Advantages of vertically adaptive coordinates in numerical models of stratified shelf seas
Advantages of vertically adaptive coordinates in numerical models of stratified shelf seas
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垂直自适应坐标在分层陆架海数值模型中的优势
DOI：
10.1016/j.ocemod.2015.05.008
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发表时间：
2015
期刊：
影响因子：
3.2
通讯作者：
H. Burchard
中科院分区：
文献类型：
--
作者：
Gräwe;P. Holtermann;K. Klingbeil;H. Burchard
北海和波罗的海等陆架海的特点是在空间和时间上变化的分层，这与其物理动态和生态系统的演变高度相关。分层可以从不稳定分层（例如，由于对流表面冷却）到密度跳跃高达10 kg/m3/m3的强烈分层（例如，在流入波罗的海）。分层对垂直湍流输送有直接影响（例如，的营养物）并影响环境水进入密集的底流的夹带速率，这又决定了层化和氧气供应，例如，波罗的海中部此外，夏季温跃层垂直扩散率的抑制是北海营养盐垂直交换的限制因素之一。由于计算资源的限制，并且由于这种密度跳跃的位置（通过盐度或温度）由模型模拟本身预测，因此预定义的垂直坐标不能总是可靠地解决这些特征。因此，所有具有预定义的垂直坐标分布的陆架海模型都固有地受到密度结构的分辨率不足的影响。（2010年）提出了海洋模型垂直自适应坐标的概念，其中对强分层（和剪切）位置的垂直坐标进行缩放。这是通过求解坐标位置的扩散方程来实现的（扩散率与分层或剪切频率成比例）。我们将展示一个耦合模型系统的北海和波罗的海（分辨率为1.8公里）如何数值混合大幅减少和模型结果变得更加现实时，垂直自适应坐标应用。此外，我们还证明了垂直自适应坐标在模拟北海和波罗的海两个动态不同的地区与一个单一的参数集。自适应坐标的计算开销的分析表明，在运行时增加了5-8%。这仍然比添加更多的sigma层以减少伪数值混合更便宜。
Shelf seas such as the North Sea and the Baltic Sea are characterised by spatially and temporally varying stratification that is highly relevant for their physical dynamics and the evolution of their ecosystems. Stratification may vary from unstably stratified (e.g., due to convective surface cooling) to strongly stratified with density jumps of up to 10 kg/m3per m (e.g., in overflows into the Baltic Sea). Stratification has a direct impact on vertical turbulent transports (e.g., of nutrients) and influences the entrainment rate of ambient water into dense bottom currents which in turn determine the stratification of and oxygen supply to, e.g., the central Baltic Sea. Moreover, the suppression of the vertical diffusivity at the summer thermocline is one of the limiting factors for the vertical exchange of nutrients in the North Sea. Due to limitations of computational resources and since the locations of such density jumps (either by salinity or temperature) are predicted by the model simulation itself, predefined vertical coordinates cannot always reliably resolve these features. Thus, all shelf sea models with a predefined vertical coordinate distribution are inherently subject to under-resolution of the density structure.To solve this problem, Burchard and Beckers (2004) and Hofmeister et al. (2010) developed the concept of vertically adaptive coordinates for ocean models, where zooming of vertical coordinates at locations of strong stratification (and shear) is imposed. This is achieved by solving a diffusion equation for the position of the coordinates (with the diffusivity being proportional to the stratification or shear frequencies). We will show for a coupled model system of the North Sea and the Baltic Sea (resolution ∼ 1.8 km) how numerical mixing is substantially reduced and model results become significantly more realistic when vertically adaptive coordinates are applied. We additionally demonstrate that vertically adaptive coordinates perform well in simulating the two dynamically different regions North Sea and Baltic Sea with a single parameter set.An analysis of the computational overhead of the adaptive coordinates indicates an increase of 5–8% in runtime. This is still less expensive than adding more sigma-layers to reduce spurious numerical mixing.
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影响因子：
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DOI：
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发表时间：
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期刊：
影响因子：
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