Numerical Methods for Large-Scale Modeling of Ocean Circulation

希格登9803331 研究人员开发改进的算法，用于计算海洋环流的数值模拟。 这项工作的动机之一是改进迈阿密等密度坐标海洋模式（MICOM）中使用的数值方法，但这项工作也有更广泛的应用。 MICOM是一个实用的海洋模型，目前正在洛斯阿拉莫斯国家实验室和其他地方进行测试，用于全球气候系统的海洋-大气耦合模型。 该模型目前使用三级时间步长方案，在实践中，需要对时间步长的限制比标准理论预期的更严格。 此外，该模型是由非物理网格尺度振荡，这是特别刺激的行为MICOM的海洋混合层的代表性的计算模式的影响。 作为替代方案，本项目研究涉及两个时间层次的方法。 这样的方法具有允许实质上更长的时间步长的潜力，需要更少的存储，并且不允许计算模式。 这些方法进行了分析和实施结合正压斜压时间分裂，这是用来分裂成单独的子系统，由不同的技术解决的快，慢动作。 海洋环流计算机模型的一个应用是帮助研究地球的气候系统。 例如，气候建模中的一个主要兴趣点是热量的向极地传输。 如果大气和海洋保持静止，热带地区会比实际温度更高，而极地地区会更冷。 然而，大气和海洋的运动有助于缓和这些极端情况。 向极地输送的热量大约有一半来自大气，另一半来自海洋。 在海洋中，大量的迁移是由于墨西哥湾流等水流的整体运动;另一种迁移机制是由于流体动力学不稳定性而从洋流中脱落的涡流造成的混合。 对这些现象进行适当的建模需要高空间分辨率和长时间间隔的计算，而海洋环流的气候尺度模拟带来了巨大的计算挑战，使最强大的计算机的能力变得紧张。 本项目的目的是提高在这种计算中使用的算法的效率和可靠性。 一个全面的气候模型需要大气模型和海洋模型，这些组成部分必须以模拟真实的大气和海洋相互作用的方式进行交流。 本项目的重点是一个现有的海洋模型，该模型正在几个地点准备进行大规模的海洋-大气耦合模拟。

Higdon 9803331 The investigator develops improved algorithms for computing numerical simulations of ocean circulation. One motivation for this work is to improve the numerical methods used in the Miami Isopycnic Coordinate Ocean Model (MICOM), but this work also has broader application. MICOM is an operational ocean model that is currently being tested at Los Alamos National Laboratory and elsewhere for use in coupled, ocean-atmosphere models of the global climate system. This model presently uses a three-level timestepping scheme that, in practice, requires a restriction on the time step that is more severe than would be expected from standard theory. In addition, the model is affected by a computational mode consisting of nonphysical grid-scale oscillations, which are particularly stimulated by the behavior of MICOM's representation of the oceanic mixed layer. As an alternative, the present project investigates methods involving two time levels. Such methods have the potential of allowing a substantially longer time step, require less storage, and do not admit a computational mode. These methods are analyzed and implemented in conjunction with a barotropic-baroclinic time splitting, which is used to split the fast and slow motions into separate subsystems that are solved by different techniques. One application of computer models of ocean circulation is to aid in the study of the earth's climate system. For example, a major point of interest in climate modeling is the poleward transport of heat. If the atmosphere and ocean were held stationary, the tropical regions would be hotter than they actually are, and the polar regions would be colder. However, the movement of the atmosphere and ocean serves to moderate these extremes. Roughly half of the poleward transport of heat is due to the atmosphere, and half is due to the ocean. In the ocean, substantial transport is due to bulk movement by currents such as the Gulf Stream; another transport mechanism is the mixing caused by eddies that are shed from ocean currents due to hydrodynamic instability. A proper modeling of these phenomena requires high spatial resolution and computations over long time intervals, and climate-scale simulations of ocean circulation pose great computational challenges that strain the capabilities of the most powerful computers. The aim of the present project is to improve the efficiency and reliability of the algorithms that are used in such computations. A full-scale climate model would require both a model of the atmosphere and a model of the ocean, and these components must communicate in a way that simulates the interaction of the real atmosphere and ocean. The present project focuses on an existing ocean model that is being prepared at several sites for large-scale, coupled ocean-atmosphere simulations.