scholarly journals Planetary Wave Breaking and Nonlinear Reflection: Seasonal Cycle and Interannual Variability

2006 ◽  
Vol 19 (23) ◽  
pp. 6139-6152 ◽  
Author(s):  
John T. Abatzoglou ◽  
Gudrun Magnusdottir
Keyword(s):  
Interannual Variability ◽  
Wave Breaking ◽  
Large Scale ◽  
Planetary Wave ◽  
Wave Train ◽  
Zonal Flow ◽  
Reanalysis Data ◽  
Nonlinear Reflection ◽  
Meridional Overturning ◽  
Pv Gradient

Abstract Forty-six years of daily averaged NCEP–NCAR reanalysis data are used to identify the occurrence of planetary wave breaking (PWB) in the subtropical upper troposphere. As large-amplitude waves propagate into the subtropics where the zonal flow is weak, they may break. PWB is diagnosed by observing the large-scale meridional overturning of potential vorticity (PV) contours on isentropic surfaces near the subtropical tropopause. PWB occurs most often during summer, and almost exclusively over the subtropical ocean basins in the Northern Hemisphere. The seasonal evolution of the zonal flow (and the associated latitudinal PV gradient) regulates the location and frequency of PWB. Significant interannual variability in PWB is associated with well-known modes of climate variability. One of the most interesting dynamical consequences of PWB is the possibility of nonlinear reflection poleward out of the wave-breaking region. Modeling studies have found nonlinear reflection following PWB. Observations show that about 36% of all PWB events are followed by nonlinear reflection back into midlatitudes. In these cases, a poleward-arching wave train can be seen propagating away from the wave-breaking region following breaking. It is suggested that a sufficiently strong latitudinal PV gradient must be present downstream of the wave-breaking region for reflection to take place. The proportion of PWB events that is reflective stays rather constant through the year, with slightly higher numbers in spring and fall compared to those in winter and summer.

scholarly journals Opposing Effects of Reflective and Nonreflective Planetary Wave Breaking on the NAO

2006 ◽  
Vol 63 (12) ◽  
pp. 3448-3457 ◽  
Author(s):  
John T. Abatzoglou ◽  
Gudrun Magnusdottir
Keyword(s):  
North Atlantic ◽  
Wave Breaking ◽  
Momentum Flux ◽  
Large Scale ◽  
Planetary Wave ◽  
Wave Train ◽  
Stationary Wave ◽  
Wave Activity ◽  
The North ◽  
The North Atlantic

Planetary wave breaking (PWB) over the subtropical North Atlantic is observed over 45 winters (December 1958–March 2003) using NCEP–NCAR reanalysis data. PWB is manifested in the rapid, large-scale and irreversible overturning of potential vorticity (PV) contours on isentropic surfaces in the subtropical upper troposphere. As breaking occurs over the subtropical North Atlantic, an upper-tropospheric PV tripole anomaly forms with nodes over the subtropical, midlatitude, and subpolar North Atlantic. The northern two nodes of this tripole are quite similar to the spatial structure of the North Atlantic Oscillation (NAO), with positive polarity. Nonlinear reflection is identified in approximately a quarter of all PWB events. Following breaking, two distinct circulation regimes arise, one in response to reflective events and the other in response to nonreflective events. For reflective events, anomalies over the North Atlantic rapidly propagate away from the breaking region along a poleward arching wave train over the Eurasian continent. The quasi-stationary wave activity flux indicates that wave activity is exported out of the Atlantic basin. At the same time, the regional poleward eddy momentum flux goes through a sign reversal, as does the polarity of the NAO. For nonreflective events, the dipole anomaly over the North Atlantic amplifies. Diagnostics for nonreflective events suggest that wave activity over the Azores gets absorbed, allowing continued enhancement of both the regional poleward eddy momentum flux and the positive NAO.

Method for Identifying and Clustering Rossby Wave Breaking Events in the Northern Hemisphere

2021 ◽  
pp. 17-28
Author(s):  
A. V. Gochakov ◽  
◽  
O. Yu. Antokhina ◽  
V. N. Krupchatnikov ◽  
Yu. V. Martynova ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Potential Vorticity ◽  
Wave Breaking ◽  
Large Scale ◽  
Method Development ◽  
Spatial Clustering ◽  
Potential Temperature ◽  
Reanalysis Data ◽  
Rossby Wave Breaking ◽  
Dynamic Phenomena

