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1.
Odim Mendes Jr. Aracy Mendes da Costa Fernando Celso Perin Bertoni 《Journal of Atmospheric and Solar》2006,68(18):2127-2137
For at least 30 years now it has been well known that the Dst index can be modelled using the solar wind as input. Since then, many attempts have been made to improve the predictability of Dst using different approaches. These attempts are useful, for instance, to understand which features of the solar wind–magnetosphere interactions are most important in producing magnetospheric activity and how the Dst index would improve the space weather forecast. The Dst index is by far the most reliable and simple indication that a magnetic storm is in progress. In this work, the effect of using more than four magnetic stations and shorter time intervals than the hourly averages used in Sugiura's procedures is evaluated. The discussion is based on the results presented by Burton in 1975 and Feldstein in 1984 considering 4 or 12 magnetic stations and time averages of 2.5 min for a magnetic disturbed period that occurred from February 7–28, 1967, including two geomagnetic storms. The analysis has shown that the global representation of a magnetic storm by the standard Dst (Sugiura) is well preserved either using 4, 6, 12 magnetic stations or using 1 h, 2.5 min 1 min averages. A brief review of the current understanding of Dst has been included to support the discussions. The analysis performed has shown that a more refined Dst index (time and number of stations>4) would be useful to investigate the intrinsic processes and the different current systems involved in the ring current development during magnetic storms; the standard Dst, as it is conceived, is quite adequate to monitor geomagnetic storms and identify their overall features; concerning the magnetic stations normally considered, the inclusion of higher magnetic latitude stations (>35) may underestimate the observed Dst. 相似文献
2.
R.R.S. De Mendonça J.-P. Raulin F.C.P. Bertoni E. Echer V.S. Makhmutov G. Fernandez 《Journal of Atmospheric and Solar》2011,73(11-12):1410-1416
We present results obtained at El Leoncito (CASLEO, San Juan, Argentina) with the CARPET charged particles detector installed in April 2006. The observed modulation of the cosmic ray flux is discussed as a function of its time variability and it is related to longer solar activity variations and to shorter variations during solar and geomagnetic transient activity. Short period (few minutes, few hours) cosmic ray modulation events are observed during rain time (precipitation) and significant variations of the atmospheric electric field. Complementary observations of the atmospheric electric field indicate that its time variations play an important role in the detected cosmic ray event. 相似文献
3.
Roberto Bertoni Wade H. Jeffrey Mireille Pujo-Pay Louise Oriol Pascal Conan Fabien Joux 《Aquatic Sciences - Research Across Boundaries》2011,73(3):377-387
The scaling of the solar ultraviolet radiation (UVR, 280–400 nm) effect on phyto- and bacterio-plankton at the ecosystem level
is difficult since its estimate is often based on short-time incubation experiments performed at fixed depths, neglecting
the previous days’ radiation history and the variable radiation caused by vertical mixing. To examine this issue, we measured
primary (PP) and bacterial (BP) production in samples from coastal water in the Northwest Mediterranean Sea incubated at fixed
depths or moving vertically within the water column (0–8 m) with a periodicity of 22 min, exposed to full sun, PAR or maintained
in dark. Three experiments were carried out on consecutive days to measure day-to-day variations in planktonic response. In
surface waters, PP was inhibited by ~32 to 42% by UVR, and BP was inhibited by ~50 to 70% by solar radiation (UVR + PAR).
We observed a general decrease in the integrated inhibition of PP due to UVR for both fixed and moving incubations over the
3 days from ~27% of inhibition to non-significant inhibition. In contrast, large discrepancies were observed in the integrated
inhibition of BP due to solar radiation (UVR + PAR) between fixed and moving incubations. Whereas both type of incubations
gave similar estimation of solar radiation inhibition on day 1 (~25%), inhibition became much higher for fixed incubation
compared to moving incubation on days 2 and 3. Differences in responses between days suggest that light history, spectral
quality, photoadaptation or acclimation may be important factors in daily observed responses. Our results also underline,
for the first time, the importance of the vertical mixing in the BP inhibition by solar radiation. 相似文献
4.
