arXiv subjects

F. J. Beron-Vera

Publications and source records attributed to F. J. Beron-Vera.

At least 19 recordsLinked to original sources

arXiv2026

The material life cycle of Koobor: separating coherent organization from potential-vorticity evolution in a wildfire-generated stratospheric vortex

Pyro-cumulonimbus convection associated with extreme wildfires can generate long-lived stratospheric vortices, yet their material coherence and life cycle remain poorly characterized. We apply geodesic vortex detection to winds from reanalysis to identify objectively defined (observer-independent) material boundaries of \emph{Koobor}, generated by the 2019--2020 Australian bushfires. These boundaries are closed material curves that undergo uniform finite-time tangential stretching and resist filamentation. We reconstruct their evolution across isentropic levels. Material coherence develops upward from 590~K, reaches maximum persistence at 690~K, and becomes progressively shorter-lived at higher levels. At 690~K, the reconstructed birth-to-death interval is approximately 40~days, while overlapping detections across levels define a nearly 60-day envelope. Analysis of potential vorticity (PV) within and around these material boundaries reveals a distinct dynamical evolution: the material boundary forms before strong PV isolation develops, a compact PV core emerges during the mature phase, and PV isolation weakens as material coherence approaches its demise. Strong PV isolation is concentrated at intermediate levels, whereas at 850~K material coherence occurs without a comparably well-defined PV core. These results provide an objective material description of the birth, vertical development, and decay of a wildfire-generated stratospheric vortex and show that material organization precedes the development of its strongest PV signature, which subsequently intensifies and weakens over the lifetime of the coherent vortex.

physics.ao-ph↗

arXiv2026

Lagrangian Rotating Contracting Structures

We identify materially defined regions in unsteady two-dimensional flows that combine finite-time contraction with elevated accumulated intrinsic rotation along trajectories, which we term \emph{Lagrangian rotating contracting structures} (LRCS). These regions are detected using existing objective diagnostics -- the Lagrangian-averaged vorticity deviation (LAVD) together with direct tests of material contraction -- without relying on the geometry of LAVD level sets. In strongly deforming flows, LAVD maxima need not correspond to vortical regions or be enclosed by regular level sets, rendering geometry-based identification unreliable. Nevertheless, regions exhibiting inward spiraling motion and contraction can be extracted by combining LAVD with a contraction criterion. Applications to atmospheric and oceanic flows show that such behavior arises both in twisted LAVD fields generated at submesoscales and in mesoscale flows where it is enhanced by inertial effects, with finite-time contraction providing the dynamical constraint that isolates materially organized regions with elevated intrinsic rotation.

nlin.CD↗

arXiv2026

Transition path theory insights into hurricane rapid intensification

We explore hurricane and ocean reanalysis data to understand how rapid intensification (RI) of tropical cyclones is impacted by the upper ocean density structure, with an emphasis on barrier layer (BL) thickness and thermocline depth in the eastern Caribbean Sea and adjacent western tropical North Atlantic. This analysis leverages transition path theory (TPT), supported by basic statistical methods. In TPT, Markov chains are constructed by discretizing data series related to weather system intensity, changes in intensity, translational speed, and BL thickness and thermocline depth. These series are viewed as trajectories in abstract state spaces, following a memoryless stochastic process. RI imminence is rigorously framed using a newly derived TPT statistic, which gives the time distribution to first reach a target -- the RI state -- from a source -- for instance, the state determined by a certain BL range and system intensity -- conditional on connecting paths exhibiting minimal detours. Increased RI frequency is observed in the eastern Caribbean and nearby Atlantic, influenced by river runoff, primarily in tropical storms and category 2 hurricanes. RI frequently correlates with a well-developed BL; however, increased translational speed is necessary for RI. TPT shows a stronger connection between RI and thermocline depth than BL presence, with RI likelihood rising for hurricanes with a thin BL, especially category 1. Across all strength categories, a deep thermocline consistently elevates RI probability, a factor missed by basic statistical analysis. Furthermore, translational speed is crucial, with faster, stronger hurricanes more susceptible to RI, while slower systems are less so.

