Prospects for improving the representation of coastal and shelf seas in global ocean models
Prospects for improving the representation of coastal and shelf seas in global ocean models
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DOI：
10.5194/gmd-10-499-2017
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发表时间：
2017-02-01
影响因子：
5.1
通讯作者：
Wood, Richard
中科院分区：
文献类型：
--
作者：
Holt, Jason;Hyder, Patrick;Wood, Richard
在全球海洋模型中准确地表示沿海和陆架海是地球系统科学的重大挑战之一。这些区域通过其提供的商品和服务、造成的危害及其在全球范围的过程和循环中的作用，例如碳通量和稠密水的形成，具有巨大的社会重要性。然而，它们在目前这一代全球海洋模型中的代表性很差。在这篇文章中，我们的目标是简要地解释这个问题，然后确定重要的物理过程，以及它们的规模，需要在全球范围内解决这些规模和不断发展的计算环境的选项的背景下解决这个问题。我们发现正压和地形尺度是很好地解决了目前国家的最先进的模式的分辨率，例如标称1/12度，仍然合理地解决在1/4度，在这里，重点是过程表示。我们确定潮汐，垂直坐标，河流流入和混合计划作为四个领域的建模方法可以很容易地从区域转移到全球建模具有很大的好处。在更细尺度的过程中，我们发现1/2度的全球模式只解决了近似8%的深度小于500米的区域的第一斜压Rossby半径，但对于1/72度的模式，这增加到近似70%，因此，要在全球范围内解决尺度问题，需要比现有技术更精细的分辨率。表示使用1/12度的全球和盆地规模的北方北大西洋核心的欧洲模式的海洋NEMO）模拟;后者包括潮汐和k-垂直混合计划。这些与全球分层观测和CMIP 5的19个模型进行了比较。在相关性和全流域均方根误差方面，高分辨率模型优于所有这些CMIP 5模型。与没有潮汐的高分辨率模型相比，潮汐模型显示出改进的季节性周期。分辨率的好处在东部边界上升流区尤为明显。为了探索全球精细化模式和多尺度模式选择（例如有限元、有限体积或双向嵌套方法）之间的平衡，我们考虑了一个简单的尺度分析和一个概念性的网格精细化方法。我们把这个分析的背景下不断发展的计算机系统，讨论模型周转时间，可扩展性和资源成本。使用简单的成本模型与参考配置进行比较（2011年采用1/4度全球模式）和英国研究委员会计算机设施的性能不断提高，我们估计，到2021年，非结构化网格多尺度方法（分辨率可达1.5 km）将使用相当份额的计算机资源，到2022年，双向嵌套多尺度方法，到2026年全球气温将达到1/72度。然而，我们也注意到，在2017年之前，1/12度全球模型的计算成本不会与1度全球模型相当。因此，我们的结论是，对于计算昂贵的模型（例如海洋学研究或业务海洋学），解决尺度类似于1.5公里将是常规实用的，在大约十年的数值和计算的发展给予大量的努力。对于复杂的地球系统模型，这将延长到大约20年，这表明这里的重点需要放在改进过程参数化上，以应对这些挑战。
Accurately representing coastal and shelf seas in global ocean models represents one of the grand challenges of Earth system science. They are regions of immense societal importance through the goods and services they provide, hazards they pose and their role in global-scale processes and cycles, e.g. carbon fluxes and dense water formation. However, they are poorly represented in the current generation of global ocean models. In this contribution, we aim to briefly characterise the problem, and then to identify the important physical processes, and their scales, needed to address this issue in the context of the options available to resolve these scales globally and the evolving computational landscape. We find barotropic and topographic scales are well resolved by the current state-of-the-art model resolutions, e.g. nominal 1/12 degrees, and still reasonably well resolved at 1/4 degrees; here, the focus is on process representation. We identify tides, vertical coordinates, river inflows and mixing schemes as four areas where modelling approaches can readily be transferred from regional to global modelling with substantial benefit. In terms of finer-scale processes, we find that a 1/2 degrees, global model resolves the first baroclinic Rossby radius for only similar to 8% of regions < 500 m deep, but this increases to similar to 70% for a 1/72 degrees model, so resolving scales globally requires substantially finer resolution than the current state of the art.We quantify the benefit of improved resolution and process representation using 1/12 degrees global- and basin-scale northern North Atlantic nucleus for a European model of the ocean NEMO) simulations; the latter includes tides and a k-epsilon vertical mixing scheme. These are compared with global stratification observations and 19 models from CMIP5. In terms of correlation and basin-wide rms error, the high-resolution models outperform all these CMIP5 models. The model with tides shows improved seasonal cycles compared to the high-resolution model without tides. The benefits of resolution are particularly apparent in eastern boundary upwelling zones.To explore the balance between the size of a globally refined model and that of multiscale modelling options (e.g. finite element, finite volume or a two- way nesting approach), we consider a simple scale analysis and a conceptual grid refining approach. We put this analysis in the context of evolving computer systems, discussing model turnaround time, scalability and resource costs. Using a simple cost model compared to a reference configuration (taken to be a 1/4 degrees global model in 2011) and the increasing performance of the UK Research Councils' computer facility, we estimate an unstructured mesh multiscale approach, resolving process scales down to 1.5 km, would use a comparable share of the computer resource by 2021, the two-way nested multiscale approach by 2022, and a 1/72 degrees global model by 2026. However, we also note that a 1/12 degrees global model would not have a comparable computational cost to a 1 degrees global model in 2017 until 2027. Hence, we conclude that for computationally expensive models (e.g. for oceanographic research or operational oceanography), resolving scales to similar to 1.5 km would be routinely practical in about a decade given substantial effort on numerical and computational development. For complex Earth system models, this extends to about 2 decades, suggesting the focus here needs to be on improved process parameterisation to meet these challenges.