Jozef SkakalaPlymouth Marine Laboratory | PML
Jozef Skakala
Ph.D (Victoria U., Wellington)
About
43
Publications
5,006
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476
Citations
Introduction
My background is in theoretical physics (PhD in General Relativity). I did postdoctoral research on various problems in black hole physics, semi-classical quantum properties of spacetime horizons, on neutron stars, gravitational radiation, quasi-normal modes, Lovelock gravity (and further). I subsequently redirected my scientific interest to more practical problems in oceanography (and climate science). My research interests include data assimilation, marine ecosystem modelling, model validation, multifractals and scale-invariance in complex (oceanographic) systems, machine learning, interdecadal climate variability and more.
Additional affiliations
September 2016 - present
Position
- Researcher
Description
- ecosystem modelling in oceanography, data assimilation, complex dynamical systems and scaling transitions, climate variability
September 2014 - September 2016
Plymouth Marine Laboratory
Position
- PostDoc Position
Description
- scale-invariance in complex systems; mathematical modelling in oceanography: stochastic multifractal modelling, analysis, parametrisation and understanding spatial heterogeneity of various oceanographic fields through their scaling properties.
September 2013 - August 2014
Position
- PostDoc Position
Description
- black holes, spacetime thermodynamics, higher-order theories of gravity
Education
December 2007 - July 2011
September 2002 - June 2007
September 1997 - June 2002
Publications
Publications (43)
We use modelling and assimilation tools to explore the impact of biogeochemistry on physics in the shelf sea environment, using North-West European Shelf (NWES) as a case study. We demonstrate that such impact is significant: the attenuation of light by biogeochemical substances heats up the upper 20 m of the ocean by up to 1 °C and by a similar ma...
Oceanography has entered an era of new observing platforms, such as biogeochemical‐Argo floats and gliders, some of which will provide three‐dimensional maps of essential ecosystem variables on the North‐West European (NWE) Shelf. In a foreseeable future operational centers will use multi‐platform assimilation to integrate those valuable data into...
We demonstrate that a simple model based on reaction-diffusion-advection (RDA) equation forced by realistic surface velocities and nutrients is skilled in reproducing the distributions of the surface phytoplankton chlorophyll in the tropical Pacific. We use the low-complexity RDA model to investigate the scale relationships in the impact of differe...
We demonstrate that a simple model based on reaction-diffusion-advection (RDA) equation forced by realistic surface velocities and nutrients is skilled in reproducing the distributions of the surface
phytoplankton chlorophyll in the tropical Pacific. We use the low-complexity RDA model to investigate the scale-relationships in the impact of differe...
Understanding ecosystem state on the North‐West European (NWE) Shelf is of major importance for both economy and climate research. The purpose of this work is to advance our modeling of in‐water optics on the NWE Shelf, with important implications for how we model primary productivity, as well as for assimilation of water‐leaving radiances. We impl...
In this work we produced a long‐term reanalysis of the phytoplankton community structure in the Mediterranean Sea and used it to define ecoregions. These were based on the spatial variability of the phytoplankton type fractions and their influence on selected carbon fluxes. A regional ocean color product of four phytoplankton functional types (PFTs...
We present a model that estimates the spectral phytoplankton absorption coefficient ( a p h ( λ ) ) of four phytoplankton groups (picophytoplankton, nanophytoplankton, dinoflagellates, and diatoms) as a function of the total chlorophyll-a concentration (C) and sea surface temperature (SST). Concurrent data on a p h ( λ ) (at 12 visible wavelengths)...
Spectrally resolved water-leaving radiances (ocean colour) and inferred chlorophyll concentration are key to studying phytoplankton dynamics at seasonal and inter-annual scales, for a better understanding of the role of phytoplankton in marine biogeochemistry; the global carbon cycle; and the response of marine ecosystems to climate variability, ch...