physics.ao-ph↗

arXiv2025

Properties and baroclinic instability of stratified thermal upper-ocean flow

We study the properties of, and investigate the stability of a baroclinic zonal current in, a thermal rotating shallow-water model, sometimes called \emph{Ripa's model}, featuring stratification for quasigeostrophic upper-ocean dynamics. The model has Lie--Poisson Hamiltonian structure. In addition to Casimirs, the model supports weak Casimirs forming the kernel of the Lie--Poisson bracket for the potential vorticity evolution independent of the details of the buoyancy as this is advected under the flow. The model sustains Rossby waves and a neutral model, whose spurious growth is prevented by a positive-definite integral, quadratic on the deviation from the motionless state. A baroclinic zonal jet with vertical curvature is found to be spectrally stable for specific configurations of the gradients of layer thickness, vertically averaged buoyancy, and buoyancy frequency. Only a subset of such states was found Lyapunov stable using the available integrals, except the weak Casimirs, whose role in constraining stratified thermal flow remains to be understood. The existence of Lyapunov-stable states enabled us to \emph{a priori} bound the nonlinear growth of perturbations to spectrally unstable states. Our results do not support the generality of earlier numerical evidence on the suppression of submesoscale wave activity as a result of the inclusion of stratification in thermal shallow-water theory, which we supported with direct numerical simulations.

physics.ao-ph↗

arXiv2024

Dynamics of inertial particles on the ocean surface with unrestricted reserve buoyancy

The purpose of this note is to present an enhancement to a Maxey-Riley theory proposed in recent years for the dynamics of inertial particles on the ocean surface. This model upgrade removes constraints on the reserve buoyancy, defined as the fraction of the particle volume above the ocean surface. The refinement results in an equation that correctly describes both the neutrally buoyant and fully buoyant particle scenarios.

physics.ao-ph↗

arXiv2024

On a priori bounding the growth of thermal instability waves

We have previously shown that the nonlinear growth of a finite-amplitude perturbation to a basic state given by a baroclinic zonal flow on the $β$-plane in a thermal quasigeostrophic reduced-gravity model can be a priori bounded. In this note we show that, unlike we stated earlier, Lyapunov stability can be proved even when buoyancy varies linearly with the meridional coordinate. In addition to rectifying our earlier results we expand them by deriving an instability saturation bound by making use of the existence of such a class of Lyapunov-stable basic states. This bound can be smaller than that one we estimated before, reinforcing our previous conclusions. We also present a numerical test of the accuracy of the derived bound.

physics.ao-ph↗

arXiv2023

Physics-informed laboratory estimation of Sargassum windage

A recent Maxey--Riley theory for \sarg raft motion, which models a raft as a network of elastically interacting finite-size, buoyant particles, predicts the carrying flow velocity to be given by the weighted sum of the water and air velocities $(1-α)\mathbf{v} + α\mathbf w$. The theory provides a closed formula for parameter $α$, referred to as \emph{windage}, depending on water-to-particle-density ratio or buoyancy ($δ$). From a series of laboratory experiments in an air--water stream flume facility under controlled conditions, we estimate $α$ ranging from 0.02 to 0.96\pct. On average, our windage estimates can be up to 9 times smaller than considered in conventional \emph{Sargassum} raft transport modeling, wherein it is customary to add a fraction of $\mathbf w$ to $\mathbf{v}$ chosen in an ad-hoc piecemeal manner. Using the formula provided by the Maxey--Riley theory, we estimate $δ$ ranging from 1.00 to 1.49. This is consistent with direct $δ$ measurements, ranging from 0.9 to 1.25, which provide support for our $α$ estimation.

