ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Publication Date: 2018-11-22
    Description: Many questions in ocean and climate modelling require the combined use of high resolution, global coverage and multi-decadal integration length. For this combination, even modern resources limit the use of traditional structured-mesh grids. Here we compare two approaches: A high-resolution grid nested into a global model at coarser resolution (NEMO with AGRIF) and an unstructured-mesh grid (FESOM) which allows to variably enhance resolution where desired. The Agulhas system around South Africa is used as a testcase, providing an energetic interplay of a strong western boundary current and mesoscale dynamics. Its open setting into the horizontal and global overturning circulations also requires global coverage. Both model configurations simulate a reasonable large-scale circulation. Distribution and temporal variability of the wind-driven circulation are quite comparable due to the same atmospheric forcing. However, the overturning circulation differs, owing each model’s ability to represent formation and spreading of deep water masses. In terms of regional, high-resolution dynamics, all elements of the Agulhas system are well represented. Owing to the strong nonlinearity in the system, Agulhas Current transports of both configurations and in comparison with observations differ in strength and temporal variability. Similar decadal trends in Agulhas Current transport and Agulhas leakage are linked to the trends in wind forcing. Although the number of 3D wet grid points used in FESOM is similar to that in the nested NEMO, FESOM uses about two times the number of CPUs to obtain the same model throughput (in terms of simulated model years per day). This is feasible due to the high scalability of the FESOM code.
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    facet.materialart.
    Unknown
    PANGAEA
    In:  Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven | Supplement to: Wang, Qiang; Danilov, Sergey; Jung, Thomas; Kaleschke, Lars; Wernecke, Andreas (2016): Sea ice leads in the Arctic Ocean: Model assessment, interannual variability and trends. Geophysical Research Letters, 43(13), 7019-7027, https://doi.org/10.1002/2016GL068696
    Publication Date: 2019-01-27
    Description: Northern Hemisphere sea ice from a Finite-Element Sea-Ice Ocean Model (FESOM) 4.5 km resolution simulation carried out by researchers from Alfred Wegener Institute (AWI), Germany. Concentration is shown with color; thickness is shown with shading. A global 1 degree mesh is used, with the "Arctic Ocean" locally refined to 4.5 km. South of CAA and Fram Strait the resolution is not refined in this simulation. The animation indicates that the 4.5 km model resolution helps to represent the small scale sea ice features, although much higher resolution is required to fully resolve the ice leads. The animation is created by Michael Böttinger from DKRZ (https://www.dkrz.de).
    Type: Dataset
    Format: text/tab-separated-values, 8 data points
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Wekerle, Claudia; Wang, Qiang; von Appen, Wilken-Jon; Danilov, Sergey; Schourup-Kristensen, Vibe; Jung, Thomas (2017): Eddy-Resolving Simulation of the Atlantic Water Circulation in the Fram Strait With Focus on the Seasonal Cycle. Journal of Geophysical Research: Oceans, 122(11), 8385-8405, https://doi.org/10.1002/2017JC012974
    Publication Date: 2018-11-19
    Description: Eddy driven recirculation of Atlantic Water (AW) in the Fram Strait modifies the amount of heat that reaches the Arctic Ocean, but is difficult to constrain in ocean models due to very small Rossby radius there. In this study we explore the effect of resolved eddies on the AW circulation in a locally eddy-resolving simulation of the global Finite-Element-Sea ice-Ocean-Model (FESOM) integrated for the years 2000-2009, by focusing on the seasonal cycle. An eddy-permitting simulation serves as a control run. Our results suggest that resolving local eddy dynamics is critical to realistically simulate ocean dynamics in the Fram Strait. Strong eddy activity simulated by the eddy-resolving model, with peak in winter and lower values in summer, is comparable in magnitude and seasonal cycle to observations from a long-term mooring array, whereas the eddy-permitting simulation underestimates the observed magnitude. Furthermore, a strong cold bias in the central Fram Strait present in the eddy-permitting simulation is reduced due to resolved eddy dynamics, and AW transport into the Arctic Ocean is increased with possible implications for the Arctic Ocean heat budget. Given the good agreement between the eddy-resolving model and measurements, it can help filling gaps that point-wise observations inevitably leave. For example, the path of the West Spitsbergen Current offshore branch, measured in the winter months by the mooring array, is shown to continue cyclonically around the Molloy Deep in the model, representing the major AW recirculation branch in this season.
