Vassilios D. Vervatis

Verified

Vassilios verified their affiliation via an institutional email.

Learn more

Verified

Vassilios verified their affiliation via an institutional email.

Learn more

• Physical Oceanography, PhD
• Professor (Assistant) at National and Kapodistrian University of Athens

In this Part 2 article of a two-part series, observations based on satellite missions were used to evaluate the empirical consistency of model ensembles generated via stochastic modelling of ocean physics and biogeochemistry. A high-resolution Bay of Biscay configuration was used as a case study to explore the model error subspace in both the open...

In this article, Part 1 of a two-part series, we run and evaluate the skill of a regional physical-biogeochemical stochastic ocean model based on NEMO. The domain covers the Bay of Biscay at 1/36° resolution, as a case study for open-ocean and coastal shelf dynamics. We generate ensembles of uncertainties from assumptions related to errors in the a...

The interannual variability of the Mediterranean overturning circulation is investigated using a high-resolution (1/36°) ocean model. As the overturning circulation regulates the replenishment and ventilation of the deep layers, we study the spatiotemporal scales of the maximum value of the overturning streamfunction over three main sub-basins of d...

Accurate modelling of air-sea processes is essential for reliable forecasts of Mediterranean tropical-like cyclones (also known as “Medicanes”). Medicanes occasionally develop in the Mediterranean causing extreme weather conditions with catastrophic potential due to excessive precipitation, windstorms, and coastal flooding. In this work, we investi...

The dynamics of fluid flows give rise to robust, persistent circulation features that underpin the flow and exert strong control over the advection of water masses, either enhancing it or supressing it, collectively known as lagrangian coherent structures. Lagrangian approaches and metrics have been shown to be better suited than eulerian ones at l...

A Bay of Biscay model configuration is used as a test case to assess the data-based consistency of ensemble-based ocean model uncertainties of several types: [A] built-in stochastic parameterizations at regional ocean scales, [B] ocean model response to a global atmospheric model ensemble and [C] both A and B simultaneously. Ensembles of varying le...

Ocean water clarity, influenced by marine chlorophyll concentration, significantly alters the distribution of shortwave radiation in the water column. This work aims to assess the effects of varying chlorophyll on the upper‐ocean physical properties and their subsequent impact on the atmosphere, using a coupled ocean‐atmosphere regional model for t...

This study examines the impact of different turbidity products on the Aegean Sea surface physical characteristics, by performing twin-experiment simulations using a high-resolution regional ocean model. The turbidity products used include an in-situ based diffuse attenuation coefficient dataset at 490 nm (kd490, in m− 1) and a satellite derived kd4...

Ocean water turbidity, influenced by marine chlorophyll concentration, significantly alters the distribution of shortwave radiation in the water column. This work aims to assess the effects of turbidity on the upper-ocean physical properties and their subsequent impact on the atmosphere, using a coupled ocean-atmosphere regional model for the Medit...

Ocean observing systems in coastal, shelf and marginal seas collect diverse oceanographic information supporting a wide range of socioeconomic needs, but observations are necessarily sparse in space and/or time due to practical limitations. Ocean analysis and forecast systems capitalize on such observations, producing data-constrained, four-dimensi...

The growing energy demand has intensified interest in marine renewable sources. This study assesses wave energy potential in the Mediterranean and Black Seas using a 15-year (2010–2024) wave hindcast with the WaveWatch III model. It examines the spatial and temporal distribution of significant wave height, wave energy period, and overall wave energ...

The weather and climate greatly affect the socioeconomic activities on multiple temporal and spatial scales. From a climate perspective, atmospheric and ocean characteristics have determined the life, evolution and prosperity of humans and other species in different areas of the world. On smaller scales, the atmospheric and sea conditions affect va...

Marine chlorophyll concentration has an impact on turbidity affecting the upper-ocean properties and regulating the air-sea fluxes. This work aims at assessing the effect of turbidity, as estimated via surface chlorophyll, on the heat content and dynamics of the Mediterranean and Black Seas. We performed twin-simulation experiments using a regional...

We investigate the impact of atmospheric forcing uncertainties on the prediction of the dispersion of pollutants in the marine environment. Ensemble simulations consisting of 50 members were carried out using the ECMWF ensemble prediction system and the oil spill model MEDSLIK-II in the Aegean Sea. A deterministic control run using the unperturbed...

We investigate the impact of atmospheric forcing uncertainties on the prediction of dispersion of pollutants in the marine environment. Ensemble simulations consisted of 50 members were carried out using the ECMWF ensemble prediction system and the oil spill model MEDSLIK-II in the Aegean Sea. A deterministic control run, using the unperturbed wind...

