scholarly journals The counter-propagating Rossby-wave perspective on baroclinic instability. Part IV: Nonlinear life cycles

2005 ◽  
Vol 131 (608) ◽  
pp. 1425-1440 ◽  
Author(s):  
J. Methven ◽  
B. J. Hoskins ◽  
E. Heifetz ◽  
C. H. Bishop
Keyword(s):  
Rossby Wave ◽  
Baroclinic Instability ◽  
Life Cycles

scholarly journals The counter-propagating Rossby-wave perspective on baroclinic instability. II: Application to the Charney model

2004 ◽  
Vol 130 (596) ◽  
pp. 233-258 ◽  
Author(s):  
E. Heifetz ◽  
J. Methven ◽  
B. J. Hoskins ◽  
C. H. Bishop
Keyword(s):  
Rossby Wave ◽  
Baroclinic Instability

scholarly journals The Effect of Lower Stratospheric Shear on Baroclinic Instability

2007 ◽  
Vol 64 (2) ◽  
pp. 479-496 ◽  
Author(s):  
Matthew A. H. Wittman ◽  
Andrew J. Charlton ◽  
Lorenzo M. Polvani
Keyword(s):  
Growth Rate ◽  
Lower Stratosphere ◽  
Baroclinic Instability ◽  
Phase Speed ◽  
Finite Amplitude ◽  
Reanalysis Data ◽  
Life Cycles ◽  
Vertical Shear ◽  
Northern Annular Mode ◽  
Jet Structure

Abstract Using a hierarchy of models, and observations, the effect of vertical shear in the lower stratosphere on baroclinic instability in the tropospheric midlatitude jet is examined. It is found that increasing stratospheric shear increases the phase speed of growing baroclinic waves, increases the growth rate of modes with low synoptic wavenumbers, and decreases the growth rate of modes with higher wavenumbers. The meridional structure of the linear modes, and their acceleration of the zonal mean jet, changes with increasing stratospheric shear, but in a way that apparently contradicts the observed stratosphere–troposphere northern annular mode (NAM) connection. This contradiction is resolved at finite amplitude. In nonlinear life cycle experiments it is found that increasing stratospheric shear, without changing the jet structure in the troposphere, produces a transition from anticyclonic (LC1) to cyclonic (LC2) behavior at wavenumber 7. All life cycles with wavenumbers lower than 7 are LC1, and all with wavenumber greater than 7 are LC2. For the LC1 life cycles, the effect of increasing stratospheric shear is to increase the poleward displacement of the zonal mean jet by the eddies, which is consistent with the observed stratosphere–troposphere NAM connection. Finally, it is found that the connection between high stratospheric shear and high-tropospheric NAM is present by NCEP–NCAR reanalysis data.

Multiple Jets as PV Staircases: The Phillips Effect and the Resilience of Eddy-Transport Barriers

2008 ◽  
Vol 65 (3) ◽  
pp. 855-874 ◽  
Author(s):  
D. G. Dritschel ◽  
M. E. McIntyre
Keyword(s):  
Rossby Wave ◽  
Positive Feedback ◽  
Baroclinic Instability ◽  
Turbulence Theory ◽  
Core Size ◽  
Radiation Stress ◽  
New Paradigm ◽  
Nonlinear Disturbances ◽  
Transport Barriers ◽  
Eddy Transport

