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181.
Pamphile?T.?RoyEmail authorView authors OrcID profile Nabil?El Mo?ayd Sophie?Ricci Jean-Christophe?Jouhaud Nicole?Goutal Matthias?De Lozzo Mélanie?C.?Rochoux 《Stochastic Environmental Research and Risk Assessment (SERRA)》2018,32(6):1723-1741
Data assimilation is widely used to improve flood forecasting capability, especially through parameter inference requiring statistical information on the uncertain input parameters (upstream discharge, friction coefficient) as well as on the variability of the water level and its sensitivity with respect to the inputs. For particle filter or ensemble Kalman filter, stochastically estimating probability density function and covariance matrices from a Monte Carlo random sampling requires a large ensemble of model evaluations, limiting their use in real-time application. To tackle this issue, fast surrogate models based on polynomial chaos and Gaussian process can be used to represent the spatially distributed water level in place of solving the shallow water equations. This study investigates the use of these surrogates to estimate probability density functions and covariance matrices at a reduced computational cost and without the loss of accuracy, in the perspective of ensemble-based data assimilation. This study focuses on 1-D steady state flow simulated with MASCARET over the Garonne River (South-West France). Results show that both surrogates feature similar performance to the Monte-Carlo random sampling, but for a much smaller computational budget; a few MASCARET simulations (on the order of 10–100) are sufficient to accurately retrieve covariance matrices and probability density functions all along the river, even where the flow dynamic is more complex due to heterogeneous bathymetry. This paves the way for the design of surrogate strategies suitable for representing unsteady open-channel flows in data assimilation. 相似文献
182.
Sophie A. Murray Jordan A. Guerra Pietro Zucca Sung-Hong Park Eoin P. Carley Peter T. Gallagher Nicole Vilmer Volker Bothmer 《Solar physics》2018,293(4):60
Coronal mass ejections (CMEs) and other solar eruptive phenomena can be physically linked by combining data from a multitude of ground-based and space-based instruments alongside models; however, this can be challenging for automated operational systems. The EU Framework Package 7 HELCATS project provides catalogues of CME observations and properties from the Heliospheric Imagers on board the two NASA/STEREO spacecraft in order to track the evolution of CMEs in the inner heliosphere. From the main HICAT catalogue of over 2,000 CME detections, an automated algorithm has been developed to connect the CMEs observed by STEREO to any corresponding solar flares and active-region (AR) sources on the solar surface. CME kinematic properties, such as speed and angular width, are compared with AR magnetic field properties, such as magnetic flux, area, and neutral line characteristics. The resulting LOWCAT catalogue is also compared to the extensive AR property database created by the EU Horizon 2020 FLARECAST project, which provides more complex magnetic field parameters derived from vector magnetograms. Initial statistical analysis has been undertaken on the new data to provide insight into the link between flare and CME events, and characteristics of eruptive ARs. Warning thresholds determined from analysis of the evolution of these parameters is shown to be a useful output for operational space weather purposes. Parameters of particular interest for further analysis include total unsigned flux, vertical current, and current helicity. The automated method developed to create the LOWCAT catalogue may also be useful for future efforts to develop operational CME forecasting. 相似文献
183.
Timothy M. Hahn Jr. Nicole G. Lunning Harry Y. McSween Jr. Robert J. Bodnar Lawrence A. Taylor 《Meteoritics & planetary science》2018,53(3):514-546
We describe petrographic, electron microprobe, and laser ablation ICP-MS analyses of Mg-rich harzburgite clasts in the Dominion Range 2010 howardites, and conclude that they are xenolithic samples of the vestan mantle. Key chemical and petrologic characteristics of these rocks provide tests for differentiation models. Our results indicate the mantle of Vesta formed through variable degrees of partial melting, which left behind a harzburgite and possibly dunite residuum. The Mg-rich clasts are composed of orthopyroxene and olivine, with minor clinopyroxene, FeNi metal, and distinctive pyroxene–chromite symplectites. We use mineral chemistry to demonstrate the absence of a genetic link between diogenites and the Mg-rich harzburgites. We propose a secondary origin for the formation of symplectites: interaction of silicate and metallic melts during primordial differentiation and core formation. The occurrence of FeNi metal containing ~1.5 wt% Cr within the assemblage indicates a very reducing environment during mantle differentiation (≪IW). Our study suggests that Vesta did not experience complete melting early in its history, and instead supports the formation of a shallow magma ocean. 相似文献
184.
185.
After the breeding season, Slavonian grebes (Podiceps auritus) leave their freshwater breeding habitats and migrate to wintering grounds in marine or brackish waters. The most important wintering area in northwestern Europe is located in the southern Baltic Sea, with the largest concentrations in the offshore area of the Pommeranian Bight. Analysis of ship-based surveys revealed that the habitat selection of Slavonian grebes in this brackish area is significantly influenced by water depth and bottom sediment type. The grebes prefer shallow waters of 4–14 m depth and occur only over sandy sediments. While the diving depths of endothermic animals is limited due to energetic constraints and thermoregulation, sediment type is regarded to be a proxy for food choice. The diet of Slavonian grebes in the Pomeranian Bight consists mainly of demersal gobies (Gobiidae) that frequently occur over sandy bottom substrates. 相似文献
186.
