Articles de revista
http://hdl.handle.net/2117/1087
Tue, 21 Nov 2017 04:52:55 GMT2017-11-21T04:52:55ZNonsingular black holes, the cosmological constant, and asymptotic safety
http://hdl.handle.net/2117/109691
Nonsingular black holes, the cosmological constant, and asymptotic safety
Torres Herrera, Ramon
Quantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.
Fri, 03 Nov 2017 08:37:15 GMThttp://hdl.handle.net/2117/1096912017-11-03T08:37:15ZTorres Herrera, RamonQuantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.Meteodiversity: a new concept for quantifying meteorological diversity
http://hdl.handle.net/2117/109263
Meteodiversity: a new concept for quantifying meteorological diversity
Mazón Bueso, Jordi; Pino González, David
Inspired by the concept of biodiversity used by biologists and ecologists, the concept of meteodiversity is proposed as a method of characterising the variety of meteorological phenomena in a defined area within a specified period. Similarly to the term biodiversity, meteodiversity takes into account the proportion of individual meteorological phenomena belonging to the main weather that occur in a defined area. The benefits and importance of using this concept are discussed.
For quantification purposes, we propose a meteodiversity index, which, in addition to events and phenomena, should include a large number of atmospheric variables obtained from instrumental and observational records. This index itemises not only events ans phenomena, but also a large number of atmospheric variables obtained from instrumental and observational records.
We use climatic data obtained from the Met Office and European Climate Assessment and Dataset project to evaluate the meteodiversity index, first on a monthly scale for the period 1981–2014 at Llanfairpwllgwyngyll (UK), and then on an annual scale for 1962–2014 at Barcelona (Spain) and Helsinki (Finland). The weather diversity and the trends over these cities have been analyzed.
This is the peer reviewed version of the following article: Mazon, J., Pino, D. Meteodiversity: a new concept for quantifying meteorological diversity. "Weather", 10 Maig 2017, vol. 72, núm. 5, p. 143-145., which has been published in final form at http://onlinelibrary.wiley.com/wol1/doi/10.1002/wea.2945/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Thu, 26 Oct 2017 12:18:55 GMThttp://hdl.handle.net/2117/1092632017-10-26T12:18:55ZMazón Bueso, JordiPino González, DavidInspired by the concept of biodiversity used by biologists and ecologists, the concept of meteodiversity is proposed as a method of characterising the variety of meteorological phenomena in a defined area within a specified period. Similarly to the term biodiversity, meteodiversity takes into account the proportion of individual meteorological phenomena belonging to the main weather that occur in a defined area. The benefits and importance of using this concept are discussed.
For quantification purposes, we propose a meteodiversity index, which, in addition to events and phenomena, should include a large number of atmospheric variables obtained from instrumental and observational records. This index itemises not only events ans phenomena, but also a large number of atmospheric variables obtained from instrumental and observational records.
We use climatic data obtained from the Met Office and European Climate Assessment and Dataset project to evaluate the meteodiversity index, first on a monthly scale for the period 1981–2014 at Llanfairpwllgwyngyll (UK), and then on an annual scale for 1962–2014 at Barcelona (Spain) and Helsinki (Finland). The weather diversity and the trends over these cities have been analyzed.Self-organized kilometer-scale shoreline sand wave generation: sensitivity to model and physical parameters
http://hdl.handle.net/2117/108666
Self-organized kilometer-scale shoreline sand wave generation: sensitivity to model and physical parameters
Idier, Déborah; Falqués Serra, Albert; Rohmer, Jérémy; Arriaga García, Jaime Alonso
The instability mechanisms for self-organized kilometer-scale shoreline sand waves have been extensively explored by modeling. However, while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves, its effect on the instability onset has not been explored. In addition, no systematic investigation of the effect of the physical parameters has been done yet. Using a linear stability model, we investigate the effect of wave conditions, cross-shore profile, closure depth, and two perturbation shapes (P1: cross-shore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 40-50°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for low-angle waves. In fact, the bathymetric perturbation shape plays a key role in low-angle wave instability: such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one. This can occur for the P2 perturbation but not for P1. The analysis of bathymetric data suggests that both curvature configurations could exist in nature. For both perturbation types, large wave angle, small wave period, and large closure depth strongly favor instability. The cross-shore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low-angle waves for a P2 perturbation. Finally, predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to ¿c0 or low-angle wave instability.