On the displacement of marked pebbles on two coarse-clastic beaches during short fair-weather periods (Marina di Pisa and Portonovo, Italy) 总被引：1，自引：1，他引：0
Duccio Bertoni Edoardo Grottoli Paolo Ciavola Giovanni Sarti Giuliano Benelli Alessandro Pozzebon 《Geo-Marine Letters》2013,33(6):463-476
The aim of the investigation was to define the mechanisms of sediment transport in the swash zone of microtidal coarse-clastic beaches in the very short term by evaluating the displacement rates of marked pebbles under low-energy wave conditions. Tests were performed at two sites (Marina di Pisa, Ligurian Sea, and Portonovo, central Adriatic Sea) to check the consistency of the data over a range of different grain sizes. Two recovery campaigns were carried out at both sites, one 6 h and the other 24 h after the injection. During the experiments wave action was at a minimum (wave heights never exceeded 0.3 m). The results show that 20% of pebbles ranging in diameter from 30–90 mm moved significantly (more than 0.5 m) already 6 h after the injection, with some tracers being lost (3%). After 24 h, 40% of the pebbles were significantly displaced and 10% were lost. The preferential downslope movement of tracers, which suggests that coarse sediment movement under low-energy conditions is mainly controlled by gravity processes enhanced by steep beachface slopes, represents the novelty of the results reported here. It would appear that swash processes on low-energy beaches cause a significant rate of pebble displacement through the destabilization induced by wave uprush and backwash. Despite the microtidal range, the position of the mean water level plays a major role in changing the beach level at which swash processes can actually trigger pebble movement. The results of this study show that considerable, and mostly seaward-directed, coarse sediment transport takes place even during short fair-weather periods. 相似文献
5.
6.
Major erosion at the end of the Messinian Salinity Crisis: evidence from the Levant Basin, Eastern Mediterranean 总被引：1，自引：0，他引：1
This paper presents a detailed analysis of the top of the Messinian evaporites (Horizon M) in the Levant region, offshore Israel, based on the integration of three‐dimensional (3D)/2D seismic and well data. 3D mapping of a series of intra‐evaporite horizons and their termination against Horizon M provides new insights into the depositional setting and structural evolution of this saline giant system. New evidence of a discordant relationship between the intra‐evaporite horizons and the top of the Messinian evaporites (Horizon M) is given by the seismic stratigraphic analysis. This confirms that the top of the Messinian evaporites represents an erosional unconformity of semiregional extent in the Levant region. The truncation of the folded and faulted intra‐evaporite horizons indicates for the first time a Messinian phase of evaporite deformation, i.e. pre‐dating the well‐documented Plio‐Pleistocene thin‐skinned tectonic phase in the region. This major erosional unconformity is interpreted as subaerial in origin, documenting the exposure of the evaporitic system at the end of the Messinian Salinity Crisis. These results give new evidence for the understanding of the events occurring during the last stages of the Messinian Salinity Crisis in the region. 相似文献
7.
Oil and gas exploration data for the Northern Somalia and Horn of Africa region have been utilised for deep freshwater resources exploration. This unique geophysical and petrophysical dataset is integrated into a regional hydrogeological study and it allows for targeting of unmapped and unknown deep aquifers that would otherwise be beyond the conventional reach of the groundwater sector. The database includes open-hole well logging surveys (resistivity, gamma ray, and spontaneous potential), mud logging and drill stem test (DST) data. The results from the data analysis are combined with the geological interpretation to assess the freshwater potential of each mapped hydrostratigraphic unit in the region. The results highlight the presence of several previously unknown deep low-to-medium salinity (<9 g/L total dissolved solids (TDS)) aquifers within the Jurassic to Eocene units, including the Adigrat, Hamanlei, Gabredarre, Gumburo, Jessoma, and Auradu formations. With tested intervals of water containing less than 3.8 g/L total dissolved solids, the Auradu, Jessoma, and Gumburo formations are the most promising deep freshwater aquifers. Additional results on the analysis of groundwater parameters, such as hydraulic head, provide the basis for further groundwater modelling. The results show that the method has good potential, in particular for use in drought-stricken areas of arid regions. Ultimately, the results from this region have global significance, as the method can provide a new means of boosting fresh groundwater resources in water-poor regions, and supporting sustainable development and utilization of the resources in the medium and long term.
相似文献8.
