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首页> 外文期刊>Journal of Physical Oceanography >The Influence of Periodic Forcing on the Time Dependence of Western Boundary Currents: Phase Locking, Chaos, and Mechanisms of Low-Frequency Variability*
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The Influence of Periodic Forcing on the Time Dependence of Western Boundary Currents: Phase Locking, Chaos, and Mechanisms of Low-Frequency Variability*

机译：周期性强迫对西方边界电流的时间依赖性的影响：锁相，混沌和低频变异机制*

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In this study an idealized gyre is put into a temporally periodic state by a steady wind stress curl forcing, and its nonlinear response to variable forcing is investigated by a detailed parameter survey varying the time-mean component of the wind and the amplitude and frequency of a periodic component. Periodic wind variations exceeding ~0.5% profoundly affect the western boundary current (WBC) time dependence, yielding regime diagrams with intricately interleaved regions of phase locking, quasiperiodicity, and chaos. In phase-locked states, the WBC period is locked to a rational multiple of the forcing period and can be shifted far outside its natural range. Quasiperiodic states can exhibit long intervals of near-synchrony interrupted periodically by brief slips out of phase with the forcing. Hysteresis and a period-doubling route to chaos are also found. The nonlinear WBC response can include variability at long time scales that are absent from both the forcing and the steadily driven current; this is a new mechanism for the generation of low-frequency WBC variability. These behaviors and their parameter dependence resemble the Devil's staircase found in the "circle map" model of a periodically forced nonlinear oscillator, but with differences attributable to higher-dimensional dynamics. These nonlinear effects occur with forcing amplitudes in the observed range of the annual wind stress curl cycle and therefore should be considered when inferring the cause of observed WBC time scales. These results suggest that studies omitting either forcing variation or nonlinearity provide an unrealistically narrow view of the possible origins of time dependence in WBCs.
机译：在这项研究中，理想的回旋通过稳定的风应力卷曲强迫进入时间周期状态，并通过详细的参数调查来研究其对变量强迫的非线性响应，具体的参数调查会改变风的时间平均分量以及风的振幅和频率周期性成分。周期性风的变化超过〜0.5％会深刻影响西边界电流（WBC）的时间依赖性，生成具有错综复杂的锁相，准周期性和混沌交错区域的状态图。在锁相状态下，WBC周期被锁定为强制周期的合理倍数，并且可以远远超出其自然范围。准周期状态可以表现出较长的近同步时间间隔，这些短时间周期会由于与强迫的短暂错位而周期性地中断。还发现了磁滞现象和导致混乱的倍增途径。非线性WBC响应可能包括长时间范围内的变化，而强迫和稳定驱动电流都没有这种变化。这是产生低频WBC变异性的新机制。这些行为及其参数依赖性类似于在周期性强制非线性振荡器的“圆图”模型中发现的魔鬼阶梯，但是由于高维动力学而存在差异。这些非线性效应会随着年度风应力卷曲周期的观测范围内的强迫幅度而发生，因此在推断观测到的WBC时间尺度的原因时应考虑这些非线性效应。这些结果表明，忽略强迫变化或非线性的研究为WBC中时间依赖性的可能起源提供了一个不切实际的狭窄观点。

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