On the terms of geomagnetic daily variation in Antarctica

The target of this work is to investigate the nature of magnetic perturbations produced by ionospheric and magnetospheric currents as recorded at high-latitude geomagnetic stations. In particular, we investigate the effects of these currents on geomagnetic data recorded in Antarctica. To this purpose we apply a mathematical method, known as Natural Orthogonal Composition, to analyze the magnetic field disturbances along the three geomagnetic field components (<I>X</I>, <I>Y</I> and <I>Z</I>) recorded at Mario Zucchelli Station (IAGA code TNB; geographic coordinates: 74.7° S, 164.1° E) from 1995 to 1998. Using this type of analysis, we characterize the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, we find that some of them are actually related to well known current patterns located at high latitudes

Geomagnetic storms, dependence on solar and interplanetary phenomena: a review

Geomagnetic storms are probably the most intensively measured perturbations of the Earth’s magnetic field. They are multi-faceted phenomena that result as a final element of a chain of processes that starts on the Sun, a ects the solar wind and the interplanetary medium, and ends on the Earth. At present, one of the key questions in the scientific community is the ability to predict the occurrence of geomagnetic storms on the basis of solar and interplanetary space observations. For these reasons, in recent years a number of investigations have been carried out to understand the solar-terrestrial relationships and to ascertain those factors that are ultimately responsible for geomagnetic storms. Here a brief review of published results on the geomagnetic storm e ectiveness from CMEs, solar flares, as well as interplanetary event observations, is presented

On the terms of geomagnetic daily variation in Antarctica

The target of this work is to investigate the nature of magnetic perturbations produced by ionospheric and magnetospheric currents as recorded at high-latitude geomagnetic stations. In particular, we investigate the effects of these currents on geomagnetic data recorded in Antarctica. To this purpose we apply a mathematical method, known as Natural Orthogonal Composition, to analyze the magnetic field disturbances along the three geomagnetic field components (X, Y and Z) recorded at Mario Zucchelli Station (IAGA code TNB; geographic coordinates: 74.7° S, 164.1° E) from 1995 to 1998. Using this type of analysis, we characterize the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, we find that some of them are actually related to well known current patterns located at high latitudes

Geomagnetic jerks: observation and theoretical modeling

A geomagnetic jerk is a phenomenon involving the geomagnetic field secular variation when it abruptly changes its slope. It is generally accepted that it occurs on timescales from months to a few years and is of internal Earth origin. It has been suggested that geomagnetic jerks may represent a reorganization of the secular variation and that they may be created by torsional oscillations in the Earth’s core. For their peculiar characteristics geomagnetic jerks have been associated to di erent geophysical phenomena of global relevance. Here is presented a brief review of published results on the possible correlations with LOD and Chandler wobble decadal variations and global temperature changes

The contribution of geomagnetic observatories and magnetic models to the study of secular variation and jerks in Antarctica

Some of the most interesting features of the geomagnetic field and its time variations are displayed in polar areas. Observatory monthly means usually provide an excellent opportunity to study the temporal changes of the magnetic field at a given location. Unfortunately, on the Antarctic continent the distribution of the permanent ground- based observatories does not permit a uniform coverage of the examined area. Furthermore, the magnetic records are characterized by intense external disturbances and noise that make the analysis of the magnetic field difficult. To improve our knowledge of the secular variation and detect the presence of secular variation impulses (geomagnetic jerks) in Antarctica, we use both observatory data and the CM4 quiet time magnetic field model. In particular CM4 improves our knowledge of geomagnetic jerks over Antarctica through the study of the sign changes of the secular acceleration maps

Influence of solar activity on magnetic network measurements

The influence of solar activity on magnetic measurements taken during the Italian repeat station surveys performed in 1999/2000 and 2009/2010 has been investigated. A method to estimate the difference between the 2000.0 and 2010.0 surveys in terms of the “residual” (i.e. not completely reduced) external contribution is proposed. This method is also based on the removal of the contribution due to the magnetic field of internal origin by means of CHAOS3 model from magnetic repeat station measurements. The origin of the observed differences is interpreted in terms of the very different level of solar activity between 2000.0 and 2010.0. Indeed, results seem to suggest that differences could be attributed to the enhanced ring current intensity during a phase of solar maximum. The investigation of the spatial patterns of these differences suggests that they could be reduced by introducing a larger number of variometer stations, especially during surveys undertaken under conditions of high solar activity