In this study we demonstrate the many strengths of scale analysis: we use it to evaluate the Nucleus for European Modelling of the Ocean model skill in representing sea surface temperature (SST) in the Southern Ocean by comparing three model resolutions: 1/12°, 1/4°, and 1°. We show that while 4–5 times resolution scale is sufficient for each model...
Pacific interdecadal variability (PIV) is an important large-scale climate phenomenon. There is growing evidence that PIV contains three spectral resonances: a decadal (13 ± 1-year) spectral peak, bidecadal (20 ± 5-year) resonance, and a pentadecadal (60 ± 10-year) resonance. Although much has been clarified about mechanisms behind PIV, there are s...
This paper proposes the use of assimilation of phytoplankton functional types (PFTs) surface chlorophyll for operational forecasting of biogeochemistry on the North-West European (NWE) Shelf. We explicitly compare the 5-day forecasting skill of three runs of a physical-biogeochemical model: (a) a free reference run, (b) a run with daily data assimi...
We assimilated phytoplankton functional types (PFTs) derived from ocean colour into a marine ecosystem model, to improve the simulation of biogeochemical indicators and emerging properties in a shelf sea. Error-characterized chlorophyll concentrations of four PFTs (diatoms, dinoflagellates, nanoplankton and picoplankton), as well as total chlorophy...
We are in an era of unprecedented data volumes generated from observations and model simulations. This is particularly true from satellite Earth Observations (EO) and global scale oceanographic models. This presents us with an opportunity to evaluate large scale oceanographic model outputs using EO data. Previous work on model skill evaluation has...
Using satellite maps this paper offers a complex analysis of chlorophyll & SST heterogeneity in the shelf seas around the south-west of the UK. The heterogeneity scaling follows a simple power law and is consequently parametrized by two parameters. It is shown that in most cases these two parameters vary only relatively little with time. The paper...
Characterization of chlorophyll and sea surface temperature (SST) structural heterogeneity using their scaling properties can provide a useful tool to estimate the relative importance of key physical and biological drivers. Seasonal, annual and also instantaneous spatial distributions of chlorophyll and SST, determined from satellite measurements,...
We extend here the result of Bekenstein (1995 Phys. Rev. D 51 6608–11, 2000 Cosmology and Gravitation pp 1–85), proving the non-existence of minimally coupled scalar black hole hair in general relativity to the Lanczos–Lovelock gravity in arbitrary dimension with non-negative coupling constants. The only physical requirement on the multiplet of min...
Newly born neutron stars can present differential rotation, even if later it should be suppressed by viscosity or a sufficiently strong magnetic field. In this early stage of its life, a neutron star is expected to have a strong emission of gravitational waves, which could be influenced by the differential rotation. We present here a new formalism...
Equations of gravity when projected on spacetime horizons resemble
Navier-Stokes equation of a fluid with a specific equation of state [1-3]. We
show that this equation of state describes massless ideal relativistic gas. We
use these results and for Schwarzschild black hole we build an explicit and
simple molecular model of the fluid. We work with...
We present a method to analyse black hole hair in the
spherical symmetric sector of the Lovelock theory in arbitrary dimensions that
is an alternative to solving the equations of motion in their complete form. We
explicitly show that the method matches with the known black hole solutions for
the vacuum and electro-vacuum spacetimes in Lovelock grav...
In this work we generalize the results for the entropy spectra typically
derived for black holes in general relativity to a generic horizon within the
spherically symmetric (asymptotically flat and non-flat) space-times of more
general theories of gravity. We use all the standard --- Bekenstein's universal
lower bound on the entropy transition, the...
We study here the r-modes in the Cowling approximation of a simple slowly
rotating and magnetized neutron star, where we neglect any deformations of the
spherical symmetry of the star. We were able to quantify the influence of the
magnetic field in both the oscillation frequency $\sigma_r$ of the r-modes and
the growth time $t_{GW}$ of the gravitat...
This is an (invited) review of my work published in the papers [1-4]. It
offers a more detailed discussion of the results than what was given in the
published papers and it links my results to some conclusions recently made by
other people. It also offers some new arguments for the conclusions previously
made. The fundamental idea of this work is t...