Atmospheric-chemical coupled models usually parameterize sea-salt aerosol (SSA) emissions using whitecap fraction estimated considering only wind speed and ignoring sea state. This approach may introduce inaccuracies in SSA simulation. This study aims to assess the impact of sea state on SSA modeling, applying a new parameterization for whitecap fr...

The impact of tides on the Bay of Biscay dynamics is investigated by means of an ocean model twin-experiment, consisted of two simulations with and without tidal forcing. The study is based on a high-resolution (1/36∘) regional configuration of NEMO (Nucleus for European Modelling of the Ocean) performing one-year simulations. The results highlight...

Understanding the governing mechanisms of atmosphere-wave-ocean interactions is critical for unraveling the formation and evolution mechanisms of severe weather phenomena. This study aims at investigating the effects of atmosphere-wave-ocean feedbacks on a Mediterranean tropical-like cyclone (medicane), occurred on 27–30 September 2018 at the centr...

The vertical distribution of the DO also presents significant variability (Fig.5). Multidecadal shifts, rather than long-term trends, are observed for the dissolved oxygen and thermohaline characteristics and are associated with known episodic dense water formation events. The latter is true, especially for the EMT period, but to a lesser extent fo...

The variability of the water mass exchange between the Arabian Gulf and the Indian Ocean is investigated using a high-resolution (1/36°) ocean model. We focus on the period from December 1996 to March 1998, having as reference in situ measurements at the Strait of Hormuz. Previous studies, based on models and observations, suggested a perpetual dee...

The interannual variability and the mechanisms controlling the dissolved oxygen concentration in the Mediterranean Sea were investigated through generating gridded fields of dissolved oxygen, salinity and temperature. The Data-Interpolating Variational Analysis (DIVA) software was used to produce a gridded dataset for the time period 1960–2011. Hig...

The representation of ocean model errors is required in ensemble-based data assimilation methods. In this study, we assess ocean model uncertainties in a high-resolution Bay of Biscay configuration, using atmospheric ensembles and stochastic ocean simulations. The atmospheric ensemble consists of 50 members produced by the European Centre for Mediu...

We downscaled a free ensemble of a regional, parent model to a high-resolution coastal, child ensemble in the Bay of Biscay. The child ensemble was forced at the open boundaries by the parent ensemble, and locally by perturbing the winds. By comparing ensembles generated by each of these forcings perturbations separately and combined we were able t...

We generate ocean biogeochemical model ensembles including several kinds of stochastic parameterizations. The NEMO stochastic modules are complemented by integrating a subroutine to calculate variable anisotropic spatial scales, which are of particular importance in high-resolution coastal configurations. The domain covers the Bay of Biscay at 1/36...

Ocean model uncertainties arise on a range of spatiotemporal scales from the formulation of forecast models themselves and erroneous surface-lateral boundary forcings. In the past two decades, successful applications of advanced ocean data assimilation methods have led to an increased interest in their estimation. This study is based on a Copernicu...

The work is based on stochastic modelling of ocean physics and biogeochemistry in the Bay of Biscay, on an identical sub-grid configuration of the IBI-MFC system in its latest CMEMS operational version V2.

The Mediterranean is expected to be one of the most prominent and vulnerable climate change "hotspots" of the twenty-first century, and the physical mechanisms underlying this finding are still not clear. Furthermore, complex interactions and feedbacks involving ocean-atmosphere-land-biogeochemical processes play a prominent role in modulating the...

A twin-experiment is carried out introducing elements of an Ensemble Kalman Filter (EnKF), to assess and correct ocean uncertainties in a high-resolution Bay of Biscay configuration. Initially, an ensemble of 102 members is performed by applying stochastic modelling of the wind forcing. The target of this step is to simulate the envelope of possibl...

The Mediterranean is expected to be one of the most prominent and vulnerable climate change “hot spots” of the 21st century, and the physical mechanisms underlying this finding are still not clear. Furthermore complex interactions and feedbacks involving ocean-atmosphere-land-biogeochemical processes play a prominent role in modulating the climate...

Results from a high-resolution hindcast model experiment, supported by available observations, reveal an increasing salinity trend in the north Aegean during the Eastern Mediterranean Transient (EMT) period, largely controlled by increases in the flow rate and salinity of water masses of Levantine origin entering the domain through the Myconos-Ikar...

In this study, a Data Assimilative (DA) twin experiment is implemented with the aim to provide the "best" estimate of the coastal ocean state via ensemble methods. The work uses a coastal configuration of NEMO in the Bay of Biscay, following the activities of LEGOS/CNRS and Mercator Ocean teams within the European MyOcean2 project. In a first step,...