Core-mantle boundary deformations triggered by the Sumatra earthquake

The devastating megathrust earthquake of December 26 2004 off the west coast of northern Sumatra has been probably the largest since the 1960 Chile event. The occurrence of this event revived the debate, among the scientific community, upon several open geophysical problems possibly connected with the energy release of giant earthquakes. One of these problems concerns the origin of geomagnetic jerks and its eventual relationship with large seismic activity. Though a final answer to this question seems not to be at hand presently, this answer (whatever positive or negative) appears to be connected with the possibility that giant seismic events could cause significant changes in the CMB topography. Until now, no attempts have been made to compute the impact of a seismic event on the CMB: the great Sumatra earthquake, for the first time, gave unambiguous instrumental evidence that the deformation field associated with a giant event is detectable at distances up to several thousands of km with a magnitude of the displacements of the order of 1 mm. Since perturbations to the CMB even smaller than this value are likely to be able to produce a geomagnetic jerk, a precise evaluation of the CMB topography perturbation associated with a giant earthquake like Sumatra has become an important scientific question

Effect of structural modifications on the drying kinetics of foods: changes in volume, surface area and product shape

Macro and micro-structural changes take place during food dehydration. Macro-structural changes encompass modifications in shape, area and volume. Studies of such changes are important because dehydration kinetics (essential for calculating industrial dryers) may be highly influenced by changes in food shape and dimensions. The overall changes in volume, surface area (“shrinkage”) and shape (Heywood factor, with provides a close description of food shape) were determined experimentally, and the results were correlated with simple expressions. Hence, although dehydration kinetics can be modeled with simplified overall shrinkage expressions, the possibility of selecting a suitable geometry and predicting the characteristics dimensions will provide higher accuracy. An additional unresolved problem is the lack of a general model that predicts macro-structural changes for various foods and diverse geometries. In this work, based on experimental data of sweet and sour cherries, and rose hip fruits, a simplified general model to predict changes in volume and surface area are proposed. To estimate how the changes in characteristic dimensions affect the kinetic studies, experimental drying curves for the three fruits by means of a diffusional model considered the following variants for the characteristic dimensions: (i) The radius of the fresh food, assumed constant; (ii) The radius of the partially dehydrated product; (iii) The radius predicted by the correlation for structural changes, especially volume, obtained in this work and generalized for the three fruits, and (iv) to demonstrate the need to study the macro-structural changes for all dehydrated foods, also be present the case of a restructured food.Facultad de Ciencias Exacta

Winter roost occupancy and behaviour at evening departure of urban long‐eared owls

Roost occupancy and behaviour at evening departure were studied in long-eased owls (Asio otus) at a large winter roost in the southern suburbs of the city of Milan, northern Italy. The number of roosting owls was strongly correlated with decreasing daylength, while it was weakly negatively correlated with temperature. Hence changes in photoperiod can be considered among the proximate factors promoting the winter aggregation of long-eared owls. Behaviour at departure was influenced by cloud cover: birds departed earlier, and departures were at a higher altitude and less concentrated, with covered sky than with clear sky; the reasons for these behavioural differences remain unclear. Directions of departure showed that owls do not use the urban area for hunting, as no birds were observed flying towards the city, consistently with dietary data

Radio Echo Sounding (RES) investigations at Talos Dome (East Antarctica): bedrock topography and ice thickness

Radio echo sounding measurements were collected during two Antarctic expeditions to determine the ice thickness and the sub-glacial morphology of Talos Dome in the region around 72°48'S; 159°06'E (about 6400 km2) on the edge of the East Antarctic plateau adjacent to Victoria Land in the western Ross Sea sector. The increasing interest in this region is due to the fact that in this area the ice accumulation is higher than in other sites in East Antarctica. Because of this, Talos Dome could be a new site for a project of a deep ice core drilling to obtain information on climate changes near the coast of Antarctica. In this frame, the knowledge of the bedrock topography is of great importance to choose the best location for the drilling site. In this paper, airborne radio echo sounding results from two Antarctic expeditions (1997 and 1999) are presented. Bedrock topography in bi- and three-dimensions for the Talos Dome region are discussed