Wed, 11 Oct 2017 16:39:52 GMThttp://hdl.handle.net/2117/1086662017-10-11T16:39:52ZIdier, DéborahFalqués Serra, AlbertRohmer, JérémyArriaga García, Jaime AlonsoThe instability mechanisms for self-organized kilometer-scale shoreline sand waves have been extensively explored by modeling. However, while the assumed bathymetric perturbation associated with the sand wave controls the feedback between morphology and waves, its effect on the instability onset has not been explored. In addition, no systematic investigation of the effect of the physical parameters has been done yet. Using a linear stability model, we investigate the effect of wave conditions, cross-shore profile, closure depth, and two perturbation shapes (P1: cross-shore bathymetric profile shift, and P2: bed level perturbation linearly decreasing offshore). For a P1 perturbation, no instability occurs below an absolute critical angle ¿c0˜ 40-50°. For a P2 perturbation, there is no absolute critical angle: sand waves can develop also for low-angle waves. In fact, the bathymetric perturbation shape plays a key role in low-angle wave instability: such instability only develops if the curvature of the depth contours offshore the breaking zone is larger than the shoreline one. This can occur for the P2 perturbation but not for P1. The analysis of bathymetric data suggests that both curvature configurations could exist in nature. For both perturbation types, large wave angle, small wave period, and large closure depth strongly favor instability. The cross-shore profile has almost no effect with a P1 perturbation, whereas large surf zone slope and gently sloping shoreface strongly enhance instability under low-angle waves for a P2 perturbation. Finally, predictive statistical models are set up to identify sites prone to exhibit either a critical angle close to ¿c0 or low-angle wave instability.Modeling the long-term diffusion and feeding capability of a mega-nourishment
http://hdl.handle.net/2117/108377
Modeling the long-term diffusion and feeding capability of a mega-nourishment
Arriaga García, Jaime Alonso; Rutten, Jantien; Ribas Prats, Francesca; Falqués Serra, Albert; Ruessink, Gerben
A morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandniotor mega-nourishment on the Dutch Delfiand coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow Migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m(2)/s, close to the observed value of 0.0022 m(2)/s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m(2)/s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches prodtices 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold.
Thu, 05 Oct 2017 12:41:58 GMThttp://hdl.handle.net/2117/1083772017-10-05T12:41:58ZArriaga García, Jaime AlonsoRutten, JantienRibas Prats, FrancescaFalqués Serra, AlbertRuessink, GerbenA morphodynamic model based on the wave-driven alongshore sediment transport, including cross-shore transport in a simplified way and neglecting tides, is presented and applied to the Zandniotor mega-nourishment on the Dutch Delfiand coast. The model is calibrated with the bathymetric data surveyed from January 2012 to March 2013 using measured offshore wave forcing. The calibrated model reproduces accurately the surveyed evolution of the shoreline and depth contours until March 2015. According to the long-term modeling using different wave climate scenarios based on historical data, for the next 30-yr period, the Zandmotor will display diffusive behavior, asymmetric feeding to the adjacent beaches, and slow Migration to the NE. Specifically, the Zandmotor amplitude will have decayed from 960 m to about 350 m with a scatter of only about 40 m associated to climate variability. The modeled coastline diffusivity during the 3-yr period is 0.0021 m(2)/s, close to the observed value of 0.0022 m(2)/s. In contrast, the coefficient of the classical one-line diffusion equation is 0.0052 m(2)/s. Thus, the lifetime prediction, here defined as the time needed to reduce the initial amplitude by a factor 5, would be 90 yr instead of the classical diffusivity prediction of 35 yr. The resulting asymmetric feeding to adjacent beaches prodtices 100 m seaward shift at the NE section and 80 m seaward shift at the SW section. Looking at the variability associated to the different wave climates, the migration rate and the slight shape asymmetry correlate with the wave power asymmetry (W vs N waves) while the coastline diffusivity correlates with the proportion of high-angle waves, suggesting that the Dutch coast is near the high-angle wave instability threshold.Nonsingular black holes, the cosmological constant and asymptotic safety
http://hdl.handle.net/2117/105850
Nonsingular black holes, the cosmological constant and asymptotic safety
Torres Herrera, Ramon
Quantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.
