Physics and dynamics of density compensated temperature and salinity anomalies
Physics and dynamics of density compensated temperature and salinity anomalies
复制标题
密度补偿温度和盐度异常的物理和动力学
DOI：
10.1175/jpo2706.1
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发表时间：
2005
影响因子：
3.5
通讯作者：
R. Tailleux
中科院分区：
文献类型：
--
作者：
R. Tailleux
俯冲温度异常被认为是中纬度地区通过太平洋和大西洋的所谓温跃层桥改变赤道地区气候变化的一种可能方式。然而，要对赤道热平衡产生重大影响，温度异常必须充分无阻尼地到达赤道地区。在海洋中，传播的温度（和盐度）异常的振幅可以被绝热（非保守）和绝热（保守）效应改变。绝热变化的重要性取决于异常是由波动动力学控制还是由与密度补偿相关的被动平流控制。由于对波浪的了解相对较好，本文试图了解由绝热效应引起的密度补偿温度和盐度异常的振幅变化，对此尚无一般方法可用。主要的假设是，这些可以独立于绝热效应引起的振幅变化来计算。由于密度补偿要求等式T/S S/保持在平均轨迹上，如果ratio /这样做，则比值T/S可能会发生较大幅度的变化，其中and分别是热膨胀系数和盐盐收缩系数。在海洋中，温带和热带纬度之间的比值S/可能降低1个数量级，但这种大的变化通常与平环流运动而不是等环流运动有关，因此在实践中很可能与绝热引起的变化叠加在一起。为了理解沿平均流线的T和S的个体变化，构建了两种不同的理论，分别使用密度/盐度和密度/辣度作为预测变量。如果忽略预测变量之间的耦合（通常是这样做的），这两种理论的预测都处于领先地位，即温度（盐度）异常在从温带向热带纬度传播时，平均而言应该有系统地显著减弱（保持或放大）。然而，沿着等斜线的特定轨迹，衰减和放大似乎都是局部可能的。假设密度/辣度公式是最准确的，这得到了高阶效应理论评估的支持，本文的结果提供了一个向赤道传播的俯冲盐度异常的放大机制，后者可能通过对赤道混合层的缓慢调制而潜在地影响赤道气候的年代际变化，可能比其衰减的温度对应物更容易。这可以通过影响屏障层来实现，例如，已知盐度会强烈影响当地的热通量和热含量。
Subducted temperature anomalies have been invoked as a possible way for midlatitudes to alter the climate variability of equatorial regions through the so-called thermocline bridge, both in the Pacific and Atlantic Oceans. To have a significant impact on the equatorial heat balance, however, temperature anomalies must reach the equatorial regions sufficiently undamped. In the oceans, the amplitude of propagating temperature (and salinity) anomalies can be altered both by diabatic (nonconservative) and adiabatic (conservative) effects. The importance of adiabatic alterations depends on whether the anomalies are controlled by wave dynamics or by passive advection associated with density compensation. Waves being relatively well understood, this paper seeks to understand the amplitude variations of density-compensated temperature and salinity anomalies caused by adiabatic effects, for which no general methodology is available. The main assumption is that these can be computed independent of amplitude variations caused by diabatic effects. Because density compensation requires the equality T/S S/ to hold along mean trajectories, the ratio T/S may potentially undergo large amplitude variations if the ratioS/ does, where andS are the thermal expansion and haline contraction coefficients, respectively. In the oceans, the ratio S/ may decrease by an order-1 factor between the extratropical and tropical latitudes, but such large variations are in general associated with diapycnal rather than isopycnal motion and hence are likely to be superimposed in practice with diabatically induced variations. To understand the individual variations of T and S along the mean streamlines, two distinct theories are constructed that respectively use density/salinity and density/spiciness as prognostic variables. If the coupling between the prognostic variables is neglected, as is usually done, both theories predict at leading order that temperature (salinity) anomalies should be systematically and significantly attenuated (conserved or amplified), on average, when propagating from extratropical to tropical latitudes. Along particular trajectories following isopycnals, however, both attenuation and amplification appear to be locally possible. Assuming that the density/spiciness formulation is the most accurate, which is supported by a theoretical assessment of higher-order effects, the present results provide an amplification mechanism for subducted salinity anomalies propagating equatorward, by which the latter could potentially affect decadal equatorial climate variability through their slow modulation of the equatorial mixed layer, perhaps more easily than their attenuated temperature counterparts. This could be by affecting, for instance, barrier layers by which salinity is known to strongly affect local heat fluxes and heat content.