Analysis of the impulsive phase of a solar flare at submillimeter wavelengths     

Raulin  Jean Pierre  Makhmutov  Vladimir S.  Kaufmann  Pierre  Pacini  Alessandra Abe  Lüthi  Thomas  Hudson  Hugh S.  Gary  Dale E. 《Solar physics》2004,223(1-2):181-199

We present a report on the strong X5.3 solar flare which occurred on 25 August 2001, producing high-level γ-ray activity, nuclear lines and a dramatic long-duration white-light continuum. The bulk of millimeter radio fluxes reached a peak of ∼100 000 solar flux units at 89.4 GHz, and a few thousands of solar flux units were detected in the submillimeter range during the impulsive phase. In this paper we focus on and discuss (i) the implications inferred from high frequency radio observations during the impulsive phase; (ii) the dynamics of the low corona active region during the impulsive phase. In particular we found that 4–5 × 10³⁶ accelerated (>20 keV) electrons s⁻¹ radiating in a 1000–1100 G region, are needed to explain the millimeter to submillimeter-wave emissions. We present evidence that the magnetic field in the active region was very dynamic, and that strong non-thermal processes were triggered by the appearance of new, compact, low-lying (few thousand kilometers) loop systems, suggesting the acceleration site(s) were also located in the low solar atmosphere.  相似文献   

Analysis of the impulsive phase of a solar flare at submillimeter wavelengths     

Jean Pierre Raulin  Vladimir S. Makhmutov  Pierre Kaufmann  Alessandra Abe Pacini  Thomas Lüthi  Hugh S. Hudson  Dale E. Gary 《Solar physics》2004,223(1):181-199

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A simple mechanism for the climatological midsummer drought along the Pacific coast of Central America     

K.B. Karnauskas  R. Seager  A. Giannini  A.J. Busalacchi 《Atmósfera》2013,26(2):261-281

The global distribution, seasonal evolution, and underlying mechanisms for the climatological midsummer drought (MSD) are investigated using a suite of relatively high spatial and temporal resolution station observations and reanalysis data with particular focus on the Pacific coast of Central America and southern Mexico. Although the MSD of Central America stands out in terms of spatial scale and coherence, it is neither unique to the Greater Caribbean Region (GCR) nor necessarily the strongest MSD on Earth based on an objective analysis of several global precipitation data sets. A mechanism for the MSD is proposed that relates the latitudinal dependence of the two climatological precipitation maxima to the biannual crossing of the solar declination (SD), driving two peaks in convective instability and hence rainfall. In addition to this underlying local mechanism, a number of remote processes tend to peak during the apex of the MSD, including the North American monsoon, the Caribbean low-level jet, and the North Atlantic subtropical high which may also act to suppress rainfall along the Pacific coast of Central America and generate interannual variability in the strength or timing of the MSD. However, our findings challenge the existing paradigm that the MSD owes its existence to a precipitation-suppressing mechanism. Rather, aided by the analysis of higher-temporal resolution precipitation records and considering variations in latitude, we suggest the MSD is essentially the result of one precipitation-enhancing mechanism occurring twice.  相似文献   

Aftershock risk assessment and the decision to open traffic on bridges     

S. Alessandri  R. Giannini  F. Paolacci 《地震工程与结构动力学》2013,42(15):2255-2275

Critical issues in emergency management after a seismic event are assessing the functionality of the main infrastructures (hospitals, road network, etc.) and deciding on their usability just after the mainshock. The use of a pure analytical tool to assess the aftershock risk of a structure can be contrasted with the limited time available to make a decision about the usability of a structure. For this reason, this paper presents a method for evaluating post‐earthquake bridge practicability based on a rational combination of information derived from numerical analyses and in situ inspections. In particular, we propose an effective tool to speed up the decision‐making process involved in evaluating the seismic risk of mainshock‐damaged bridges in the context of aftershocks. The risk is calculated by combining the aftershock hazard using the Omori law and the fragility curves of the structure, which are calculated using the regression analysis of a sample of results obtained with data randomly generated by the Latin Hypercube Sampling technique and updated based on the results of in situ inspection. Different decision criteria regarding the practicability of bridges are discussed, and a new criterion is proposed. This tool was applied to an old highway RC viaduct. There are two main findings, including the high sensitivity to Bayesian updating (especially when the damage predicted by numerical analysis does not match the real damage) and the criteria used to decide when re‐open bridges to traffic. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Explosion craters associated with shallow submarine gas venting off Panarea island, Italy     

