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.

The Role of Planetary-scale Eddies on the Recent Isentropic Slope Trend during Boreal Winter

2021 ◽  
Author(s):  
MINGYU PARK ◽  
SUKYOUNG LEE
Keyword(s):  
Baroclinic Instability ◽  
Temperature Response ◽  
Heat Fluxes ◽  
Boreal Winter ◽  
Systematic Change ◽  
Latent Heating ◽  
Synoptic Scale ◽  
Planetary Scale ◽  
Zonal Wavenumber ◽  
Tropical Heating

AbstractAccording to baroclinic adjustment theory, the isentropic slope maintains its marginal state for baroclinic instability. However, the recent trend of Arctic warming raises the possibility that there could have been a systematic change in the extratropical isentropic slope. In this study, global reanalysis data is used to investigate this possibility. The result shows that tropospheric isentropes north of 50°N have been flattening significantly for the recent 25-yr winters. This trend pattern fluctuates at intraseasonal time scales. An examination of the temporal evolution indicates that it is the planetary-scale (zonal wavenumber 1-3) eddy heat fluxes, not the synoptic-scale eddy heat fluxes, that flatten the isentropes; synoptic-scale eddy heat fluxes instead respond to the subsequent changes in isentropic slope. This extratropical planetary scale wave growth is preceded by an enhanced zonal asymmetry of tropical heating and poleward wave activity vectors.A numerical model is used to test if the observed latent heating can generate the observed isentropic slope anomalies. The result shows that the tropical heating indeed contributes to the isentropic slope trend. The agreement between the model solution and the observation improves substantially if extratropical latent heating is also included in the forcing. The model temperature response shows a pattern resembling the warm-Arctic-cold-continent pattern. From these results, it is concluded that the recent flattening trend of isentropic slope north of 50°N is mostly caused by planetary scale eddy activities generated from latent heating, and that this change is accompanied by a warm-Arctic-cold-continent pattern that permeates the entire troposphere.

scholarly journals A Barotropic Envelope Rossby Soliton Model for Block–Eddy Interaction. Part I: Effect of Topography

2005 ◽  
Vol 62 (1) ◽  
pp. 5-21 ◽  
Author(s):  
Dehai Luo
Keyword(s):  
Large Scale ◽  
Plane Channel ◽  
Geographical Location ◽  
Synoptic Scale ◽  
Analytical Treatment ◽  
Soliton Model ◽  
Zonal Scale ◽  
Planetary Scale ◽  
Dipole Component ◽  
Zonal Wavenumber

Abstract A new forced envelope Rossby soliton model in an equivalent barotropic beta-plane channel is proposed to describe the interaction between an incipient block (planetary scale) and short synoptic-scale eddies. This model is based on two assumptions, motivated by observations that (i) there exists a zonal scale separation between the planetary-scale and synoptic-scale waves and (ii) that the range of synoptic-scale zonal wavenumber is comparable to the planetary-scale zonal wavenumber. These assumptions allow an analytical treatment. The evolution of the planetary-scale block under the influence of synoptic-scale eddies is described by a forced nonlinear Schrödinger equation that is solved numerically, while the feedback of block development on the preexisting synoptic-scale eddies is derived analytically. It is shown that the planetary-scale projection of the nonlinear interaction between synoptic-scale eddies is the most important contributor to the amplification and decay of the planetary-scale blocking dipole or anticyclone, while the synoptic–planetary-scale interaction contributes significantly to the downstream development of preexisting synoptic-scale eddies. Large-scale topography plays a secondary role compared to the synoptic-scale eddies in exciting the block. However, it plays a role in inducing a standing planetary-scale ridge prior to block onset, which fixes the geographical location of the block and induces meridional asymmetry in the flow. In particular, the topographically induced planetary-scale ridge that is almost in phase with a dipole component of blocking flow is found to be a controlling factor for the northward deflection of storm tracks associated with blocking anticyclones.

A Causality-Based View of the Interaction between Synoptic- and Planetary-Scale Atmospheric Disturbances

2020 ◽  
Vol 77 (3) ◽  
pp. 925-941
Author(s):  
Savini M. Samarasinghe ◽  
Yi Deng ◽  
Imme Ebert-Uphoff
Keyword(s):  
Spherical Harmonics ◽  
Graphical Model ◽  
Structure Learning ◽  
Spatial Scales ◽  
Storm Track ◽  
Boreal Winter ◽  
Synoptic Scale ◽  
Planetary Scale ◽  
Causal Pathways ◽  
Zonal Wavenumber