Abstract A review is given that focuses on why the sideways mixing of potential vorticity (PV) across its background gradient tends to be inhomogeneous, arguably a reason why persistent jets are commonplace in planetary atmospheres and oceans, and why such jets tend to sharpen themselves when disturbed. PV mixing often produces a sideways layering or banding of the PV distribution and therefore a corresponding number of jets, as dictated by PV inversion. There is a positive feedback in which mixing weakens the “Rossby wave elasticity” associated with the sideways PV gradients, facilitating further mixing. A partial analogy is drawn with the Phillips effect, the spontaneous layering of a stably stratified fluid, in which vertically homogeneous stirring produces vertically inhomogeneous mixing of the background buoyancy gradient. The Phillips effect has been extensively studied and has been clearly demonstrated in laboratory experiments. However, the “eddy-transport barriers” and sharp jets characteristic of extreme PV inhomogeneity, associated with strong PV mixing and strong sideways layering into Jupiter-like “PV staircases,” with sharp PV contrasts Δqbarrier, say, involve two additional factors besides the Rossby wave elasticity concentrated at the barriers. The first is shear straining by the colocated eastward jets. PV inversion implies that the jets are an essential, not an incidental, part of the barrier structure. The shear straining increases the barriers’ resilience and amplifies the positive feedback. The second is the role of the accompanying radiation-stress field, which mediates the angular-momentum changes associated with PV mixing and points to a new paradigm for Jupiter, in which the radiation stress is excited not by baroclinic instability but by internal convective eddies nudging the Taylor–Proudman roots of the jets. Some examples of the shear-straining effects for strongly nonlinear disturbances are presented, helping to explain the observed resilience of eddy-transport barriers in the Jovian and terrestrial atmospheres. The main focus is on the important case where the nonlinear disturbances are vortices with core sizes ∼LD, the Rossby (deformation) length. Then a nonlinear shear-straining mechanism that seems significant for barrier resilience is the shear-induced disruption of vortex pairs. A sufficiently strong vortex pair, with PV anomalies ±Δqvortex, such that Δqvortex ≫ Δqbarrier, can of course punch through the barrier. There is a threshold for substantial penetration through the barrier, related to thresholds for vortex merging. Substantial penetration requires Δqvortex ≳ Δqbarrier, with an accuracy or fuzziness of order 10% when core size ∼LD, in a shallow-water quasigeostrophic model. It is speculated that, radiation stress permitting, the barrier-penetration threshold regulates jet spacing in a staircase situation. For instance, if a staircase is already established by stirring and if the stirring is increased to produce Δqvortex values well above threshold, then the staircase steps will be widened (for given background PV gradient β) until the barriers hold firm again, with Δqbarrier increased to match the new threshold. With the strongest-vortex core size ∼LD this argument predicts a jet spacing 2b = Δqbarrier/β ∼ L2Rh (Uvortex)/LD in order of magnitude, where LRh(Uvortex) = (Uvortex/β)1/2, the Rhines scale based on the peak vortex velocity Uvortex, when 2b ≳ LD. The resulting jet speeds Ujet are of the same order as Uvortex; thus also 2b ∼ L2Rh(Ujet)/LD. Weakly inhomogeneous turbulence theory is inapplicable here because there is no scale separation between jets and vortices, both having scales ∼LD in this situation.

scholarly journals Supplementary material to "Synoptic-scale drivers of the Mistral wind: link to Rossby wave life cycles and seasonal variability"

2021 ◽  
Author(s):  
Yonatan Givon ◽  
Douglas Keller Jr. ◽  
Romain Pennel ◽  
Philippe Drobinski ◽  
Shira Raveh-Rubin
Keyword(s):  
Rossby Wave ◽  
Seasonal Variability ◽  
Life Cycles ◽  
Synoptic Scale ◽  
Supplementary Material

scholarly journals Large-scale drivers of the mistral wind: link to Rossby wave life cycles and seasonal variability

2021 ◽  
Vol 2 (3) ◽  
pp. 609-630
Author(s):  
Yonatan Givon ◽  
Douglas Keller Jr. ◽  
Vered Silverman ◽  
Romain Pennel ◽  
Philippe Drobinski ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Clustering Algorithm ◽  
Life Cycles ◽  
Heat Fluxes ◽  
Extreme Weather Events ◽  
Turbulent Heat ◽  
Low Level ◽  
Lee Cyclogenesis ◽  
The Mediterranean ◽  
Upper Level

Abstract. The mistral is a northerly low-level jet blowing through the Rhône valley in southern France and down to the Gulf of Lion. It is co-located with the cold sector of a low-level lee cyclone in the Gulf of Genoa, behind an upper-level trough north of the Alps. The mistral wind has long been associated with extreme weather events in the Mediterranean, and while extensive research focused on the lower-tropospheric mistral and lee cyclogenesis, the different upper-tropospheric large- and synoptic-scale settings involved in producing the mistral wind are not generally known. Here, the isentropic potential vorticity (PV) structures governing the occurrence of the mistral wind are classified using a self-organizing map (SOM) clustering algorithm. Based upon a 36-year (1981–2016) mistral database and daily ERA-Interim isentropic PV data, 16 distinct mistral-associated PV structures emerge. Each classified flow pattern corresponds to a different type or stage of the Rossby wave life cycle, from broad troughs to thin PV streamers to distinguished cutoffs. Each of these PV patterns exhibits a distinct surface impact in terms of the surface cyclone, surface turbulent heat fluxes, wind, temperature and precipitation. A clear seasonal separation between the clusters is evident, and transitions between the clusters correspond to different Rossby-wave-breaking processes. This analysis provides a new perspective on the variability of the mistral and of the Genoa lee cyclogenesis in general, linking the upper-level PV structures to their surface impact over Europe, the Mediterranean and north Africa.