    Type: Dataset
    Format: text/tab-separated-values, 100 data points
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    facet.materialart.
    Unknown
    PANGAEA
    In:  Supplement to: Scholz, Patrick; Lohmann, Gerrit; Wang, Qiang; Danilov, Sergey (2013): Evaluation of a Finite-Element Sea-Ice Ocean Model (FESOM) set-up to study the interannual to decadal variability in the deep-water formation rates. Ocean Dynamics, 63(4), 347-370, https://doi.org/10.1007/s10236-012-0590-0
    Publication Date: 2019-04-30
    Description: The characteristics of a global set-up of the Finite-Element Sea-Ice Ocean Model under forcing of the period 1958-2004 are presented. The model set-up is designed to study the variability in the deep-water mass formation areas and was therefore regionally better resolved in the deep-water formation areas in the Labrador Sea, Greenland Sea, Weddell Sea and Ross Sea. The sea-ice model reproduces realistic sea-ice distributions and variabilities in the sea-ice extent of both hemispheres as well as sea-ice transport that compares well with observational data. Based on a comparison between model and ocean weather ship data in the North Atlantic, we observe that the vertical structure is well captured in areas with a high resolution. In our model set-up, we are able to simulate decadal ocean variability including several salinity anomaly events and corresponding fingerprint in the vertical hydrography. The ocean state of the model set-up features pronounced variability in the Atlantic Meridional Overturning Circulation as well as the associated mixed layer depth pattern in the North Atlantic deep-water formation areas.
    Type: Dataset
    Format: text/tab-separated-values, 32 data points
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2017-01-27
    Description: The seasonal variability of Weddell Sea Bottom Water (WSBW) transport and its driving mechanisms are examined using FESOM simulations. Pronounced seasonal variability is present in both the Filchner shelf water export rate and the WSBW transport rate near the Antarctic Peninsula (AP) tip. The variabilities at both locations are linked to the surface wind forcing. The Filchner shelf water export rate responds to the onshore propagating density anomaly, which is caused by the wind-induced variation of the isopycnal depression at the coast. The variability near the AP tip originates from upstream variations at the Filchner Depression and from seasonal variability of the Weddell gyre strength.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2018-02-16
    Description: The polar shelf zones are highly dynamic and diverse systems. In the Arctic shelf region multiple river deltas accumulate organic carbon. They host a unique and very diverse northern fauna and flora. One of the final goals of my work is following ecosystem dynamic of Lena Delta region, Laptev Sea. In framework of this purpose the main task is to tune a basic numerical model which is able to reproduce the climatic changes in the region and to estimate the variability of the climate system. To design appropriate model we are using Finite Volume Coastal Ocean Model. FVCOM is a prognostic, unstructured-grid, finitevolume, free-surface, 3-D primitive equation coastal ocean circulation model developed by UMASSD-WHOI joint efforts. The main objective of current research is to verify the model and analyze temperature and salinity local pattern of mixed layer (up to 50 meters) in the Lena Delta Region of Laptev Sea in a short period of time (less than half a year). Also assess the degree of influence the Lena River runoff temperature, local wind pattern and tides dynamics to temperature and salinity variability in the considered area. The particular attention is paid to assessment of impact local bathymetry data to temperature and salinity local pattern. The calculation processes were carried out on the basis of FVCOM. We used high quality unstructured grid, which allows to take into account complexity of coastline, characteristics of the bathymetry data and features of the problem (the necessity to reduce the size of elements on a main ways of Lena fresh water plumb). Elements sizes are vary from 400m to 3 km. The model contains 6 vertical sigma-layers with 250000 nodes on each of them. The input data (bathymetry and coastline data, atmospheric forcing, temperature and salinity fields for first time step for every depth layer, temperature and salinity on the open boundary nodes for nudging, runoff date) are taken from NOAA, GEBCO, from German and Russian Institutes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2018-02-16
    Description: The shelf zone of the Laptev Sea and the Lena Delta in particular, has shown pronounced changes over the last 100 years. Despite growing interest into the region, the still insufficient amount of observational data as well as the lack of modeling efforts with fine resolution over the shelf leaves many challenging questions. Certain observational evidence has, however, already accumulated, leading to valuable insights about dynamics in the current region. We collected the data about temperature and salinity profiles, dissolved oxygen and pH for the Lena Delta region of the Laptev Sea for different years. Additionally, the newly organized expedition to the Lena Delta allowed collecting the particulate carbon content and chemical composition in the main Lena freshwater channels. Based on these data, the dominant environmental factors driving the biological system were established. Given the large territory, the direct measurement data have to be supplemented by a hydrodynamical and bio-optical analysis via remote sensing and modeling. The goal of our modeling approach is to simulate the shelf circulation dynamics under the action of varying atmospheric forcing, Lena runoff and tidal forcing, and their impact on ecosystem dynamics.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    facet.materialart.