physics.ao-ph↗

arXiv2023

Stability of temporal statistics in Transition Path Theory with sparse data

Transition Path Theory (TPT) provides a rigorous statistical characterization of the ensemble of trajectories connecting directly, i.e., without detours, two disconnected (sets of) states in a Markov chain, a stochastic process that undergoes transitions from one state to another with probability depending on the state attained in the previous step. Markov chains can be constructed using trajectory data via counting of transitions between cells covering the domain spanned by trajectories. With sparse trajectory data, the use of regular cells is observed to result in unstable estimates of the total duration of transition paths. Using Voronoi cells resulting from k-means clustering of the trajectory data, we obtain stable estimates of this TPT statistic, which is generalized to frame the remaining duration of transition paths, a new TPT statistic suitable for investigating connectivity.

cond-mat.stat-mech↗

arXiv2022

Do eddies connect the tropical Atlantic Ocean and the Gulf of Mexico?

Consistent with satellite-tracked trajectories of drogued drifters, but at odds with Eulerian assessment of satellite-altimetry measurements of sea-surface height, we show that North Brazil Currents Rings (NBCRs) are incapable of bypassing the Lesser Antilles as structures that coherently transport material. The nature of the inability of the de-facto oceanographic Eulerian, streamline-based eddy detection technique to produce a correct assessment is rooted in its lack of objectivity. We arrive at this conclusion by applying \emph{geodesic eddy detection} on the altimetric dataset over nearly its entire extent. While we detect northwestward translating NBCRs that can be classified as coherent Lagrangian eddies, they typically experience strong filamentation and complete loss of coherence prior to reaching the Lesser Antilles. Moreover, the filamented material hardly penetrates into the Caribbean Sea, let alone the Gulf of Mexico, and not without substantively mixing with the ambient fluid east of the archipelago.

physics.ao-ph↗

arXiv2022

Exploring the use of Transition Path Theory in building an oil spill prediction scheme

The Transition Path Theory (TPT) of complex systems has proven a robust means for statistically characterizing the ensemble of trajectories that connect any two preset flow regions, say $\mathcal A$ and $\mathcal B$, directly. More specifically, transition paths are such that they start in $\mathcal A$ and then go to $\mathcal B$ without detouring back to $\mathcal A$ or $\mathcal B$. This way, they make an effective contribution to the transport from $\mathcal A$ to $\mathcal B$. Here, we explore its use for building a scheme that enables predicting the evolution of an oil spill in the ocean. This involves appropriately adapting TPT such that it includes a reservoir that pumps oil into a typically open domain. Additionally, we lift up the restriction of the oil not to return to the spill site en route to a region that there is interest to be protected. TPT is applied on oil trajectories available up to the present, e.g., as integrated using velocities produced by a data assimilative system or as inferred from high-frequency radars, to make a prediction of transition oil paths beyond, without relying on forecasted oil trajectories. As a proof of concept we consider a hypothetical oil spill in the Trion oil field, under development within the Perdido Foldbelt in the northwestern Gulf of Mexico, and the \emph{Deepwater Horizon} oil spill. This is done using trajectories integrated from climatological and hindcast surface velocity and winds as well as produced by satellite-tracked surface drifting buoys, in each case discretized into a Markov chain that provides a framework for the TPT-based prediction.

physics.ao-ph↗

arXiv2022

Dynamical geography and transition paths of Sargassum in the tropical Atlantic

By analyzing a time-homogeneous Markov chain constructed using trajectories of undrogued drifting buoys from the NOAA's Global Drifter Program, we find that probability density can distribute in a manner that resembles very closely the recently observed recurrent belt of high Sargassum density in the tropical Atlantic between 5--10$^{\circ}$N, coined the \emph{Great Atlantic Sargassum Belt} (\emph{GASB}). A spectral analysis of the associated transition matrix further unveils a forward attracting almost-invariant set in the northwestern Gulf of Mexico with a corresponding basin of attraction disconnected from the Sargasso Sea, but including the nutrient-rich regions around the Amazon and Orinoco rivers mouths and also the upwelling system off the northern coast of west Africa. This represents a data-based inference of potential remote sources of Sargassum recurrently invading the Intra-Americas Seas (IAS). By further applying Transition Path Theory (TPT) on the data-derived Markov chain model, two potential pathways for Sargassum into the IAS from the upwelling system off the coast of Africa are revealed. One TPT-inferred pathway takes place along the GASB. The second pathway is more southern and slower, first going through the Gulf of Guinea, then across the tropical Atlantic toward the mouth of the Amazon River, and finally along the northeastern South American margin. The existence of such a southern TPT-inferred pathway may have consequences for bloom stimulation by nutrients from river runoff.