Thomas Monecke  Sven Petersen  Mark D. Hannington  Marco Anzidei  Alessandra Esposito  Guido Giordano  Dieter Garbe-Sch?nberg  Nico Augustin  Bernd Melchert  Mike Hocking 《Bulletin of Volcanology》2012,74(9):1937-1944

Explosions of hot water, steam, and gas are common periodic events of subaerial geothermal systems. These highly destructive events may cause loss of life and substantial damage to infrastructure, especially in densely populated areas and where geothermal systems are actively exploited for energy. We report on the occurrence of a large number of explosion craters associated with the offshore venting of gas and thermal waters at the volcanic island of Panarea, Italy, demonstrating that violent explosions similar to those observed on land also are common in the shallow submarine environment. With diameters ranging from 5 to over 100?m, the observed circular seafloor depressions record a history of major gas explosions caused by frequent perturbation of the submarine geothermal system over the past 10,000?years. Estimates of the total gas flux indicate that the Panarea geothermal system released over 70?Mt of CO₂ over this period of time, suggesting that CO₂ venting at submerged arc volcanoes contributes significantly to the global atmospheric budget of this greenhouse gas. The findings at Panarea highlight that shallow submarine gas explosions represent a previously unrecognized volcanic hazard around populated volcanic islands that needs to be taken into account in the development of risk management strategies.  相似文献   

Seismic reliability of V‐braced frames: Influence of design methodologies     

Alessandra Longo  Rosario Montuori  Vincenzo Piluso 《地震工程与结构动力学》2009,38(14):1587-1608

According to the most modern trend, performance‐based seismic design is aimed at the evaluation of the seismic structural reliability defined as the mean annual frequency (MAF) of exceeding a threshold level of damage, i.e. a limit state. The methodology for the evaluation of the MAF of exceeding a limit state is herein applied with reference to concentrically ‘V’‐braced steel frames designed according to different criteria. In particular, two design approaches are examined. The first approach corresponds to the provisions suggested by Eurocode 8 (prEN 1998—Eurocode 8: design of structures for earthquake resistance. Part 1: general rules, seismic actions and rules for buildings), while the second approach is based on a rigorous application of capacity design criteria aiming at the control of the failure mode (J. Earthquake Eng. 2008; 12 :1246–1266; J. Earthquake Eng. 2008; 12 :728–759). The aim of the presented work is to focus on the seismic reliability obtained through these design methodologies. The probabilistic performance evaluation is based on an appropriate combination of probabilistic seismic hazard analysis, probabilistic seismic demand analysis (PSDA) and probabilistic seismic capacity analysis. Regarding PSDA, nonlinear dynamic analyses have been carried out in order to obtain the parameters describing the probability distribution laws of demand, conditioned to given values of the earthquake intensity measure. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Morphologic and sedimentologic patterns of active aeolian dune‐fields on the east coast of Maranhão,northeast Brazil          下载免费PDF全文

Natalia Naches Hilbert  Carlos C. F. Guedes  Paulo C. F. Giannini 《地球表面变化过程与地形》2016,41(1):87-97