    Unknown
    Publication Date: 2015-05-08
    Description: Nesting is used for local refinement to resolve eddy dynamics that would not be accessible otherwise. Unstructured meshes offer this functionality too by adjusting their resolution according to some goal function. However, by locally refining the mesh one does not necessarily achieves the goal resolution, because the eddy dynamics and the ability of eddies to release the available potential energy in particular, also depend on the dynamics on the upstream part of the coarse mesh. It is shown through a suite of simple experiments with a zonally re-entrant channel that baroclinic turbulence can be away from equilibrium in wide (compared to a typical eddy size) zones downstream into the refined area. The effect depends on whether or not the coarse part is eddy resolving, being much stronger if it is not, and almost disappearing if it is. Biharmonic viscosity scaled as cube of mesh element size is generally sufficient to control the smoothness of solutions on the variable mesh. However, noise in the vertical velocity field may be present at locations where the mesh is varied if momentum advection is implemented in the vector invariant form, which points to a variant of the Hollingsworth instability. Smoothness of vertical velocity is recovered for the flux form of momentum advection.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2015-05-08
    Description: Finite-volume discretizations can be formulated on unstructured meshes composed of different polygons. A staggered cell-vertex finite-volume discretization, keeping the velocity degree of freedom on cell centroids and scalar degrees of freedom on vertices presents one possible choice. Its performance is analyzed on mixed meshes composed of triangles and quads. Although triangular meshes are most flexible geometrically, quads are more efficient numerically and do not support spurious inertial modes of the triangular cell-vertex discretization. Mixed meshes composed of triangles and quads combine benefits of both. In particular, triangular transitional zones can be used to join quadrilateral meshes of differing resolution, i. e., to provide smooth nesting of a fine mesh into a coarse one. Based on a set of examples involving shallow water equations it is shown that mixed meshes offer a viable approach provided some background biharmonic viscosity (or the biharmonic filter) is used to stabilize the triangular part of the mesh.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2015-07-23
    Description: The numerical simulation code TsunAWI was developed in the framework of the German-Indonesian Tsunami Early Warning System (GITEWS). The numerical simulation of prototypical tsunami scenarios plays a decisive role in the a priory risk assessment for coastal regions and in the early warning process itself. TsunAWI is based on a finite element discretization, employs unstructured grids with high resolution along the coast, and includes inundation. This contribution gives an overview of the model itself and presents two applications. For GITEWS, the existing scenario database covering 528 epicenters / 3450 scenarios from Sumatra to Bali was extended by 187 epicenters / 1100 scenarios in the Eastern Sunda Arc. Furthermore, about 1100 scenarios for the Western Sunda Arc were recomputed on the new model domain covering the whole Indonesian Seas. These computations would not have been feasible in the beginning of the project. The unstructured computational grid contains 7 million nodes and resolves all coastal regions with 150m, some project regions and the surrounding of tide gauges with 50m, and the deep ocean with 12km edge length. While in the Western Sunda Arc, the large islands of Sumatra and Java shield the Northern Indonesian Archipelago, tsunamis in the Eastern Sunda Arc can propagate to the North. The unstructured grid approach allows TsunAWI to easily simulate the complex propagation patterns with the self-interactions and the reflections at the coastal regions of myriads of islands. For the Hydrographic and Oceanographic Service of the Chilean Navy (SHOA), we calculated a small scenario database of 100 scenarios (sources by Universidad de Chile) to provide data for a lightweight decision support system prototype (built by DLR). This work is part of the initiation project "Multi hazard information and early warning system in cooperation with Chile" and aims at sharing our experience from GITEWS with the Chilean partners.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...