There exists a long term debate about a possible link of the asymptotic
quasinormal (QNM) modes to the black hole thermodynamics. The first
conjecture providing a link between the classical asymptotic black hole
oscillation frequencies and black hole thermodynamics was formulated
more than a decade ago by Hod. The conjecture was later modified by
M...
Newly born neutron stars can present differential rotation, even if later it
should be suppressed by viscosity or a sufficiently strong magnetic field. And
in this early stage of its life, a neutron star is expected to have a strong
emission of gravitational waves, which could be influenced by the differential
rotation. We present here a new formal...
We explore the question of what happens with the asymptotically highly damped
quasi-normal modes ($\ell$ fixed, $|\omega_{I}|\to\infty$) when the underlying
spacetime has no event horizons. We consider the characteristic oscillations of
a scalar field in a large class of asymptotically flat spherically symmetric
static spacetimes without (absolute)...
What should be the quasinormal modes associated with a spacetime that
contains a naked singularity instead of a black hole? In the present work we
address this problem by studying the scattering of scalar fields on a curved
background described by a Reissner-Nordstr\"om spacetime with $|q| > m$. We
show that there is a qualitative difference betwee...
We suggest an interpretation for the highly damped QNM frequencies of the spherically symmetric multi-horizon spacetimes (Reissner-Nordström, Schwarzschild-deSitter, Reissner-Nordström-deSitter) following Maggiore’s proposal about the link between the asymptotic QNM frequencies and the black hole thermodynamics. We show that the behavior of the asy...
There is a need in general relativity for a consistent and useful
mathematical theory defining the multiplication of tensor distributions in a
geometric (diffeomorphism invariant) way. Significant progress has been made
through the concept of Colombeau algebras, and the construction of full
Colombeau algebras on differential manifolds for arbitrary...
We analyze the largely accepted formulas for the asymptotic quasi-normal frequencies of the non-extremal Reissner-Nordström black hole, (for the electromagnetic-gravitational/scalar perturbations). We focus on the question of whether the gap in the spacing in the imaginary part of the QNM frequencies has a well defined limit as n goes to infinity a...
Black hole highly-damped quasi-normal frequencies (QNFs) are very often of
the form (offset)} + i n (gap). We have investigated the genericity of this
phenomenon for the Schwarzschild--deSitter (SdS) black hole by considering a
model potential that is piecewise Eckart (piecewise Poeschl-Teller), and
developing an analytic ``quantization condition''...
This thesis is based on three different projects, all of them are directly
linked to the classical general theory of relativity, but they might have
consequences for quantum gravity as well. The first chapter deals with
pseudo-Finsler geometric extensions of the classical theory, these being ways
of naturally representing high-energy Lorentz symmet...
Finsler spacetimes have become increasingly popular within the theoretical physics community over the last two decades. However, because physicists need to use pseudo-Finsler structures to describe propagation of signals, there will be nonzero null vectors in both the tangent and cotangent spaces — this causes significant problems in that many of t...
There is a by now well-established isomorphism between stationary
4-dimensional spacetimes and 3-dimensional purely spatial Randers geometries -
these Randers geometries being a particular case of the more general class of
3-dimensional Finsler geometries. We point out that in stably causal
spacetimes, by using the (time-dependent) ADM decompositio...
Generic master equations governing the highly-damped quasi-normal frequencies [QNFs] of one-horizon, two-horizon, and even three-horizon spacetimes can be obtained through either semi-analytic or monodromy techniques. While many technical details differ, both between the semi-analytic and monodromy approaches, and quite often among various authors...
The last decade has seen considerable interest in the quasi-normal frequencies [QNFs] of black holes (and even wormholes), both asymptotically flat and with cosmological horizons. There is wide agreement that the QNFs are often of the form ω
n
= (offset) + in (gap), though some authors have encountered situations where this behaviour seems to fail....
