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1.
Improvement of Nakamura technique by singular spectrum analysis 总被引:1,自引:1,他引:1
Roberto Carniel Fausto Barazza Paolo Pascolo 《Soil Dynamics and Earthquake Engineering》2006,26(1):55-63
In this work we investigate the application of the Singular Spectrum Analysis to improve Nakamura Technique. The SSA has a wide and multidisciplinary range of applications; it allows a time series to be decomposed into different components, e.g. the signal itself, as well as various noise components, which can be subsequently removed from the data. Removal of the minor component of the data can lead to significant improvements in the identification of the system. In this paper the use of SSA Technique allows to optimize the signal to noise ratio before computing the classical Nakamura spectral ratios. A number of typical applications are also presented. 相似文献
2.
Though ubiquitous in the global oceans, double diffusive mixing has been largely ignored or poorly represented in the models of turbulent mixing in the ocean and in 3-D ocean models, until recently. Salt fingers occur in the interior of many marginal seas and ocean basins, the Tyrrhenian Sea and the subtropical Atlantic being two examples. Diffusive convection type of double diffusion occurs in the upper layers of many sub-polar seas and polar oceans due to cold melt water from sea ice. Consequently, it is important to be able to properly parameterize double diffusive mixing in basin scale and global ocean models, so that the water mass structure in the interior of the ocean can be properly simulated. This note describes a model for double diffusive mixing in the presence of background shear, based on Mellor–Yamada type second moment closure, more specifically Kantha, 2003, Kantha and Clayson, 2004 second moment closure models of resulting turbulence, following Canuto et al. (2008a) but employing a different strategy for modeling the pertinent terms in the second moment equations. The resulting model is suitable for inclusion in ocean general circulation models. 相似文献
3.
Ezer Tal Carniel Sandro Amin Chabchoub de Camargo Ricardo Estrada-Allis Sheila N. Gao Guoping Greatbatch Richard J. Lermusiaux Pierre F. J. Liu Zhiyu Miyazawa Yasumasa Forster Alejandro Orfila Panickal Swapna Phillips Helen Pinones Andrea Stanev Emil Volker Christoph Xu Fanghua Young Emma 《Ocean Dynamics》2023,73(1):35-38
4.
Marta Tárraga Servando De La Cruz-Reyna Ana T. Mendoza-Rosas Roberto Carniel Alicia Martínez-Bringas Alicia García Ramon Ortiz 《Acta Geophysica》2012,60(3):664-681
The continuous background seismic activity contains information on the internal state of a volcanic system. Here, we report
the influence of major regional tectonic earthquakes (M > 5 in most cases) on such state, reflected as changes in the spectral and dynamical parameters of the volcano continuous
seismic data. Although changes do not always occur, analysis of five cases of earthquake-induced variations in the signals
recorded at Popocatépetl volcano in central México reveal significant fluctuations following the tectonic earthquakes. External
visible volcanic activity, such as small to moderate explosions and ash emissions, were related to those fluctuations. We
briefly discuss possible causes of the variations. We conclude that recognition of fluctuations in the dynamical parameters
in volcano monitoring seismic signals after tectonic earthquakes, even those located in the far field, hundreds of kilometers
away, may provide an additional criterion for eruption forecasting, and for decision making in the definition of volcanic
alert levels. 相似文献
5.
Roberto Carniel Marta Tárraga Fausto Barazza Alicia García 《Bulletin of Volcanology》2008,70(9):1113-1121
Continuous seismic noise is recorded in the volcanic island of Tenerife (Canary Islands, Spain). The origin of this noise,
strongly augmented by anthropogenic contamination, is still under debate. In this paper, we discuss the relationship between
this noise and the occurrence of local tectonic events in the same area. In particular, transitions are sought in the time
evolution of dynamic parameters computed on the seismic noise, and examples are shown where abrupt transitions may be associated
with the occurrence of tectonic events. These transitions provide further evidence of the existence of a natural origin for
at least part of the seismic noise, which is strongly contaminated—if not dominated—by anthropogenic sources. 相似文献
6.