Mon, 26 Jun 2017 08:31:46 GMThttp://hdl.handle.net/2117/1058502017-06-26T08:31:46ZTorres Herrera, RamonQuantum gravitational effects in black hole spacetimes with a cosmological constant ¿ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement of classical solutions obtained in the framework of unimodular gravity (a theory which is identical to general relativity at a classical level). This allows us to avoid the usual divergences associated with the presence of a running ¿. The horizons and causal structure of the improved black holes are discussed, taking into account the current observational bounds for the cosmological constant. It is shown that the resulting effective quantum black hole spacetimes are always devoid of singularities.Non-singular quantum improved rotating black holes and their maximal extension
http://hdl.handle.net/2117/105845
Non-singular quantum improved rotating black holes and their maximal extension
Torres Herrera, Ramon
We add a prescription to the Newman–Janis algorithm in order to use it as a means of finding new extended rotating black hole spacetimes from static spherically symmetric ones. Then, we apply the procedure to a quantum improved black hole spacetime coming from Quantum Einstein Gravity in order to get the maximally extended spacetime corresponding to a non-singular rotating black hole. We rigourously check for the existence of scalar curvature singularities in the quantum improved rotating spacetime and we show that it is devoid of them. We also analyze the horizons and causal structure of the rotating black hole and provide Penrose diagrams for the maximally extended spacetime.
The final publication is available at Springer via 10.1007/s10714-017-2236-5
Mon, 26 Jun 2017 08:04:46 GMThttp://hdl.handle.net/2117/1058452017-06-26T08:04:46ZTorres Herrera, RamonWe add a prescription to the Newman–Janis algorithm in order to use it as a means of finding new extended rotating black hole spacetimes from static spherically symmetric ones. Then, we apply the procedure to a quantum improved black hole spacetime coming from Quantum Einstein Gravity in order to get the maximally extended spacetime corresponding to a non-singular rotating black hole. We rigourously check for the existence of scalar curvature singularities in the quantum improved rotating spacetime and we show that it is devoid of them. We also analyze the horizons and causal structure of the rotating black hole and provide Penrose diagrams for the maximally extended spacetime.Formation mechanisms for self-organized kilometer-scale shoreline sand waves
http://hdl.handle.net/2117/105391
Formation mechanisms for self-organized kilometer-scale shoreline sand waves
Falqués Serra, Albert; Ribas Prats, Francesca; Idier, Déborah; Arriaga García, Jaime Alonso
The feedbacks between morphology and waves through sediment transport are investigated as a source of kilometer-scale shoreline sand waves. In particular, the observed sand waves along Srd. Holmslands Tange, Denmark, are examined. We use a linear stability model based on the one-line approximation, linking the bathymetry to the perturbed shoreline. Previous models that consider the link by shifting the equilibrium profile and neglecting the curvature of the depth contours predict a positive feedback only if the offshore wave incidence angle (¿c) is above a threshold, ¿c¿42°. Considering curvilinear depth contours and using a linearly decaying perturbation in bed level, we find that ¿c can vary over the range 0–90° depending on the background bathymetric profile and the depth of closure, Dc. Associated to the perturbed wave refraction, there are two sources of instability: the alongshore gradients in wave angle, wave angle mechanism, and the alongshore gradients in wave energy induced by wave crest stretching, wave energy mechanism. The latter are usually destabilizing, but the former are destabilizing only for large enough Dc, steep foreshores, and gently sloping shorefaces. The critical angle comes out from the competition between both mechanisms, but when both are destabilizing, ¿c=0. In contrast with earlier studies, the model predicts instability for the Holmslands Tange coast so that the observed sand waves could have emerged from such instability. The key point is considering a larger Dc that is reasonably supported by both observations and wave climate, which brings the wave angle mechanism near the destabilizing threshold.