physics.ao-ph↗

arXiv2022

Sampling--Dependent Transition Paths of Iceland-Scotland Overflow Water

In this note, we apply Transition Path Theory (TPT) from Markov chains to shed light on the problem of Iceland-Scotland Overflow Water (ISOW) equatorward export. A recent analysis of observed trajectories of submerged floats demanded revision of the traditional abyssal circulation theory, which postulates that ISOW should steadily flow along a deep boundary current (DBC) around the subpolar North Atlantic prior to exiting it. The TPT analyses carried out here allow to focus the attention on the portions of flow from the origin of ISOW to the region where ISOW exits the subpolar North Atlantic and suggest that insufficient sampling may be biasing the aforementioned demand. The analyses, appropriately adapted to represent a continuous input of ISOW, are carried out on three time-homogeneous Markov chains modeling the ISOW flow. One is constructed using a high number of simulated trajectories homogeneously covering the flow domain. The other two use much fewer trajectories which heterogeneously cover the domain. The trajectories in the latter two chains are observed trajectories or simulated trajectories subsampled at the observed frequency. While the densely sampled chain supports a well-defined DBC, the more heterogeneously sampled chains do not, irrespective of whether observed or simulated trajectories are used. Studying the sampling sensitivity of the Markov chains, we can give recommendations for enlarging the existing float dataset to improve the significance of conclusions about time-asymptotic aspects of the ISOW circulation.

physics.ao-ph↗

arXiv2022

Transition paths of North Atlantic Deep Water

We use Transition Path Theory (TPT) to frame, in a statistically more robust fashion than earlier analyses, equatorward routes of North Atlantic Deep Water (NADW) in the subpolar North Atlantic. TPT is applied on all available RAFOS and Argo floats in the area by means of a discretization of the Lagrangian dynamics described by their trajectories. By considering floats at different depths, we investigate transition paths of NADW in its upper (UNADW) and lower (LNADW) layers. We find that the majority of UNADW transition paths sourced in the Labrador and southwestern Irminger Seas reach the western side of a target arranged zonally along the southern edge of the subpolar North Atlantic domain visited by the floats. This is accomplished in the form of a well-organized deep boundary current (DBC). LNADW transition paths sourced west of the Reykjanes Ridge reveal a similar pattern, while those sourced east of the ridge are found to hit the western side of the target via a DBC and also several other places along it in a less organized fashion, indicating southward flow along the eastern and western flanks of the Mid-Atlantic Ridge. Naked-eye inspection of trajectories suggest generally much more diffusive equatorward NADW routes. A source-independent dynamical decomposition of the flow domain into analogous backward-time basins of attraction, beyond the reach of direct inspection of trajectories, reveals a much wider influence of the western side of the target for UNADW than for LNADW. For UNADW, the average expected duration of the pathways from the Labrador and Irminger Seas was found to be of 2 to 3 years. For LNADW, the duration was found to be influenced by the Reykjanes Ridge, being as long as 8 years from the western side of the ridge and of about 3 years on average from its eastern side.

physics.ao-ph↗

arXiv2021

Carriers of \emph{Sargassum} and mechanism for coastal inundation in the Caribbean Sea

We identify effective carriers of \emph{Sargassum} in the Caribbean Sea and describe a mechanism for coastal choking. Revealed from satellite altimetry, the carriers of \emph{Sargassum} are mesoscale eddies (vortices of 50-km radius or larger) with coherent material (i.e., fluid) boundaries. These are observer-independent -- \emph{unlike} eddy boundaries identified with instantaneously closed streamlines of the altimetric sea-surface height field -- and furthermore harbor finite-time attractors for networks of elastically connected finite-size buoyant or "inertial" particles dragged by ocean currents and winds, a mathematical abstraction of \emph{Sargassum} rafts. The mechanism of coastal inundation, identified using a minimal model of surface-intensified Caribbean Sea eddies, is thermal instability in the presence of bottom topography.

