scholarly journals A Fuzzy-Based Framework for Assessing Uncertainty in Drift Prediction Using Observed Currents and Winds

2021 ◽  
Vol 8 ◽  
Author(s):  
Hauke Blanken ◽  
Caterina Valeo ◽  
Charles Hannah ◽  
Usman T. Khan ◽  
Tamás Juhász
Keyword(s):  
Surface Wind ◽  
Model Performance ◽  
Ocean Surface ◽  
Near Surface ◽  
Traditional Assessment ◽  
Object Based ◽  
Ocean Surface Currents ◽  
Surface Drifters ◽  
Ocean Station Papa ◽  
Empirical Coefficients

This paper proposes a fuzzy number—based framework for quantifying and propagating uncertainties through a model for the trajectories of objects drifting at the ocean surface. Various sources of uncertainty that should be considered are discussed. This model is used to explore the effect of parameterizing direct wind drag on the drifting object based on its geometry, and using measured winds to parameterize shear and rotational dynamics in the ocean surface currents along with wave-driven circulation and near-surface wind shear. Parameterizations are formulated in a deterministic manner that avoids the commonly required specification of empirical leeway coefficients. Observations of ocean currents and winds at Ocean Station Papa in the northeast Pacific are used to force the trajectory model in order to focus on uncertainties arising from physical processes, rather than uncertainties introduced by the use of atmospheric and hydrodynamic models. Computed trajectories are compared against observed trajectories from five different types of surface drifters, and optimal combinations of forcing parameterizations are identified for each type of drifter. The model performance is assessed using a novel skill metric that combines traditional assessment of trajectory accuracy with penalties for overestimation of uncertainty. Comparison to the more commonly used leeway method shows similar performance, without requiring the specification of empirical coefficients. When using optimal parameterizations, the model is shown to correctly identify the area in which drifters are expected to be found for the duration of a seven day simulation.

Effect of Uni- and Bi-Directional Coupling of Ocean-Met Interaction on Significant Wave Height and Local Wind

2017 ◽  
Author(s):  
Adil Rasheed ◽  
Jakob Kristoffer Süld ◽  
Mandar Tabib
Keyword(s):  
Wave Height ◽  
Significant Wave Height ◽  
Surface Wind ◽  
Wave Model ◽  
Ocean Surface ◽  
Observation Data ◽  
Local Wind ◽  
Near Surface ◽  
Significant Wave ◽  
Bidirectional Coupling

Accurate prediction of near surface wind and wave height are important for many offshore activities like fishing, boating, surfing, installation and maintenance of marine structures. The current work investigates the use of different methodologies to make accurate predictions of significant wave height and local wind. The methodology consists of coupling an atmospheric code HARMONIE and a wave model WAM. Two different kinds of coupling methodologies: unidirectional and bidirectional coupling are tested. While in Unidirectional coupling only the effects of atmosphere on ocean surface are taken into account, in bidirectional coupling the effects of ocean surface on the atmosphere are also accounted for. The predicted values of wave height and local wind at 10m above the ocean surface using both the methodologies are compared against observation data. The results show that during windy conditions, a bidirectional coupling methodology has better prediction capability.

Estimation of wave-induced contribution to Sentinel-1 Doppler shift observations

2020 ◽  
Author(s):  
Artem Moiseev ◽  
Harald Johnsen ◽  
Johnny Johannessen
Keyword(s):  
Doppler Shift ◽  
Incidence Angle ◽  
Wind Waves ◽  
Surface Wind ◽  
Surface Current ◽  
Ocean Surface ◽  
Reliable Information ◽  
Near Surface ◽  
Ocean Surface Current ◽  
Wave Induced

<p>The Doppler Centroid Anomaly (DCA) registered by microwave Synthetic Aperture Radar (SAR) contains information about ocean surface motion in the radar line-of-sight direction. The recorded signal is associated with the motion induced by the total wavefield (i.e., both wind waves and swell) and underlying ocean surface currents. Hence, accurate estimates of the wave-induced contribution to the observed DCA is required in order to obtain reliable information about underlying ocean surface current. In this study, we develop an empirical geophysical model function for the estimation of the wave-induced DCA. The study is based on two months of Sentinel-1 SAR Wave mode (WV) DCA observations collocated with wind field at 10m height from the ECMWF model and sea state information from the WAVEWATCH III model.</p><p>Analysis of two months of observations acquired over land showed that thanks to the novel Sentinel-1 DCA calibration, the uncertainty in the data does not exceed 3Hz (corresponding to a radial velocity of 0.21/014 m/s in the near/far range. The relationship between the DCA and the near-surface wind is in agreement with previously reported findings under the assumption of fully developed seas; the DCA is about 24% of the range wind speed at 23° incidence angle and decreasing (up to 50%) with increasing incidence angle from 23° to 36°. However, the difference between upwind (i.e., the wind blows towards antenna) and downwind (i.e., wind blows away from the antenna) configurations is inconsistent from study to study. Reliable information about the wave field indeed helps to describe the spread in the DCA, especially at low and moderate wind speeds, and when the ocean surface is dominated by the remotely generated swell.</p><p>The CDOP model is used as a baseline for estimating the wind-wave-induced Doppler shift. Retraining of the CDOP model for the Sentinel-1 SAR observations (CDOP-S) yielded a significantly better fit. Then, we extended the GMF with parameters of the wavefield (significant wave height, mean wave period and direction) in the moment of SAR acquisition. Combining information about near-surface wind and ocean surface wave fields also considerably improves the accuracy of the wave-induced Doppler shift estimates. In turn,  the accuracy of the ocean surface current retrievals are improved as demonstrated by the promising agreement with the near-surface ocean surface current climatology based on multiyear drifter observations.</p>

