Quantifying barotropic and baroclinic eddy feedbacks in the persistence of the Southern Annular Mode

Nie, Yu; Zhang, Yang; Chen, Gang; Yang, Xiu‐Qun; Burrows, D. A.

doi:10.1002/2014gl062210

Cited by 42 publications

(53 citation statements)

References 34 publications

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“…As the persistence of the SAM is mostly extended through the positive eddy‐zonal flow feedback in which both barotropic and baroclinic mechanisms play important roles [ Nie et al , ], in this study, we adopt the FAWA analysis [ Nakamura and Zhu , ] to investigate how the SAM‐induced SST anomaly can influence the barotropic and baroclinic processes in such positive feedback thus finally affect the SAM variability. Same as in Nie et al [, equation (1)], the FAWA (denoted by A ) is defined by the waviness of quasi‐geostrophic potential vorticity (PV, denoted by Q ) contours at a constant pressure level. Following the formalism, the eddy momentum flux convergence, which is the dominant forcing governing the variability of eddy‐driven jet, is rewritten as in Chen et al []:

M \equiv - \frac{1}{a \cos^{2} ϕ} \frac{\partial ((), [u^{*} v^{*}] \cos^{2} ϕ)}{∂ϕ} = \underset{baroclinic}{\underset{- \frac{\partial}{∂p} ((), \frac{f [v^{*} θ^{*}]}{\partial θ_{s} / ∂p})}{false}} \underset{barotropic}{\underset{- \frac{k_{eff}}{a} \frac{∂Q}{\partial ϕ_{e}}}{false}} - \frac{∂A}{∂t} + ΔΣ,

where [] denotes the zonal average and ∗ denotes the eddy component.…”

Section: Methodssupporting

confidence: 91%

“…The persistence of the SAM is thought to be maintained by the positive feedback between the zonal mean zonal wind and the eddy momentum forcing [ Lorenz and Hartmann , ]. As shown by Nie et al [], both barotropic mechanisms [ Hartmann and Lo , ; Chen et al , ] and baroclinic mechanisms [ Robinson , ; Lorenz and Hartmann , ; Chen and Plumb , ; Zhang et al , ] contribute to this positive feedback.…”

Section: Introductionmentioning

confidence: 99%

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On the role of extratropical air‐sea interaction in the persistence of the Southern Annular Mode

Xiao

Zhang

Yang

et al. 2016

Geophysical Research Letters

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Using the daily atmosphere and ocean reanalysis data, this study highlights the role of extratropical air‐sea interaction in the variability of the Southern Annular Mode (SAM). Our analysis shows that the SAM‐induced meridional dipolar sea surface temperature (SST) anomalies, through surface heat fluxes, can maintain persistent lower tropospheric temperature anomalies, which further results in anomalous eddy momentum forcing enhancing the persistence of the SAM. With the Finite Amplitude Wave Activity diagnosis, we illustrate that response of the eddy momentum forcing to SST anomalies can be attributed to changes in both baroclinic processes as baroclinic eddy generation and barotropic processes as wave breaking thus resultant diffusive eddy mixing, with the former confined at high latitudes and the latter strongest at midlatitudes. Spectral analysis further suggests that the above air‐sea interactions are important for bimonthly and longer time scale SAM variations. The dipolar SST pattern may be an indicator for predicting subseasonal and interseasonal variabilities of the SAM.

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M \equiv - \frac{1}{a \cos^{2} ϕ} \frac{\partial ((), [u^{*} v^{*}] \cos^{2} ϕ)}{∂ϕ} = \underset{baroclinic}{\underset{- \frac{\partial}{∂p} ((), \frac{f [v^{*} θ^{*}]}{\partial θ_{s} / ∂p})}{false}} \underset{barotropic}{\underset{- \frac{k_{eff}}{a} \frac{∂Q}{\partial ϕ_{e}}}{false}} - \frac{∂A}{∂t} + ΔΣ,

where [] denotes the zonal average and ∗ denotes the eddy component.…”

Section: Methodssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

On the role of extratropical air‐sea interaction in the persistence of the Southern Annular Mode

Xiao

Zhang

Yang

et al. 2016

Geophysical Research Letters

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“…As discussed in section 1, isolating and quantifying the eddy-feedbacks is another difficulty in developing a full mechanistic understanding of problems in which eddymean flow interaction plays an important role; examples of such problems include the dynamics of the Annular Modes and their overestimated persistence in GCMs (Feldstein and Lee 1998;Robinson 2000;Lorenz and Hartmann 2001;Simpson et al 2013a;Nie et al 2014), poleward shift of the midlatitude jets under climate change (Chen and Held 2007;Kidston et al 2011;Lorenz 2014) and troposphere-stratosphere coupling (Kushner and Polvani 2004;Song and Robinson 2004;Domeisen et al 2013). The EFMÊ E E and similar matrices for eddy-phase speed and eddy length-scale can be used to isolate and quantify the response of eddies to a given change in the mean-flow, which combined with well-controlled GCM experiments made possible usingM M M, can help with developing a deeper dynamical understanding of these problems.…”

