Eddy Around Zhoushan Island: Observations with Synthetic Aperture Radar at C-band

We studied mesoscale (∼100 km length) eddy around the Zhoushan Island (one Sentinel-1 (S-1) image at coastal East China Sea). The simultaneous sea surface temperature (SST) data from the Advanced Very High-Resolution Radiometer (AVHRR) confirms the existence of upwelling in the Western Pacific Ocean, although, the AVHRR data around the Zhoushan Islands were not available. The difference in the root mean square error (RMSE) between the simulations with the Region Ocean Modelling System (ROMS) and that of the AVHRR data was around 1 °C. Also, the RMSE of the model-simulated current speed compared with that of the Climate Forecast System Version 2 (CFSv2) data was 0.04 m/s. We concluded that natural biogenic slicks mainly contributed to damping Bragg waves for sub-mesoscale upwelling, while ocean currents are an important factor affecting the roughness of mesoscale cold eddies.

Improve Ocean Modelling Software NEMO 4.0 benchmarking and communication efficiency

Communications in distributed memory supercomputers are still limiting scalability of geophysical models. Consid-ering the recent trends of the semiconductor industry, we think this problem is here to stay. We present the optimisations thathave been implemented in the actual 4.0 reference version of the ocean model NEMO 4.0 to improve its scalability. Thanksto the collaboration of oceanographers and HPC experts, we identified and removed the unnecessary communications in twobottleneck routines, the computation of free surface pressure gradient and the forcing in the straights or unstructured open5boundaries. Since a wrong parallel decomposition choice could undermine computing performance, we impose its automaticdefinition in all cases, including when subdomains containing land points only are excluded from the decomposition. For asmaller audience of developers and vendors, we propose a new benchmark configuration, easy to use while offering the fullcomplexity of operational versions.

Interconnection between the Southern South China Sea and the Java Sea through the Karimata Strait

This study aims to investigate the interconnection between the southern South China Sea (SSCS) and Java Sea (JS) by simulating seasonal circulations and associated transports using the Regional Ocean Modelling System (ROMS). The seasonal circulation was predominantly driven by monsoonal wind stress and water exchanges between the SSCS and the JS. During the boreal winter, cooler and saltier waters from the SSCS were advected into the JS, while during the boreal summer, cooler waters from the JS were advected into the SSCS, with the advection of fresher water onto the Peninsular Malaysia’s east coast in the SSCS being the new finding provided by this study. The various water transports were driven southward into the JS during the boreal winter and northward into the SSCS during the boreal summer. The various water transports estimated by ROMS peaked in May during the inflow months from the JS into the SSCS, which was attributed to the simulated anticyclonic eddy in the SSCS, which differed from previous studies that peaked between June and August. The annual mean volume, freshwater, heat, and salt transports were 0.96 Sv, 0.04 Sv, 0.10 PW, and 0.03 × 109 kg s−1, respectively, directed from the SSCS into the JS.

MARINE-EO project: Monitoring and forecast of eutrophication around fish farms, a Maliakos Gulf case (Eastern Mediterranean).

<p>Keywords: eutrophication; high resolution ocean modeling ; Chla satellite data ; biogeochemistry</p><p>Maliakos Gulf corresponds to mesotrophic waters that can reach eutrophic conditions and are occasionally subject to Harmful Algal Blooms (HAB) (Varkitzi et al. 2018). At the same time, it is an important fish farming and aquaculture production area. A large issue is thus related to the monitoring and forecasting of the risk of occurrence of algae blooms in the Gulf. For this purpose, the present study couples predictions from a high-resolution numerical ocean model with satellite observation to improve the monitoring and anticipation of threats for the local fish farms induced by occasional eutrophication.</p><p>This solution is developed in the frame of the MARINE-EO project (https://marine-eo.eu/). It combines satellite observation with high-resolution ocean modelling to provide detailed information as a support to fish farms management and operations. It is implemented in an operational platform, which provides continuous information in real time as well as short term predictions. The deployed solution uses CMEMS physical products as an input data and offers to refine this solution in order to provide a local information on site using a downscaling strategy. High resolution satellite products and ocean modelling allow to include the impact of local coastal processes on currents and water quality parameters to provide a proper monitoring and forecasting solution at the scale of a specific fish farm.</p><p>To model specific eutrophication processes, a NPZD (Nutrients-Phytoplankton-Zooplankton-Detritus) biogeochemical model is used. Included in the MOHID Water modelling system, the water quality module (Mateus, 2006) considering 18 properties: nutrients and organic matter (nitrogen, phosphorus and silica biogeochemical cycles), oxygen and organisms (phytoplankton and zooplankton) was deployed in the western Aegean Sea. The simulated chlorophyll a concentrations are used to compute a risk level for the eutrophication occurrence. To complete this indicator, another risk level was based on the eutrophication variation following Primpas et al. (2010) formulation. In addition to model forecasts, ocean color observations from the Sentinel-2 MSI and Landsat-8 OLI sensors are used to provide high resolution chlorophyll a concentrations maps in case of bloom events. The processing chain uses the sixth version of the Quasi-Analytical Algorithm initially developed by Lee et al. (2002) and an empirical relation based on a database built using the HydroLight software to compute chlorophyll a concentration.</p><p>Two past eutrophication events monitored in situ (Varkitzi et al. 2018) were studied to assess the accuracy of the developed tool. Although few in situ data were available on environmental input (as rivers flow and nutrient concentrations), it was possible using statistics to reproduce qualitatively these blooms. Finally, an operational demonstration was conducted during 2 months of the 2020 autumn season, to showcase real time monitoring and predictive perspectives.</p>