scholarly journals Decadal-Mean Impact of Including Ocean Surface Currents in Bulk Formulas on Surface Air–Sea Fluxes and Ocean General Circulation

2017 ◽  
Vol 30 (23) ◽  
pp. 9511-9525 ◽  
Author(s):  
Yang Wu ◽  
Xiaoming Zhai ◽  
Zhaomin Wang
Keyword(s):  
Wind Stress ◽  
General Circulation ◽  
Surface Wind ◽  
Ocean Surface ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Turbulent Heat ◽  
Surface Currents ◽  
Ocean Surface Currents ◽  
Ocean General Circulation

The decadal-mean impact of including ocean surface currents in the bulk formulas on surface air–sea fluxes and the ocean general circulation is investigated for the first time using a global eddy-permitting coupled ocean–sea ice model. Although including ocean surface currents in air–sea flux calculations only weakens the surface wind stress by a few percent, it significantly reduces wind power input to both geostrophic and ageostrophic motions, and damps the eddy and mean kinetic energy throughout the water column. Furthermore, the strength of the horizontal gyre circulations and the Atlantic meridional overturning circulation are found to decrease considerably (by 10%–15% and ~13%, respectively). As a result of the weakened ocean general circulation, the maximum northward global ocean heat transport decreases by about 0.2 PW, resulting in a lower sea surface temperature and reduced surface heat loss in the northern North Atlantic. Additional sensitivity model experiments further demonstrate that it is including ocean surface currents in the wind stress calculation that dominates this decadal impact, with including ocean surface currents in the turbulent heat flux calculations making only a minor contribution. These results highlight the importance of properly accounting for ocean surface currents in surface air–sea fluxes in modeling the ocean circulation and climate.

scholarly journals Properties of the frequency spectra of the temperature anomalies of ocean surface and near-surface air in a simple stochastic climate model with fluctuating parameters

2019 ◽  
Vol 55 (4) ◽  
pp. 27-36
Author(s):  
D. A. Petrov
Keyword(s):  
Surface Wind ◽  
Sensible Heat Flux ◽  
Ocean Surface ◽  
Small Scale ◽  
Model Parameters ◽  
Radiation Balance ◽  
Frequency Spectra ◽  
Near Surface ◽  
Temperature Anomalies ◽  
First Case

The frequency properties of the ocean surface temperature anomalies (SST) and near-surface air (SAT) spectra are analyzed on the basis of a simple energy balance model of the climate, taking into account the fluctuations of the radiation balance, the latent and sensible heat flux and the velocity of the near-surface wind in two particular cases when the statistical properties of the model parameters are the white noise (small-scale-mesoscale subintervals) and the combined case when the properties of the synoptic subinterval of this parameters are taken into account in the SAT block. It was found that in the first case, the spectra have no features, and in the second they contain selected frequencies in the synoptic and low- frequency intervals. The dependent of their frequencies on model parameters are analyzed. The properties of standard deviations of SST and SAT are investigated.

scholarly journals Coincident Observations of Dye and Drifter Relative Dispersion over the Inner Shelf

2019 ◽  
Vol 49 (9) ◽  
pp. 2447-2468
Author(s):  
Leonel Romero ◽  
J. Carter Ohlmann ◽  
Enric Pallàs-Sanz ◽  
Nicholas M. Statom ◽  
Paula Pérez-Brunius ◽  
...  
Keyword(s):  
Surface Wind ◽  
Relative Dispersion ◽  
Small Scale ◽  
Langmuir Circulation ◽  
Physical Processes ◽  
Inner Shelf ◽  
Near Surface ◽  
Wide Range ◽  
Surface Drifters

