The onset of the barotropic sudden warming in a global model

Liu, Y. S.; Scott, R. K.

doi:10.1002/qj.2580

Cited by 17 publications

(37 citation statements)

References 19 publications

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“…They concluded that no persistent vacillations exist in shallow water, again due in part to the build‐up of tropical easterlies, and that the vacillations obtained by Rong and Waugh were essentially a remnant of initial transience of the integrations resulting from the non‐zero initial conditions and relatively rapid initial growth of the topographic forcing. More recently, analysis of the barotropic sudden warming in a global shallow‐water model (Liu and Scott, ) hinted at the existence of vacillation regimes in a quasi‐stationary context, although integrations of that model over longer times again suffered the effects of unconstrained growth of equatorial easterlies present in Rong and Waugh.…”

Section: Introductionsupporting

confidence: 58%

A new class of vacillations of the stratospheric polar vortex

Scott

2016

Quart J Royal Meteoro Soc

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A new class of persistent vacillations of the winter polar vortex, under the action of topographic wave forcing and radiative cooling, is identified in numerical integrations of the rotating shallow-water equations. The vacillations are obtained provided only that care is taken to prevent the unconstrained growth of tropical easterlies that otherwise develop as the result of persistent angular momentum deposition at low latitudes. The vacillation cycle involves purely barotropic dynamics and is characterized by a dynamically controlled rapid splitting and rapid reformation of the vortex, followed by a more gradual period of vortex intensification under the influence of radiative relaxation. The onset of the splitting occurs when the frequency of the free mode of the vortex approaches that of the forcing and resembles a resonant excitation. Experiments with an alternative basic state suggest that the vacillations are a robust feature of the topographically forced and radiatively relaxed vortex. In contrast to the behaviour found in models with vertical structure, the period of the vacillation cycles here increases with increasing forcing amplitude. A wide range of forcing amplitudes exists over which the vortex exhibits distinct regime transitions between a strong, vacillating state and a state in which the vortex is weak and the zonal mean polar flow nearly zero. Comparison with observational reanalysis suggests that the vacillation cycles obtained here may be relevant to the dynamics of some sudden warming events and that the onset of a radiatively dominated regime may usefully be linked to the loss of vortex area following such an event.

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Section: Introductionsupporting

confidence: 58%

A new class of vacillations of the stratospheric polar vortex

Scott

2016

Quart J Royal Meteoro Soc

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“…This system, which has been widely used in studies of Earth's stratospheric polar vortex (e.g., Juckes 1989;Norton 1994;Rong and Waugh 2004;Liu and Scott 2015;Scott 2016), allows us to isolate the dynamics associated with barotropic instability from those due to vertically propagating waves. In vorticity-divergence form, these equations are…”

Section: Model and Experimental Design A Shallow-water Modelmentioning

confidence: 99%

“…, which is the relevant vertical structure of the barotropic mode in a compressible atmosphere (Liu and Scott 2015). Here k 5 1 /4 (the appropriate value for a triatomic gas such as CO 2 , which is the major constituent of the Martian atmosphere), f 5 2V sinf, N 5 0.01 s 21 is the Brunt-Väisälä frequency, and D 5 11 km is the density scale height (approximate values taken from http://nssdc.gsfc.nasa.gov/planetary/ factsheet/marsfact.html).…”

Section: Model and Experimental Design A Shallow-water Modelmentioning

confidence: 99%

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The Stability of Mars’s Annular Polar Vortex

Seviour

Waugh

Scott

2017

Journal of the Atmospheric Sciences

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The Martian polar atmosphere is known to have a persistent local minimum in potential vorticity (PV) near the winter pole, with a region of high PV encircling it. This finding is surprising, since an isolated band of PV is barotropically unstable, a result going back to Rayleigh. Here the stability of a Mars-like annular vortex is investigated using numerical integrations of the rotating shallow-water equations. The mode of instability and its growth rate is shown to depend upon the latitude and width of the annulus. By introducing thermal relaxation toward an annular equilibrium profile with a time scale similar to that of the instability, a persistent annular vortex with similar characteristics as that observed in the Martian atmosphere can be simulated. This time scale, typically 0.5-2 sols, is similar to radiative relaxation time scales for Mars's polar atmosphere. The persistence of an annular vortex is also shown to be robust to topographic forcing, as long as it is below a certain amplitude. It is therefore proposed that the persistence of this barotropically unstable annular vortex is permitted owing to the combination of short radiative relaxation time scales and relatively weak topographic forcing in the Martian polar atmosphere.

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“…Mitchell et al () used extreme value theory and 2‐D moment diagnostics to characterize Arctic and Antarctic polar vortices and showed that moment diagnostics were a useful measure of vortex variability and could be used to help distinguish vortex‐split/displacement SSWs. Many studies of the polar vortex, stratospheric variability, and their connections have since made extensive use of geometric and moment diagnostics for studies based on modeling (e.g., Liu and Scott, ; Matthewman & Esler, ), reanalyses (e.g., Hannachi et al, ; Mitchell et al, ; Seviour et al, ), and climate model data (e.g., Maycock & Hitchcock, ; Seviour et al, ; Zhang et al, )…”

Section: Introductionmentioning

confidence: 99%

Characterizing Stratospheric Polar Vortex Variability With Computer Vision Techniques

Lawrence

Manney

2018

JGR Atmospheres

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Computer vision techniques are used to characterize the Arctic stratospheric polar vortex in 38 years of reanalysis data. Such techniques are typically applied to analyses of digital images, but they represent powerful tools that are more widely applicable: basic techniques and considerations for geophysical applications are outlined herein. Segmentation, descriptive, and tracking algorithms are combined in the Characterization and Analysis of Vortex Evolution using Algorithms for Region Tracking (CAVE‐ART) package, which was developed to comprehensively describe dynamical and geometrical evolution of polar vortices. CAVE‐ART can characterize and track multiple vortex regions through time, providing an extensive suite of region, moments, and edge diagnostics for each. CAVE‐ART is valuable for identifying vortex‐splitting events including, but not limited to, previously cataloged vortex‐split sudden stratospheric warmings. An algorithm for identifying such events detects 52 potential events between 1980 and 2017; of these, 38 are subjectively classified as distinct “split‐like” events. The algorithm based on CAVE‐ART is also compared with moment‐based methods previously used to detect split events. Furthermore, vortex edge‐averaged wind speeds from CAVE‐ART are used to define extreme weak and strong polar vortex events over multiple vertical levels; this allows characterization of their occurrence frequencies and extents in time and altitude. Weak and strong events show distinct signatures in CAVE‐ART diagnostics: in contrast to weak events, strong vortices are more cylindrical and pole centered, and less filamented, than the climatological state. These results from CAVE‐ART exemplify the value of computer vision techniques for analysis of geophysical phenomena.

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The onset of the barotropic sudden warming in a global model

Cited by 17 publications

References 19 publications

A new class of vacillations of the stratospheric polar vortex

A new class of vacillations of the stratospheric polar vortex

The Stability of Mars’s Annular Polar Vortex

Characterizing Stratospheric Polar Vortex Variability With Computer Vision Techniques

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