Successive CTD profiles of an Argo float trapped within a deep (~1250 m) sub-basin of the North A... more Successive CTD profiles of an Argo float trapped within a deep (~1250 m) sub-basin of the North Aegean Sea during 2014–2015 enabled identification of deep-water ventilation episodes and inference of a bulk (budget-based) vertical eddy diffusivity during the period that followed these events. Independent effective eddy diffusivity profiles were computed under the assumption that the turbulent exchange of heat, salt and buoyancy through each isobath below 400 m will balance the rate of change of the corresponding variable’s content of the water volume within the basin below that depth. The initially estimated thermal, saline and density diffusivity profiles were significantly different from each other. Assuming turbulence was the dominant mixing process between the intermediate and deep water masses led to identification of conductivity sensor drift rate of 4.6 E-6 S/ (m day). After correcting the sensor’s drift, bulk eddy diffusivities Kρ ; KS and KT were found to span (2–30)E-3 m2/s , in close agreement below 400 m depth. These estimates are at least one order of magnitude higher than eddy diffusivities based on a finescale internal-wave strain parameterization. Enhanced boundary mixing and double diffusion are examined as candidates to explain the high effective diffusivity values. A hypsometric correction appears to provide sufficient diapycnal transport along the boundaries to reproduce bulk buoyancy transports.
In this study, 17 hydrologists with different experience in hydrological modelling applied the sa... more In this study, 17 hydrologists with different experience in hydrological modelling applied the same conceptual catchment model (HBV) to a Greek catchment, using identical data and model code. Calibration was performed manually. Subsequently, the modellers were asked for their experience, their calibration strategy, and whether they enjoyed the exercise. The exercise revealed that there is considerable modellers' uncertainty even among the experienced modellers. It seemed to be equally important whether the modellers followed a good calibration strategy, and whether they enjoyed modelling. The exercise confirmed previous studies about the benefit of model ensembles: Different combinations of the simulation results (median, mean) outperformed the individual model simulations, while filtering the simulations even improved the quality of the model ensembles. Modellers' experience, decisions, and attitude, therefore, have an impact on the hydrological model application and should be considered as part of hydrological modelling uncertainty.
Successive CTD profiles of an ARGO float trapped within a deep sub-basin of the North Aegean Sea ... more Successive CTD profiles of an ARGO float trapped within a deep sub-basin of the North Aegean Sea during 2014-2015 enabled the identification of deep-water ventilation episodes and the determination of effective vertical eddy diffusivity during the stagnation period that followed these events. The assumption of turbulent mixing between the intermediate and deep water masses led to the identification of a conductivity sensor drift rate of 4.6×10^−6 Sm^−1 day^−1. After correcting the sensor’s drift, the eddy diffusion coefficients KT, KS and Kσθ were found to range between 2×10^−4 and 2-3×10^−3 m^2s^−1 for the deeper than 400m waters. These estimates are at least one order of magnitude higher than eddy diffusivities based on the internal wave strain method, suggesting that open ocean internal waves cannot maintain the observed mixing rates.
The study of the Tyrrhenian deep water properties and their distribution over time and space seem... more The study of the Tyrrhenian deep water properties and their distribution over time and space seems to be particularly relevant to the impact of climatic variability on the Mediterranean Sea. This work aims to contribute to a better understanding of the thermohaline variability, the main deep-water formation mechanisms, such as heat-salt fluxes associated with the double-diffusive activity, and tries to provide a representation of the deep-water characteristics based on long-term hydrological measurements in the Tyrrhenian basin. The analysis of these measurements (ARGO floats, CTD probes, gliders, expendable bathythermographs (XBT) and fixed moorings) enables to follow the evolution of the water mass characteristics under the influence of the climatic variability, which modified both the intermediate and the deep water. The analysis of these measurements appears to be crucial in order to perceive the role of mixing water masses from the eastern and western Mediterranean and to estimate the ocean heat content, its redistribution and the relationship with the air-sea interface, which is fundamental for understanding climate variability and change.
This project was carried out within the course Satellite Oceanography under the academic supervis... more This project was carried out within the course Satellite Oceanography under the academic supervision of Konstantinos Topouzelis. The main object of this study was to classify and map the underwater habitats in a shallow coastal area northeast of the Greek island Lesvos. This was done by a combination of high spatial resolution WorldView-2 imagery and in-field observations, after applying atmospheric and water-column corrections. Focus was, to survey the meadows of Posidonia oceanica, which form the major benthic ecosystem dominating the soft bottom of the sublittoral zone in the Mediterranean Sea.