Tue, 13 Jun 2017 16:56:47 GMThttp://hdl.handle.net/2117/1053912017-06-13T16:56:47ZFalqués Serra, AlbertRibas Prats, FrancescaIdier, DéborahArriaga García, Jaime AlonsoThe feedbacks between morphology and waves through sediment transport are investigated as a source of kilometer-scale shoreline sand waves. In particular, the observed sand waves along Srd. Holmslands Tange, Denmark, are examined. We use a linear stability model based on the one-line approximation, linking the bathymetry to the perturbed shoreline. Previous models that consider the link by shifting the equilibrium profile and neglecting the curvature of the depth contours predict a positive feedback only if the offshore wave incidence angle (¿c) is above a threshold, ¿c¿42°. Considering curvilinear depth contours and using a linearly decaying perturbation in bed level, we find that ¿c can vary over the range 0–90° depending on the background bathymetric profile and the depth of closure, Dc. Associated to the perturbed wave refraction, there are two sources of instability: the alongshore gradients in wave angle, wave angle mechanism, and the alongshore gradients in wave energy induced by wave crest stretching, wave energy mechanism. The latter are usually destabilizing, but the former are destabilizing only for large enough Dc, steep foreshores, and gently sloping shorefaces. The critical angle comes out from the competition between both mechanisms, but when both are destabilizing, ¿c=0. In contrast with earlier studies, the model predicts instability for the Holmslands Tange coast so that the observed sand waves could have emerged from such instability. The key point is considering a larger Dc that is reasonably supported by both observations and wave climate, which brings the wave angle mechanism near the destabilizing threshold.Cold outbreaks at the mesoscale in the Western Mediterranean basin: from Raincells to rainbands
http://hdl.handle.net/2117/104892
Cold outbreaks at the mesoscale in the Western Mediterranean basin: from Raincells to rainbands
Mazón Bueso, Jordi; Pino González, David
This paper investigates cold outbreaks that form offshore density currents within the whole mesoscale over the Western
Mediterranean basin. Reflectivity radar and satellite images are used to detect clouds and precipitation that are associated with these
density currents in the meso-
훼
,meso-
훽
, and meso-
훾
over the Western Mediterranean basin (WMB). Version 3.3 of the WRF-ARW
model is used to describe the formation and evolution of these density currents and to estimate their lifetime as well as horizontal
and vertical scales. Based on the observations and simulations, this paper suggests that a new perspective could effectively be
adopted regarding the WMB region delineated by the Balearic Islands, the northeastern Iberian Peninsula, and the Gulf of Lion,
where inland cold outbreaks develop into density currents that move offshore and can produce precipitation ranging from raincells
to rainbands at the whole mesoscale.
Fri, 26 May 2017 08:49:52 GMThttp://hdl.handle.net/2117/1048922017-05-26T08:49:52ZMazón Bueso, JordiPino González, DavidThis paper investigates cold outbreaks that form offshore density currents within the whole mesoscale over the Western
Mediterranean basin. Reflectivity radar and satellite images are used to detect clouds and precipitation that are associated with these
density currents in the meso-
훼
,meso-
훽
, and meso-
훾
over the Western Mediterranean basin (WMB). Version 3.3 of the WRF-ARW
model is used to describe the formation and evolution of these density currents and to estimate their lifetime as well as horizontal
and vertical scales. Based on the observations and simulations, this paper suggests that a new perspective could effectively be
adopted regarding the WMB region delineated by the Balearic Islands, the northeastern Iberian Peninsula, and the Gulf of Lion,
where inland cold outbreaks develop into density currents that move offshore and can produce precipitation ranging from raincells
to rainbands at the whole mesoscale.The influence of an increase of the Mediterranean Sea Surface Temperature on two nocturnal offshore rainbands: a numerical experiment
http://hdl.handle.net/2117/104218
The influence of an increase of the Mediterranean Sea Surface Temperature on two nocturnal offshore rainbands: a numerical experiment
Mazón Bueso, Jordi; Pino González, David
Using the Weather Research and Forecasting (WRF) – Advanced Research WRF (ARW)
mesoscale model (WRF–ARW), we investigate how two nocturnal offshore rainbands occurring in
the Mediterranean basin are modified in a warmer sea surface temperature (SST). After sunset, the
thermal difference between land and sea air increases. Driven by drainage winds or land breeze, the
inland cold air interacts with the relatively warmer and moister air over the sea. Vertical movement
of sea air over the boundary between the two air masses may induce cloud and rain bands offshore.