Within the framework of activities of the EC funded Project ‘Processes of Vertical Exchange in Shelf Seas’ (PROVESS), the seasonal thermal behaviour during 1998 at a station in the North Sea has been investigated using COHERENS, a three-dimensional fully non-linear hydrodynamic model. Extensive hydrographic measurements were carried out at the Northern North Sea (NNS) station, located at (59°20′N, 1°E). The collected data are used to validate the model results, showing an acceptable agreement between modelled temperatures and those obtained from CTDs and moored thermistors. This is valid both for surface and bottom temperatures, while the mixed layer thickness appears to be underestimated. A series of 3-D runs, testing different turbulence schemes, an internal wave mixing (IWM) parameterisation and the sensitivity to an increase of the surface stress, have been performed with the aim of assessing the relative importance of the advective and mixing processes. The model comparisons mostly evidenced differences in the behaviour of the bottom layer temperature during the last part of the year, which may be due to advection processes. The adoption of an internal wave mixing parameterisation, though managing to reproduce a deeper thermocline, overestimates the mixing around the period of the thermocline breakdown. The run adopting a wind stress increased by 50% provides a better agreement between observed and modelled thermocline. This applies also for surface velocities when compared to Acoustic Doppler Current Profiler (ADCP) measurements, while the bottom ones appear slightly underestimated only in the U-component. The Northern North Sea site appears to be located close to a gyre induced by thermal fronts. Comparisons with nearby wind data measured by an oil rig and by the ships operating in the area seem to confirm that the wind forcing values adopted during the integration are underestimated. 相似文献
7.
A number of parameterisations for the simulation of mixing processes in the thermocline are compared and tested against the microstructure data of the PROVESS campaigns, conducted in the northern part of the North Sea during the autumn of 1998. The transport term in the turbulent kinetic energy equation is parameterised via the introduction of a third stability function Sk for turbulent energy diffusion. The formulations are compared with a simpler scheme based upon limiting conditions for turbulence variables. Improved results are obtained with a new form of Sk. The best agreement is, however, found with the simpler limiting scheme. This is explained in terms of a turbulence length scale theory for stably stratified turbulence. In agreement with previous laboratory and ocean data it is found that the ratios of the Thorpe and Kolmogorov scales to the Ozmidov length scale approach critical limiting values in the thermocline. The first of these conditions is satisfied when limiting conditions are implemented into the scheme, providing the necessary minimum value for the dissipation rate, whereas the schemes without limiting conditions fail to produce this critical ratio. The basic reason for this failure is that the Thorpe scale is overestimated, which is shown to be connected to an even larger overprediction of the dissipation rate of temperature variance. To investigate the impact of non-resolved advective processes and salinity stratification on the turbulence predictions, additional numerical experiments were conducted using a simple scheme for data assimilation. The best agreement is found again with the limiting scheme, which is able to make reasonable predictions for the dissipation rate without knowing the detailed shape of the mean stratification profile. It is shown that advective transport due to tidally and wind-driven motions has a non-negligible impact on vertical mixing. This is seen in the data and the models by periodic enhancements of turbulent mixing inside the thermocline. 相似文献
8.
Debora Bellafiore Edoardo Bucchignani Silvio Gualdi Sandro Carniel Vladimir Djurdjević Georg Umgiesser 《Ocean Dynamics》2012,62(4):555-568
Modeling studies of future changes in coastal hydrodynamics, in terms of storm surges and wave climate, need appropriate wind
and atmospheric forcings, a necessary requirement for the realistic reproduction of the statistics and the resolution of small
scale features. This work compares meteorological results from different climate models in the Mediterranean area, with a
focus on the Adriatic Sea, in order to assess their capability to reproduce coastal meteorological features and their possibility
to be used as forcings for hydrodynamic simulations. Five meteorological datasets are considered. They are obtained from two
regional climate models, implemented with different spatial resolutions and setups and are downscaled from two different global
climate models. Wind and atmospheric pressure fields are compared with measurements at four stations along the Italian Adriatic
coast. The analysis is carried out both on simulations of the control period 1960–1990 and on the A1B Intergovernmental Panel
for Climate Change scenario projections (2070–2100), highlighting the ability of each model in reproducing the statistical
coastal meteorological behavior and possible changes. The importance of simulated global- and regional-scale meteorological
processes, in terms of correct spatial resolution of the phenomena, is also discussed. Within the Adriatic Sea, the meteorological
climate is influenced by the local orography that controls the strengthening of north-eastern katabatic winds like Bora. Results
show indeed that the increase in spatial resolution provides a more realistic wind forcing for the hydrodynamic simulations.
