Bishop Stuart P, Small R Justin, Bryan Frank O
Department of Marine, Earth, & Atmospheric Sciences North Carolina State University at Raleigh Raleigh NC USA.
National Center for Atmospheric Research Boulder CO USA.
J Adv Model Earth Syst. 2020 Oct;12(10):e2020MS002118. doi: 10.1029/2020MS002118. Epub 2020 Oct 21.
The thermal component of oceanic eddy available potential energy (EPE) generation due to air-sea interaction is proportional to the product of anomalous sea surface temperature (SST) and net air-sea heat flux (SHF). In this study we assess EPE generation and its timescale and space-scale dependence from observations and a high-resolution coupled climate model. A dichotomy exists in the literature with respect to the sign of this term, that is, whether it is a source or a sink of EPE. We resolve this dichotomy by partitioning the SST and net heat flux into climatological mean, climatological seasonal cycle, and remaining transient contributions, thereby separating the mesoscale eddy variability from the forced seasonal cycle. In this decomposition the mesoscale air-sea SST-SHF feedbacks act as a 0.1 TW global sink of EPE. In regions of the ocean with a large seasonal cycle, for example, midlatitudes of the Northern Hemisphere, the EPE generation by the forced seasonal cycle exceeds the mesoscale variability sink, such that the global generation by seasonal plus eddy variability acts as a 0.8 TW source. EPE destruction is largest in the midlatitude western boundary currents due to mesoscale air-sea interaction and in the tropical Pacific where SST variability is due mainly to the El Niño-Southern Oscillation. The EPE sink in western boundary currents is spatially aligned with SST gradients and offset to the poleward side of currents, while the mean and seasonal generation are aligned with the warm core of the current. By successively smoothing the data in space and time we find that half of the EPE sink is confined to timescales less than annual and length scales less than 2°, within the oceanic mesoscale band.
由于海气相互作用产生的海洋涡旋有效势能（EPE）的热分量与海表面温度异常（SST）和海气净热通量（SHF）的乘积成正比。在本研究中，我们根据观测数据和一个高分辨率耦合气候模型评估了EPE的产生及其时间尺度和空间尺度依赖性。关于这一项的符号，即它是EPE的源还是汇，文献中存在分歧。我们通过将SST和净热通量划分为气候平均、气候季节循环和其余瞬态贡献来解决这一分歧，从而将中尺度涡旋变率与强迫季节循环分开。在这种分解中，中尺度海气SST - SHF反馈作为EPE的一个0.1 TW的全球汇。在海洋季节性循环较大的区域，例如北半球中纬度地区，强迫季节循环产生的EPE超过了中尺度变率汇，使得季节性加涡旋变率的全球产生作为一个0.8 TW的源。由于中尺度海气相互作用，EPE的破坏在中纬度西边界流中最大，而在热带太平洋，SST变率主要归因于厄尔尼诺 - 南方涛动。西边界流中的EPE汇在空间上与SST梯度对齐，并偏向流场的极向一侧，而平均和季节性产生则与流的暖核对齐。通过在空间和时间上对数据进行连续平滑处理，我们发现EPE汇的一半局限于时间尺度小于年且长度尺度小于2°的范围内，属于海洋中尺度带。
