The Role of Deformation and Potential Vorticity in Southern Hemisphere Blocking Onsets

2005 ◽  
Vol 62 (11) ◽  
pp. 4043-4056 ◽  
Author(s):  
Li Dong ◽  
Stephen J. Colucci
Keyword(s):  
Southern Hemisphere ◽  
Potential Vorticity ◽  
Geostrophic Wind ◽  
Positive Contribution ◽  
Synoptic Scale ◽  
Planetary Scale ◽  
Sheared Flow ◽  
Westerly Flow ◽  
Quasigeostrophic Model

Abstract The relative importance of interactions between deformation and potential vorticity (PV) as a block-onset mechanism is examined in 30 cases of atmospheric blocking over the Southern Hemisphere (SH). The blocking cases are diagnosed with a quasigeostrophic model for the u component of the geostrophic wind tendency. In this model, two mechanisms, the advection of the meridional gradient of PV and interactions between deformation and PV, can force the weakening of westerly flow or increasing easterly flow associated with blocking. The first forcing mechanism, which does not directly include deformation, indicates that the advection of equatorward increasing cyclonic PV (or equatorward decreasing anticyclonic PV) could force a local weakening of geostrophic westerlies or increasing easterlies. The second forcing mechanism, which represents the net effect of interactions between deformation and PV, indicates that eastward increasing PV embedded in a cyclonically sheared flow or equatorward increasing PV coincident with a stretching (diffluent) flow could each force a weakening in the westerlies. While deformation is a distinct signature of blocking, it may not always actively participate in the formation of blocking. Advection and interaction contributions generally opposed each other in both the diagnosed blocking and nonblocking cases. Weakening westerlies associated with block onset would occur when one effect (usually the advection effect) contributes more negatively to the wind tendency than the opposing, positive contribution from the other effect. When deformation is actively involved in the formation of blocking, self-interactions between synoptic-scale PV and deformation and self-interactions between planetary-scale PV and deformation contribute more importantly than synoptic-to-planetary-scale interactions between PV and deformation fields to the weakening of westerlies associated with block onsets.

scholarly journals The Role of Nonquasigeostrophic Forcing in Southern Hemisphere Blocking Onsets

2015 ◽  
Vol 143 (4) ◽  
pp. 1455-1471 ◽  
Author(s):  
Li Dong ◽  
Stephen J. Colucci
Keyword(s):  
Southern Hemisphere ◽  
Zonal Wind ◽  
Geostrophic Wind ◽  
Relative Vorticity ◽  
Geostrophic Flow ◽  
Quasigeostrophic Model ◽  
Geostrophic Advection ◽  
Blocking Event

Abstract A generalized frictionless, adiabatic geostrophic zonal wind tendency equation is derived to diagnose the nonquasigeostrophic forcings to blocking onset in the Southern Hemisphere through case study and composite analysis. In general, the quasigeostrophic model is capable of representing the key physical processes associated with blocking onset in the troposphere reasonably well in most blocking cases. The consideration of nonquasigeostrophic forcings moderately improves the quasigeostrophic representation in a majority of the blocking events selected for this study, but not all events. This suggests that the nonquasigeostrophic terms could be important in a specific blocking event but not in a composite meaning. Furthermore, the nonquasigeostrophic forcing of geostrophic advection of ageostrophic relative vorticity term, , is extensively examined in this study. This forcing is found to be the leading nonquasigeostrophic forcing term among all nonquasigeostrophic forcings. In a composite sense, the forcing appears to have an alternative contribution that is dependent upon the curvature of the geostrophic flow within the blocking structure. In general, the southwesterly flow is likely associated with the -favoring effect to blocking onset whereas northwesterly flow is associated with the -opposing effect. Therefore, it is important to use the geostrophic flow pattern prior to blocking onset to foresee this ageostrophic-related nonquasigeostrophic forcing to blocking onset. Finally, a pronounced overestimation of geostrophic zonal wind tendency by the quasigeostrophic model is commonly found for selected blocking events within the stratosphere, in comparison to the nonquasigeostrophic model. This overestimation is essentially caused by geostrophic wind approximation.