Moreover, the chosen setup and the global climate models that drive the regional downscalings appear to play an important
role in reproducing correct atmospheric pressure fields. The comparison between scenario and control simulations shows a small
increase in the mean atmospheric pressure values, while a decrease in mean wind speed and in extreme wind events is observed,
particularly for the datasets with higher spatial resolution. Finally, results suggest that an ensemble of downscaled climate
models is likely to provide the most suitable climatic forcings (wind and atmospheric pressure fields) for coastal hydrodynamic
modeling. 相似文献
9.
Moritz Beyreuther Roberto Carniel Joachim Wassermann 《Journal of Volcanology and Geothermal Research》2008
A possible interaction of (volcano-) tectonic earthquakes with the continuous seismic noise recorded in the volcanic island of Tenerife was recently suggested. Also recently the zone close to Las Canadas caldera shows unusual high number of near (< 25 km), possibly volcano-tectonic, earthquakes indicating signs of reawakening of the volcano putting high pressure on the risk analyst. Certainly for both tasks consistent earthquake catalogues provide valuable information and thus there is a strong demand for automatic detection and classification methodologies generating such catalogues. Therefore we adopt methodologies of speech recognition where statistical models, called Hidden Markov Models (HMMs), are widely used for spotting words in continuous audio data. In this study HMMs are used to detect and classify volcano-tectonic and/or tectonic earthquakes in continuous seismic data. Further the HMM detection and classification is evaluated and discussed for a one month period of continuous seismic data at a single seismic station. Being a stochastic process, HMMs provide the possibility to add a confidence measure to each classification made, basically evaluating how “sure” the algorithm is when classifying a certain earthquake. Moreover, this provides helpful information for the seismological analyst when cataloguing earthquakes. Combined with the confidence measure the HMM detection and classification can provide precise enough earthquake statistics, both for further evidence on the interaction between seismic noise and (volcano-) tectonic earthquakes as well as for incorporation in an automatic early warning system. 相似文献
10.
Francesco Barbariol Jose-Henrique G. M. Alves Alvise Benetazzo Filippo Bergamasco Luciana Bertotti Sandro Carniel Luigi Cavaleri Yung Y. Chao Arun Chawla Antonio Ricchi Mauro Sclavo Hendrik Tolman 《Ocean Dynamics》2017,67(3-4):535-549
A novel implementation of parameters estimating the space-time wave extremes within the spectral wave model WAVEWATCH III (WW3) is presented. The new output parameters, available in WW3 version 5.16, rely on the theoretical model of Fedele (J Phys Oceanogr 42(9):1601-1615, 2012) extended by Benetazzo et al. (J Phys Oceanogr 45(9):2261–2275, 2015) to estimate the maximum second-order nonlinear crest height over a given space-time region. In order to assess the wave height associated to the maximum crest height and the maximum wave height (generally different in a broad-band stormy sea state), the linear quasi-determinism theory of Boccotti (2000) is considered. The new WW3 implementation is tested by simulating sea states and space-time extremes over the Mediterranean Sea (forced by the wind fields produced by the COSMO-ME atmospheric model). Model simulations are compared to space-time wave maxima observed on March 10th, 2014, in the northern Adriatic Sea (Italy), by a stereo camera system installed on-board the “Acqua Alta” oceanographic tower. Results show that modeled space-time extremes are in general agreement with observations. Differences are mostly ascribed to the accuracy of the wind forcing and, to a lesser extent, to the approximations introduced in the space-time extremes parameterizations. Model estimates are expected to be even more accurate over areas larger than the mean wavelength (for instance, the model grid size). 相似文献