scholarly journals Experimental Investigation of the Flow Field of Deep Rotating Stall in a Centrifugal Compressor

1994 ◽  
Author(s):  
Y. N. Chen ◽  
U. Seidel ◽  
J. Chen ◽  
U. Haupt ◽  
M. Rautenberg
Keyword(s):  
Rossby Wave ◽  
Centrifugal Compressor ◽  
Reverse Flow ◽  
Baroclinic Instability ◽  
Wave Theory ◽  
Polar Front ◽  
Rotating Stall ◽  
Squall Line ◽  
Two Dimensional ◽  
Pressure Pattern

The pressure field of deep rotating stall of a centrifugal compressor with two stall cells is analysed by means of the two-dimensional pressure pattern in the impeller determined by Chen et al. (1993). These authors transferred the pressure pattern measured on the shroud surface (i.e. in the absolute frame) to that related to the rotating blade channels. The transferred pressure pattern is thus a two-dimensional one. The existence of the low and high pressure vortices according to the Rossby wave theory is confirmed by this experiment. The development stages of the two vortices, in combination with the Rossby wave that steers the rotating stall, can be evaluated very well. The vortex low is developed from the front between the reverse flow (with high temperature and entropy) and the forward flow (with low temperature and entropy) due to baroclinic instability. Its center is situated within the channel of the splitter blade. This front is accompanied by a squall line of small-scaled eddies. This is the same phenomenon as can be observed on the meteorological polar front. The vortex high is induced by the vortex low. Its embryo starts on the pressure surface. Its center is situated behind the inlet edge of the splitter blade. It can be further verified that the stall cell is caused by the backflows of the induction fields of the two vortices (low and high).

scholarly journals Synoptic-scale drivers of the Mistral wind: link to Rossby wave life cycles and seasonal variability

2021 ◽  
Author(s):  
Yonatan Givon ◽  
Douglas Keller Jr. ◽  
Romain Pennel ◽  
Philippe Drobinski ◽  
Shira Raveh-Rubin
Keyword(s):  
Rossby Wave ◽  
Clustering Algorithm ◽  
Life Cycles ◽  
Extreme Weather Events ◽  
Turbulent Heat ◽  
Synoptic Scale ◽  
Low Level ◽  
Lee Cyclogenesis ◽  
The Mediterranean ◽  
Upper Level

Abstract. The mistral is a northerly low level jet blowing through the Rhône valley in southern France, and down to the Gulf of Lions. It is co-located with the cold sector of a low level lee-cyclone in the Gulf of Genoa, behind an upper level trough north of the Alps. The mistral wind has long been associated with extreme weather events in the Mediterranean, and while extensive research focused on the low-tropospheric mistral and lee-cyclogenesis, the different upper-tropospheric large- and synoptic-scale settings involved in producing the mistral wind are not generally known. Here, the isentropic potential vorticity (PV) structures governing the occurrence of the mistral wind are classified using a self-organizing map (SOM) clustering algorithm. Based upon a 36-year (1981–2016) mistral database and daily ERA-Interim isentropic PV data, 16 distinct mistral-associated PV structures emerge. Each classified flow pattern corresponds to a different type or stage of the Rossby wave life-cycle, from broad troughs, thin PV streamers, to distinguished cut-offs. Each of these PV patterns exhibit a distinct surface impact in terms of the surface cyclone, surface turbulent heat fluxes, wind, temperature and precipitation. A clear seasonal separation between the clusters is evident and transitions between the clusters correspond to different Rossby wave-breaking processes. This analysis provides a new perspective on the variability of the mistral, and of the Genoa lee-cyclogenesis in general, linking the upper-level PV structures to their surface impact over Europe, the Mediterranean and north Africa.

scholarly journals The three-dimensional life cycles of potential vorticity cutoffs: a global and selected regional climatologies in ERA-Interim (1979–2018)