Section: Applications Of the Lrf And Efmmentioning

confidence: 99%

“…Such methods include FDT, to construct LRFs, and lag-regression (Lorenz and Hartmann 2001;Simpson et al 2013b) and finite-amplitude wave-activity (Nakamura and Zhu 2010;Nie et al 2014), to diagnose eddy feedbacks. As an example, in Part 2 of this study, we useM M M to investigate why the LRF constructed using the FDT performs poorly in some cases.…”

Section: Applications Of the Lrf And Efmmentioning

confidence: 99%

The Linear Response Function of an Idealized Atmosphere. Part I: Construction Using Green’s Functions and Applications

Hassanzadeh

Kuang

2016

Journal of the Atmospheric Sciences

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A linear response function (LRF) determines the mean-response of a nonlinear climate system to weak imposed forcings, and an eddy flux matrix (EFM) determines the eddy momentum and heat flux responses to mean-flow changes. Neither LRF nor EFM can be calculated from first principles due to the lack of a complete theory for turbulent eddies. Here the LRF and EFM for an idealized dry atmosphere are computed by applying numerous localized weak forcings, one at a time, to a GCM with Held-Suarez physics and calculating the mean-responses. The LRF and EFM for zonally-averaged responses are then constructed using these forcings and responses through matrix inversion. Tests demonstrate that LRF and EFM are fairly accurate. Spectral analysis of the LRF shows that the most excitable dynamical mode, the neutral vector, strongly resembles the model's Annular Mode. The framework described here can be employed to compute the LRF/EFM for zonally-asymmetric responses and more complex GCMs. The potential applications of the LRF/EFM constructed here are i) forcing a specified mean-flow for hypothesis-testing, ii) isolating/quantifying the eddyfeedbacks in complex eddy-mean flow interaction problems, and iii) evaluating/improving more generallyapplicable methods currently used to construct LRFs or diagnose eddy-feedbacks in comprehensive GCMs or observations. As an example for iii, in Part 2, the LRF is also computed using the fluctuation-dissipation theorem (FDT), and the previously-calculated LRF is exploited to investigate why FDT performs poorly in some cases. It is shown that dimension-reduction using leading EOFs, which is commonly used to construct LRFs from the FDT, can significantly degrade the accuracy due to the non-normality of the operator.

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“…In recent years, observational studies with high-resolution satellite data (Nakamura et al 2004;Small et al 2008) and numerical studies with high-resolution GCM Taguchi et al 2009;Sampe et al 2010;Czaja and Blunt 2011;Feliks et al 2004Feliks et al , 2007Feliks et al , 2011 have shown that the SST anomalies associated with midlatitude oceanic front zones can influence the time-mean atmospheric circulation beyond planetary boundary layer. Therefore, the transient eddies not only play an important role in driving and maintaining midlatitude atmospheric circulation (Ren et al 2011;Xiang and Yang 2012;Zhang et al 2012;Nie et al 2013Nie et al , 2014, but also may act as a main dynamical process through which the midlatitude ocean thermal condition can affect the atmosphere (Ren et al 2007). …”

Section: Introductionmentioning

confidence: 99%

Structure and dynamics of decadal anomalies in the wintertime midlatitude North Pacific ocean–atmosphere system

2015

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it is suggested that the midlatitude ocean-atmosphere interaction can provide a positive feedback mechanism for the development of initial anomaly, in which the oceanic front and the atmospheric transient eddy are the indispensable ingredients. Such a positive ocean-atmosphere feedback mechanism is fundamentally responsible for the observed decadal anomalies in the midlatitude North Pacific ocean-atmosphere system.

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Quantifying barotropic and baroclinic eddy feedbacks in the persistence of the Southern Annular Mode

Cited by 42 publications

References 34 publications

On the role of extratropical air‐sea interaction in the persistence of the Southern Annular Mode

On the role of extratropical air‐sea interaction in the persistence of the Southern Annular Mode

The Linear Response Function of an Idealized Atmosphere. Part I: Construction Using Green’s Functions and Applications

Structure and dynamics of decadal anomalies in the wintertime midlatitude North Pacific ocean–atmosphere system

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