NCOM forecasts (1 km resolution) during the SCOPE experiment (December, 2013) in the Gulf of Mexico

The numerical model is the Navy Coastal Ocean Model (NCOM) (Barron et. al, 2006). A single-nested domain is constructed for the experiment covering the entire Gulf of Mexico. The domain is forced by boundary conditions from the operational global NCOM (Barron et al., 2006). The vertical setup is uses with 34 sigma levels >and 16 Z levels beneath (50 total levels). Sigma levels cover the surface to 550m depth, and the Z levels cover the lower water column. The thinnest layer at the surface has a thickness of 0.5m, and deeper layers telescope to the thickest sigma layer of 85m at a depth of 510m. The high resolution in the surface is intended to properly represent submesoscale physics. Both model experiments are forced by the same atmospheric conditions from the Navy Operational Global Atmospheric Prediction System (NOGAPS, Rosmond et. al, 2002; Goerss, 2009). The surface wind stress is determined from the atmospheric model wind velocity. Surface heat fluxes are computed using bulk flux formulations that use the 10-m air-temperature and humidity along with the ocean model SST. Tidal potential forcing is applied to the inner domain, and tidal boundary conditions for water level and barotropic velocity are provided by the Oregon State University global Ocean Tide Inverse Solution (OTIS) (Egbert and Erofeeva, 2002). Thus, locally generated internal tides are present in the model. Data assimilation is used to produce similar mesoscale structure in the experiment. In the analysis cycle each day, all data over the 24 hours prior to 00Z for the present day are used in the analysis. The analysis is accomplished through a 3D variational (3DVar) approach (Cummings, 2005). Observation increments are computed by differencing observation values and model forecasts at the same time. The analysis increment is inserted into a 24 hour hindcast by rerunning the model over the prior 24 hours and adding the analysis divided by the number of time steps to the state variables throughout the 24 hour hindcast. This represents a correction to the slowly evolving state field rather than resetting the initial condition at 00Z. Direct insertion of the corrections and resetting the initial conditions can generate spurious internal and inertial waves that, in ocean models, require several days to damp out. The 24 hour forecast then provides the background for the next assimilation cycle. The horizontal covariance length scales used are based on latitudinally varying Rossby radius of deformation and vertical scales are based vertical gradients. The Rossby radius varies from 80 km at the southern extent of the domain to 31 km at the northern extent. A factor of 0.82 is used to scale the Rossby radius to provide the decorrelation length scales in the MVOI resulting in an average decorrelation scale of 45 km. Satellite SSH and SST observations are used to construct synthetic profiles through subsurface covariances (Fox et al., 2002) which are used in the 3DVar. Barron, C.N., A.B. Kara, P.J. Martin, and R.C. Rhodes (2006), Formulation, implementation and examination of the vertical coordinate choices in the Global Navy Coastal Ocean Model (NCOM), Ocean Modelling, 11, 347-375. Egbert, G. D., and S. Y. Erofeeva (2002), Efficient inverse modeling of barotropic ocean tides. J. Atmos. Oceanic Tec., 19, 183-204. Fox, D. N., C. N. Barron, M. R. Carnes, M. Booda, G. Peggion and J. V. Gurley (2002), The Modular Ocean Data Assimilation System, Oceanography, 15, 22-28. Rosmond, T. E., J. Teixeira, M. Peng, T. F. Hogan and R. Pauley (2002), Navy Operational Global Atmospheric Prediction System (NOGAPS): Forcing for ocean models, Oceanography, 15, 99–108. Barron, C.N., A.B. Kara, R.C. Rhodes, C. Rowley and L.F. Smedstad (2007), Validation Test Report for the 1/8 Global Navy Coastal Ocean Model Nowcast/Forecast System, NRL Tech Report NRL/MR/7320--07-9019, Naval Research Laboratory, Washington, DC. This is NCOM run B06. This dataset was created by the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE). This research was made possible by a grant from BP/The Gulf of Mexico Research Initiative.

