Identification of jets and mixing barriers from sea level and vorticity measurements using simple statistics

Hughes, Chris W.; Thompson, Andrew F.; Wilson, Chris

doi:10.1016/j.ocemod.2009.10.004

Cited by 28 publications

(35 citation statements)

References 14 publications

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“…That skewness should be expected to naturally accompany jet streams has already been demonstrated in an oceanographic context, where patterns of skewness and kurtosis can be used to identify the location of ocean jet streams using satellite altimetry data (Thompson and Demirov 2006;Hughes et al 2010), but we are not aware of its discussion in the atmospheric literature. It is consistent, however, with the recent derivation of atmospheric flow patterns of maximal skewness, since these patterns resemble jet stream shifts (Pasmanter and Selten 2010).…”

Section: Introductionmentioning

confidence: 91%

“…Hughes et al (2010) modeled a jet stream as a step function between two regions of constant potential vorticity (PV) of different values. In this framework they were able to derive a theory that predicted not only that the skewness of PV changes sign across the jet stream, but also that the climatological jet axis should coincide with a minimum of kurtosis.…”

Section: Observationsmentioning

confidence: 99%

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A Simple Kinematic Source of Skewness in Atmospheric Flow Fields

Luxford

Woollings

2012

Journal of the Atmospheric Sciences

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Geopotential height fields exhibit a well-known pattern of skewness, with distributions that are positively skewed on the poleward side of the midlatitude jets/storm tracks and negatively skewed on the equatorward side. This pattern has often been interpreted as a signature of nonlinear dynamical features, such as blocking highs and cutoff lows, and there is renewed interest in the higher moments of flow variables as indicators of the nature of the underlying dynamics. However, this paper suggests that skewness can arise as a simple kinematic consequence of the presence of jet streams and so may not be a reliable indicator of nonlinear dynamical behavior. In support of this, reanalysis data are analyzed to demonstrate a close link between the jet streams and the skewness patterns. Further evidence is provided by a simple stochastic kinematic model of a jet stream as a Gaussian wind profile. The parameters of this model are fitted to data from the reanalysis and also from an aquaplanet general circulation model. The skewness of the model's geopotential height and zonal wind fields are then compared to those of the original data. This shows that a fluctuating jet stream can produce patterns of skewness that are qualitatively similar to those observed, although the magnitude of the skewness is significantly overestimated by the kinematic model. These results suggest that this simple kinematic effect does contribute to the observed patterns of skewness but that other processes (such as nonlinear dynamics) likely also play a role.

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Section: Introductionmentioning

confidence: 91%

Section: Observationsmentioning

confidence: 99%

A Simple Kinematic Source of Skewness in Atmospheric Flow Fields

Luxford

Woollings

2012

Journal of the Atmospheric Sciences

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“…The PV staircase concept may be considered as a new theoretical paradigm that explains the existence of multiple zonal jets by the formation of PV staircases, which result from a complex dynamical self‐organization of forced turbulent flows in rotating fluids [ Baldwin et al ., ; Dritschel and McIntyre , ; Hughes et al ., ; Dritschel , , and references therein]. In this paradigm, the positive feedback interaction of waves and turbulence are responsible for the generation and maintenance of multiple jet structures, which constitute efficient transport barriers across them.…”

Section: The Sicc and Two Pv Paradigmsmentioning

confidence: 99%

South Indian Countercurrent and associated fronts

et al. 2014

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A striking feature of the South Indian Ocean circulation is the presence of the eastward South Indian Countercurrent (SICC) that flows in a direction opposite to that predicted by the classical theories of wind-driven circulation. Several authors suggest that the SICC resembles the subtropical countercurrents (STCCs) observed in other oceans, which are defined as narrow eastward jets on the equatorward side of subtropical gyres, where the depth-integrated flow is westward. These jets are associated with subsurface thermal fronts at thermocline depths by the thermal wind relation. However, the subsurface thermal front associated with the SICC has not been described to date. Other studies conjecture an important role for salinity in controlling the SICC. In the present work, we analyze three Argo-based atlases and data from six hydrographic cruises to investigate whether the SICC is accompanied by permanent thermal and density fronts including salinity effects. The seasonal cycle of these fronts in relation to the SICC strength is also investigated. We find that the SICC is better described as composed of three distinct jets, which we name the northern, central, and southern SICC. We find that the southern SICC around 26 S has an associated thermal front at subsurface depths around 100-200 m with salinity being of secondary importance. The southern branch strength is related to mode waters poleward of the front, similar to a STCC-like current. However, the SICC multiple jet structure seems to be better described as resulting from PV staircases.

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“…Finally, it is argued that anisotropic transport and mixing associated with the oceanic jets can be important for distributions of chemical tracers influencing the global climate, and therefore developing various diagnostics for this transport and mixing is an active research area (e.g. Hughes, Thompson & Wilson 2010;Beron-Vera et al 2010). Overall, the issue of the contrast between the partial barriers and mixing zones, as well as the corresponding distinctions between the oceanic and atmospheric jets, will be resolved only with progress toward more physically complete models and with more complete understanding of the various physical processes that affect the jets.…”

Section: On Latency Of Multiple Zonal Jets In the Oceansmentioning

confidence: 99%

On latency of multiple zonal jets in the oceans

et al. 2011

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Most of the nearly zonal, multiple, alternating jets observed in the oceans are latent, that is, their amplitudes are weak relative to the ambient mesoscale eddies. Yet, relatively strong jets are often observed in dynamical simulations. To explore mechanisms controlling the degree of latency, we analyse solutions of an idealized, eddy-resolving and flat-bottom quasigeostrophic model, in which dynamically generated mesoscale eddies maintain and interact with a set of multiple zonal jets. We find that the degree of the latency is controlled primarily by the bottom friction: the larger the friction parameter, the more latent are the jets; and the degree of the latency is substantial for a realistic range of the oceanic bottom friction coefficient. This result not only provides a plausible explanation for the latency of the oceanic jets, but it may also be relevant to the prominent atmospheric multiple jets observed on giant gas planets, such as Jupiter. We hypothesize that these jets can be so strong because of the relative absence of the bottom friction. The mechanism controlling the latency in our solutions is understood in terms of the changes induced in the linear eigenmodes of the time-mean flow by varying the bottom friction coefficient; these changes, in turn, affect and modify the jets. Effects of large Reynolds numbers on the eddies, jets, and the latency are also discussed.

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Identification of jets and mixing barriers from sea level and vorticity measurements using simple statistics

Cited by 28 publications

References 14 publications

A Simple Kinematic Source of Skewness in Atmospheric Flow Fields

A Simple Kinematic Source of Skewness in Atmospheric Flow Fields

South Indian Countercurrent and associated fronts

On latency of multiple zonal jets in the oceans

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