scholarly journals Role of Surface-Layer Coherent Eddies in Potential Vorticity Transport in Quasigeostrophic Turbulence Driven by Eastward Shear

Fluids ◽  
2019 ◽  
Vol 5 (1) ◽  
pp. 2
Author(s):  
Wenda Zhang ◽  
Christopher L. P. Wolfe ◽  
Ryan Abernathey
Keyword(s):  
Surface Layer ◽  
Potential Vorticity ◽  
Model Driven ◽  
Wide Range ◽  
Stirring Effect ◽  
Geophysical Turbulence ◽  
Quasigeostrophic Model ◽  
Vorticity Transport ◽  
Pv Gradient

The transport by materially coherent surface-layer eddies was studied in a two-layer quasigeostrophic model driven by eastward mean shear. The coherent eddies were identified by closed contours of the Lagrangian-averaged vorticity deviation obtained from Lagrangian particles advected by the flow. Attention was restricted to eastward mean flows, but a wide range of flow regimes with different bottom friction strengths, layer thickness ratios, and background potential vorticity (PV) gradients were otherwise considered. It was found that coherent eddies become more prevalent and longer-lasting as the strength of bottom drag increases and the stratification becomes more surface-intensified. The number of coherent eddies is minimal when the shear-induced PV gradient is 10–20 times the planetary PV gradient and increases for both larger and smaller values of the planetary PV gradient. These coherent eddies, with an average core radius close to the deformation radius, propagate meridionally with a preference for cyclones to propagate poleward and anticyclones to propagate equatorward. The meridional propagation preference of the coherent eddies gives rise to a systematic upgradient PV transport, which is in the opposite direction as the background PV transport and not captured by standard Lagrangian diffusivity estimates. The upgradient PV transport by coherent eddy cores is less than 15% of the total PV transport, but the PV transport by the periphery flow induced by the PV inside coherent eddies is significant and downgradient. These results clarify the distinct roles of the trapping and stirring effect of coherent eddies in PV transport in geophysical turbulence.

scholarly journals On the Poleward Motion of Midlatitude Cyclones in a Baroclinic Meandering Jet

2013 ◽  
Vol 70 (8) ◽  
pp. 2629-2649 ◽  
Author(s):  
Ludivine Oruba ◽  
Guillaume Lapeyre ◽  
Gwendal Rivière
Keyword(s):  
Potential Vorticity ◽  
Statistical Study ◽  
Rossby Waves ◽  
Lower Layer ◽  
Finite Amplitude ◽  
Synoptic Scale ◽  
Beta Plane ◽  
The Cross ◽  
Quasigeostrophic Model ◽  
Pv Gradient

Abstract The motion of surface depressions evolving in a background meandering baroclinic jet is investigated using a two-layer quasigeostrophic model on a beta plane. Synoptic-scale finite-amplitude cyclones are initialized in the lower and upper layer to the south of the jet in a configuration favorable to their baroclinic interaction. The lower-layer cyclone is shown to move across the jet axis from its warm-air to cold-air side. It is the presence of a poleward-oriented barotropic potential vorticity (PV) gradient that makes possible the cross-jet motion through the beta-drift mechanism generalized to a baroclinic atmospheric context. The potential vorticity gradient associated with the jet is responsible for the dispersion of Rossby waves by the cyclones and the development of an anticyclonic anomaly in the upper layer. This anticyclone forms a PV dipole with the upper-layer cyclone that nonlinearly advects the lower-layer cyclone across the jet. In addition, the background deformation is shown to modulate the cross-jet advection. Cyclones evolving in a deformation-dominated environment (south of troughs) are strongly stretched while those evolving in a rotation-dominated environment (south of ridges) remain quasi isotropic. It is shown that the more stretched cyclones trigger a more efficient dispersion of energy, create a stronger upper-layer anticyclone, and move perpendicularly to the jet faster than the less stretched ones. Both the intensity and location of the upper-layer anticyclone explain the distinct cross-jet speeds. A statistical study consisting in initializing cyclones at different locations south of the jet core confirms that the cross-jet motion is faster for the more meridionally elongated cyclones evolving in areas of strongest barotropic PV gradient.

