The Deep Western Boundary Current and Adjacent Interior Circulation at 24°-30° N: Mean Structure and Mesoscale Variability
The Deep Western Boundary Current and Adjacent Interior Circulation at 24°-30° N: Mean Structure and Mesoscale Variability
复制标题
DOI：
10.1175/jpo-d-20-0094.1
复制
发表时间：
2020-09-01
影响因子：
3.5
通讯作者：
Johns, William E.
中科院分区：
文献类型：
--
作者：
Bilo, Tiago Carrilho;Johns, William E.
根据近20年的速度和水文观测，以及30年的涡旋解析全球模拟结果，研究了巴哈马阿巴科近海26.5°N的北大西洋深水（NADW, 1000 < z < 5000 m）环流和深水西部边界流（DWBC）的平均变率。在北纬26.5度和argo的地转速度观测显示，在NADW层存在一个平均阿巴科环流，由大约北纬24度和30度以及西纬72度和77度之间的封闭气旋环流组成。该环流的向南流动部分（DWBC）被限制在距离西边界约150公里的范围内，平均输送量约为30 Sv (1 Sv相当于10(6)m（3) s(-1)）。在DWBC近海，数据显示了一个持续的向北再环流，净输送量从6.5到16 Sv不等。数值模拟支持的2008- 2017年的海流记录表明，DWBC输运变率主要由两种不同类型的波动主导：1)在整个时间序列中定期发生的250-280天周期；2)每5-6年偶尔发生的400 - 700天周期的高能振荡，迫使DWBC在离岸很远的地方徘徊数月。较短周期的振荡与沿大陆坡向南传播的涡旋引起的DWBC蜿蜒有关，而较长周期的振荡似乎与大型反气旋涡旋有关，这些涡旋在20°至26.5°N之间缓慢向西北传播，与DWBC流动相反。观测和理论证据表明，这两种类型的变率可能分别产生。由DWBC不稳定过程和罗西比波从西边界反射。
The mean North Atlantic Deep Water (NADW, 1000 < z < 5000 m) circulation and deep western boundary current (DWBC) variability offshore of Abaco, Bahamas, at 26.5 degrees N are investigated from nearly two decades of velocity and hydrographic observations, and outputs from a 30-yr-long eddy-resolving global simulation. Observations at 26.5 degrees N and Argo-derived geostrophic velocities show the presence of a mean Abaco Gyre spanning the NADW layer, consisting of a closed cyclonic circulation between approximately 24 degrees and 30 degrees N and 72 degrees and 77 degrees W. The southward-flowing portion of this gyre (the DWBC) is constrained to within similar to 150 km of the western boundary with a mean transport of similar to 30 Sv (1 Sv equivalent to 10(6) m(3) s(-1)). Offshore of the DWBC, the data show a consistent northward recirculation with net transports varying from 6.5 to 16 Sv. Current meter records spanning 2008-17 supported by the numerical simulation indicate that the DWBC transport variability is dominated by two distinct types of fluctuations: 1) periods of 250-280 days that occur regularly throughout the time series and 2) energetic oscillations with periods between 400 and 700 days that occur sporadically every 5-6 years and force the DWBC to meander far offshore for several months. The shorter-period variations are related to DWBC meandering caused by eddies propagating southward along the continental slope at 248-30 degrees N, while the longer-period oscillations appear to be related to large anticyclonic eddies that slowly propagate northwestward counter to the DWBC flow between similar to 20 degrees and 26.5 degrees N. Observational and theoretical evidence suggest that these two types of variability might be generated, respectively, by DWBC instability processes and Rossby waves reflecting from the western boundary.