A Climatology of Rossby Wave Breaking on the Southern Hemisphere Tropopause

Ndarana, Thando; Waugh, Darryn W.

doi:10.1175/2010jas3460.1

Cited by 46 publications

(54 citation statements)

References 45 publications

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“…The equatorward displacement of strong TT frequency at the eastern boundaries of the North Pacific and North Atlantic basins is consistent with enhanced RWB at the exits of the midlatitude 330-K waveguides as shown by Martius et al (2008). The strong TT frequency is more zonally uniform in the Southern Hemisphere although the presence of the polar front jet south of the South Atlantic basin and south Indian Basin reduces Rossby wave activity in the region, particularly in the early summer season (Ndarana and Waugh 2011). By the late summer, wave breaking on the 330-K isentropic surface occurs across most of the southern oceans, leading to a zonal expansion of the high-frequency (.75%) strong TT region as shown in Fig.…”

Section: Pathway Climatologysupporting

confidence: 71%

“…In the Southern Hemisphere, a single peak in troughinduced frequency is evident near the equator in the central South Pacific. These regions lie equatorward and westward of the primary subtropical RWB centers (Postel and Hitchman 1999;Ndarana and Waugh 2011), identifiable in Fig. 4 as areas in which the separation between the plotted isentropes increases.…”

Section: Pathway Climatologymentioning

confidence: 97%

“…The East Australian Current (Hamon 1965) transports warm water poleward along the east coast of the continent, beneath a region with a weak local maximum in wave activity on the subtropical jet (Postel and Hitchman 1999;Ndarana and Waugh 2011). This establishes a favorable configuration for the trough-induced, weak TT, and strong TT pathways that rely on jet-level perturbations (Figs.…”

Section: ) South Pacific Basinmentioning

confidence: 98%

“…From a thermodynamic perspective, the formation and maintenance of the TUTTs can be explained by radiatively induced subsidence driven by sensible and latent heating contrasts between the continents and adjacent oceans (Fitzpatrick et al 1995). Dynamically, the midocean regions are shown to be active areas of summer anticyclonic Rossby wave breaking (RWB) by Postel and Hitchman (1999) and Ndarana and Waugh (2011). These characterizations of the troughs are not contradictory, since the dominant anticyclonic PV anomaly displaced poleward during anticyclonic RWB is necessarily eroded by radiative processes, leading to net radiational cooling in the midocean regions.…”

Section: Terminologymentioning

confidence: 99%

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A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

McTaggart‐Cowan¹,

Galarneau²,

Bosart³

et al. 2013

Monthly Weather Review

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Tropical cyclogenesis is generally considered to occur in regions devoid of baroclinic structures; however, an appreciable number of tropical cyclones (TCs) form in baroclinic environments each year. A global climatology of these baroclinically influenced TC developments is presented in this study. An objective classification strategy is developed that focuses on the characteristics of the environmental state rather than on properties of the vortex, thus allowing for a pointwise ''development pathway'' classification of reanalysis data. The resulting climatology shows that variability within basins arises primarily as a result of local surface thermal contrasts and the positions of time-mean features on the subtropical tropopause. The pathway analyses are sampled to generate a global climatology of 1948-2010 TC developments classified by baroclinic influence: nonbaroclinic (70%), low-level baroclinic (9%), trough induced (5%), weak tropical transition (11%), and strong tropical transition (5%). All basins other than the North Atlantic are dominated by nonbaroclinic events; however, there is extensive interbasin variability in secondary development pathways. Within each basin, subregions and time periods are identified in which the relative importance of the development pathways also differs. The efficiency of tropical cyclogenesis is found to be highly dependent on development pathway. The peak efficiency defined in the classification subspace straddles the nonbaroclinic/ trough-induced boundary, suggesting that the optimal environment for TC development includes a baroclinic contribution from an upper-level disturbance. By assessing the global distribution of baroclinically influenced TC formations, this study identifies regions and pathways whose further study could yield improvements in our understanding of this important subset of TC developments.

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Section: Pathway Climatologysupporting

confidence: 71%

Section: Pathway Climatologymentioning

confidence: 97%

Section: ) South Pacific Basinmentioning

confidence: 98%

Section: Terminologymentioning

confidence: 99%

See 2 more Smart Citations

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

McTaggart‐Cowan¹,

Galarneau²,

Bosart³

et al. 2013

Monthly Weather Review

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show abstract

“…Previous studies have shown that wave breaking in the troposphere and in the tropopause regions depends on the wave number (Orlanski, 2003;Riviere and Orlanski, 2007), and on the zonal variation of the zonal flow along jets Waugh, 1996, 2003;Swanson et al, 1997;Swanson, 2000;Ndarana and Waugh, 2011;Esler and Haynes, 1999). It was suggested that wave breaking tends to occur in regions where the mean zonal wind is weak.…”

Section: Introductionmentioning

confidence: 99%

Observation and simulation of wave breaking in the southern hemispheric stratosphere during VORCORE

2013

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An interesting occurrence of a Rossby wave breaking event observed during the VORCORE experiment is presented and explained. Twenty-seven balloons were launched inside the Antarctic polar vortex. Almost all of these balloons evolved in the stratosphere around 500K within the vortex, except the one launched on 28 October 2005. In this case, the balloon was caught within a tongue of high potential vorticity (PV), and was ejected from the polar vortex. The evolution of this event is studied for the period between 19 and 25 November 2005. It is found that at the beginning of this period, the polar vortex experienced distortions due to the presence of Rossby waves. Then, these waves break and a tongue of high PV develops. On 25 November, the tongue became separated from the vortex and the balloon was ejected into the surf zone. Lagrangian simulations demonstrate that the air masses surrounding the balloon after its ejection were originating from the vortex edge. The wave breaking and the development of the tongue are confined within a region where a planetary Quasi-Stationary Wave 1 (QSW1) induces wind speeds with weaker values. The QSW1 causes asymmetry in the wind speed and the horizontal PV gradient along the edge of the polar vortex, resulting in a localized jet. Rossby waves with smaller scales propagating on top of this jet amplify as they enter the jet exit region and then break. The role of the QSW1 on the formation of the weak flow conditions that caused the non-linear wave breaking observed near the vortex edge is confirmed by three-dimensional numerical simulations using forcing with and without the contribution of the QSW1

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Extreme upper level cyclonic vorticity events in relation to the Southern Hemisphere jet stream

Harnik

2014

Geophysical Research Letters

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The mean seasonal variation in the frequency of occurrence of extreme upper level cyclonic vorticity events, and its relation to the jet stream, is examined in the Southern Hemisphere. During the austral summer to fall, extreme cyclonic vorticity occurs most frequently at the upper level jet stream core, while during the austral winter to spring, there is a main peak on the poleward flank of the subtropical jet and a secondary peak on the poleward flank of the eddy‐driven jet. Composite analysis shows that the extremes in both seasons are associated with wave breaking and the formation of elongated vorticity tongues. In summer, extreme events occur when waves propagating on the eddy‐driven jet break nonlinearly, while in winter, extreme events occur when waves on the eddy‐driven jet interact with waves on the subtropical jet. In both seasons, these extreme upper level vorticity events are associated with significant positive precipitation anomalies and a pattern of alternating positive and negative surface temperature anomalies.

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A Climatology of Rossby Wave Breaking on the Southern Hemisphere Tropopause

Cited by 46 publications

References 45 publications

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

A Global Climatology of Baroclinically Influenced Tropical Cyclogenesis

Observation and simulation of wave breaking in the southern hemispheric stratosphere during VORCORE

Extreme upper level cyclonic vorticity events in relation to the Southern Hemisphere jet stream

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