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Stability Analysis of the Labrador Current

机译：拉布拉多流的稳定性分析

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摘要

Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 and 5 days and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in the LC: 1) a balanced interior mode with along-flow wavelengths of about 30-45 km, phase velocities of 0.3 ms~(-1), maximal growth rates of 1day~(-1), and surface-intensified but deep-reaching amplitudes; 2) a balanced shallow mode with along-flow wavelengths of about 0.3-1.5 km, phase velocities of 0.55 m s~(-1) about 3 times larger growth rates, but amplitudes confined to the mixed layer (ML); and 3) an unbalanced symmetric mode with the largest growth rates, vanishing phase speeds, and along-flow structure, and very small cross-flow wavelengths, also confined to the ML. Both balanced modes are akin to baroclinic instability but operate at moderate-to-small Richardson numbers Ri with much larger growth rates as for the quasigeostrophic limit of Ri(＞＞) 1. The interior mode is found to be responsible for the instability of the LC during winter. Weak stratification and enhanced vertical shear due to local buoyancy loss and the advection of convective water masses from the interior result in small Ri within the LC and up to 3 times larger growth rates of the interior mode in March compared to summer and fall conditions. Both the shallow and the symmetric modes are not resolved by the model, but it is suggested that they might also play an important role for the instability in the LC and for lateral mixing.
机译：系泊观测和模型模拟表明，冬季拉布拉多洋流（LC）不稳定，在2至5天之间的涡动能（EKE）增强，而其他季节的EKE少得多。使用模型的垂直切变和分层进行的线性稳定性分析揭示了LC中三种主要的不稳定性模式：1）平衡的内部模式，其沿流波长约为30-45 km，相速度为0.3 ms〜（-1），最大生长速度为1day〜（-1），且表面增强但幅度较大。 2）平衡的浅波模式，其沿流波长为约0.3-1.5 km，相速度为0.55 m s〜（-1），大约是增长速度的3倍，但幅度仅限于混合层（ML）； 3）具有最大增长率，消失的相速度和沿流结构以及非常小的横流波长的不平衡对称模式，也仅限于ML。两种平衡模式都类似于斜压不稳定，但以中等至较小的理查森数Ri运行，其增长速度远大于Ri（准＞ 1）的准营养极限。冬季LC。由于局部浮力损失以及内部对流水团的平流而导致的弱分层和垂直剪切增加，导致LC内的Ri较小，与夏季和秋季相比，3月份内部模式的增长率高达3倍。模型无法解析浅模式和对称模式，但建议它们对于LC的不稳定性和横向混合也可能起重要作用。

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  • 来源
    《Journal of Physical Oceanography》 |2014年第2期|445-463|共19页
  • 作者

    Soeren Thomsen; Carsten Eden; Lars Czeschel;

  • 作者单位

    Institut fuer Meereskunde, KlimaCampus, Universitaet Hamburg, Hamburg, and Helmholtz Centre for Ocean Research (GEOMAR), Kiel, Germany;

    Institut fuer Meereskunde, Universitaet Hamburg, Bundesstr. 53, 20146 Hamburg, Germany;

    Institut fuer Meereskunde, KlimaCampus, Universitaet Hamburg, Hamburg, Germany;

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