Application of the Regional Ocean Modelling System (ROMS) for Baltic Sea area

<p>The Regional Ocean Modelling System has been begun to implement for region of Baltic Sea.  A preliminary curvilinear grid with horizontal resolution ca. 2.3 km has been prepared based on the grid, which was used in previous application in our research group (in Parallel Ocean Program and in standalone version of Los Alamos Sea Ice Model - CICE).  Currently the grid has 30 sigma layers, but the final number of levels will be adjusted accordingly.</p><p>So far we’ve successfully compiled the model on our machine, run test cases and created Baltic Sea case, which is working with mentioned Baltic grid. The following parameters: air pressure, humidity, surface temperature, long and shortwave radiation, precipitation and wind components are used as an atmospheric forcing. The data arrive from our operational atmospheric model - Weather Research and Forecasting Model (WRF).</p><p>Our main goal is to create efficient system for hindcast and forecast simulations of Baltic Sea together with sea ice component by coupling ROMS with CICE. The reason for choosing these two models is an active community that takes care about model’s developments and updates. Authors also intend to work more closely with the CICE model to improve its agreement with satellite measurements in the Baltic region.<br><br>Calculations were carried out at the Academic Computer Centre in Gdańsk.</p>

The impact of the vertical discretization scheme on the accuracy of a model of the European north-west shelf

<p>The choice of the vertical coordinate system is the single most important factor affecting the quality of ocean model simulations (e.g. Griffies et al. 2000). This is especially true in regions such as the European North-West Shelf (NWS), where complex ocean dynamics result from the combination of a variety of multi-scale physical processes.</p><p>As part of the Copernicus Marine Environment Monitoring Service, the Met Office runs an operational coupled ocean-wave forecasting system of the NWS. The ocean model employed is a regional implementation of NEMO hydrodynamic code (Madec 2017), further developed by both the Met Office and the National Oceanography Centre under the umbrella of the Joint Marine Modelling Programme (JMMP). Here we describe the work of the JMMP group in assessing the impact of different vertical coordinate systems on the accuracy of the solution of the free-running NWS ocean model. </p><p>Five different vertical discretization schemes are compared: i) geopotential z-levels with partial steps, ii) s-levels following a smooth version of the bottom topography using either the Song & Haidvogel (1994) or iii) the Siddorn & Furner (2013) stretching functions, iv) the hybrid Harle et al. (2013) s-z with partial step scheme, and v) the multi-envelope s-coordinate system of Bruciaferri et al. (2018). Three different type of numerical experiments with increasing level of complexity are conducted: i) an idealised test for horizontal pressure gradient errors (HPGE), ii) a barotropic simulation forced only by the astronomical tides (TIDE) and iii) a fully baroclinic simulation using realistic initial condition and external forcing (REAL).      </p><p>Numerical results of the HPGE test show that s-levels models develop the highest spurious currents (order of cm/s),  the multi-enveloping method allows relatively reduction of the error of pure s-levels grids while z-levels with partial steps or the hybrid s-z scheme are affected by the smallest error (order of mm/s).  The TIDE experiment reveals some differences between the models for amplitude and phase of the major tidal components. Preliminary results of the REAL experiment show that models differing only in the vertical discretization schemes broadly represent the same general ocean dynamics, although presenting non-trivial differences in the active tracers and flow fields especially in the proximity of the shelf-break.        </p><p>Song, Y. & Haidvogel, D.B., 1994. A semi-implicit ocean circulation model using a generalized topography-following coordinate system. Journal of Computational Physics 115, 228–244</p><p>Griffies, S.M. et al. 2000. Developments in ocean climate modelling. Ocean Modelling 2, 123–192, 10.1016/S1463-5003(00)00014-7</p><p>Siddorn, J.R. & Furner, R., 2013. An analytical stretching function that combines the best attributes of geopotential and terrain-following vertical coordinates. Ocean Modelling 66, 1–13, 10.1016/j.ocemod.2013.02.001</p><p>Harle, J.D. et al. 2013. Report on role of biophysical interactions on basin-scale C and N budgets. Deliverable 6.5, European Basin-scale Analysis, Synthesis and Integration (EURO-BASIN) Project, http://eurobasin.dtuaqua.dk/eurobasin/documents/deliverables/D6.5%20Report%20on%20role%20of%20biophysical%20interactions%20on%20C%20N%20budget.pdf</p><p>Madec G. et al. (2017). NEMO ocean engine. Notes Du Pôle De Modélisation De L'institut Pierre-simon Laplace (IPSL). http://doi.org/10.5281/zenodo.3248739</p><p>Bruciaferri, D. et al. 2018. A multi-envelope vertical coordinate system for numerical ocean modelling. Ocean Dynamics, 68 (10), 1239-1258, 10.1007/s10236-018-1189-x</p>

A multi-resolution ocean simulation of the anthropogenic radiocarbon transient

<p>We have implemented <sup>14</sup>C and further abiotic tracers (<sup>39</sup>Ar, CFC-12, and SF<sub>6</sub>) into the state-of-the-art ocean circulation model FESOM2. Different to other global ocean circulation models, FESOM2 employs unstructured meshes with variable horizontal resolution. This approach allows for improvements in areas which are commonly poorly resolved in global ocean modelling studies such as upwelling regions, while keeping the overall computational costs still sufficiently moderate. Here, we present results of a transient simulation running from 1850-2015 CE tracing the evolution of the bomb radiocarbon pulse with a focus on the evolution of marine radiocarbon ages. In addition we explore the potential of <sup>39</sup>Argon to complement <sup>14</sup>C dating of marine waters.</p>