Climatology of Coherent Structures on the Extratropical Tropopause

Hakim, Gregory J.

doi:10.1175/1520-0493(2000)128<0385:cocsot>2.0.co;2

Cited by 56 publications

(60 citation statements)

References 71 publications

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“…McWilliams 1980; Butchart et al 1989), relatively little attention has been devoted to applying these solutions to mobile disturbances of synoptic scales and smaller. Hakim (2000a) suggests that relative-vorticity maxima at 500 hPa typically are associated with monopolar rather than dipolar vortices; however, examples of asymmetric dipolar vortices in the extratropical upper troposphere have been documented, an example of which is provided in section 2. Moreover, given the success of CK in describing the essential dynamics of jet streaks in terms of barotropic vortex dipoles, it is suggested that an investigation of dipolar vortices in the context of the stratified QG system may prove insightful from the perspective of a basic dynamical understanding of jet streaks.…”

Section: Jet Streaks In Terms Of Dipolar Vorticesmentioning

confidence: 99%

“…Lackmann et al 1997;Hakim 2000a;Meade 2001;Pyle et al 2004, sections 4(a) and (c)). The studies by Meade (2001) and Pyle et al (2004) in particular identify such localized disturbances accompanying the majority of jet streaks examined.…”

Section: Introductionmentioning

confidence: 99%

“…The studies by Meade (2001) and Pyle et al (2004) in particular identify such localized disturbances accompanying the majority of jet streaks examined. These disturbances have lengthscales of approximately 500 km (Hakim 2000a), and are seen as localized maxima of Ertel potential vorticity (EPV) on tropopause-intersecting isentropes, or as localized minima of potential temperature on surfaces of constant EPV defining the dynamic tropopause. The presence of localized extrema with closed contours of a materially conserved quantity such as EPV or potential temperature is indicative of significant nonlinearity and is a defining characteristic of coherent vortices.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, jet streaks are often associated with monopolar rather than dipolar vortices (e.g. Hakim 2000a;Meade 2001). Consequently, by considering both monopolar and dipolar vortices, and by incorporating vertical structure and divergent circulations, the present study serves to address some of the limitations of CK, and to provide the next level of complexity in a hierarchical dynamical explanation of jet streaks.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of jet streaks in a stratified quasi‐geostrophic atmosphere: Steady‐state representations

Cunningham

Keyser

2004

Quart J Royal Meteoro Soc

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SUMMARYThe structure and dynamics of jet streaks in the extratropical upper troposphere are examined in the context of a continuously stratified quasi-geostrophic (QG) framework. It is hypothesized that jet streaks may result from the superposition of monopolar or dipolar vortices of mesoscale dimensions with the enhanced potential-vorticity gradients constituting the tropopause. Based on this hypothesis, steady-state monopolar and dipolar vortices in a uniform zonal background flow on an f -plane are investigated for their applicability as idealized dynamical representations of jet streaks. The representations of jet streaks satisfy the nonlinear governing equations of the continuously stratified QG framework: the monopolar vortex is specified in terms of axisymmetric distributions of QG potential vorticity in the interior of the domain and perturbation potential temperature on upper (tropopause) and lower (surface) boundaries, whereas the dipolar vortex is adapted from a closed-form analytical solution for the geostrophic stream function. Through the incorporation of vertical structure and divergent circulations, these representations of jet streaks extend those presented previously by the authors using a non-divergent barotropic model.It is shown that these vortex representations display characteristic signatures similar to those observed in atmospheric jet streaks. In particular, both the monopole and the dipole exhibit an ageostrophic wind directed towards lower geopotential height in the entrance region of the streak and towards higher geopotential height in the exit region. For the monopole, this ageostrophic wind is entirely rotational and there is no vertical motion. For the dipole, the rotational part of the ageostrophic wind dominates the divergent part; the latter is associated with a four-cell pattern of vertical velocity similar to that described in conceptual models of straight jet streaks. For both the monopole and the dipole, the jet streak is induced by the vortex structure such that the wind speed maximum translates at the same speed as the individual vortices; this translation speed is slower than the maximum wind speed in the core of the speed maximum, consistent with observations of jet streaks.It is proposed that the above representations provide a formal theoretical foundation for the conceptual models of jet streaks prevalent in the literature; these conceptual models typically are based on heuristic kinematic or parcel arguments and not on consistent solutions to a physically plausible set of equations. The representations also provide a foundation upon which to explore the unsteady behaviour of jet streaks in terms of the superposition of monopolar and dipolar vortices with non-uniform zonal background flows.