Caroline Aubry-Wake Lauren D. Somers Haley Alcock Aspen M. Anderson Amin Azarkhish Samuel Bansah Nicole M. Bell Kelly Biagi Mariana Castaneda-Gonzalez Olivier Champagne Anna Chesnokova Devin Coone Tasha-Leigh J. Gauthier Uttam Ghimire Nathan Glas Dylan M. Hrach Oi Yin Lai Pierrick Lamontagne-Hallé Nicolas R. Leroux Laura Lyon Sohom Mandal Bouchra R. Nasri Nataša Popović Tracy E. Rankin Kabir Rasouli Alexis Robinson Palash Sanyal Nadine J. Shatilla Brandon Van Huizen Sophie Wilkinson Jessica Williamson Majid Zaremehrjardy 《水文研究》2020,34(8):2001-2006
187.
This work investigates the spatial relation between coronal X-ray sources and coherent radio emissions, both generally thought to be signatures of particle acceleration. Two limb events were selected during which the radio emission was well correlated in time with hard X-rays. The radio emissions were of the type of decimetric pulsations as determined from the spectrogram observed by Phoenix-2 of ETH Zurich. The radio positions were measured from observations with the Nançay Radioheliograph between 236 and 432 MHz and compared to the position of the coronal X-ray source imaged with RHESSI. The radio pulsations originated at least 30?–?240 Mm above the coronal hard X-ray source. The altitude of the radio emission increases generally with lower frequency. The average positions at different frequencies are on a line pointing approximately to the coronal hard X-ray source. Thus, the pulsations cannot be caused by electrons trapped in the flare loops, but are consistent with emission from a current sheet above the coronal source. 相似文献
188.
Sophistication at a country pace: community sustainability and amenity-based development 总被引:1,自引:0,他引:1
Nicole Laliberte 《GeoJournal》2012,77(2):279-292
There is a lot at stake in the control of landscapes; not only rights and access to resources, but also the symbolic construction
of community identities. Having one’s identity represented in the landscape is critical to understanding one’s position within
that community—either as an insider or outsider. This paper examines Great Barrington, Massachusetts as a case study of the
links between discourses of landscape and community and their relations to processes of social exclusion during amenity-based
development. Building upon conceptions of community as a process of creating boundaries between insiders and outsiders, this
paper argues that the sustainability of a town cannot be assessed merely from inside a particular community identity but must
situate that town within complex multi-scalar processes to determine if it is merely externalizing its unsustainable aspects,
people and practices. I extend this argument by examining the ways to concept of multifunctionality has been used both in
Great Barrington and in international discourses to promote sustainability through processes of exclusion. The research for
this paper was done in collaboration with the Alliance for a Healthier Great Barrington. 相似文献
189.
Abstract Edge waves are known to give rise to beach cusps. This paper investigates the topographic feed-back upon the waves. For edge waves generated by subharmonic resonance with incident waves, the topography acts to decrease the edge wave response. As well as causing frequency detuning (Guza and Bowen, 1981) the topography can cause the scattering of edge wave energy. For synchronous waves the topographic irregularities have the opposite effect, and there can be a feed of energy into the edge waves by scattering from the incident waves. 相似文献
190.
Tom Akkermans Anton Van Rompaey Nicole Van Lipzig Pieter Moonen Bruno Verbist 《自然地理学》2013,34(6):417-440
State-of-the-art impact-modeling studies in environmental and climatological sciences require detailed future deforestation scenarios that allow forest to be replaced by a mosaic of multiple successional land-cover types, rather than the simple conversion of forest to a single land-cover type, such as bare soil or cropland. Therefore, not only the amount and location of forest removal has to be known (as is typically provided by scenarios), but also knowledge about the successional land-cover types and their relative areal proportions is needed. The main objective of this study was to identify these successional land-cover types and quantify their areal proportions in regions deforested during the past 37 years around the city of Kisangani, D.R. Congo. The fallow vegetation continuum was categorized in different stages, adapted from existing classifications. Ground-truth points describing the present-day vegetation were obtained during a field campaign and used for supervised and validated land-cover classification of these categories, using the Landsat image of 2012. Areal proportions of successional land-cover types were then derived from the resulting land-cover map. The second objective of this study was to relate these areal proportions to time since deforestation, which is expected to influence fallow landscapes. Landsat images of 1975, 1990, and 2001 were analyzed. Present-day mature tree fallow is less abundant on areas deforested during 1975–1990. The relative areal proportions were used to refine a deforestation scenario and apply it to existing data-sets of LAI and canopy height (CH). Assuming a simple conversion of forest to cropland, the deforestation scenario projected a reduction of grid-cell-averaged CH from 25.5 to 7.5 m (within deforested cells), whereas the refined scenarios that we propose show more subtle changes, with a reduced CH of 13 m. This illustrates the importance of taking successional land cover correctly into account in environmental and climatological modeling studies. 相似文献