32 research outputs found
Improving the simulation of landfast ice by combining tensile strength and a parameterization for grounded ridges
ABSTRACT: In some coastal regions of the Arctic Ocean, grounded ice ridges contribute to stabilizing andmaintaining a landfast ice cover. Recently, a grounding scheme representing this effect on sea ice dynamicswas introduced and tested in a viscous-plastic sea ice model. This grounding scheme, based on a basalstress parameterization, improves the simulation of landfast ice in many regions such as in the East SiberianSea, the Laptev Sea, and along the coast of Alaska. Nevertheless, in some regions like the Kara Sea, the areaof landfast ice is systematically underestimated. This indicates that another mechanism such as ice archingis at play for maintaining the ice cover fast. To address this problem, the combination of the basal stressparameterization and tensile strength is investigated using a 0.258Pan-Arctic CICE-NEMO configuration.Both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in the Kara Seabut also in the Laptev Sea. However, the simulated landfast ice season for the Kara Sea is too short com-pared to observations. This is especially obvious for the onset of the landfast ice season which systematical-ly occurs later in the model and with a slower build up. This suggests that improvements to the sea icethermodynamics could reduce these discrepancies with the data. Key Points - A grounding scheme is not enough to simulate landfast ice in Pan-Arctic simulations; - Both uniaxial and isotropic tensile strengths notably improve the simulation of landfast ice in deep coastal regions; - Simulated landfast ice season in the Kara Sea is still too short suggesting that thermodynamics should be improved
High Energy QCD: Stringy Picture from Hidden Integrability
We discuss the stringy properties of high-energy QCD using its hidden
integrability in the Regge limit and on the light-cone. It is shown that
multi-colour QCD in the Regge limit belongs to the same universality class as
superconformal =2 SUSY YM with at the strong coupling
orbifold point. The analogy with integrable structure governing the low energy
sector of =2 SUSY gauge theories is used to develop the brane picture
for the Regge limit. In this picture the scattering process is described by a
single M2 brane wrapped around the spectral curve of the integrable spin chain
and unifying hadrons and reggeized gluons involved in the process. New
quasiclassical quantization conditions for the complex higher integrals of
motion are suggested which are consistent with the duality of the
multi-reggeon spectrum. The derivation of the anomalous dimensions of the
lowest twist operators is formulated in terms of the Riemann surfacesComment: 37 pages, 3 figure
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Variation in climate sensitivity and feedback parameters during the historical period
We investigate the climate feedback parameter α (W mâ2 Kâ1) during the historical period (since 1871) in experiments using the HadGEM2 and HadCM3 atmosphere general circulation models (AGCMs) with constant preindustrial atmospheric composition and time-dependent observational sea surface temperature (SST) and sea ice boundary conditions. In both AGCMs, for the historical period as a whole, the effective climate sensitivity is âŒ2 K (αâ1.7 W mâ2 Kâ1), and α shows substantial decadal variation caused by the patterns of SST change. Both models agree with the AGCMs of the latest Coupled Model Intercomparison Project in showing a considerably smaller effective climate sensitivity of âŒ1.5 K (α = 2.3 ± 0.7 W mâ2 Kâ1), given the time-dependent changes in sea surface conditions observed during 1979â2008, than the corresponding coupled atmosphere-ocean general circulation models (AOGCMs) give under constant quadrupled CO2 concentration. These findings help to relieve the apparent contradiction between the larger values of effective climate sensitivity diagnosed from AOGCMs and the smaller values inferred from historical climate change
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OceanâOnly FAFMIP: Understanding Regional Patterns of Ocean Heat Content and Dynamic Sea Level Change
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Causes of differences in model and satellite tropospheric warming rates
In the early twenty-first century, satellite-derived tropospheric warming trends were generally smaller than trends estimated from a large multi-model ensemble. Because observations and coupled model simulations do not have the same phasing of natural internal variability, such decadal differences in simulated and observed warming rates invariably occur. Here we analyse global-mean tropospheric temperatures from satellites and climate model simulations to examine whether warming rate differences over the satellite era can be explained by internal climate variability alone. We find that in the last two decades of the twentieth century, differences between modelled and observed tropospheric temperature trends are broadly consistent with internal variability. Over most of the early twenty-first century, however, model tropospheric warming is substantially larger than observed; warming rate differences are generally outside the range of trends arising from internal variability. The probability that multi-decadal internal variability fully explains the asymmetry between the late twentieth and early twenty-first century results is low (between zero and about 9%). It is also unlikely that this asymmetry is due to the combined effects of internal variability and a model error in climate sensitivity. We conclude that model overestimation of tropospheric warming in the early twenty-first century is partly due to systematic deficiencies in some of the post-2000 external forcings used in the model simulations
A review of progress towards understanding the transient global mean surface temperature response to radiative perturbation
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PDRMIP: a precipitation driver and response model intercomparison project - protocol and preliminary results
PDRMIP investigates the role of various drivers of climate change for mean and extreme precipitation changes, based on multiple climate model output and energy budget analyses.
As the global temperature increases with changing climate, precipitation rates and patterns are affected through a wide range of physical mechanisms. The globally averaged intensity of extreme precipitation also changes more rapidly than the globally averaged precipitation rate. While some aspects of the regional variation in precipitation predicted by climate models appear robust, there is still a large degree of inter-model differences unaccounted for. Individual drivers of climate change initially alter the energy budget of the atmosphere leading to distinct rapid adjustments involving changes in precipitation. Differences in how these rapid adjustment processes manifest themselves within models are likely to explain a large fraction of the present model spread and needs better quantifications to improve precipitation predictions. Here, we introduce the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), where a set of idealized experiments designed to understand the role of different climate forcing mechanisms were performed by a large set of climate models. PDRMIP focuses on understanding how precipitation changes relating to rapid adjustments and slower responses to climate forcings are represented across models. Initial results show that rapid adjustments account for large regional differences in hydrological sensitivity across multiple drivers. The PDRMIP results are expected to dramatically improve our understanding of the causes of the present diversity in future climate projections