scholarly journals The Planetary- and Synoptic-Scale Interactions in a Southeast Pacific Blocking Episode Using PV Diagnostics

2005 ◽  
Vol 62 (6) ◽  
pp. 1901-1916 ◽  
Author(s):  
John P. Burkhardt ◽  
Anthony R. Lupo
Keyword(s):  
Potential Vorticity ◽  
Synoptic Scale ◽  
Atlantic Region ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Scale Interactions ◽  
Planetary Scale ◽  
Southeast Pacific ◽  
Forcing Mechanisms ◽  
Environmental Prediction

Abstract The synoptic- and planetary-scale forcing in two blocking anticyclones occurring over the southeast Pacific Ocean was examined using potential vorticity diagnostics. While many studies have examined the dynamic and thermodynamic forcing associated with blocking events in the Northern Hemisphere (NH), very few studies have examined blocking in the Southern Hemisphere (SH). Climatological analysis suggests SH blocking events in the Pacific region have similar characteristics to their NH counterparts. However, the occurrence of blocking is rare elsewhere in the SH, and these events are relatively short-lived. Some studies of NH blocking dynamics have also shown that the extent to which the planetary- and synoptic-scale and planetary–synoptic-scale interaction forcing that contribute to the genesis and maintenance of Pacific and Atlantic region events can be different. Thus, a study of the relevant atmospheric dynamics associated with blocking events in the SH was carried out in order to determine whether or not these events are associated with similar dynamic mechanisms to those in the NH. Using the National Center for Atmospheric Research and National Centers for Environmental Prediction (NCAR–NCEP) reanalyses dataset and applying a low-pass filter to the relevant variables, the authors examined the scale interactions associated with two blocking events that occurred during July and August 1986 and applied potential vorticity diagnostics. Results demonstrate that blocking in the southeast Pacific was associated with similar synoptic features, and the forcing mechanisms on the planetary, synoptic scales, and interactions were more similar to North Pacific blocking events rather than those occurring over the NH Atlantic region. However, these results also demonstrated that blocking events in the NH were associated with synergistically interacting synoptic- and planetary-scale waves, while in the SH, blocking events resulted from the superposition of synoptic and planetary waves. This result may explain the paucity of blocking occurrences and their tendency to be weaker and less persistent over much of the SH.

scholarly journals Interpreting the Opposition between Two Block-Onset Forcing Mechanisms

2007 ◽  
Vol 64 (6) ◽  
pp. 2091-2104 ◽  
Author(s):  
Li Dong ◽  
Stephen J. Colucci
Keyword(s):  
Southern Hemisphere ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Long Waves ◽  
Synoptic Scale ◽  
Short Waves ◽  
Idealized Model ◽  
Dominant Wave ◽  
Critical Wavelength ◽  
Forcing Mechanisms

The opposition between two block-onset forcing mechanisms, previously identified in midtropospheric analyses over the Southern Hemisphere midlatitudes, is analytically interpreted with an idealized model. These mechanisms are the interaction (Finter) between deformation and potential vorticity and the advection (Fadv) of meridionally varying potential vorticity. Weather systems of concern, primarily consisting of planetary- and synoptic-scale waves, mostly fall into two regimes of zonal and meridional wavenumber space in which the opposition between the two block-onset forcing mechanisms is analytically derived. A synoptic interpretation of this opposition is schematically presented within the framework of barotropic dynamics. It is found that whether blocking occurs in diffluent or confluent flow depends upon the critical wavelength associated with the geostrophic flow. Blocking tends to take place in the diffluent flow of long waves in which Finter dominates over Fadv. In addition, blocking also tends to occur in the confluent flow of relative short waves in which Fadv prevails over Finter. An investigation of Rossby wave phase speeds in one diagnosed case reveals a lengthening with time of the dominant wave until it reaches the stationary wavelength on the block-onset day. In this context blocking may be understood as a stationarity and thus persistence of one of the two block-onset forcing mechanisms.

