygen (DO), hydrogen sulfide and ammonia within 10 cm of the bottom were conducted in August, September and November 2000. The SPI images revealed black sediments at or just below the sediment-water interface at a high proportion of stations in both 1999 and 2000, suggesting strongly reducing conditions and elevated levels of sulfides and other reduced end-products in sediment pore-water. Visual redox depths were relatively shallow (less than 2 cm) and spatially variable, and benthic communities appeared to be dominated by small, surface-dwelling opportunists. In August 2000, near-bottom DO concentrations < 2 mg I⁻¹ coincided with shallow redox depths at stations in the Western Narrows region. As DO levels increased from August to November 2000, visual redox depths remained shallow. Both sulfide and ammonia were detected in samples of bottom water taken within about 10 cm of the seafloor in all three 2000 surveys. The results suggest that anaerobic decomposition processes within the organic-rich sediments of WLIS strongly influence conditions at the sediment-water interface during late summer-early fall, the time of year that the lobster mortality event of 1999 began. Releases of reduced end-products (e.g., sulfide and ammonia) into overlying waters, combined with low DO levels and abnormally high water temperatures, represent multiple environmental stressors that may have physiologically weakened the lobsters and increased their susceptibility to deadly pathogens.     

Inception of debris avalanches: remarks on geomechanical modelling

Debris avalanches are complex phenomena due to the variety of mechanisms that control the failure stage and the avalanche formation. Regarding these issues, in the literature, either field evidence or qualitative interpretations can be found while few experimental laboratory tests and rare examples of geomechanical modelling are available for technical and/or scientific purposes. As a contribution to the topic, the paper firstly highlights as the problem can be analysed referring to a unique mathematical framework from which different modelling approaches can be derived based on limit equilibrium method (LEM), finite element method (FEM), or smooth particle hydrodynamics (SPH). Potentialities and limitations of these approaches are then tested for a large study area where huge debris avalanches affected shallow deposits of pyroclastic soils (Sarno-Quindici, Southern Italy). The numerical results show that LEM as well as uncoupled and coupled stress–strain FEM analyses are able to individuate the major triggering mechanisms. On the other hand, coupled SPH analyses outline the relevance of erosion phenomena, which can modify the kinematic features of debris avalanches in their source areas, i.e. velocity, propagation patterns and later spreading of the unstable mass. As a whole, the obtained results encourage the application of the introduced approaches to further analyse real cases in order to enhance the current capability to forecast the inception of these dangerous phenomena.     

A self-sufficient approach for GERB cloudy radiance detection

Geostationary Earth Radiation Budget (GERB) is the broadband radiometer onboard the Meteosat Second Generation (MSG) platform, launched at the end of August 2002 and still in commissioning phase. GERB data is planned to be used in many applications concerning Earth Radiation Budget (ERB) calculation. In order to evaluate the impact of clouds on ERB, a cloud detection is required and, at present, a cloud mask based on higher spatial and spectral resolution data acquired by Spinning Enhanced Visible and Infrared Imager (SEVIRI), the imager onboard the same MSG platform, is planned to be used in order to identify cloudy GERB soundings.As an alternative, a self-sufficient (only based on GERB data) method (OCA, the One-channel Cloudy-radiance-detection Approach) is proposed, as a time-saving and, probably, more suitable solution than the planned co-location approach.In this paper, preliminary results obtained by using several years of Meteosat data as well as GERB synthetic radiances (produced from Meteosat-7 observations) are presented. It is shown how results obtained by using GERB data alone can be comparable (and better in terms of number and spatial distribution of clear-sky GERB soundings identified) to the ones achieved if the co-location of a higher resolution cloud mask is used.     

A Simple Model for Spatially-averaged Wind Profiles Within and Above an Urban Canopy

This paper deals with the modelling of the flow in the urban canopy layer. It critically reviews a well-known formula for the spatially-averaged wind profile, originally proposed by Cionco in 1965, and provides a new interpretation for it. This opens up a number of new applications for modelling mean wind flow over the neighbourhood scale. The model is based on a balance equation between the obstacle drag force and the local shear stress as proposed by Cionco for a vegetative canopy. The buildings within the canopy are represented as a canopy element drag formulated in terms of morphological parameters such as λ _f and λ _p (the ratios of plan area and frontal area of buildings to the lot area). These parameters can be obtained from the analysis of urban digital elevation models. The shear stress is parameterised using a mixing length approach. Spatially-averaged velocity profiles for different values of building packing density corresponding to different flow regimes are obtained and analysed. The computed solutions are compared with published data from wind-tunnel and water-tunnel experiments over arrays of cubes. The model is used to estimate the spatially-averaged velocity profile within and above neighbourhood areas of real cities by using vertical profiles of λ _f .