2021 ◽  
Vol 2 (2) ◽  
pp. 507-534
Author(s):  
Raphael Portmann ◽  
Michael Sprenger ◽  
Heini Wernli
Keyword(s):  
Life Cycle ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Wave Breaking ◽  
Three Dimensional ◽  
Life Cycles ◽  
Type I ◽  
Type Ii ◽  
Rossby Wave Breaking ◽  
Precipitation Type

Abstract. The aim of this study is to explore the nature of potential vorticity (PV) cutoff life cycles. While climatological frequencies of such near-tropopause cyclonic vortices are well known, their life cycle and in particular their three-dimensional evolution is poorly understood. To address this gap, a novel method is introduced that uses isentropic air parcel trajectories to track PV cutoffs as three-dimensional objects. With this method, we can distinguish the two fundamentally different PV cutoff lysis scenarios on isentropic surfaces: complete diabatic decay vs. reabsorption by the stratospheric reservoir. This method is applied to the ERA-Interim dataset (1979–2018), and the first global climatology of PV cutoffs is presented that is independent of the selection of a vertical level and identifies and tracks PV cutoffs as three-dimensional features. More than 150 000 PV cutoff life cycles are identified and analyzed. The climatology confirms known frequency maxima of PV cutoffs and identifies additional bands in subtropical areas in the summer hemispheres and a circumpolar band around Antarctica. The first climatological analysis of diabatic decay and reabsorption shows that both scenarios occur equally frequently – in contrast to the prevailing opinion that diabatic decay dominates. Then, PV cutoffs are classified according to their position relative to jet streams (equatorward (Type I), between two jets (Type II), and poleward (Type III)). A composite analysis shows distinct dynamical scenarios for the genesis of the three types. Type I forms due to anticyclonic Rossby wave breaking above subtropical surface anticyclones and hardly results in precipitation. Type II results from anticyclonic Rossby wave breaking in mid-latitudes in regions with split-jet conditions and is frequently accompanied by surface cyclogenesis and substantial precipitation. Type III cutoffs preferentially form due to cyclonic Rossby wave breaking within extratropical cyclones in the storm track regions. We show that important track characteristics (speed, travel distance, frequency of decay and reabsorption, isentropic levels) differ between the categories, while lifetime is similar in all categories. Finally, 12 PV cutoff genesis regions in DJF and JJA are selected to study the regional characteristics of PV cutoff life cycles. As a particularly novel aspect, the vertical evolution of PV cutoffs along the life cycle is investigated. We find that, climatologically, PV cutoffs reach their maximum vertical extent about one day after genesis in most regions. However, while in some regions PV cutoffs rapidly disappear at lower levels by diabatic decay, they can grow downward in other regions. In addition, regional differences in lifetimes, the frequencies of diabatic decay and reabsorption, and the link to surface cyclones are identified that cannot be explained only by the preferred regional occurrence of the different cutoff types as defined above. Finally, we also show that in many regions PV cutoffs can be involved in surface cyclogenesis even after their formation. This study is an important step towards quantifying fundamental dynamical characteristics and the surface impacts of PV cutoffs. The proposed classification according to the jet-relative position provides a useful way to improve the conceptual understanding of PV cutoff life cycles in different regions of the globe. However, these life cycles can be substantially modified by specific regional conditions.

Modal Interpretation for the Ekman Destabilization of Inviscidly Stable Baroclinic Flow in the Phillips Model

2010 ◽  
Vol 40 (4) ◽  
pp. 830-839 ◽  
Author(s):  
Gordon E. Swaters
Keyword(s):  
Phase Velocity ◽  
Boundary Layers ◽  
Rossby Wave ◽  
Classical Theory ◽  
Baroclinic Instability ◽  
Ekman Layer ◽  
Modal Interpretation ◽  
Phase Velocities ◽  
Phillips Model ◽  
Baroclinic Flow

Abstract Ekman boundary layers can lead to the destabilization of baroclinic flow in the Phillips model that, in the absence of dissipation, is nonlinearly stable in the sense of Liapunov. It is shown that the Ekman-induced instability of inviscidly stable baroclinic flow in the Phillips model occurs if and only if the kinematic phase velocity associated with the dissipation lies outside the interval bounded by the greatest and least neutrally stable Rossby wave phase velocities. Thus, Ekman-induced destabilization does not correspond to a coalescence of the barotropic and baroclinic Rossby modes as in classical inviscid baroclinic instability. The differing modal mechanisms between the two instability processes is the reason why subcritical baroclinic shears in the classical theory can be destabilized by an Ekman layer, even in the zero dissipation limit of the theory.

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