scholarly journals Tropical Upper-Tropospheric Potential Vorticity Intrusions during Sudden Stratospheric Warmings

2016 ◽  
Vol 73 (6) ◽  
pp. 2361-2384 ◽  
Author(s):  
John R. Albers ◽  
George N. Kiladis ◽  
Thomas Birner ◽  
Juliana Dias
Keyword(s):  
Potential Vorticity ◽  
Wave Breaking ◽  
Polar Vortex ◽  
Synoptic Scale ◽  
Mean Flow ◽  
Rossby Wave Breaking ◽  
Planetary Scale ◽  
The Pacific ◽  
Geographic Distributions ◽  
The Tropics

Abstract The intrusion of lower-stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings (SSWs) is examined. The analysis reveals that SSW-related PV intrusions are significantly stronger, penetrate more deeply into the tropics, and exhibit distinct geographic distributions compared to their climatological counterparts. While climatological upper-tropospheric and lower-stratospheric (UTLS) PV intrusions are generally attributed to synoptic-scale Rossby wave breaking, it is found that SSW-related PV intrusions are governed by planetary-scale wave disturbances that deform the extratropical meridional PV gradient maximum equatorward. As these deformations unfold, planetary-scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical UTLS. In addition, the material PV deformations also reorganize the geographic structure of the UTLS waveguide, which alters where synoptic-scale waves break. In combination, these two intrusion mechanisms provide a robust explanation describing why displacement and split SSWs—or, more generally, anomalous stratospheric planetary wave events—produce intrusions with unique geographic distributions: displacement SSWs have a single PV intrusion maximum over the Pacific Ocean, while split SSWs have intrusion maxima over the Pacific and Indian Oceans. It is also shown that the two intrusion mechanisms involve distinct time scales of variability, and it is highlighted that they represent an instantaneous and direct link between the stratosphere and troposphere. This is in contrast to higher-latitude stratosphere–troposphere coupling that occurs indirectly via wave–mean flow feedbacks.

scholarly journals A Barotropic Envelope Rossby Soliton Model for Block–Eddy Interaction. Part II: Role of Westward-Traveling Planetary Waves

2005 ◽  
Vol 62 (1) ◽  
pp. 22-40 ◽  
Author(s):  
Dehai Luo
Keyword(s):  
Surf Zone ◽  
Planetary Waves ◽  
Storm Tracks ◽  
Synoptic Scale ◽  
Zone Structure ◽  
Planetary Scale ◽  
Blocking Anticyclone ◽  
Zonal Wavenumber ◽  
Dipole Soliton

Abstract The role of westward-traveling planetary waves in the block onset and the deformation of eddies during the interaction between synoptic-scale eddies and an incipient block is first examined by constructing an incipient block that consists of a stationary dipole wave for zonal wavenumber 2 and a westward-traveling monopole wave with constant amplitude (C wave) for zonal wavenumber 1 or 2. It is shown that the C-wave can affect the onset and strength of blocking through influencing the preblock (diffluent) flow even though it does not affect the amplification of the dipole wave associated with the synoptic-scale eddies. Whether the storm tracks organized by the deformed eddies deflect northward depends upon the zonal wavenumber, amplitude, and phase of the C wave relative to the stationary dipole wave. A typical retrograde blocking anticyclone can arise through the interaction of an incipient block with synoptic-scale perturbations when the C-wave ridge with zonal wavenumber 1 shifts westward from the east of the dipole wave in an incipient block. In this process, a slight northward deflection of organized storm tracks is also observed, particularly under the condition of a large-amplitude C wave. In addition, the interaction between a diffluent flow, consisting of a coupled dipole and monopole waves, and upstream synoptic-scale eddies is investigated. It is found that the eddy forcing tends to not only periodically amplify the dipole soliton and to retard its eastward movement, but to make the monopole wave break up. The breaking of the traveling monopole wave will suppress the eddy-induced blocking ridge that exhibits a surf zone structure where the negative meridional gradient of planetary-scale potential vorticity exists and cause the planetary-scale blocking field to lose its closed circulation compared to that without coupling.

