In the past years, the Helmholtz Zentrum Geesthacht put in place the Coastal Observing System for... more In the past years, the Helmholtz Zentrum Geesthacht put in place the Coastal Observing System for the North and Arctic Seas (COSYNA) in the frame of which different aspects of forecasting the marine environment have been developed. This paper describes these developments, which are based on recent advances in coastal ocean forecasting in the field of numerical modelling, data assimilation and observational array design. The region of interest is the North and Baltic Sea; most of the coastal examples discussed in the paper are for the German Bight. Several pre-operational applications are presented exemplifying the outcome of using the best available science in coastal ocean predictions. They help to identify new challenges; most of them are associated with resolving the non-linear behavior of coastal ocean, which for the studied region, is manifested by the tidal distortion and generation of shallow-water tides. Led by the motivation to maximize the benefit from observations, the au...
The studies featured in this Research Topic allow us to examine the research on offshore wind ene... more The studies featured in this Research Topic allow us to examine the research on offshore wind energy development across several continents, including Asia, Africa, America, and Europe. The papers cover many of the most relevant subjects, including wind resource and energy management for bottom-fixed and floating turbines.
Sea level in the North Sea is densely monitored by tide gauges. These measurements are used for v... more Sea level in the North Sea is densely monitored by tide gauges. These measurements are used for validation as well as for the detection of extreme events. Here, we focus on the detection of sea level states with anomalous spatial correlations. An autoassociative neural network emulates the spatial correlations of gauges in a lower dimensional subspace. Anomalous sea-level states are defined by means of failure of the reconstruction model. Using spatially distributed data as input to the network thus reveals sea-level conditions with unusual spatial correlations. The corresponding atmospheric conditions indicate high wind tendencies and pressure anomalies. Quantitative analysis of such states might help assess and improve numerical model quality in the future as well as provide new insights into the nonlinear processes involved. The method has the advantage of being easily applicable to any tide gauge array without preprocessing the data or acquiring any additional information.
Integration of observations of the coastal ocean continuum, from regional oceans to shelf seas an... more Integration of observations of the coastal ocean continuum, from regional oceans to shelf seas and estuaries/deltas with models, can substantially increase the value of observations and enable a wealth of applications. In particular, models can play a critical role at connecting sparse observations, synthesizing them, and assisting the design of observational networks; in turn, whenever available, observations can guide coastal model development. Coastal observations should sample the two-way interactions between nearshore, estuarine and shelf processes and open ocean processes, while accounting for the different pace of circulation drivers, such as the fast atmospheric, hydrological and tidal processes and the slower general ocean circulation and climate scales. Because of these challenges, high-resolution models can serve as connectors and integrators of coastal continuum observations. Data assimilation approaches can provide quantitative, validated estimates of Essential Ocean Variables in the coastal continuum, adding scientific and socioeconomic value to observations through applications (e.g., sea-level rise monitoring, coastal management under a sustainable ecosystem approach, aquaculture, dredging, transport and fate of pollutants, maritime safety, hazards under natural variability or climate change). We strongly recommend an internationally coordinated approach in support of the proper integration of global and coastal continuum scales, as well as for critical tasks such as community-agreed bathymetry and coastline products.
The sea level in the North Sea is densely monitored by tide gauges. The data they provide can be ... more The sea level in the North Sea is densely monitored by tide gauges. The data they provide can be used to solve different scientific and practical problems, including the validation of numerical models and the detection of extreme events. This study focuses on the detection of sea-level states with anomalous spatial correlations using autoassociative neural networks (AANNs), trained with different sets of observation-and model-based data. Such sea-level configurations are related to nonlinear ocean dynamics; therefore, neural networks appear to be the right candidate for their identification. The proposed network can be used to accurately detect such anomalies and localize them. We demonstrate that the atmospheric conditions under which anomalous sea-level states occur are characterized by high wind tendencies and pressure anomalies. The results show the potential of AANNs for accurately detecting the occurrence of such events. We show that the method works with AANNs trained on tide gauge records as well as with AANN trained with modelbased sea surface height outputs. The latter can be used to enhance the representation of anomalous sea-level events in ocean models. Quantitative analysis of such states may help assess and improve numerical model quality in the future as well as provide new insights into the nonlinear processes involved. This method has the advantage of being easily applicable to any tide gauge array without preprocessing the data or acquiring any additional information.