When an increase of SST is prescribed in the WRF simulations, a change in the precipitation pattern is
simulated. The numerical experiments show an increase both in the extension and location of the
rainbands and in the precipitation rate. These changes, induced by the modified SST, are analyzed by
estimating and comparing several parameters such as the location of level of free convection (LFC),
Convective Available Potential Energy (CAPE), or the triggering, deceleration and blockage terms of
simplified conceptual models.
Tue, 09 May 2017 08:02:07 GMThttp://hdl.handle.net/2117/1042182017-05-09T08:02:07ZMazón Bueso, JordiPino González, DavidUsing the Weather Research and Forecasting (WRF) – Advanced Research WRF (ARW)
mesoscale model (WRF–ARW), we investigate how two nocturnal offshore rainbands occurring in
the Mediterranean basin are modified in a warmer sea surface temperature (SST). After sunset, the
thermal difference between land and sea air increases. Driven by drainage winds or land breeze, the
inland cold air interacts with the relatively warmer and moister air over the sea. Vertical movement
of sea air over the boundary between the two air masses may induce cloud and rain bands offshore.
When an increase of SST is prescribed in the WRF simulations, a change in the precipitation pattern is
simulated. The numerical experiments show an increase both in the extension and location of the
rainbands and in the precipitation rate. These changes, induced by the modified SST, are analyzed by
estimating and comparing several parameters such as the location of level of free convection (LFC),
Convective Available Potential Energy (CAPE), or the triggering, deceleration and blockage terms of
simplified conceptual models.Emergence of spatio-temporal dynamics from exact coherent solutions in pipe flow
http://hdl.handle.net/2117/104197
Emergence of spatio-temporal dynamics from exact coherent solutions in pipe flow
Ritter, Paul; Mellibovsky Elstein, Fernando; Avila Cañellas, Marc
Turbulent-laminar patterns are ubiquitous near transition in wall-bounded shear flows. Despite recent progress in describing their dynamics in analogy to non-equilibrium phase transitions, there is no theory explaining their emergence. Dynamical-system approaches suggest that invariant solutions to the Navier–Stokes equations, such as traveling waves and relative periodic orbits in pipe flow, act as building blocks of the disordered dynamics. While recent studies have shown how transient chaos arises from such solutions, the ensuing dynamics lacks the strong fluctuations in size, shape and speed of the turbulent spots observed in experiments. We here show that chaotic spots with distinct dynamical and kinematic properties merge in phase space and give rise to the enhanced spatio-temporal patterns observed in pipe flow. This paves the way for a dynamical-system foundation to the phenomenology of turbulent-laminar patterns in wall-bounded extended shear flows.
Mon, 08 May 2017 12:21:38 GMThttp://hdl.handle.net/2117/1041972017-05-08T12:21:38ZRitter, PaulMellibovsky Elstein, FernandoAvila Cañellas, MarcTurbulent-laminar patterns are ubiquitous near transition in wall-bounded shear flows. Despite recent progress in describing their dynamics in analogy to non-equilibrium phase transitions, there is no theory explaining their emergence. Dynamical-system approaches suggest that invariant solutions to the Navier–Stokes equations, such as traveling waves and relative periodic orbits in pipe flow, act as building blocks of the disordered dynamics. While recent studies have shown how transient chaos arises from such solutions, the ensuing dynamics lacks the strong fluctuations in size, shape and speed of the turbulent spots observed in experiments. We here show that chaotic spots with distinct dynamical and kinematic properties merge in phase space and give rise to the enhanced spatio-temporal patterns observed in pipe flow. This paves the way for a dynamical-system foundation to the phenomenology of turbulent-laminar patterns in wall-bounded extended shear flows.