Abstract This paper reports preliminary yet encouraging findings on the use of causal discovery methods to understand the interaction between atmospheric planetary- and synoptic-scale disturbances in the Northern Hemisphere. Specifically, constraint-based structure learning of probabilistic graphical models is applied to the spherical harmonics decomposition of the daily 500-hPa geopotential height field in boreal winter for the period 1948–2015. Active causal pathways among different spherical harmonics components are identified and documented in the form of a temporal probabilistic graphical model. Since, by definition, the structure learning algorithm used here only robustly identifies linear causal effects, we report only causal pathways between two groups of disturbances with sufficiently large differences in temporal and/or spatial scales, that is, planetary-scale (mainly zonal wavenumbers 1–3) and synoptic-scale disturbances (mainly zonal wavenumbers 6–8). Daily reconstruction of geopotential heights using only interacting scales suggest that the modulation of synoptic-scale disturbances by planetary-scale disturbances is best characterized by the flow of information from a zonal wavenumber-1 disturbance to a synoptic-scale circumglobal wave train whose amplitude peaks at the North Pacific and North Atlantic storm-track region. The feedback of synoptic-scale to planetary-scale disturbances manifests itself as a zonal wavenumber-2 structure driven by synoptic-eddy momentum fluxes. This wavenumber-2 structure locally enhances the East Asian trough and western Europe ridge of the wavenumber-1 planetary-scale disturbance that actively modulates the activity of synoptic-scale disturbances. The winter-mean amplitude of the actively interacting disturbances are characterized by pronounced fluctuations across interannual to decadal time scales.

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.

Planetary and synoptic-scale dynamic control of extreme cold wave patterns over the United States

2020 ◽  
Author(s):  
Zuowei Xie ◽  
Robert Black ◽  
Yi Deng
Keyword(s):  
United States ◽  
The United States ◽  
Planetary Waves ◽  
Height Anomaly ◽  
Cold Wave ◽  
Synoptic Scale ◽  
Planetary Scale ◽  
Southeastern Us ◽  
Extreme Cold ◽  
Upper Level

<p>The roles of planetary and synoptic-scale waves in extreme cold wave (ECW) events over the southeastern (SE) and northwestern (NW) United States (US) are studied using a spherical harmonic decomposition in conjunction with piecewise tendency diagnosis (PTD). Planetary waves and synoptic waves jointly work together to initiate ECW events. Notably, the planetary waves not only provide a direct contribution to circulation field enacting ECW events but also alter the background circulation field in such a manner that promotes synoptic waves growth via increases in regional barotropic deformation. The SE-ECW events, concurrent with the Northern Hemisphere annular mode (NAM) negative phase, feature high latitude intensification and subsequent southeastward movement of cold surface air temperature (SAT) anomalies. The planetary-scale pattern provides a sizable contribution to the total wave pattern on both sea level pressure (SLP) and upper level. Moreover, the negative NAM planetary anomaly acts to displace the jet equatorward and thereby increases the barotropic deformation of the synoptic-scale anomaly over southeastern US. PTD confirms that the planetary-scale barotropic deformation plays a key role in deepening the negative height anomaly with a secondary contribution from baroclinic growth. In contrast, NW-ECW events feature a regional SAT cold anomaly that intensified in situ in association with a quasi-stationary positive SLP anomaly with a substantial planetary-scale wave component. The upper level circulation is characterized by a pronounced anomalous ridge over the Gulf of Alaska and a northeast-southwest tilted negative height anomaly to its east. The negative height anomaly axis is orthogonal to the planetary-scale dilatation, result in a stronger planetary barotropic deformation of the incipient negative height anomaly.</p>

scholarly journals Southern Annular Mode Dynamics in Observations and Models. Part II: Eddy Feedbacks

2013 ◽  
Vol 26 (14) ◽  
pp. 5220-5241 ◽  
Author(s):  
Isla R. Simpson ◽  
Theodore G. Shepherd ◽  
Peter Hitchcock ◽  
John F. Scinocca
Keyword(s):  
Negative Feedback ◽  
Planetary Wave ◽  
Southern Annular Mode ◽  
Summer Season ◽  
Substantial Contribution ◽  
Mean Flow ◽  
Annular Mode ◽  
Planetary Scale ◽  
Zonal Wavenumber ◽  
Climatological Circulation

Abstract Many global climate models (GCMs) have trouble simulating southern annular mode (SAM) variability correctly, particularly in the Southern Hemisphere summer season where it tends to be too persistent. In this two-part study, a suite of experiments with the Canadian Middle Atmosphere Model (CMAM) is analyzed to improve the understanding of the dynamics of SAM variability and its deficiencies in GCMs. Here, an examination of the eddy–mean flow feedbacks is presented by quantification of the feedback strength as a function of zonal scale and season using a new methodology that accounts for intraseasonal forcing of the SAM. In the observed atmosphere, in the summer season, a strong negative feedback by planetary-scale waves, in particular zonal wavenumber 3, is found in a localized region in the southwest Pacific. It cancels a large proportion of the positive feedback by synoptic- and smaller-scale eddies in the zonal mean, resulting in a very weak overall eddy feedback on the SAM. CMAM is deficient in this negative feedback by planetary-scale waves, making a substantial contribution to its bias in summertime SAM persistence. Furthermore, this bias is not alleviated by artificially improving the climatological circulation, suggesting that climatological circulation biases are not the cause of the planetary wave feedback deficiency in the model. Analysis of the summertime eddy feedbacks in the models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) confirms that this is indeed a common problem among GCMs, suggesting that understanding this planetary wave feedback and the reason for its deficiency in GCMs is key to improving the fidelity of simulated SAM variability in the summer season.

Sign in / Sign up

Export Citation Format

Share Document