U.K. HiGEM Shaffrey, L. C.; Stevens, I.; Norton, W. A. ...
Journal of climate,
04/2009, Letnik:
22, Številka:
8
Journal Article
Recenzirano
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This article describes the development and evaluation of the U.K.’s new High-Resolution Global Environmental Model (HiGEM), which is based on the latest climate configuration of the Met Office ...Unified Model, known as the Hadley Centre Global Environmental Model, version 1 (HadGEM1). In HiGEM, the horizontal resolution has been increased to 0.83° latitude × 1.25° longitude for the atmosphere, and 1/3° × 1/3° globally for the ocean. Multidecadal integrations of HiGEM, and the lower-resolution HadGEM, are used to explore the impact of resolution on the fidelity of climate simulations.
Generally, SST errors are reduced in HiGEM. Cold SST errors associated with the path of the North Atlantic drift improve, and warm SST errors are reduced in upwelling stratocumulus regions where the simulation of low-level cloud is better at higher resolution. The ocean model in HiGEM allows ocean eddies to be partially resolved, which dramatically improves the representation of sea surface height variability. In the Southern Ocean, most of the heat transports in HiGEM is achieved by resolved eddy motions, which replaces the parameterized eddy heat transport in the lower-resolution model. HiGEM is also able to more realistically simulate small-scale features in the wind stress curl around islands and oceanic SST fronts, which may have implications for oceanic upwelling and ocean biology.
Higher resolution in both the atmosphere and the ocean allows coupling to occur on small spatial scales. In particular, the small-scale interaction recently seen in satellite imagery between the atmosphere and tropical instability waves in the tropical Pacific Ocean is realistically captured in HiGEM. Tropical instability waves play a role in improving the simulation of the mean state of the tropical Pacific, which has important implications for climate variability. In particular, all aspects of the simulation of ENSO (spatial patterns, the time scales at which ENSO occurs, and global teleconnections) are much improved in HiGEM.
A suite of application benchmarks, designed to be broadly representative of UK HPC usage, has been developed to stress a broad range of architectural features of large scale parallel HPC resources. A ...generic methodology to investigate application performance and scaling characteristics has been defined, resulting in a detailed understanding of the performance of these applications. This methodology is transferable to other applications and systems: it is of practical value to developers and users who are aiming for optimal utilisation of HPC resources. An understanding of the performance characteristics of a range of large-scale HPC resources has been obtained using low-level synthetic benchmarks. A relatively simple, qualitative mechanism to assess and predict application performance on current and future architectures using synthetic benchmark results together with application performance analysis results is explored.
The effect on stratospheric temperature of changing ozone is investigated by comparing two 5‐member ensembles of 20‐year Unified Model transient runs, one with a linear trend in ozone and one ...without. A significant stratospheric mean temperature trend of −0.17 K/decade is attributed to ozone depletion. It is found that, although increasing the ensemble size to 20 members would have considerable benefits, increasing the ensemble size further would not dramatically improve confidence in the results. The timeslice approach to climate change modeling is found to produce similar temperature trends to the transient approach for this experiment.
The computational challenges of Earth-system science O'Neill, Alan; Steenman-Clark, Lois
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
06/2002, Letnik:
360, Številka:
1795
Journal Article
Recenzirano
The Earth system-comprising atmosphere, ocean, land, cyrosphere and biosphere-is an immensely complex system, involving processes and interactions on a wide range of space- and time-scales. To ...understand and predict the evolution of the Earth system is one of the greatest challenges of modern science, with success likely to bring enormous societal benefits. High-performance computing, along with the wealth of new observational data, is revolutionizing our ability to simulate the Earth system with computer models that link the different components of the system together. There are, however, considerable scientific and technical challenges to be overcome. This paper will consider four of them: complexity, spatial resolution, inherent uncertainty and time-scales. Meeting these challenges requires a significant increase in the power of high-performance computers. The benefits of being able to make reliable predictions about the evolution of the Earth system should, on their own, amply repay this investment.
Wavelengths and intensities of dielectronic satellite lines of the type 1snl−2pnl have been calculated for n = 2, 3 and 4 in iron. These are compared with previous calculations for n = 2. The effect ...of cascades from higher satellite levels is shown to be negligible. An approximation is used to scale for all n > 4, in order to produce the total satellite spectrum, including the contribution to the apparent resonance line intensity. A technique is proposed for using this spectrum to measure the electron temperature in the source. An estimate is made of the dielectronic recombination rate, which is compared with the result of earlier semi-empirical formulae.
High-resolution solar spectra of the Mg XI 1s2 1S0-1s2p 1P1 resonance line at 9.169 A and the associated nearby satellite lines obtained from two rocket-borne crystal spectrometer measurements are ...presented. Comparisons with two independent sets of theoretical calculations for the 1s2nl-1s2pnl dielectronic satellite lines with n = 3-7 indicate electron temperatures of 4-4.5 million K. Measured line widths indicate either that the ion temperature exceeds the electron temperature by about a million K or that about 28 km/s of turbulence is present.
New calculations of the atomic parameters for the dielectronic satellites of the Mg XII resonance lines 1s–2p, 1s–3p, 1s–4p, have been performed in a multiconfiguration intermediate coupling scheme. ...The satellite lines correspond to transitions of the type $1s \,nl-n^{\prime} l^{\prime} n^{\prime\prime} l^{\prime\prime}$ for $n, n^{\prime}, n^{\prime\prime} = 2, 3 \,\text{and} \,4.$ The effect on the satellite level population of cascades from higher excited levels is discussed and the cascade correction for the relative intensity ratio of the satellite to resonance line is derived. Comparison is made with previous calculations for n = 2 satellites, Vainshtein & Safronova (1978).
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