This study is aimed at exploring the errors of a regional model of the Bay of Biscay, a regional zoom of the IBI configuration of the ocean model NEMO, with the ultimate objective of guiding the choice and implementation of a data assimilation system in that region. An ensemble experiment was carried out by randomly perturbing winds along a base of...

Based on the observed variability of the deep-water characteristics in the Eastern Mediterranean Sea, multidecadal high-resolution model simulations, at the basin scale, were carried out in order to identify the major pattern and processes of deep-water formation variability in the Aegean Sea and its influence in the adjacent basins deep circulatio...

An important factor of any Data Assimilation (DA) scheme is the estimation of the background error covariances. This study is linked to the design of a DA system, based on the ensemble Kalman Filter and the ocean model NEMO. The work is part of the Research and Development activities of LEGOS/CNRS and Mercator-Ocean French teams within the European...

Recent dramatic changes of the thermohaline circulation of the Eastern Mediterranean and the observed long-term variability of the thermohaline structure of the various sub-basins (Aegean, Adriatic, Levantine, Ionian) reveal the very sensitive character of the regional thermohaline circulation pattern. We examine deep-water variability, during the...

The Ionian Sea, located in the center of the Mediterranean basin, represents the crossroad between water masses originated in the Western and in the Eastern Mediterranean. The interannual variability of the circulation pattern of this basin and its role as a "water mass distributor" is studied by performing a hindcast simulation using the Princeton...

Saudi Aramco is the oil industry of the Kingdom of Saudi Arabia with several activities related to the environment. In order to optimize daily operations and minimize environmental risks a forecasting system has been employed and setup in operations. The objectives of the system include prevention and mitigation of environmental problems, as well a...

The Eastern Mediterranean deep-water variability during the last 60 years, in relation to new water mass sources, is studied and analyzed through a comprehensive and most complete data set of temperature and salinity profiles. Decadal to multi-decadal variability is present in all sub-basins (Aegean, Adriatic, Levantine, Ionian) with the Eastern Me...

Recent changes of the thermohaline circulation in the Eastern Mediterranean (i.e. the Eastern Mediterranean Transient) and older observations of the thermohaline structure of the Aegean-Levantine region (with events of dramatic changes of deep water characteristics) reveal the very sensitive character of the regional thermohaline circulation patter...

The long term variability of the sea surface temperature (SST) of the Mediterranean basin and its sub‐basins for the period 1869–2006 (138 years) is investigated using the International Comprehensive Ocean—Atmosphere Data Set (I‐COADS). Analysis of the SST time‐series revealed a positive trend in both basin and sub‐basin scale. During the last cen...

Aiming at portraying the Aegean's water mass structure and identifying Dense Water Formation processes, two winter cruises were conducted in 2005-2006, across the plateaus and depressions of the Aegean Sea. The most prominent feature of the water mass distribution in the basin is a distinct "X-shape" of the Θ-S characteristics, suggesting a complic...

Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985–2008) and 35years of NOCS (V.2) in situ-based SST data (1973–2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in relation to local air–sea interaction and large-scale atmospheric variability. Satellite and in situ-deriv...

Twenty four years of AVHRR-derived sea surface temperature (SST) daily data (1985-2008) are used to investigate the long-term variability of this parameter in the Mediterranean Sea. Results indicate a strong eastward increasing sea surface warming trend with a mean annual warming rate of about 0.035 °C/yr for the western sub-basin and of about 0.05...

Twenty four years of AVHRR-derived sea surface temperature (SST) daily data (1985-2008) are used to investigate the long-term variability of this parameter in the Mediterranean Sea. Results indicate a strong eastward increas-ing sea surface warming trend with a mean annual warming rate of about 0.035 °C/yr for the western sub-basin and of about 0.0...

The influence of Black Sea Water (BSW) on the circulation and the water masses of the North Aegean Sea is examined using a high resolution numerical model. The experiments performed focus on changes of the mean annual volume of BSW that enters the North Aegean Sea and on the seasonality of the BSW inflow. The increase of the BSW inflow influences t...

Eight years of AVHRR-derived Sea Surface Temperature (SST) and SeaWiFS-derived surface Chlorophyll (Chl) data (1998-2005) are used to investigate key processes affecting the spatial and temporal variability of the two parameters in the Aegean Sea. Climatological SST and Chl maps are constructed using daily data to study seasonal dynamics whereas Em...

Four years of CTD surveys and profiling float measurements were conducted in various Aegean Sea basins, supplemented by numerical model experiments, in order to monitor the circulation and stratification of the complex environment in the Aegean Sea. There is a remarkable difference of the Θ-S characteristics between the north and south Aegean sub-b...