A century of land subsidence in Ravenna, Italy 总被引：4，自引：2，他引：4
P. Teatini M. Ferronato G. Gambolati W. Bertoni M. Gonella 《Environmental Geology》2005,47(6):831-846
Over the last century the Ravenna area has been affected by a widespread land subsidence process of both natural and anthropogenic origin which has become a matter of increasingly great concern. Land settlement, initially of the order of a few mm/year, dramatically increased up to 110 mm/year after World War II primarily due to groundwater pumping and, subordinately, gas production from a number of deep on-shore and off-shore reservoirs. Spirit leveling was carried out in the area of the Ravenna Municipality by various authorities and agencies ever since the end of the nineteenth century using an increasingly refined network of benchmarks. The available information, spanning the time interval from 1897 to 2002, has been implemented and homogenized into a Geographic Information System (GIS). Measurements processed by kriging provide the pattern of the subsidence rates over the municipal territory during eight sub-periods. The reliability of data processing is discussed for both magnitude and areal distribution of the occurrence, showing a pronounced nonlinear behavior in time, as related to the major responsible factors. Cumulative land subsidence approaches almost 1 m over more than one third of the municipality area including the city and a significant fraction of the coastland, with peaks larger than 1.5 m over a 10 km2 zone located between the historical center and the coastline. Most recent records show that at present the mainland appears to be substantially stable, whereas some coastal areas are still subsiding at a rate of about 10 mm/year with a significant threat to the environment and the infrastructures as well, although to a lesser extent than in the past decades. 相似文献
9.
This paper documents the importance of three‐dimensional (3D) seismic data for integrated stratigraphic–morphological analysis of slope systems. Furthermore, it contributes to the general understanding of the evolutionary mechanisms of slope‐confined submarine canyons on continental margins and their significance in a sequence stratigraphic framework. Recently acquired 3D seismic data from the Ebro Continental Margin (Western Mediterranean) have been used to study a series of remarkably well‐imaged submarine canyons in the Plio‐Pleistocene succession. Detailed mapping shows that these canyons are restricted to the slope, and thus can be compared with slope‐confined canyons observed on the present day seabed of many continental margins. The slope‐confined canyons are typically 0.5–2 km wide, 10–15 km long, and incise more than 50 m into the slope units. Their most striking characteristic is an upslope branching geometry in the head region involving up to three orders of bifurcation, with downslope development of a single incisional axis. The submarine canyons are characterized by a nested stacking pattern, undergoing alternating phases of cutting and filling. Limited parts of the upper and middle slope remain outside the canyon system, confined in sharp depositional ridges. The canyons are observed on closely spaced surfaces and exhibit a geometry that allowed the construction and discussion of a local sequence stratigraphic model for their evolution. In general, active incision of the canyons is observed at times throughout almost the entire cycle of base‐level change. However, erosional activity is more significant during the later stages of the relative sea level rise and the entire falling stage, with the timing of maximum erosion observed at the end of the cycle. The minimum erosional activity of the canyons is linked instead to the earliest part of the relative sea level rise. 相似文献
10.
Magda A. S. Duro Pierre Kaufmann Fernando C. P. Bertoni Emilio C. N. Rodrigues José Pissolato Filho 《Surveys in Geophysics》2012,33(5):973-989
High-voltage transmission networks represent a large electrical circuit just above the ground subjected to a number of transient overcharges of various kinds, some of which may lead to failures. Some failures might be related to anomalies of the geophysical environment. We have analyzed one unprecedented long series of transmission grid failures (9?years) on high-voltage networks located in S?o Paulo state, southeastern Brazil, from 1998 to 2006, which includes an important fraction of the past solar activity cycle 23. Ninety-five distinct failure causes were given by the power line operator to explain the transmission grid shut downs. Most failures were attributed to atmospheric discharges, corresponding to 1,957 failures out of a total of 4,572 for the whole period at 138?kV, and 170 out of 763 at 440?kV, respectively. They correspond to less than one ten thousandth of the actual number of atmospheric discharges recorded in the same area, demonstrating the grid’s high resilience to breakdowns due to lightning. A clear concentration of failures in the region’s thunderstorm season has been found. A significant 67 and 77?% reduction in the number of failure rates per year has been found for the 138 and 440?kV grids, respectively, for the period studied, in good correspondence with the decay in the sunspot numbers. No obvious correlation was found between power failures and the planetary index of geomagnetic activity or major geomagnetic storms in the period, either on short or on long time scales. Assuming that the dependence of the electrosphere/ionosphere-ground coupling on the external geophysical environment plays a major role in explaining the reduction in power failures as the solar cycle wanes, it is suggested that the increase in atmosphere conductivity caused by the larger cosmic ray flux then reduces the threshold voltage required to produce lightning strokes, so reducing their effectiveness in disrupting high-voltage power lines. 相似文献