On the Buoyancy Forcing and Residual Circulation in the Southern Ocean: The Feedback from Ekman and Eddy Transfer
On the Buoyancy Forcing and Residual Circulation in the Southern Ocean: The Feedback from Ekman and Eddy Transfer
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DOI：
10.1175/2009jpo4080.1
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发表时间：
2010-02-01
影响因子：
3.5
通讯作者：
Williams, Richard G.
中科院分区：
文献类型：
--
作者：
Badin, Gualtiero;Williams, Richard G.
从两种不同的角度考察了浮力强迫对南大洋剩余环流的影响。首先，利用Walin开发的等环流框架中的热和淡水的海气通量估算了水团转化和形成的速率，该框架应用于两种不同的海气通量气体学和再分析数据集。在无绝热混合的极限和稳定状态下，这些对水团转化和形成的海气通量估计分别相当于对上层海洋剩余环流和俯冲速率的估计。所有三个数据集都揭示了在sigma = 526.8和27.2之间稠密水向轻水的转变，以及正形成率在sigma = 26.6时达到峰值，而负形成率在sigma = 27时达到峰值。这种转化可以通过地表加热或淡水输入来实现，尽管每种情况下形成速率的大小各不相同。其次，本文采用混合层和绝热温跃层的理想模式来说明混合层中的海洋动力学变化和淡水通量如何改变浮力通量，从而改变剩余环流。向北增加的冷水Ekman平流增强了海气温差和进入海洋的地表热通量，从而增加了剩余环流；风应力增加0.05 N m（-2）通常会使地表热通量增加8 W m(-2)，并使形成率的峰值改变高达8 Sv (1 Sv相当于10(6)m（3) s(-1)）。相反，增加涡旋平流和扩散导致相反的弱效应；每增加500 m(2) s(-1)，地表热通量减少3 W m(-2)，形成速率峰值改变1 Sv。
The effect of buoyancy forcing on the residual circulation in the Southern Ocean is examined in two different ways. First, the rates of water-mass transformation and formation are estimated using air-sea fluxes of heat and freshwater in the isopycnal framework developed by Walin, which is applied to two different air-sea flux climatologies and a reanalysis dataset. In the limit of no diabatic mixing and at a steady state, these air-sea flux estimates of water-mass transformation and formation are equivalent to estimating the residual circulation and the subduction rates in the upper ocean, respectively. All three datasets reveal a transformation of dense to light waters between sigma = 526.8 and 27.2, as well as positive formation rates peaking at sigma = 26.6, versus negative rates peaking at sigma = 27. The transformation is achieved either by surface heating or freshwater inputs, although the magnitude of the formation rates varies in each case. Second, an idealized model of a mixed layer and adiabatic thermocline for a channel is used to illustrate how changes in ocean dynamics in the mixed layer and freshwater fluxes can modify the buoyancy fluxes and, thus, alter the residual circulation. Increasing the Ekman advection of cold water northward enhances the air-sea temperature difference and the surface heat flux into the ocean, which then increases the residual circulation; an increase in wind stress of 0.05 N m(-2) typically increases the surface heat flux by 8 W m(-2) and alters the peaks in formation rate by up to 8 Sv (1 Sv equivalent to 10(6) m(3) s(-1)). Conversely, increasing the eddy advection and diffusion leads to an opposing weaker effect; an increase in the eddy transfer coefficient of 500 m(2) s(-1) decreases the surface heat flux by 3 W m(-2) and alters the peaks in formation rate by 1 Sv.