Ongoing searches for a quantum theory of gravity have repeatedly led to the suggestion that space–time might ultimately be anisotropic (Finsler-like) and/or exhibit multirefringence (multiple signal cones). Multiple (and even anisotropic) signal cones can be easily dealt with in a unified manner, by writing down a single Fresnel equation to simulta...
Highly damped quasinormal frequencies are very often of the form ωn=(offset)+in(gap). We investigate the genericity of this phenomenon by considering a model potential that is piecewise Eckart (piecewise Pöschl-Teller), and developing an analytic “quantization condition” for the highly damped quasinormal frequencies. We find that this ωn=(offset)+i...
Based on the analogue spacetime programme, and many other ideas currently mooted in "quantum gravity", there is considerable ongoing speculation that the usual pseudo-Riemannian (Lorentzian) manifolds of general relativity might eventually be modified at short distances. Two specific modifications that are often advocated are the adoption of Finsle...
Consider a rotating and possibly pulsating "star" in (2+1) dimensions. If the star is axially symmetric, then in the vacuum region surrounding the star, (a region that we assume at most contains a cosmological constant), the Einstein equations imply that under physically plausible conditions the geometry is in fact stationary. Furthermore, the geom...
It is reasonably well-known that birefringent crystal optics can to some extent be described by the use of pseudo-Finslerian spacetimes (an extension of the natural pseudo-Riemannian Minkowski spacetime one encounters in mono-refringent situations). What is less commonly appreciated is that there are two separate and quite disjoint pseudo-Finsler s...
Projects
Projects (2)
The project OPTIMA will advance the capacity of CMEMS to accurately assess the state of the marine environment, by developing the first system that assimilates ocean-colour absorption data of plankton functional types (PFTs) into an ecosystem model endued with a new bio-optical module. OPTIMA goes beyond state-of-the-art operational models, which assimilate ocean-colour data of total chlorophyll, and which are currently challenged by simulating reliably the underwater light fields, the phytoplankton groups and their optical and biogeochemical feedbacks. The new assimilation system will be an upgrade to the operational model in use at the CMEMS North West Shelf (NWS) Monitoring and Forecasting Centre (MFC). Firstly, a new algorithm will produce time series of spectral absorption of PFTs from ocean colour in the NWS; secondly, a spectral bio-optical module will be implemented in the CMEMS NWS MFC; thirdly, the CMEMS NWS MFC model will be upgraded to assimilate optical data of PFT absorption; finally, the new system will be applied to produce a reanalysis of optical and biogeochemical indicators in the NWS. Ultimately, by enhancing CMEMS capability to monitor and simulate optical and biogeochemical indicators, this project will help end-users to achieve their requirements and help marine policy to safeguard ocean ecosystems.
This project will evolve the capability of the EU Copernicus Marine Environment Monitoring Service (CMEMS) to monitor and simulate biogeochemical indicators of the health of European shelf-seas, by developing the first system assimilating ocean colour data of size-class chlorophyll (SCC) into pre-operational ecosystem models. This project goes beyond state-of-the-art operational models, which assimilate ocean colour data of total chlorophyll, and which are currently challenged by simulating reliably the phytoplankton groups and their biogeochemical and ecological feedbacks. The new assimilation system will be an upgrade to the operational model in use at the CMEMS North West Shelf (NWS) Monitoring and Forecasting Centre (MFC). Firstly, a new algorithm will produce time series of SCC in the NWS; secondly, an operational assimilation system will be upgraded to assimilate SCC; thirdly, the new system will be applied to produce a quality-assessed pre-operational reanalysis of biogeochemical indicators in the NWS. We expect the approach to be exportable to other CMEMS MFCs and to support CMEMS in assessing the state of the ocean. Ultimately, by enhancing CMEMS capability to monitor and simulate biogeochemical indicators, this project will evolve both the ability of end-users to achieve their requirements and marine policy to safeguard marine ecosystems through cutting-edge CMEMS products