本数值模型采用海军沿岸海洋模型（Navy Coastal Ocean Model, NCOM）（Barron等人，2006）。本实验构建了单个嵌套网格域，覆盖整个墨西哥湾海域。该网格域的边界条件由业务化全球NCOM（Barron等人，2006）提供。垂直分层设置包含34个σ层与16个Z层，总计50层。σ层覆盖从海面至550米水深的范围，Z层则覆盖下层水体。海面处的最薄分层厚度为0.5米，随着深度增加，分层逐渐增厚，在510米深度处达到最大厚度85米的σ层。海面处的高分辨率设置旨在准确表征亚中尺度物理过程。

两组模型实验均采用相同的大气强迫场，数据来自海军业务化全球大气预报系统（Navy Operational Global Atmospheric Prediction System, NOGAPS）（Rosmond等人，2002；Goerss，2009）。海面风应力由大气模式的风速计算得到。海表热通量采用整体通量公式计算，输入参数包括10米高度的气温、相对湿度以及海洋模式的海表温度（Sea Surface Temperature, SST）。

内域施加潮汐势能强迫，水位和正压流速的潮汐边界条件由俄勒冈州立大学全球海洋潮汐反演解（Oregon State University global Ocean Tide Inverse Solution, OTIS）（Egbert与Erofeeva，2002）提供。因此，模型中可模拟局地生成的内潮现象。本实验采用数据同化方法以生成与实际相符的中尺度结构。在每日的分析循环中，分析过程使用当日00世界时（00Z）前24小时内的所有观测数据。分析过程采用三维变分（3D variational, 3DVar）方法（Cummings，2005）。观测增量通过同一时刻的观测值与模式预报值之差计算得到。将分析增量嵌入24小时后报过程：先对前24小时的模式进行重新运行，再将分析增量除以总时间步长后，添加至24小时后报过程的所有状态变量中。该流程实现对缓慢演变的状态场的校正，而非在00Z时刻重置初始条件。直接插入校正值并重置初始条件可能会产生虚假内波与惯性波，在海洋模式中这类波需耗时数日才能消散。完成的24小时预报将作为下一次同化循环的背景场。

所采用的水平协方差长度尺度基于随纬度变化的罗斯贝变形半径（Rossby radius of deformation），垂直尺度则基于垂直梯度。罗斯贝变形半径在网格域南边界处为80千米，北边界处为31千米。采用0.82的缩放因子对罗斯贝变形半径进行缩放，以得到MVOI中的去相关长度尺度，最终得到平均去相关尺度为45千米。卫星观测的海表高度（Sea Surface Height, SSH）与海表温度数据被用于通过次表层协方差构建合成剖面（Fox等人，2002），该剖面将用于三维变分同化过程。

Barron, C.N.、A.B. Kara、P.J. Martin与R.C. Rhodes（2006），《全球海军沿岸海洋模型（NCOM）中垂直坐标选择的构建、实现与检验》，《海洋模式》，11卷，347-375页。
Egbert, G.D.与S.Y. Erofeeva（2002），《正压海洋潮汐的高效反演模拟》，《大气与海洋技术杂志》，19卷，183-204页。
Fox, D.N.、C.N. Barron、M.R. Carnes、M. Booda、G. Peggion与J.V. Gurley（2002），《模块化海洋数据同化系统》，《海洋学》，15卷，22-28页。
Rosmond, T.E.、J. Teixeira、M. Peng、T.F. Hogan与R. Pauley（2002），《海军业务化全球大气预报系统（NOGAPS）：海洋模式强迫场》，《海洋学》，15卷，99-108页。
Barron, C.N.、A.B. Kara、R.C. Rhodes、C. Rowley与L.F. Smedstad（2007），《1/8度全球海军沿岸海洋模式实时预报/预报系统的验证测试报告》，海军研究实验室技术报告NRL/MR/7320--07-9019，美国华盛顿特区海军研究实验室。

本数据集为NCOM运行案例B06。本数据集由环境碳氢化合物输送高级研究联盟（Consortium for Advanced Research on Transport of Hydrocarbon in the Environment, CARTHE）构建。本研究得到BP/墨西哥湾研究倡议项目的资助。