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Section: Jet Streaks In Terms Of Dipolar Vorticesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Dynamics of jet streaks in a stratified quasi‐geostrophic atmosphere: Steady‐state representations

Cunningham

Keyser

2004

Quart J Royal Meteoro Soc

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“…It may be argued that values of Ro max in excess of unity are unrealistically large. However, Hakim (2000) and Hoskins & Hodges (2002) have shown this not to be the case. In fact, the former study shows relative vorticity values in excess of f in 40 % of the 500 hPa weather charts considered.…”

Section: Generation Of Geostrophic Datamentioning

confidence: 98%

Balance dynamics in rotating stratified turbulence

Kafiabad

Bartello

2016

J. Fluid Mech.

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If classical quasigeostrophic (QG) flow breaks down at smaller scales, it gives rise to questions of whether higher-order nonlinear balance can be maintained, to what scale and for how long. These are naturally followed by asking how this is affected by stratification and rotation. To address these questions, we perform non-hydrostatic Boussinesq simulations where the initial data is balanced using the Baer-Tribbia nonlinear normal mode initialization scheme (NNMI), which is accurate to second order in the Rossby number, as the next-order improvement to first-order QG theory. The NNMI procedure yields an ageostrophic contribution to the energy spectrum that has a very steep slope. However, as time passes, a shallow range emerges in the ageostrophic spectrum when the Rossby number is large enough for a given Reynolds number. It is argued that this shallow range is the unbalanced part of the motion that develops spontaneously in time and eventually dominates the energy at small scales. If the initial flow is not nonlinearly balanced, the shallow range emerges at even lower Rossby number and it appears at larger scales. Through numerous simulations at different rotation and stratification, this study gives a clear picture of how energy is cascaded in different initially balanced regimes of rotating stratified flow. We find that at low Rossby number the flow mainly consists of a geostrophic part and a balanced ageostrophic part with a steep spectrum. As the Rossby number increases, the unbalanced part of the ageostrophic energy increases at a rate faster than the balanced part. Hence, the total energy spectrum displays a shallow range above a transition wavenumber. This wavenumber evolves to smaller values as rotation weakens.

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Kinematic processes contributing to the intensification of anomalously strong North Atlantic jets

Winters

2021

Quart J Royal Meteoro Soc

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Anomalously strong North Atlantic jets, defined in this study as jets with wind speeds exceeding 100 m·s−1, are notable due to their potential to induce high‐impact weather. This study examines the kinematic processes that contribute to the intensification of anomalously strong North Atlantic jets, as well as the variability in those processes across a large number of events. Anomalously strong jets are objectively identified during September–May 1979–2018 within the Climate Forecast System Reanalysis and composited to reveal the synoptic‐scale flow evolution associated with jet intensification. The analysis demonstrates that anomalously strong North Atlantic jets are most frequent during the winter compared with the fall and spring, and that their development is preceded by low‐level warm‐air advection, poleward moisture advection, and moist ascent within the warm conveyor belt of a surface cyclone beneath the equatorward jet‐entrance region. A diagnosis of the irrotational and nondivergent components of the ageostrophic wind within the near‐jet environment reveals that both wind components facilitate jet intensification via their nonnegligible contributions to negative potential vorticity (PV) advection and PV frontogenesis in the vicinity of the dynamic tropopause. Weather Research and Forecasting (WRF) model simulations of a jet event from December 2013 with and without latent heating further suggest that the ageostrophic wind field within the near‐jet environment is substantially modulated by latent heating. The foregoing results indicate that a diagnosis of jet intensification during anomalously strong jet events is dependent on an accurate representation of the cumulative effects of latent heating within the near‐jet environment.

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Climatology of Coherent Structures on the Extratropical Tropopause

Cited by 56 publications

References 71 publications

Dynamics of jet streaks in a stratified quasi‐geostrophic atmosphere: Steady‐state representations

Dynamics of jet streaks in a stratified quasi‐geostrophic atmosphere: Steady‐state representations

Balance dynamics in rotating stratified turbulence

Kinematic processes contributing to the intensification of anomalously strong North Atlantic jets

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