Variability in the South Indian Ocean gyre circulation derived from Argo floats

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The Nature of Eddy Kinetic Energy in the Labrador Sea: Different Types of Mesoscale Eddies, their Temporal Variability and Impact on Deep Convection

Oceanic eddies are an important component in preconditioning the central Labrador Sea (LS) for deep convection and in restratifying the convected water. This study investigates the different sources and impacts of Eddy Kinetic Energy (EKE) and its temporal variability in the LS with the help of a 52-year long hindcast simulation of a 1/20° ocean model. Irminger Rings (IR) are generated in the West Greenland Current (WGC) between 60 and 62°N, mainly affect preconditioning and limit the northward extent of the convection area. The IR exhibit a seasonal cycle and decadal variations linked to the WGC strength, varying with the circulation of the subpolar gyre. The mean and temporal variations of IR generation can be attributed to changes in deep ocean baroclinic and upper ocean barotropic instabilities at comparable magnitudes. The main source of EKE and restratification in the central LS are Convective Eddies (CE). They are generated by baroclinic instabilities near the bottom of the mixed layer during and after convection. The CE have a mid-depth core and reflect the hydrographic properties of the convected water mass with a distinct minimum in potential vorticity. Their seasonal to decadal variability is tightly connected to the local atmospheric forcing and the associated air-sea heat fluxes. A third class of eddies in the LS are the Boundary Current Eddies shed from the Labrador Current (LC). Since they are mostly confined to the vicinity of the LC, these eddies appear to exert only minor influence on preconditioning and restratification

MOMBA 1.1 - a high-resolution Baltic Sea configuration of GFDL's modular ocean model

We present a new coupled ocean-circulation–ice model configuration of the Baltic Sea. The model features, contrary to most existing configurations, a high horizontal resolution of ≈ 1 nautical mile (≈ 1.85 km), which is eddy-resolving over much of the domain. The vertical discretisation comprises a total of 47 vertical levels. Results from a 1987 to 1999 hindcast simulation show that the model's fidelity is competitive. As suggested by a comparison with sea surface temperatures observed from space, this applies especially to near-surface processes. Hence, the configuration is well suited to serve as a nucleus of a fully fledged coupled ocean-circulation–biogeochemical model (which is yet to be developed). A caveat is that the model fails to reproduce major inflow events. We trace this back to spurious vertical circulation patterns at the sills which may well be endemic to high-resolution models based on geopotential coordinates. Further, we present indications that – so far neglected – eddy/wind effects exert significant control on wind-induced up- and downwelling

Identifying potentially high risk areas for environmental pollution in the Baltic Sea

The study aims at the identification of areas in the Baltic Sea from where potential pollution is transported to vulnerable regions. Generally, there is higher risk of ship accidents along the shipping routes and along the approaching routes to the harbors. The spreading of harmful substances is mainly controlled by prevailing atmospheric conditions and wind-induced local sea surface currents. Especially, spawning, nursery and tourist areas are considered high-vulnerable areas. With sophisticated high resolution numerical models, the complex current system of the Baltic Sea has been simulated, and with subsequent drift modeling areas of reduced risk or high-risk areas for environmental pollution could be identified. In a further step, optimum fairways of reduced risk could be obtained by following probability minima of coastal hits or maxima for the time it takes to reach the coast. The results could be useful for environmental management for the maritime industry to minimize the risk of environmental pollution in case of ship accidents

On the suitability of North Brazil Current transport estimates for monitoring basin-scale AMOC changes

The North Brazil Current (NBC) constitutes a bottleneck for the mean northward return flow of the Atlantic Meridional Overturning Circulation (AMOC) in the tropical South Atlantic. Previous studies suggested a link between interannual to multidecadal NBC and AMOC transport variability and proposed to use NBC observations as an index for the AMOC. Here we use a set of hindcast, sensitivity, and perturbation experiments performed within a hierarchy of ocean general circulation models to show that decadal to multidecadal buoyancy-forced changes in the basin-scale AMOC transport indeed manifest themselves in the NBC. The relation is, however, masked by a strong interannual to decadal wind-driven gyre variability of the NBC. While questioning the NBC transport as a direct index for the AMOC, the results support its potential merit for an AMOC monitoring system, provided that the wind-driven circulation variability is properly accounted for

THREDDS Data Server a simplified way to discover and access scientific data at GEOMAR

One of today‘s challenge is the effective access to scientific data either within research groups or across different institutions to allow and increase the reusability of the data. While large operational modeling and service centers have enabled query and access to data via common web services, this is often not the case for smaller research groups. Especially the maintenance of the infrastructure and simple workflows to make the data available is a common challenge for scientists and data management. Here we would like to introduce the updated THREDDS Data Server (TDS) available at GEOMAR to provide, query, access and explore scientific data in netcdf format. This includes a simple and well documented workflow with step-by-step guidelines to provide data to the TDS system. This workflow aims to maximize the use of semi-automated processes, such as data integrity including standard metadata, checksums and persistent identifiers. By doing so, this workflow minimizes extra workload for persons involved in the data provision procedure such as scientists, data stewards and data managers but maximizes data reusibility under the FAIR principles. The TDS is a system developed and maintained by Unidata,a division of the University Corporation for Atmospheric Research (UCAR). The aim of the TDS is 1) to make it simple to enable web service access to existing output files, 2) using free technologies that are easy to deploy and configure, and 3) provide standardized, service-based tools that work in existing research environments. The TDS provides catalog, metadata, and data access services for scientific datasets with remote data access protocols including OPeNDAP, OGC WCS, OGC WMS, and HTTPS. These standardized services enable reusability and increase the visibility of scientific datasets. We will show examples using viewer technologies to access datasets or directly explore these within common development environments such as Python or MATLAB