Many large-scale dynamic phenomena in the Earth’s atmosphere are associated with the processes of propagation and breaking of Rossby waves. A new method for identifying the Rossby wave breaking (RWB) is proposed. It is based on the detection of breakings centers by analyzing the shape of the contours of potential vorticity or temperature on quasimaterial surfaces: isentropic and iserthelic (surfaces of constant Ertel potential vorticity (PV)), with further RWB center clustering to larger regions. The method is applied to the set of constant PV levels (0.3 to 9.8 PVU with a step of 0.5 PVU) at the level of potential temperature of 350 K for 12:00 UTC. The ERA-Interim reanalysis data from 1979 to 2019 are used for the method development. The type of RWB (cyclonic/anticyclonic), its area and center are determined by analyzing the vortex geometry at each PV level for every day. The RWBs obtained at this stage are designated as elementary breakings. Density-Based Spatial Clustering of Applications with Noise algorithm (DBSCAN) was applied to all elementary breakings for each month. As a result, a graphic dataset describing locations and dynamics of RWBs for every month from 1979 to 2019 is formed. The RWB frequency is also evaluated for each longitude, taking into account the duration of each RWB and the number of levels involved, as well as the anomalies of these parameters.

scholarly journals A Hydroclimatological Analysis of Precipitation in the Ganges–Brahmaputra–Meghna River Basin

Water ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1359 ◽  
Author(s):  
Scott Curtis ◽  
Thomas Crawford ◽  
Munshi Rahman ◽  
Bimal Paul ◽  
M. Miah ◽  
...  
Keyword(s):  
Interannual Variability ◽  
River Basin ◽  
Significant Relationship ◽  
Large Scale ◽  
Monsoon Rainfall ◽  
Southern Oscillation ◽  
Wave Train ◽  
Principal Component ◽  
South Atlantic ◽  
The Ganges

Understanding seasonal precipitation input into river basins is important for linking large-scale climate drivers with societal water resources and the occurrence of hydrologic hazards such as floods and riverbank erosion. Using satellite data at 0.25-degree resolution, spatial patterns of monsoon (June-July-August-September) precipitation variability between 1983 and 2015 within the Ganges–Brahmaputra–Meghna (GBM) river basin are analyzed with Principal Component (PC) analysis and the first three modes (PC1, PC2 and PC3) are related to global atmospheric-oceanic fields. PC1 explains 88.7% of the variance in monsoonal precipitation and resembles climatology with the center of action over Bangladesh. The eigenvector coefficients show a downward trend consistent with studies reporting a recent decline in monsoon rainfall, but little interannual variability. PC2 explains 2.9% of the variance and shows rainfall maxima to the far western and eastern portions of the basin. PC2 has an apparent decadal cycle and surface and upper-air atmospheric height fields suggest the pattern could be forced by tropical South Atlantic heating and a Rossby wave train stemming from the North Atlantic, consistent with previous studies. Finally, PC3 explains 1.5% of the variance and has high spatial variability. The distribution of precipitation is somewhat zonal, with highest values at the southern border and at the Himalayan ridge. There is strong interannual variability associated with PC3, related to the El Nino/Southern Oscillation (ENSO). Next, we perform a hydroclimatological downscaling, as precipitation attributed to the three PCs was averaged over the Pfafstetter level-04 sub-basins obtained from the World Wildlife Fund (Gland, Switzerland). While PC1 was the principal contributor of rainfall for all sub-basins, PC2 contributed the most to rainfall in the western Ganges sub-basin (4524) and PC3 contributed the most to the rainfall in the northern Brahmaputra (4529). Monsoon rainfall within these two sub-basins were the only ones to show a significant relationship (negative) with ENSO, whereas four of the eight sub-basins had a significant relationship (positive) with sea surface temperature (SST) anomalies in the tropical South Atlantic. This work demonstrates a geographic dependence on climate teleconnections in the GBM that deserves further study.

scholarly journals Stationary Wave Reflection as a Mechanism for Zonalizing the Atlantic Winter Jet at the LGM

2016 ◽  
Vol 73 (8) ◽  
pp. 3329-3342 ◽  
Author(s):  
Marcus Löfverström ◽  
Rodrigo Caballero ◽  
Johan Nilsson ◽  
Gabriele Messori
Keyword(s):  
North Atlantic ◽  
Wave Breaking ◽  
Planetary Wave ◽  
Wave Reflection ◽  
Stationary Wave ◽  
Laurentide Ice Sheet ◽  
The North ◽  
Nonlinear Reflection ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract Current estimates of the height of the Laurentide Ice Sheet (LIS) at the Last Glacial Maximum (LGM) range from around 3000 to 4500 m. Modeling studies of the LGM, using low-end estimates of the LIS height, show a relatively weak and northeastward-tilted winter jet in the North Atlantic, similar to the modern jet, while simulations with high-end LIS elevations show a much more intense and zonally oriented jet. Here, an explanation for this response of the Atlantic circulation is sought using a sequence of LGM simulations spanning a broad range of LIS elevations. It is found that increasing LIS height favors planetary wave breaking and nonlinear reflection in the subtropical North Atlantic. For high LIS elevations, planetary wave reflection becomes sufficiently prevalent that a poleward-directed flux of wave activity appears in the climatology over the midlatitude North Atlantic. This entails a zonalization of the stationary wave phase lines and thus of the midlatitude jet.

