http://hdl.handle.net/2122/96 Ricerca nel canale cerca http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/5022 Titolo: Pre-storm NmF2 enhancements at middle latitudes: delusion or reality?<br/><br/>Autori: Mikhailov, A. V.; Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Moscow Region 142190, Russia; Perrone, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia<br/><br/>Abstract: A critical analysis of recent publications devotedto the NmF2 pre-storm enhancements is performed.There are no convincing arguments that the observed casesof NmF2 enhancements at middle and sub-auroral latitudesbear a relation to the following magnetic storms. In all casesconsidered the NmF2 pre-storm enhancements were due toprevious geomagnetic storms, moderate auroral activity orthey presented the class of positive quiet time events (Q-disturbances).Therefore, it is possible to conclude that thereis no such an effect as the pre-storm NmF2 enhancement asa phenomenon inalienably related to the following magneticstorm. The observed nighttime NmF2 enhancements at subaurorallatitudes may result from plasma transfer from theplasma ring area by meridional thermospheric wind. Enhancedplasmaspheric fluxes into the nighttime F2-region resultedfrom westward substorm-associated electric fields isanother possible source of nighttime NmF2 enhancements.Daytime positive Q-disturbances occurring under very lowgeomagnetic activity level may be related to the dayside cuspactivity. http://hdl.handle.net/2122/4165 Titolo: EFFECTS OF ENERGETIC SOLAR PARTICLES ON OZONE AND MINOR ATMOSPHERIC COMPONENTS INSIDE THE POLAR REGIONS<br/><br/>Autori: Damiani, A.; INAF-IFSI<br/><br/>Abstract: Solar activity influences the Earth’s environment, in particular the atmosphericozone, by the direct output of the e.m. radiation or through the variability of theincoming cosmic ray flux (solar and galactic particles). Especially energetic particles,arising from huge explosions on the Sun’s surface, travel in the interplanetarymedium and, if the circumstances were favorable, they could enter the terrestrialatmosphere (driven by the geomagnetic field lines of our planet) and reach the polarcap regions (geomagnetic latitude > 60°). There, they provide additional externalenergy and are able to produce ionizations, dissociations, dissociative ionizationsand excitations phenomena by interacting with the minor constituents. The inducedchanges are not confined to the ion chemistry but also to the neutral components. Inthis way a rise of the concentration of HOx and NOx species and the triggering ofcatalytic cycles which lead to short (hours) and medium (days) term ozonedestruction occur. Finally, also no-reactive reservoir species (e.g., HNO3, HCl, HOCl)are involved in these processes and endure large variations.The present thesis highlights the chemical variability of the middle atmosphereduring and after some Solar Energetic Particle (SEP) events recorded during thecurrent solar cycle. Special attention has been paid to the relationship betweenozone and HOx data (retrieved from the Microwave Limb Sounder of EOS AURAsatellite) for four events referred to 2005. The HOx data, recorded for the first timeduring the intense ionization caused by the SEP flux, have pointed out some featuresrelated to these phenomena not wholly captured by the current theoretical models. Inaddition, they have highlighted that the HOx rise is able to destroy the so-called thirdozone peak at the polar latitudes of the winter hemisphere and it occurs also duringmedium intensity events. Besides, the analyses of January 2005 SEP events haveshown that the changes on the hydrogen species leaded to variability in theconcentration and partitioning of chlorine family, not discernible in the summerhemisphere. Further, the use of data coming from the HALOE instrument, referred toSEP events occurred in July 2000 and April 2002, has in short confirmed pastexperimental results. Finally, the study of a little SEP event occurred during May 2003has pointed out that SEP events are not the unique ionization source inside the polarlatitudes during the winter. http://hdl.handle.net/2122/1688 Titolo: Modelling the light-ion densities in the ionosphere<br/><br/>Autori: Stankov, S. M.; Geophysical Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria<br/><br/>Abstract: A steady-state theoretical model is used to obtain variations of the H+/O+ and He+/O+ density ratios in the upper ionosphere at middle latitudes. The model results are compared with the existing data from satellite measurements. Analytical functions are constructed approximating the latitude and altitude variations of these ratios. http://hdl.handle.net/2122/416 Titolo: Geochemical processes governing the chemistry of groundwater hosted within the Hyblean aquifers<br/><br/>Autori: Grassa, F.; PhD Thesis<br/><br/>Abstract: A raingauge network made of six stations was installed in the Hyblean region. Stations were located at different altitudes (from 5 m to 986 m a.s.l.) and along two directions (E-W and SW-NE). Rainwater samples were monthly collected for stable isotope measurements.Spatial distribution of rainwater isotope composition has confirmed the wet air massesmove from South-East/South-West toward North. Water balance has highlighted that the annual volume of infiltrating waters is in the range of 1-1.5 *105 m3 Km-2.82 well waters and 12 spring waters located within the Hyblean Plateau (South-Estern Sicily), were also collected from 1999 to 2001 during several surveys for chemical (major,minor and trace elements) analyses. Water chemistry allowed to identify two main aquifers: the first aquifer hosted within sedimentary rocks is characterized by earthalkaline bicarbonate waters, while the second aquifer, located within the volcanic deposits (mainly towards North- North-East) is characterized by groundwaters evolving from earthalkaline bicarbonate water-type towards a Na-HCO3-type.A slightly anomaly in water temperature (24-28°C) have been identified along the northern margin, while the lower Eh values have been recorded along the M.Lauro-Scicli and the Hyblean Malta Escarpment fault systems. Isotope composition of groundwaters has suggested the occurrence of evaporative processes during soil infiltration having a dD/d18O slope close to 4.5.Chemical and isotope composition of dissolved gases (d13CTDIC, d13CCH4, 3He/4He) haverevealed, as expected, that deeply-derived gases rise along the main tectonic discontinuities. Chemical and isotope analyses of dissolved carbon have revealed the existence of two sampling sites (NA and FE samples) attesting the interaction between groundwaters and a consistent amount of deep inorganic carbon dioxide.He isotope ratios (from 0.81Ra to 6.19 Ra) have revealed the occurrence of mixing process,in different proportions, between crustal and mantle components.On the base of the obtained results, a clear picture of the groundwaters circulation withinthe Hyblean aquifers has been drawn. In framework of projecting of a geochemical network for the continuous monitoring of the local seismic activity the most suitable geochemical parameters and the sites of great interest have been identified.