Alpha-Effect, Current and Kinetic Helicities for Magnetically Driven Turbulence, and Solar Dynamo

2000 ◽  
Vol 179 ◽  
pp. 387-388
Author(s):  
Gaetano Belvedere ◽  
V. V. Pipin ◽  
G. Rüdiger
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Convection Zone ◽  
Solar Surface ◽  
Momentum Transport ◽  
Angular Momentum Transport ◽  
Magnetic Buoyancy ◽  
Alpha Effect ◽  
Current Helicity

Extended AbstractRecent numerical simulations lead to the result that turbulence is much more magnetically driven than believed. In particular the role ofmagnetic buoyancyappears quite important for the generation ofα-effect and angular momentum transport (Brandenburg & Schmitt 1998). We present results obtained for a turbulence field driven by a (given) Lorentz force in a non-stratified but rotating convection zone. The main result confirms the numerical findings of Brandenburg & Schmitt that in the northern hemisphere theα-effect and the kinetic helicityℋkin= 〈u′ · rotu′〉 are positive (and negative in the northern hemisphere), this being just opposite to what occurs for the current helicityℋcurr= 〈j′ ·B′〉, which is negative in the northern hemisphere (and positive in the southern hemisphere). There has been an increasing number of papers presenting observations of current helicity at the solar surface, all showing that it isnegativein the northern hemisphere and positive in the southern hemisphere (see Rüdigeret al. 2000, also for a review).

scholarly journals The Lockean Influence on Newman’s Epistemology: An Historical Analysis Describing Newman’s Engagement with Locke’s Ideas

2019 ◽  
Vol 84 (1) ◽  
pp. 77-91
Author(s):  
Becky Walker
Keyword(s):  
Historical Analysis ◽  
Positive Contribution ◽  
Deductive Logic ◽  
Personal Nature ◽  
Christian Message

This article discusses John Locke’s positive contribution to Newman’s epistemology throughout the latter’s career. Beginning with one of Newman’s earliest published works, his Essay on Miracles, he borrowed and further developed ideas from Locke’s A Discourse on Miracles regarding the necessity of miracles to validate the Christian message and the personal nature and cumulative method of weighing evidence. Later, in Newman’s most mature epistemological work, An Essay in Aid of a Grammar of Assent, one can discern Locke’s influence on Newman’s views on the weaknesses of deductive logic, the personal nature of knowledge, and the role of connecting ideas to arrive at knowledge.

Secondary Traumatization Among Social Work Students—The Contribution of Personal, Professional, and Environmental Factors

2020 ◽  
Author(s):  
Anat Ben-Porat ◽  
Shahar Shemesh ◽  
Ronit Reuven Even Zahav ◽  
Shelly Gottlieb ◽  
Tehila Refaeli
Keyword(s):  
Social Work ◽  
Social Work Students ◽  
Positive Contribution ◽  
Unique Contribution ◽  
Raising Awareness ◽  
The Mean ◽  
Explained Variance ◽  
Second Year ◽  
Self Differentiation

Abstract This study examined the rate of secondary traumatic stress (STS) among social work students and the contribution of background variables, personal resources (mastery and self-differentiation) and environmental resources (supervision satisfaction and peer support) to STS. The sample consisted of 259 social work students at three social work schools in Israel. The findings indicated that the mean level of STS was mild. Of the students, 36 per cent suffered STS to a mild extent, 19 per cent to a moderate extent and 18 per cent reported a ‘high to extreme extent’. A significant contribution was made by the student’s year of study, students in their second year of social work school suffered more severely from STS than did students in their first or third years. A positive contribution was made by the student’s level of exposure and a unique contribution was made by mastery and supervision satisfaction to the explained variance of STS. The findings highlight the importance of raising awareness of STS and its implications for social work students, as well as the necessity of helping students cope with this phenomenon. In addition, the study emphasises the significant role of supervisors in the training agencies and the importance of increasing students’ sense of mastery.

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