scholarly journals On the impact of vertical coordinate choice for innovation when assimilating hydrographic profiles into isopycnal ocean models

2021 ◽  
pp. 101917
Author(s):  
F.B. Costa ◽  
C.A.S. Tanajura
Keyword(s):  
Vertical Coordinate ◽  
Ocean Models ◽  
The Impact

scholarly journals Adjustment of Transceiver Lever Arm Offset and Sound Speed Bias for GNSS-Acoustic Positioning

2019 ◽  
Vol 11 (13) ◽  
pp. 1606 ◽  
Author(s):  
Guanxu Chen ◽  
Yang Liu ◽  
Yanxiong Liu ◽  
Ziwen Tian ◽  
Jingnan Liu ◽  
...  
Keyword(s):  
Shallow Water ◽  
Sound Velocity ◽  
Functional Model ◽  
Systematic Errors ◽  
Vertical Coordinate ◽  
Sea Trial ◽  
Lever Arm ◽  
Main Technique ◽  
The Impact ◽  
Velocity Bias

Global Navigation Satellite System––Acoustic (GNSS-A) positioning is the main technique for seafloor geodetic positioning. A transceiver lever arm offset and sound velocity bias in seawater are the main systematic errors of the GNSS-A positioning technique. Based on data from a sea trial in shallow water, this paper studies the functional model of GNSS-A positioning. The impact of the two systematic errors on seafloor positioning is analysed and corresponding processing methods are proposed. The results show that the offset in the lever arm measurement should be parameterised in the observation equation. Given the high correlation between the vertical lever arm offset and the vertical coordinate of the seafloor station, a sample search method was introduced to fix the vertical offset correction. If the calibration of the sound velocity profiler cannot be ensured, the correction parameter of the sound velocity bias should be solved. According to the refined functional model and corrections, the position of a seafloor station in shallow water can be determined with a precision of better than 1 cm.

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

2021 ◽  
Author(s):  
Diego Bruciaferri ◽  
James Harle ◽  
Anthony Wise ◽  
Enda O'Dea ◽  
Jeff Polton
Keyword(s):  
Coordinate System ◽  
Ocean Model ◽  
Ocean Dynamics ◽  
Ocean Modelling ◽  
Vertical Coordinate ◽  
North West ◽  
European North ◽  
Basin Scale ◽  
Discretization Schemes ◽  
The Impact

<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>

Anoxic metabolism after the 21st century in oxygen minimum zones

2020 ◽  
Author(s):  
Wolfgang Koeve ◽  
Angela Landolfi
Keyword(s):  
Organic Matter ◽  
Ocean Circulation ◽  
Large Scale ◽  
Deep Ocean ◽  
Sulphate Reduction ◽  
Oxygen Minimum Zones ◽  
The Future ◽  
Ocean Models ◽  
The Impact ◽  
Oxygen Minimum

<p>Global models project a decrease of marine oxygen over the course of the 21th century. The future of marine oxygen becomes increasingly uncertain further into the future after yr 2100 , partly because ocean models differ in the way organic matter remineralisation continues under oxygen- and nitrate-free conditions. Using an Earth system model of intermediate complexity we found that under a business-as-usual CO2-emission scenario ocean deoxygenation further intensifies for several centuries until eventually ocean circulation re-establishes and marine oxygen increases again. (Oschlies et al. 2019, DOI 10.1038/s41467-019-10813-w).</p><p>In the Pacific Ocean the deoxygenation after yr 2100 goes along with the large scale loss of nitrate from oxygen minimum zones. Here we explore the impact on simulated ocean biogeochemistry of three different process formulation of anoxic metabolism, which have been used in other ocean models: (1) implicit sulphate reduction (organic matter degradation continues without oxidant), (2) no sulphidic metabolism (organic matter is not degraded under anoxic conditions), and (3) explicit sulphate reduction (with H2S as explicit model tracer). The model with explicit sulfphate reduction supports larger regional organic matter fluxed into the deep ocean and an increase in respired carbon storage, compared with the model applying implicit sulphate. We discuss the impact of anoxic metabolism on the coupling between export production and respired carbon stored in the ocean interior.</p>

scholarly journals A method for applying lateral surface eddy diffusion in ocean models with a general vertical coordinate

2021 ◽  
Author(s):  
Gustavo M. Marques ◽  
Andrew E. Shao ◽  
Scott D. Bachman ◽  
Gokhan Danabasoglu ◽  
Frank O. Bryan
Keyword(s):  
Lateral Surface ◽  
Eddy Diffusion ◽  
Vertical Coordinate ◽  
Ocean Models

scholarly journals Climate Simulations with an Isentropic Finite-Volume Dynamical Core

2012 ◽  
Vol 25 (8) ◽  
pp. 2843-2861 ◽  
Author(s):  
Chih-Chieh Chen ◽  
Philip J. Rasch
Keyword(s):  
Finite Volume ◽  
Climate Models ◽  
Transport Processes ◽  
Climate Simulation ◽  
Modeling Framework ◽  
Dynamical Core ◽  
Vertical Coordinate ◽  
Upper Troposphere ◽  
Isentropic Model ◽  
The Impact

Abstract This paper discusses the impact of changing the vertical coordinate from a hybrid pressure to a hybrid-isentropic coordinate within the finite-volume (FV) dynamical core of the Community Atmosphere Model (CAM). Results from a 20-yr climate simulation using the new model coordinate configuration are compared to control simulations produced by the Eulerian spectral and FV dynamical cores of CAM, which both use a pressure-based (σ − P) coordinate. The same physical parameterization package is employed in all three dynamical cores. The isentropic modeling framework significantly alters the simulated climatology and has several desirable features. The revised model produces a better representation of heat transport processes in the atmosphere leading to much improved atmospheric temperatures. The authors show that the isentropic model is very effective in reducing the long-standing cold temperature bias in the upper troposphere and lower stratosphere, a deficiency shared among most climate models. The warmer upper troposphere and stratosphere seen in the isentropic model reduces the global coverage of high clouds, which is in better agreement with observations. The isentropic model also shows improvements in the simulated wintertime mean sea level pressure field in the Northern Hemisphere.

scholarly journals Natural ocean carbon cycle sensitivity to parameterizations of the recycling in a climate model

2013 ◽  
Vol 10 (7) ◽  
pp. 11111-11153
Author(s):  
A. Romanou ◽  
J. Romanski ◽  
W. W. Gregg
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Deep Ocean ◽  
Ocean Model ◽  
Pump Efficiency ◽  
Biological Pump ◽  
Vertical Coordinate ◽  
Ocean Models ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon

Abstract. Sensitivities of the oceanic biological pump within the GISS climate modeling system are explored here. Results are presented from twin control simulations of the air-sea CO2 gas exchange using two different ocean models coupled to the same atmosphere. The two ocean models (Russell ocean model and Hybrid Coordinate Ocean Model, HYCOM) use different vertical coordinate systems, and therefore different representations of column physics. Both variants of the GISS climate model are coupled to the same ocean biogeochemistry module (the NASA Ocean Biogeochemistry Model, NOBM) which computes prognostic distributions for biotic and abiotic fields that influence the air-sea flux of CO2 and the deep ocean carbon transport and storage. In particular, the model differences due to remineralization rate changes are compared to differences attributed to physical processes modeled differently in the two ocean models such as ventilation, mixing, eddy stirring and vertical advection. The Southern Ocean emerges as a key region where the CO2 flux is as sensitive to biological parameterizations as it is to physical parameterizations. Mixing in the Southern Ocean is shown to be a~good indicator of the magnitude of the biological pump efficiency regardless of physical model choice.

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