88 research outputs found
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Comparison of elastic-viscous-plastic and viscous-plastic dynamics models using a high resolution Arctic sea ice model
No full textA nonlinear viscous-plastic (VP) rheology proposed by Hibler (1979) has been demonstrated to be the most suitable of the rheologies commonly used for modeling sea ice dynamics. However, the presence of a huge range of effective viscosities hinders numerical implementations of this model, particularly on high resolution grids or when the ice model is coupled to an ocean or atmosphere model. Hunke and Dukowicz (1997) have modified the VP model by including elastic waves as a numerical regularization in the case of zero strain rate. This modification (EVP) allows an efficient, fully explicit discretization that adapts well to parallel architectures. The authors present a comparison of EVP and VP dynamics model results from two 5-year simulations of Arctic sea ice, obtained with a high resolution sea ice model. The purpose of the comparison is to determine how differently the two dynamics models behave, and to decide whether the elastic-viscous-plastic model is preferable for high resolution climate simulations, considering its high efficiency in parallel computation. Results from the first year of this experiment (1990) are discussed in detail in Hunke and Zhang (1997)
Icepack schematic
No full textColumn based physical processes that affect the area and volume of sea ice, which are represented or accounted for within the Icepack software package.</p
What controls primary production in the Arctic Ocean? Results from an intercomparison of five general circulation models with biogeochemistry
No full textAs a part of Arctic Ocean Intercomparison Project, results from five coupled physical and biological ocean models were compared for the Arctic domain, defined here as north of 66.6°N. The global and regional (Arctic Ocean (AO)–only) models included in the intercomparison show similar features in terms of the distribution of present-day water column–integrated primary production and are broadly in agreement with in situ and satellite-derived data. However, the physical factors controlling this distribution differ between the models. The intercomparison between models finds substantial variation in the depth of winter mixing, one of the main mechanisms supplying inorganic nutrients over the majority of the AO. Although all models manifest similar level of light limitation owing to general agreement on the ice distribution, the amount of nutrients available for plankton utilization is different between models. Thus the participating models disagree on a fundamental question: which factor, light or nutrients, controls present-day Arctic productivity. These differences between models may not be detrimental in determining present-day AO primary production since both light and nutrient limitation are tightly coupled to the presence of sea ice. Essentially, as long as at least one of the two limiting factors is reproduced correctly, simulated total primary production will be close to that observed. However, if the retreat of Arctic sea ice continues into the future as expected, a decoupling between sea ice and nutrient limitation will occur, and the predictive capabilities of the models may potentially diminish unless more effort is spent on verifying the mechanisms of nutrient supply. Our study once again emphasizes the importance of a realistic representation of ocean physics, in particular vertical mixing, as a necessary foundation for ecosystem modeling and predictions
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The time-dependent transformed Eliassen balanced vortex model of a tropical cyclone.
No full textThe time-dependent, transformed Eliassen balanced vortex model of a tropical cyclone is analyzed mathematically and integrated numerically. The simulated vortices have characteristics resembling aspects of real tropical cyclones. Based on the principle of potential vorticity invertibility, the baroclinic model vortex evolves on an f-plane, assumes Boussinesq and hydrostatic approximations, and is posed in absolute angular momentum coordinates with circular symmetry. Theoretical analysis of the model equations is used to derive efficient numerical methods. Linear operator theory is applied to elliptic, diagnostic equations for the tangential velocity potential function and the transverse circulation streamfunction, which are then solved by successive line overrelaxation methods. Equations for the potential vorticity and potential temperature are solved using a fourth-order Runge Kutta method. A maximum growth rate estimated for the potential vorticity equation limits the size of the timestep, yet reveals the presence of exponentially growing modes for given profiles of the thermal forcing. Initial potential vorticity and potential temperature distributions are based on a mesocyclone study. Vortex evolution is computed for a specified forcing that emulates condensational heating and a heating function parameterized in terms of the model variables. The specified heating produces a realistic circulation but does not allow the vortex to decay. When a parameterized heating function is used, the transverse circulation requires external forcing through frictionally induced vertical motion at the surface boundary. Mathematical and physical descriptions of the boundary conditions are discussed and compared; the surface conditions are insufficient for maintenance or amplification of the vortex under the parameterized heating. In addition to analyzing physical and dynamical relationships among model variables, the simulations can be used as a 2-D basic state for a perturbation study using 3-D primitive equations. Such an investigation would illuminate nonaxisymmetric features of hurricanes such as rain bands and outflow jets.This item was digitized from a paper original and/or a microfilm copy. If you need
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Polar boundary layer processes: Important factors for investigating biogeochemistry and climate
No full textShrap[no]babble
No full textShrap[no]babble, a creative thesis collection of short stories, is a portmanteau of shrapnel and technobabble, reflecting the author\u27s military roots and desire to infuse the work with a sense of kinetic unpredictability. This collection features nine short stories and one novella, predominantly exploring the sub-genres of science fiction and magic realism, while also delving into hope-punk, urban fantasy, and post-apocalyptic fiction. Character-driven narratives are at the heart of these tales, which are crafted with lyrical, literary prose to create an engaging reading experience. By experimenting with various speculative fiction genres and narrative styles, Shrap[no]babble aims to expand the boundaries of conventional storytelling and contribute to contemporary speculative fiction
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