The eastern portion of the Maranhão coast is characterized by large active dune‐fields located in a tropical setting. This article combines the analysis of dune‐field morphologic patterns with the classical analysis of grain size and heavy minerals to study the sedimentary dynamics of the active aeolian system in this region. Based on the heavy mineral analysis, the main sedimentary suppliers feeding the system are the westward alongshore drift bringing sand from the coast east of the Parnaíba River mouth and the river itself. The absence of well‐defined variation patterns of the two morphometric parameters studied, dune spacing and crest length, reflects complex sedimentary dynamics and transport pathways, inside the aeolian system, despite the unidirectional wind. During the wet season, the interdune plains are flooded and the system is intensely reworked by intermittent drainages. During the dry season, the deposits formed by the drainages and interdune lakes become temporary internal sedimentary sources for the system. Due to this combined aeolian‐fluvial transport, the sediment source area has a planar geometry, with contributions from the beach and interdune plains, and not linear as expected in a typical case of source only in the beach. The areal limits of the dune‐fields is the main boundary condition controlling the dune‐field patterns, as dune spacing and crest length, by changing the sedimentary inflow–outflow balance and interactions between migration dunes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Effects of vegetation on flow and sediment transport: comparative analyses and validation of predicting models   总被引：1，自引：0，他引：1       下载免费PDF全文

Andrés Vargas‐Luna  Alessandra Crosato  Wim S.J. Uijttewaal 《地球表面变化过程与地形》2015,40(2):157-176

The presence of vegetation modifies flow and sediment transport in alluvial channels and hence the morphological evolution of river systems. Plants increase the local roughness, modify flow patterns and provide additional drag, decreasing the bed‐shear stress and enhancing local sediment deposition. For this, it is important to take into account the presence of vegetation in morphodynamic modelling. Models describing the effects of vegetation on water flow and sediment transport already exist, but comparative analyses and validations on extensive datasets are still lacking. In order to provide practical information for modelling purposes, we analysed the performance of a large number of models on flow resistance, vegetation drag, vertical velocity profiles and bed‐shear stresses in vegetated channels. Their assessments and applicability ranges are derived by comparing their predictions with measured values from a large dataset for different types of submerged and emergent vegetation gathered from the literature. The work includes assessing the performance of the sediment transport capacity formulae of Engelund and Hansen and van Rijn in the case of vegetated beds, as well as the value of the drag coefficient to be used for different types of vegetation and hydraulic conditions. The results provide a unique comparative overview of existing models for the assessment of the effects of vegetation on morphodynamics, highlighting their performances and applicability ranges. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Linear time history analysis for the out-of-plane seismic demand of infill walls in RC framed buildings     

Alessandra De Angelis  Marisa Pecce  Fernando Rossi 《Bulletin of Earthquake Engineering》2015,13(11):3325-3352

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Thermal segmentation along the N. Ecuador–S. Colombia margin (1–4°N): Prominent influence of sedimentation rate in the trench     

Boris Marcaillou  George Spence  Kelin Wang  Jean-Yves Collot  Alessandra Ribodetti 《Earth and Planetary Science Letters》2008,272(1-2):296-308

Along the deformation front of the North Ecuador–South Colombia (NESC) margin, both surface heat flow and trench sediment thickness show prominent along-strike variations, indicating significant spatial variations in sedimentation rate. Investigating these variations helps us address the important question of how trench sedimentation influences the temperature distribution along the interplate contact and the extent of the megathrust seismogenic zone. We examine this issue by analysing 1/ a new dense reflection data set, 2/ pre-stack depth migration of selected multichannel seismic reflection lines, 3/ numerous newly-identified bottom-simulating reflectors and 4/ the first heat probe measurements in the region. We develop thermal models that include sediment deposition and compaction on the cooling oceanic plate as well as viscous corner flow in the mantle wedge. We estimate that the temperature from 60–150 °C to 350–450 °C, commonly associated with the updip and downdip limits of the seismogenic zone, extends along the plate interface over a downdip distance of 160 to 190 ± 20 km. We conclude that the updip limit of the seismogenic zone for the great megathrust earthquake of 1979 is associated with low-temperature (60–70 °C) processes. Our models also suggest that 60–70% of the two-fold decrease in measured heat flow from 3°N to 2.8°N is related to an abrupt southward increase in sedimentation rate in the trench. Such a change may potentially induce a landward shift of the 60–150 °C isotherms, and thus the updip limit of the seismogenic zone, by 10 to 20 km.  相似文献