Posters - High Resolution Ocean Climate Modeling
A Biogeochemical Model Assessment Platform
Andreas Oschlies, Iris Kriest, Olaf Duteil (GEOMAR, Germany)
Ocean biogeochemistry has a large effect on marine biogeochemical tracer distribution, comparable to that of circulation. However, the exact form of many biogeochemical processes, and therefore their parameterisation in global models, is not well known. Using the "Transport Matrix Method" (Khatiwala et al., 2005) as an offline tool to quickly equilibrate global coupled ocean biogeochemical models, we carry out sensitivity analyses to assess the skill of different biogeochemical, physical, and numerical setups. The ultimate aim is to find the "best" (with respect to metrics tailored for specific research questions) biogeochemical model, that may eventually be integrated into e.g. high-resolution models,or models that simulate transient scenarios.
Denmark Strait circulation scheme in an eddy-resolving mode
D. Iovino (CMCC, Italy), C. Herbaut (LOCEAN, France), M.N. Houssais (LOCEAN, France), S. Masina (INGV-CMCC, Italy)
The Denmark Strait overﬂow (DSO), one of the main components of the thermohaline circulation in the North Atlantic, is a complex mixture of several water masses. There has been no consensus yet on where it is formed and by which way it is brought to the strait. Its primary source is generally attributed to the East Greenland Current (EGC), but recent observations and numerical studies have showed that the North Icelandic Jet (NIJ), a barotropic current ﬂowing along the continental slope north of Iceland, has a main role in the formation of the dense overﬂow. Investigating the NIJ within the Nordic Seas system is a significant step to improve our understanding of the dense overflow. In this study, emphasis is given to the pathways and transports of dense water feeding the DSO. We used an ocean/sea-ice general circulation model in a nested Nordic Seas configuration at eddy-resolving (1/16° degree) resolution, forced by the atmospheric reanalysis ERA-Interim.The current system across the sill and the characteristics of the overflow water are presented and compared to recent observations. In particular, we analyze the circulation northwest of Iceland to gain better insight into the NIJ sources and to quantify its contribution to the overflowing waters.
Spin up of a high resolution climate model
Dewi Le Bars, Henk Dijkstra and Michael Kliphuis (Institute for Marine and Atmospheric Research, Utrecht University)
I will present preliminary results of the spin up of the CESM version 1.0.4 model. The CAM5 atmospheric model is used with the finite volume dynamical core at a resolution of 0.5º. For the ocean the POP2 model is used with a resolution of 0.1º. I will discuss the climate state generated by this model and comment on the technical difficulties and performance reached.
Toward Parameterizing Submesoscales
Scott Bachman (DAMPT, U. Cambridge, UK)
The oceanic submesoscale in particular is a popular topic of study in regional ocean models, due to its role as a "bridge" between the large-scale circulation and small-scale flows where mixing and dissipation can occur. Here we present a series of numerical simulations that are being conducted to understand the role that submesoscales play in modulating the stratification of the mixed layer. In the short term these simulations will help with our understanding of submesoscale dynamics in the presence of atmospheric forcing; in the long term, they will aid in the development of parameterizations for different submesoscale processes.
Modeling ENSO with ECHAM6-FESOM - influence of the ocean resolution
Thomas Rackow1, Dmitry Sidorenko1, Helge F. Goessling1, Axel Timmermann2, and Thomas Jung1
(1: Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Germany, 2: IPRC, Department of Oceanography, SOEST, University of Hawaii, USA)
A new climate model supporting multi-resolution meshes in the ocean component has been established at the Alfred Wegener Institute (AWI) in Bremerhaven. The atmospheric component is ECHAM6 with T63L47 setting, while the ocean is simulated by the AWI multi-resolution model FESOM, supporting triangular unstructured meshes. Two multi-century simulations with ECHAM6-FESOM, REF and TRO, document the beneficial role of an increased tropical ocean resolution for ENSO simulations. REF features a tropical ocean resolution of about 1°, TRO employs more than 0.25° in a narrow equatorial band, with resolution gradually decreasing to 1° as in REF. Outside the tropical belt (15°N to 15°S), both meshes are identical. REF and TRO simulate a mean climate comparable to some of the best CMIP5 models. In TRO, however, both the cold tongue SST bias and the western Pacific SST standard deviation bias appear to improve along with the Nino-3 index statistics. Also, advanced ENSO diagnostics including the Nino-3.4 seasonal variance, the annual cycle representation, and its interaction with ENSO tend to improve. The robustness of these improvements is analyzed and their physical explanations are explored.
Intertropical ocean-atmosphere coupling: Representation of turbulent air-sea fluxes in IPSL-CM5
Alina Gainusa Bogdan, Pascale Braconnot (IPSL, Laboratoire des Sciences du Climat et de l’Environnement, France)
The representation of air-sea turbulent fluxes in coupled ocean-atmosphere models play an important role in the model energetics and relative role of the ocean and atmosphere in heat and water transports. The evaluation of these fluxes is difficult because of the large uncertainties in available observational product. To address this problem for large-scale, climatological flux evaluation, we assemble a comprehensive database of 14 climatological surface flux products, including in situ-based, satellite, hybrid and reanalysis data sets. We develop an associated analysis protocol and use it together with this database to offer an observational ensemble approach to model flux evaluation. We use this approach to perform an evaluation of the representation of the intertropical turbulent air-sea fluxes in a suite of CMIP5 historical simulations run with different recent versions of the IPSL model. To enhance model understanding, we consider both coupled and forced atmospheric model configurations. For the same purpose, we not only analyze the surface fluxes, but also their associated meteorological state variables and inter-variable relationships. We identify an important, systematic underestimation of the near-surface wind speed and a significant exaggeration of the sea-air temperature contrast in all the IPSL model versions considered. Furthermore, the coupled model simulations develop important sea surface temperature and associated air humidity bias patterns. Counterintuitively, these biases do not systematically transfer to significant biases in the surface fluxes. This is due to a combination of compensation of effects and the large flux observational spread. Our analyses reveal several inconsistencies in inter-variable relationships between the different model versions and the observations, which could represent process-oriented constraints for future model development.