Numerical modelling of extreme wave events in the Southwestern South Atlantic
<p>Severe ocean surface waves generated by wind (hereafter waves) have a st... more <p>Severe ocean surface waves generated by wind (hereafter waves) have a strong impact on socio-economic activities such as navigation, harbours, oil exploitation, and coastal infrastructure. The South Atlantic monitoring remains behind regarding high-resolution wave products that can support the understanding and impacts of extreme wave events over the region. In this work, we present a high-resolution wave hindcast for the Southwestern South Atlantic (SWSA) evaluated under extreme conditions. Such a product can be used by several sectors to contribute to a more predictive and open data ocean, engaging the goals proposed by the UN Ocean Decade. The hindcast is produced using the WAM model forced by 1-hourly ERA5 surface winds. Three horizontal grids are used for downscaling, to keep a smooth resolution increase: a Global grid (0.25°), an intermediate grid that covers the Eastern coast of South America (0.1°), and a finer grid, focusing on the SWSA (0.05°). The spectral domain is discretized into 30 logarithmically spaced frequency bins and the wave propagating directions are set with a resolution of 24°. Sensibility runs are performed to obtain the more suitable configuration to represent the extreme wave climate in the region. The physics parameterization for the input and open ocean dissipation are tested between Jansen and Ardhuin formulations. The analyses showed that Ardhuin's parameterization (ST4) with Betamax of 1.60 performed better in comparison with buoys and satellite measurements during storm conditions. Moreover, the sea ice inclusion improved the wave height and wave direction in the coastal region, particularly on the southern Brazilian coast. Including depth refraction in both intermediate and finer grids also played an important role in the wave direction, improving the wave model performance against in situ data. We also present the wave hindcast evaluation against buoy and satellite data from 2017 to 2021, focusing on extreme wave events. Furthermore, significant wave height and wind speed are assimilated and the benefits of data assimilation in predicting extreme waves in the region are evaluated.</p>
Adaptation to the impacts of climate change and human intervention in the Elbe estuary: model-based identification of possible trade-offs
<p>The Elbe estuary ensures the connection between one of the largest ports... more <p>The Elbe estuary ensures the connection between one of the largest ports in Europe, Hamburg, and the North Sea. The need to adapt the navigational channel to the increasing demands of ship transport as well as the necessities of coastal protection and of ensuring the functioning of the ecosystem are leading to contradicting demands. In order to decide on possible trade-offs, a detailed understanding of present and possible future interactions between local and global processes is necessary. In this study, we use realistic modeling and observations to show the functioning of the current hydrodynamic and biogeochemical estuarine system. We demonstrate the increasing importance of the formation of stratification in the low-salinity reaches, which is related to an increase in salt intrusion, sedimentation and the risk of hypoxia. The model results reveal that dry and hot summers are leading to dangerous oxygen minima in the artificially deepened tidal Elbe. To examine the effect of a more natural expansion of the navigational channel, we further use an idealized model of the estuary. In this exercise, we study the influence of sinusoidal meanders on the tides, the thermohaline dynamics and the estuarine ecosystem. It turns out that this deregulation of the shipping channel leads to a reduction of the tidal range and of silting in the port area. Furthermore, the channel curvature enhances oxygen levels in the area of the estuariane oxygen minimum zone in comparison with the straight channel. Sensitivity experiments demonstrate the sustainability of such an adaptation strategy towards the dominant trends of climate change such as sea level rise and global warming. Finally we assess the plausibility of the measure in terms of its potential to conciliate contradicting demands in the intensively used estuarine environment.</p>
The ability of forecasting systems to simulate tropical cyclones is still insufficient, and curre... more The ability of forecasting systems to simulate tropical cyclones is still insufficient, and currently, there is an increased interest in improving model performance for intense tropical cyclones. In this study, the impact of reducing surface drag at high wind speeds on modeling wind and wave conditions during the super Typhoon Lingling event over the northwest Pacific Ocean in 2019 is investigated. The model response with respect to the parameterization for momentum exchange at the ocean surface is demonstrated using a fully coupled regional atmosphere model (the Consortium for Small-Scale Modeling-Climate Limited-area Modeling, CCLM) and a wind wave model (WAM). The active two-way coupling between the atmosphere and ocean waves model is enabled through the introduction of sea state-dependent surface drag into the CCLM and updated winds into the WAM. The momentum exchange with the sea surface is modeled via the dependency of the roughness length (Z0) on the surface stress itself and...