AbstractCoincident Lagrangian observations of coastal circulation with surface drifters and dye tracer were collected to better understand small-scale physical processes controlling transport and dispersion over the inner shelf in the Gulf of Mexico. Patches of rhodamine dye and clusters of surface drifters at scales of O(100) m were deployed in a cross-shelf array within 12 km from the coast and tracked for up to 5 h with airborne and in situ observations. The airborne remote sensing system includes a hyperspectral sensor to track the evolution of dye patches and a lidar to measure directional wavenumber spectra of surface waves. Supporting in situ measurements include a CTD with a fluorometer to inform on the stratification and vertical extent of the dye and a real-time towed fluorometer for calibration of the dye concentration from hyperspectral imagery. Experiments were conducted over a wide range of conditions with surface wind speed between 3 and 10 m s−1 and varying sea states. Cross-shelf density gradients due to freshwater runoff resulted in active submesoscale flows. The airborne data allow characterization of the dominant physical processes controlling the dispersion of passive tracers such as freshwater fronts and Langmuir circulation. Langmuir circulation was identified in dye concentration maps on most sampling days except when the near surface stratification was strong. The observed relative dispersion is anisotropic with eddy diffusivities O(1) m2 s−1. Near-surface horizontal dispersion is largest along fronts and in conditions dominated by Langmuir circulation is larger in the crosswind direction. Surface convergence at fronts resulted in strong vertical velocities of up to −66 m day−1.

scholarly journals Empirical Lagrangian parametrization for wind-driven mixing of buoyant particles at the ocean surface

2021 ◽  
Author(s):  
Victor Onink ◽  
Erik van Sebille ◽  
Charlotte Laufkötter
Keyword(s):  
Turbulent Mixing ◽  
Model Performance ◽  
Ocean Surface ◽  
Additional Parameter ◽  
Concentration Profiles ◽  
Surface Mixed Layer ◽  
Vertical Diffusion ◽  
Near Surface ◽  
Global Circulation Models ◽  
Stochastic Transport

Abstract. Turbulent mixing is a vital component of vertical particulate transport, but ocean global circulation models (OGCMs) generally have low resolution representations of near-surface mixing. Furthermore, turbulence data is often not provided in reanalysis products. We present 1D parametrizations of wind-driven turbulent mixing in the ocean surface mixed layer, which are designed to be easily included in 3D Lagrangian model experiments. Stochastic transport is computed by Markov-0 or Markov-1 models, and we discuss the advantages/disadvantages of two vertical profiles for the vertical diffusion coefficient Kz. All vertical diffusion profiles and stochastic transport models lead to stable concentration profiles for buoyant particles, which for particles with rise velocities of 0.03 and 0.003 m s−1 agree relatively well with concentration profiles from field measurements of microplastics. Markov-0 models provide good model performance for integration timesteps of Δt ≈ 30 seconds, and can be readily applied in studying the behaviour of buoyant particulates in the ocean. Markov-1 models do not consistently improve model performance relative to Markov-0 models, and require an additional parameter that is poorly constrained.

scholarly journals Decoding the dynamics of poleward shifting climate zones using aqua-planet model simulations

2022 ◽  
Author(s):  
Hu Yang ◽  
Jian Lu ◽  
Qiang Wang ◽  
Xiaoxu Shi ◽  
Gerrit Lohmann
Keyword(s):  
Ocean Circulation ◽  
Surface Wind ◽  
Ocean Surface ◽  
Ocean Warming ◽  
Ocean Dynamics ◽  
Causal Mechanism ◽  
Near Surface ◽  
Climate Zones ◽  
Surface Warming ◽  
Poleward Shift

AbstractGrowing evidence indicates that the atmospheric and oceanic circulation experiences a systematic poleward shift in a warming climate. However, the complexity of the climate system, including the coupling between the ocean and the atmosphere, natural climate variability and land-sea distribution, tends to obfuscate the causal mechanism underlying the circulation shift. Here, using an idealised coupled aqua-planet model, we explore the mechanism of the shifting circulation, by isolating the contributing factors from the direct CO$$_2$$ 2 forcing, the indirect ocean surface warming, and the wind-stress feedback from the ocean dynamics. We find that, in contrast to the direct CO$$_2$$ 2 forcing, ocean surface warming, in particular an enhanced subtropical ocean warming, plays an important role in driving the circulation shift. This enhanced subtropical ocean warming emerges from the background Ekman convergence of surface anomalous heat in the absence of the ocean dynamical change. It expands the tropical warm water zone, causes a poleward shift of the mid-latitude temperature gradient, hence forces a corresponding shift in the atmospheric circulation and the associated wind pattern. The shift in wind, in turn drives a shift in the ocean circulation. Our simulations, despite being idealised, capture the main features of the observed climate changes, for example, the enhanced subtropical ocean warming, poleward shift of the patterns of near-surface wind, sea level pressure, storm tracks, precipitation and large-scale ocean circulation, implying that increase in greenhouse gas concentrations not only raises the temperature, but can also systematically shift the climate zones poleward.

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