Collaborative Research: Impact of Bottom Boundary Layer Drag and Topographic Wave Drag on the Eddying General Circulation

近年来，海洋能源和汇的量化产生了很大的兴趣，由于争论，混合驱动的能量耗散施加了强大的控制对流的热量和碳的传输。本计画探讨二次型底边界层阻力与地形内波阻力对海洋环流能量收支有重要贡献，并对中尺度涡旋的动力学与统计学有重大影响的假设。将通过在理想化模式和现实的涡旋全球海洋环流模式中采用各种强度的底阻力系数，并通过在现实模式中采用波浪阻力来检验这一假设。模型中的海洋表面涡动动能的水平长度尺度和能级将与卫星高度计观测结果进行比较，模型涡动动能的垂直结构将与次表层海流计观测数据库进行比较。根据研究人员以前用理想化的两层准地转模式所做的工作，预计当底阻力中等强时，涡旋将与观测结果最接近。它也假设，底部边界层阻力和波阻力都有助于显着的能量收支的大气环流。智力优点：底阻力的敏感性将在模型中进行研究，这些模型弥补了PI以前采用的两层准地转模型的几个不足之处;海洋分层截断为两层，缺少表面边界效应，平底和水平均匀平均流。该项目将利用一个新的理想化模式，同时解决多个内部准地转模式和表面模式，以及现实的涡旋大气环流模式，具有高的垂直分辨率，不均匀的强迫，粗糙的地形。调查人员将建立在他们以前的经验，将地形内波阻力插入海洋潮汐模式，波阻力插入海洋大气环流模式。研究人员手头上有一个波阻方案，它适合于这里感兴趣的低频流动。该方案来自大气界的一个合作者，该合作者在大气环流模式中对低频流的波阻采用方案已有20多年。波阻计算还建立在与海洋气象学家的合作基础上，这导致了小尺度（1-10公里量级）地形粗糙度的合成数据集的构建。小尺度粗糙度在最先进的全球测深数据集中没有得到充分的代表，然而，根据理论，小尺度粗糙度是粗糙地形上低频流动产生内波的原因。更广泛的影响：这里提出的工作将通过调查两个可能的能量汇及其对涡旋环流动力学的影响，有助于讨论海洋能量耗散。这里提出的工作也应该导致改进的涡流海洋模型，这是敏感的阻尼系数，他们采用。随着计算机能力的不断提高，气候模拟中使用的海洋模型很快就会变得具有涡流分辨率。因此，改进和检验涡旋分辨海洋模式的气候研究和其他应用十分重要。这里提出的工作将有助于实现这一目标。该项目将资助一名博士后科学家和一名研究生。博士后将使用现实模型，研究生将使用理想化模型。该项目还为首席PI提供资金，继续与高中生和本科生暑期实习生一起工作，因为他从2006年开始每年夏天都这样做。最后，该项目为首席研究员Arbic博士提供旅费，使其继续参加Jurgen Theiss博士每年举行的出发前会议，为学生参加国家科学基金会资助的桑给巴尔通道项目做好准备。

In recent years the quantification of oceanic energy sources and sinks has generated much interest, due to arguments that mixing driven by energy dissipation exerts a strong control on meridional heat and carbon transport. This project examines the hypothesis that both quadratic bottom boundary layer drag and topographic internal wave drag contribute significantly to the energy budget of the oceanic general circulation, and have a major impact on the dynamics and statistics of mesoscale eddies. The hypothesis will be tested by employing bottom drag coefficients of various strengths in both idealized models and realistic eddying global ocean general circulation models, and by employing wave drag in the realistic models. Horizontal length scales and energy levels of ocean surface eddy kinetic energy in the models will be compared to satellite altimeter observations, and the vertical structure of modeled eddy kinetic energy will be compared to a database of subsurface current meter observations. Based on previous work by the investigators with idealized two-layer quasi-geostrophic models, it is expected that eddies will compare most closely to observations when the bottom drag is moderately strong. It is also hypothesized that bottom boundary layer drag and wave drag both contribute significantly to the energy budget of the general circulation. Intellectual merit: Bottom drag sensitivity will be investigated in models which remedy several deficiencies of the two-layer quasi-geostrophic models previously employed by the PIs; the truncation of oceanic stratification to two layers, the missing surface boundary effects, the flat bottom, and the horizontally homogeneous mean flows. The project will utilize a new idealized model which simultaneously resolves multiple interior quasi-geostrophic modes and the surface mode, as well as realistic eddying general circulation models with high vertical resolution, inhomogeneous forcing, and rough topography.The investigators will build upon their previous experience inserting topographic internal wave drag into ocean tide models, to insert wave drag into ocean general circulation models. The investigators have on hand a wave drag scheme which is appropriate for the low-frequency flows of interest here. The scheme comes from a collaborator in the atmospheric community, which has been employing schemes for wave drag on low-frequency flows in general circulation models for over twenty years. The wave drag calculation also builds upon collaborations with marine geophysicists, which have resulted in the construction of synthetic datasets of small-scale (on order 1-10 km) topographic roughness. Small-scale roughness is insufficiently represented in state-of-the-art global bathymetric datasets, yet, according to theory, is responsible for the generation of internal waves by low-frequency flows over rough topography.Broader impacts: The work proposed here will contribute to the discussion of oceanic energy dissipation, through investigations of two plausible energy sinks and their impacts on the dynamics of the eddying circulation. The work proposed here should also lead to improvements in eddying ocean models, which are sensitive to the damping coefficients they employ. As computer power continues to increase, the ocean models used in climate simulations will soon become eddy-resolving. Thus it is important for climate studies as well as other applications for eddy-resolving ocean models to be improved and tested. The work proposed here will contribute to that goal. The project will support a post-doctoral scientist and a graduate student. The post-doc will work with the realistic models, and a graduate student will work with the idealized models. The project also provides funding for the lead PI to continue working with high school student and undergraduate summer interns, as he has every summer starting in 2006. Finally, the project provides travel funds for the lead investigator, Dr. Arbic, to continue to participate in the pre-departure meetings Dr. Jurgen Theiss will hold every year to prepare students for their involvement in the NSF-funded Zanzibar Channel Project.