scholarly journals Dynamical Evolution of North Atlantic Ridges and Poleward Jet Stream Displacements

2011 ◽  
Vol 68 (5) ◽  
pp. 954-963 ◽  
Author(s):  
Tim Woollings ◽  
Joaquim G. Pinto ◽  
João A. Santos
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Large Scale ◽  
Wave Train ◽  
Jet Stream ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic ◽  
Circulation Anomalies

Abstract The development of a particular wintertime atmospheric circulation regime over the North Atlantic, comprising a northward shift of the North Atlantic eddy-driven jet stream and an associated strong and persistent ridge in the subtropics, is investigated. Several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the North Atlantic Oscillation and East Atlantic pattern. First, the authors identify a close relationship between northward shifts of the eddy-driven jet, the establishment and maintenance of strong and persistent ridges in the subtropics, and the occurrence of upper-tropospheric anticyclonic Rossby wave breaking over Iberia. Clear tropospheric precursors are evident prior to the development of the regime, suggesting a preconditioning of the Atlantic jet stream and an upstream influence via a large-scale Rossby wave train from the North Pacific. Transient (2–6 days) eddy forcing plays a dual role, contributing to both the initiation and then the maintenance of the circulation anomalies. During the regime there is enhanced occurrence of anticyclonic Rossby wave breaking, which may be described as low-latitude blocking-like events over the southeastern North Atlantic. A strong ridge is already established at the time of wave-breaking onset, suggesting that the role of wave-breaking events is to amplify the circulation anomalies rather than to initiate them. Wave breaking also seems to enhance the persistence, since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking.

A Mechanism for the Poleward Propagation of Zonal Mean Flow Anomalies

2007 ◽  
Vol 64 (3) ◽  
pp. 849-868 ◽  
Author(s):  
Sukyoung Lee ◽  
Seok-Woo Son ◽  
Kevin Grise ◽  
Steven B. Feldstein
Keyword(s):  
Wave Propagation ◽  
Zonal Wind ◽  
Wave Breaking ◽  
Observational Studies ◽  
Mean Flow ◽  
Radiative Relaxation ◽  
Meridional Overturning ◽  
Rossby Wave Propagation ◽  
The Tropics ◽  
Pv Gradient

Abstract Observational studies have shown that tropospheric zonal mean flow anomalies frequently undergo quasi-periodic poleward propagation. A set of idealized numerical model runs is examined to investigate the physical mechanism behind this poleward propagation. This study finds that the initiation of the poleward propagation is marked by the formation of negative zonal wind anomalies in the Tropics. These negative anomalies arise from meridional overturning/breaking of waves that originate in midlatitudes. This wave breaking homogenizes the potential vorticity (PV) within the region of negative zonal wind anomalies, and also leads to the formation of positive zonal wind anomalies in the subtropics. Subsequent equatorward radiation of midlatitude waves is halted, which results in wave breaking at the poleward end of the homogenized PV region. This in turn generates new positive and negative zonal wind anomalies, which enables a continuation of the poleward propagation. The shielding of the homogenized PV region from equatorward wave propagation allows the model’s radiative relaxation to reestablish undisturbed westerlies in the Tropics, while extratropical westerly anomalies arise from eddy vorticity fluxes. The above process indicates that the poleward zonal mean anomaly propagation is caused by an orchestrated combination of linear Rossby wave propagation, nonlinear wave breaking, and radiative relaxation. The importance of the meridional wave propagation and breaking is consistent with the fact that the poleward propagation occurs only in the parameter space of the model where the PV gradient is of moderate strength. Implications for predictability are briefly discussed.

scholarly journals The North Atlantic Oscillation Response to Large-Scale Atmospheric Anomalies in the Northeastern Pacific