physics.ao-ph↗

arXiv2021

Extended shallow-water theories with thermodynamics and geometry

Driven by growing momentum in two-dimensional geophysical flow modeling, this paper introduces a general family of "thermal" rotating shallow-water models. The models are capable of accommodating thermodynamic processes, such as those acting in the ocean mixed layer, by allowing buoyancy to vary in horizontal position and time as well as with depth, in a polynomial fashion up to an arbitrary degree. Moreover, the models admit Euler--Poincare variational formulations and possess Lie--Poisson Hamiltonian structure. Such a geometric property provides solid fundamental support to the theories described with consequences for numerical implementation and the construction of unresolved motion parametrizations. In particular, it is found that stratification halts the development of small-scale filament rollups recently observed in a popular model, which, having vertically homogeneous density, represents a special case of the models presented here.

physics.flu-dyn↗

arXiv2021

Geometry of shallow-water dynamics with thermodynamics

We review the geometric structure of the IL$^0$PE model, a rotating shallow-water model with variable buoyancy, thus sometimes called ``thermal'' shallow-water model. We start by discussing the Euler--Poincaré equations for rigid body dynamics and the generalized Hamiltonian structure of the system. We then reveal similar geometric structure for the IL$^0$PE. We show, in particular, that the model equations and its (Lie--Poisson) Hamiltonian structure can be deduced from Morrison and Greene's (1980) system upon ignoring the magnetic field ($\vec{\mathrm B} = 0$) and setting $U(ρ,s) = \frac{1}{2}ρs$, where $ρ$ is mass density and $s$ is entropy per unit mass. These variables play the role of layer thickness ($h$) and buoyancy ($\t$) in the IL$^0$PE, respectively. Included in an appendix is an explicit proof of the Jacobi identity satisfied by the Poisson bracket of the system.

nlin.CD↗

arXiv2021

Nonlinear saturation of thermal instabilities

Low-frequency simulations of a one-layer model with lateral buoyancy variations (i.e., thermodynamically active) have revealed circulatory motions resembling quite closely submesoscale observations in the surface ocean rather than indefinitely growing in the absence of a high-wavenumber instability cutoff. In this note it is shown that the existence of a convex pseudoenergy--momentum integral of motion for the inviscid, unforced dynamics provides a mechanism for the nonlinear saturation of such thermal instabilities in the zonally symmetric case. The result is an application of \citet{Arnold-66} and \citet{Shepherd-88a} methods.

physics.ao-ph↗

arXiv2020

Multilayer shallow-water model with stratification and shear

The purpose of this paper is to present a shallow-water-type model with multiple inhomogeneous layers featuring variable linear velocity vertical shear and startificaion in horizontal space and time. This is achieved by writing the layer velocity and buoyancy fields as linear functions of depth, with coefficients that depend arbitrarily on horizontal position and time. The model is a generalization of Ripa's (1995) single-layer model to an arbitrary number of layers. Unlike models with homogeneous layers the present model is able to represent thermodynamics processes driven by heat and freshwater fluxes through the surface or mixing processes resulting from fluid exchanges across contiguous layers. A model configuration with only one layer has been previously shown to provide: a very good representation of the exact vertical normal modes up to the first internal mode; an exact representation of long-perturbation (free boundary) baroclinic instability; and a very reasonable representation of short-perturbation (classical Eady) baroclinic instability. Here it is shown that substantially more accurate overall results with respect to single-layer calculations can be achieved by considering a stack of only a few layers. A similar behavior is found in ageostrophic (classical Stone) baroclinic instability by describing accurately the dependence of the solutions on the Richardson number with only two layers.

physics.ao-ph↗