Direct sensing of total ocean surface currents with microwave Doppler signals is a growing topic ... more Direct sensing of total ocean surface currents with microwave Doppler signals is a growing topic of interest for oceanography, with relevance to several new ocean mission concepts proposed in recent years. Since 2014, the spaceborne C-band SAR instruments of the Copernicus Sentinel-1 (S1) mission routinely acquire microwave Doppler data, distributed to users through operational S1 Level-2 ocean radial velocity (L2 OCN RVL) products. S1 L2 RVL data could produce high-resolution maps of ocean surface currents that would benefit ocean observing and modelling, particularly in coastal regions. However, uncorrected platform effects and instrument anomalies continue to impact S1 RVL data and prevent direct exploitation. In this paper, a simple empirical method is proposed to calibrate and correct operational S1 L2 RVL products and retrieve two-dimensional maps of surface currents in the radar line-of-sight. The study focuses on the German Bight where wind, wave and current data from marine stations and an HF radar instrumented site provide comprehensive means to evaluate S1 retrieved currents. Analyses are deliberately limited to Sentinel-1A (S1A) ascending passes to focus on one single instrument and fixed SAR viewing geometry. The final dataset comprises 78 separate S1A acquisitions over 2.5 years, of which 56 are matched with collocated HF radar data. The empirical corrections bring significant improvements to S1A RVL data, producing higher quality estimates and much better agreement with HF radar radial currents. Comparative evaluation of S1A against HF radar currents for different WASV corrections reveal that best results are obtained in this region when computing the WASV with sea state rather than wind vector input. Accounting for sea state produces S1 radial currents with a precision (std of the difference) around 0.3 m/s at ~1 km resolution. Precision improves to ~0.24 m/s when averaging over 21 × 27 km 2 , with correlations with HF radar data reaching up to 0.93. Evidence of wind-current interactions when tides and wind align and short fetch conditions call for further research with more satellite data and other sites to better understand and correct the WASV in coastal regions. Finally, 1 km resolution maps of climatological S1A radial currents obtained over 2.5 years reveal strong coastal jets and fine scale details of the coastal circulation that closely match the known bathymetry and deepwater coastal channels in this region. The wealth of oceanographic information in corrected S1 RVL data is encouraging for Doppler oceanography from space and its application to observing small scale ocean dynamics, atmosphere and ocean vertical exchanges and marine ecosystem response to environmental change.
Just as CryoSat-2, Sentinel-3 embarks on board a radar altimeter (SRAL) with the novel Synthetic ... more Just as CryoSat-2, Sentinel-3 embarks on board a radar altimeter (SRAL) with the novel Synthetic Aperture Radar (SAR) mode that enables higher resolution and more accurate altimeter-derived parameters in the coastal zone, thanks to the reduced along-track footprint. Exploiting the SAR data in the recent years, many researchers have already proven that the performance of SAR altimetry with specific coastal retrackers is superior to collocated Pseudo-Low Resolution Mode (PLRM) coastal altimetry algorithms but they also pointed out that residual errors due to land contamination are still present in the very proximity of the land (0-3 km). The objective of this work is to further improve these results by exploiting extra information provided by SAR altimeters, namely the so-called Range Integrated Power (RIP), the new waveform built by a simple integration of the Doppler beams in the range direction. The RIP characterizes the backscattering state of the ground cell, towards which all the Doppler beams have been steered. These developments lead to a new retracker, here coined SAMOSA++, in which the RIP, as computed from the L1B-S data, is converted into a surface backscattering profile and directly integrated in the SAMOSA retracker as part of the model formulation itself. In this way, the modified SAMOSA model is automatically and autonomously able to cope with the different return waveform shapes from different surface types: either diffusive or specular. The mean square slope computed from the RIP is also estimated, representing a new output of the retracker. The performance of this new retracker is here cross-compared against its previous version, SAMOSA+, and against the standard Sentinel-3 marine PDGS (Payload Data Ground Segment) SAR retracker (SAMOSA2) in both coastal zone and open ocean in order to ensure a seamless transition between these zones. The new retracker SAMOSA++ is validated in the North East Atlantic region, where appropriate in situ validation data are available. The retrievals from the new retracker are cross-compared against the network of tide gauges and buoys in the German Bight and versus the output of the GCOAST Helmholtz-Zentrum Geesthacht (HZG) regional circulation and wave model. In addition, sea level estimates derived with different ocean tide and wet path delay geophysical correction models are compared. Results indicate that in this
GCOAST: Skill assessments of coupling wave and circulation models (NEMO-WAM)
Journal of Physics: Conference Series, 2021
The coupling of models is a commonly used approach when addressing the complex interactions betwe... more The coupling of models is a commonly used approach when addressing the complex interactions between different components of the Earth system. This study presents the development of a new, high -resolution, coupled ocean and wave model system for the North Sea and the Baltic Sea, which is part of the Geestacht COAstal model SysTem GCOAST. We focus on the nonlinear feedback between strong tidal currents and wind -waves, which can no longer be ignored, in particular in the coastal zone where its role seems to be dominant. The proposed coupling parameterisations account for the feedback between of the upper ocean on the atmospheric circulation by accounting for the effects of the sea level, and ocean temperature and salinity. A focus is given on the newly implemented parameterisations that consider the effect of non-liner contribution and the component transfer of the momentum and energy fluxes from the atmosphere to the ocean thought the waves interface. Sensitivity experiments are per...
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Papers by Joanna STANEVA