2013 ◽  
Vol 70 (9) ◽  
pp. 2854-2874 ◽  
Author(s):  
Marie Drouard ◽  
Gwendal Rivière ◽  
Philippe Arbogast
Keyword(s):  
North Atlantic Oscillation ◽  
North Atlantic ◽  
Wave Breaking ◽  
Large Scale ◽  
Wave Train ◽  
Low Frequency ◽  
The North ◽  
Northeastern Pacific ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Ingredients in the North Pacific flow influencing Rossby wave breakings in the North Atlantic and the intraseasonal variations of the North Atlantic Oscillation (NAO) are investigated using both reanalysis data and a three-level quasigeostrophic model on the sphere. First, a long-term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the NAO. Furthermore, a large-scale, low-frequency ridge anomaly is identified in the northeastern Pacific in the days prior to the maximum of the positive NAO phase both in the reanalysis and in the model. A large-scale northeastern Pacific trough anomaly is observed during the negative NAO phase but does not systematically precede it. Then, short-term linear and nonlinear simulations are performed to understand how the large-scale ridge anomaly can act as a precursor of the positive NAO phase. The numerical setup allows for analysis of the propagation of synoptic waves in the eastern Pacific in the presence of a large-scale ridge or trough anomaly and their downstream impact onto the Atlantic jet when they break. The ridge acts in two ways. First, it tends to prevent the downstream propagation of small waves compared to long waves. Second, it deflects the propagation of the wave trains in such a way that they mainly propagate equatorward in the Atlantic. The two modes of action favor the anticyclonic wave breaking and, therefore, the positive NAO phase. With the trough, the wave train propagation is more zonal, disturbances are more meridionally elongated, and cyclonic wave breaking is more frequent in the Atlantic than in the ridge case.

scholarly journals The Interannual Variability of the Tropical Divergence Tilt and Its Connection with the Extratropical Circulation

2021 ◽  
Vol 34 (1) ◽  
pp. 259-275
Author(s):  
Pablo Zurita-Gotor
Keyword(s):  
Interannual Variability ◽  
Momentum Flux ◽  
Large Scale ◽  
Theoretical Work ◽  
Stationary Wave ◽  
Reanalysis Data ◽  
Boreal Winter ◽  
The Pacific ◽  
Divergence Field ◽  
Two Parameters

AbstractPrevious theoretical work has suggested that the strength of the divergent eddy momentum flux in the deep tropics, due to correlations between rotational zonal velocities and divergent meridional velocities, increases with the meridional tilt of the large-scale divergence field. To test that idea, this work investigates the interannual variability of the divergent eddy momentum flux in reanalysis data. Consistent with the theory, it is found that the eddy momentum flux variability is driven by two main parameters: the amplitude of the tropical stationary wave and the tilt of the divergence field. Together, these two parameters account for 80% (90%) of the interannual eddy momentum flux variance during boreal (austral) winter. The interannual variability of these parameters is governed by the internal atmospheric dynamics. During boreal winter, interannual changes in MJO variability explain nearly half of the interannual variance in the stationary wave amplitude, depending on whether on average MJO anomalies interfere constructively or destructively with the stationary wave. The interannual variability of the divergence phase tilt is modulated by tropical–extratropical interactions in the Pacific. The tilt increases during the negative phase of the west Pacific Oscillation associated with a dipole of upper-level divergence (convergence) on the northern (southern) side of the Pacific jet exit region.

A Seasonal Climatology of Rossby Wave Breaking in the 320–2000-K Layer

2007 ◽  
Vol 64 (6) ◽  
pp. 1922-1940 ◽  
Author(s):  
Matthew H. Hitchman ◽  
Amihan S. Huesmann
Keyword(s):  
Rossby Wave ◽  
Wave Breaking ◽  
Reanalysis Data ◽  
Polar Night ◽  
Rossby Wave Breaking ◽  
Polar Stratosphere ◽  
Differential Advection ◽  
Shed Light ◽  
Pv Gradient ◽  
Westerly Jets

Differential advection in Rossby waves can lead to potential vorticity (PV; P) contours on isentropic surfaces folding over in latitude (Py < 0) in a process called Rossby wave breaking (RWB). Exploring the properties of RWB may shed light on underlying dynamics and enable quantification of irreversible transport. A seasonal climatology of Py and RWB statistics is presented for the 320–850-K layer using NCEP reanalysis data during 1979–2005 and for the 320–2000-K layer using the Met Office (UKMO) data during 1991–2003. A primary goal is to depict the spatial extent and seasonality of RWB maxima. This analysis shows seven distinct RWB regimes: poleward and equatorward of the subtropical westerly jets, poleward and equatorward of the stratospheric polar night jets, flanking the equator in the stratosphere and mesosphere, equatorward of subtropical monsoon anticyclones, and the summertime polar stratosphere. A striking PV gradient maximum exists at the equator throughout the layer 360–2000 K, flanked by subtropical RWB maxima, integral components of the Lagrangian cross-equatorial flow. Strong RWB occurs in the polar night vortex where β is small. Over the summer pole, strong poleward RWB associated with synoptic waves decays into small amplitude motions in the upper stratosphere, where heating gradients cause Py < 0. The seven spatial regimes are linked to three different dynamical causes of reversals: wave breaking associated with westerly jets, a combined barotropic/inertial instability in cross-equatorial flow, and on the periphery of monsoon anticyclones.

scholarly journals Interannual Variability of the Global Meridional Overturning Circulation Dominated by Pacific Variability

2020 ◽  
Vol 50 (3) ◽  
pp. 559-574
Author(s):  
Neil F. Tandon ◽  
Oleg A. