[en] At the ENEA (National Agency for New Technology, Energy and the Environment) research centre of Brasimone (Bologna, Italy) a narrowband multifilter radiometer for 4 wavelengths of UVB radiation has been tested and operated; its use for long duration measurements campaigns of ultraviolet flux at ground level is foreseen, operating the separation of direct and diffuse components of the radiation. Experimental results have been compared with those obtained by means of the PREMAR-2 code, which uses the Monte Carlo method to simulate the transport of radiation in the atmosphere. To this aim, data obtained by using the radiance-transmittance LOWTRAN-7 code have been exploited to build up a library data set of the above code. Comparisons between experimental and computational results on a fine meteorological day, for the diffuse/total radiation ratio on the ground, were found to agree

[en] In this paper, the main loss processes occurring in the Earth's inner magnetosphere are reviewed. It is shown that the most significant loss process is the charge exchange between the energetic ions (1-300 keV) and the exospheric particles. Through this process, the energetic ions are neutralised, so that they can escape from the magnetosphere. The detection of the ENA (energetic neutral atoms) would allow the long-distance imaging of the magnetospheric plasma regimes. The available ENA observations, as well as the simulated ENA fluxes, are reviewed, and the expectations coming from this new tool for magnetospheric diagnostics are discussed

[en] Several days of global raw TOVS (Tiros-N Operational Vertical Sounder) data are processed to evaluate the ability of different forecast models to describe, using sequences of short-range forecasts, features contained in the measured data. Radiance simulations are based on model fields obtained from a short-range (24 to 48 hours) forecast so that spin-up effects are mostly avoided and the description of the dynamical field is still accurate. The simulations involve cloud parameters, cloud fraction and cloud liquid water. Estimates of outgoing long-wave flux obtained from the measured and from the simulated radiances, using the same statistical regression, are compared with each other and with the quantity computed by the forecast model

[en] A low-activity liquid-xenon scintillator is running at the Gran Sasso National Laboratory of INFN using liquid Kr-free xenon enriched at 99.5% in ¹²⁹Xe. The result of a dark matter direct search -looking also for the annual modulation effect- is presented. Preliminary exclusion plots both for coherent and spin-dependent coupled WIMPs are evaluated

[en] An inversion technique for estimating sea wave directional spectra from Synthetic Aperture Radar (SAR) images is applied to a set of ERS-1 data relevant to selected Mediterranean areas. The approach followed is based on the analytical definition of the transform which maps the sea wave spectrum onto the corresponding SAR image spectrum. The solution of the inverse problem is determined through a numerical procedure which minimises a proper functional. A suitable iterative scheme is adopted, involving the use of the above transform. Although widely applied to the ocean case, the method has not been yet extensively tested widely applied to the ocean case, the method has not been yet extensively tested in smaller scale basins, as for instance the Mediterranean sea. The results obtained demonstrate the effectiveness of the numerical procedure discussed for retrieving the sea wave spectrum from SAR images. This work provides new experimental data relevant to the Mediterranean Sea, discusses the results obtained by the above inversion technique and compares them with buoy derived sea truth measurements

[en] The paper illustrates a possible way of combining SAR images over the sea with scatterometer derived with fields, to study the spatial characteristics of the marine atmospheric boundary layer (MABL). Both instruments are active microwave radars, relying upon the same physical mechanisms of electromagnetic wave sea surface interaction. Sensing the sea surface with different spatial resolutions, they make possible to investigate the horizontal and vertical structure of the MABL from the mesoscale (< 100 km) down to the intermediate (< 100 km) and small (< 2 km) scales. An example of the multi-scale description of the MABL is provided analysing overlapping SAR image and scatterometer wind field in the Mediterranean Sea. Environmental conditions of this case study were characterized by moderate wind (8 to 10 m s^-1) and unstable air-sea conditions. The radar backscatter modulations exhibited by the SAR image reveal the presence of large-scale atmospheric variations, orographic wind distortions and wind rolls. The majority of the large-scale modulations of radar backscatter are obviously related to the wind speed; some other large-scale feature, which does not seem directly related to the wind, could be explained by the weak Ekman vertical velocity, derived from the scatterometer wind field. The analyses of the wind rolls have been performed through the bi-dimensional spectrum of the SAR image, which shows a two-scale orthogonal wave system with wavelengths of 7 km and 1.5 km. The paper points out the importance of other parameters, such as the sea and air temperatures, in the interpretations of the SAR images and in the full exploitation of the scatterometer winds

[en] The formation, stationary and stability of tri-polar vortices are investigated in a two-layer quasi-geostrophic model. On the f-plane, these tripoles form from the barotropic and baroclinic instabilities of circular isolated vortices. Various horizontal and vertical potential vorticity distributions, both piecewise constant and continuous, are considered here for these circular vortices

[en] The problem of reconstructing dielectric permittivity of a buried object from the knowledge of the scattered field is considered for a two-dimensional rectangular geometry at a fixed frequency. The linearization of the mathematical relationship between the dielectric permittivity function and the scattered field about a constant reference profile function and the approximation of actual internal field with the unperturbed field leads to the so-called Distorted Born Approximation. To analyze the limitations and capabilities of the linear inversion algorithms, it is investigated the class of the retrievable profiles. This analysis makes it possible to point out that a very reduced number of independent data is available, so requiring to employ regularization techniques in order to perform in a reliable and stable way the linear inversions. In this paper it is presented a general algorithm consisting in a regularized Singular Value Decomposition of the matrix resulting from a discretization of the problem. Finally, numerical results of linear inversions are given

[en] A new tilt meter, based on the technology for building a space-borne high-sensitivity accelerometer and manufactured at IFSI/CNR, has a been operating during several years in the INFN Gran Sasso underground laboratory. The results of the analysis of a three-year data set, processed with the program package ETERNA, to estimate earth tidal parameters are reported. For the best series of data (1998) tide measurement accuracies are: 0.5-1% for the M₂ (lunar principal) amplitude and 3-4% for the O₁ (lunar declination) amplitude. The tilt meter installed at a depth of 1400 m shows no clear evidence of meteorological effects. Observed tidal parameters are compared with theoretical tidal parameters predicted for a non-hydrostatic inelastic Earth model and demonstrate good agreement for the M₂ component. Due to the high accuracy of the tidal components prediction (better than 1%) tidal measurements were used to estimate the long-term stability of the instrument response

[en] A solid-state riometer has been installed at Terra Nova Bay (74 degrees 42^' S and 164 degrees 06^' E) during the 9. italian Antarctic expedition (1993/1994) to provide, in the frame of the geophysical observatories, studies on the ionospheric absorption in the lower part of the ionosphere. This kind of measurements will integrate the already existing active vertical ionospheric sounding and the magnetic absolute vector observations, with the objective of investigating the state of the ionosphere-magnetosphere coupling. In order to evaluate the base disturbance to the riometer, a remote campaign has been performed at McCarthy Ridge, rather far from the base station, where no atropic noise is expected. Preliminary data analysis confirms the good quality of the antarctic riometer observations