Successive CTD profiles of an Argo float trapped within a deep (~1250 m) sub-basin of the North A... more Successive CTD profiles of an Argo float trapped within a deep (~1250 m) sub-basin of the North Aegean Sea during 2014–2015 enabled identification of deep-water ventilation episodes and inference of a bulk (budget-based) vertical eddy diffusivity during the period that followed these events. Independent effective eddy diffusivity profiles were computed under the assumption that the turbulent exchange of heat, salt and buoyancy through each isobath below 400 m will balance the rate of change of the corresponding variable’s content of the water volume within the basin below that depth. The initially estimated thermal, saline and density diffusivity profiles were significantly different from each other. Assuming turbulence was the dominant mixing process between the intermediate and deep water masses led to identification of conductivity sensor drift rate of 4.6 E-6 S/ (m day). After correcting the sensor’s drift, bulk eddy diffusivities Kρ ; KS and KT were found to span (2–30)E-3 m2/s , in close agreement below 400 m depth. These estimates are at least one order of magnitude higher than eddy diffusivities based on a finescale internal-wave strain parameterization. Enhanced boundary mixing and double diffusion are examined as candidates to explain the high effective diffusivity values. A hypsometric correction appears to provide sufficient diapycnal transport along the boundaries to reproduce bulk buoyancy transports.
In this study, 17 hydrologists with different experience in hydrological modelling applied the sa... more In this study, 17 hydrologists with different experience in hydrological modelling applied the same conceptual catchment model (HBV) to a Greek catchment, using identical data and model code. Calibration was performed manually. Subsequently, the modellers were asked for their experience, their calibration strategy, and whether they enjoyed the exercise. The exercise revealed that there is considerable modellers' uncertainty even among the experienced modellers. It seemed to be equally important whether the modellers followed a good calibration strategy, and whether they enjoyed modelling. The exercise confirmed previous studies about the benefit of model ensembles: Different combinations of the simulation results (median, mean) outperformed the individual model simulations, while filtering the simulations even improved the quality of the model ensembles. Modellers' experience, decisions, and attitude, therefore, have an impact on the hydrological model application and should be considered as part of hydrological modelling uncertainty.
Successive CTD profiles of an ARGO float trapped within a deep sub-basin of the North Aegean Sea ... more Successive CTD profiles of an ARGO float trapped within a deep sub-basin of the North Aegean Sea during 2014-2015 enabled the identification of deep-water ventilation episodes and the determination of effective vertical eddy diffusivity during the stagnation period that followed these events. The assumption of turbulent mixing between the intermediate and deep water masses led to the identification of a conductivity sensor drift rate of 4.6×10^−6 Sm^−1 day^−1. After correcting the sensor’s drift, the eddy diffusion coefficients KT, KS and Kσθ were found to range between 2×10^−4 and 2-3×10^−3 m^2s^−1 for the deeper than 400m waters. These estimates are at least one order of magnitude higher than eddy diffusivities based on the internal wave strain method, suggesting that open ocean internal waves cannot maintain the observed mixing rates.
The study of the Tyrrhenian deep water properties and their distribution over time and space seem... more The study of the Tyrrhenian deep water properties and their distribution over time and space seems to be particularly relevant to the impact of climatic variability on the Mediterranean Sea. This work aims to contribute to a better understanding of the thermohaline variability, the main deep-water formation mechanisms, such as heat-salt fluxes associated with the double-diffusive activity, and tries to provide a representation of the deep-water characteristics based on long-term hydrological measurements in the Tyrrhenian basin. The analysis of these measurements (ARGO floats, CTD probes, gliders, expendable bathythermographs (XBT) and fixed moorings) enables to follow the evolution of the water mass characteristics under the influence of the climatic variability, which modified both the intermediate and the deep water. The analysis of these measurements appears to be crucial in order to perceive the role of mixing water masses from the eastern and western Mediterranean and to estimate the ocean heat content, its redistribution and the relationship with the air-sea interface, which is fundamental for understanding climate variability and change.
This project was carried out within the course Satellite Oceanography under the academic supervis... more This project was carried out within the course Satellite Oceanography under the academic supervision of Konstantinos Topouzelis. The main object of this study was to classify and map the underwater habitats in a shallow coastal area northeast of the Greek island Lesvos. This was done by a combination of high spatial resolution WorldView-2 imagery and in-field observations, after applying atmospheric and water-column corrections. Focus was, to survey the meadows of Posidonia oceanica, which form the major benthic ecosystem dominating the soft bottom of the sublittoral zone in the Mediterranean Sea.
Uploads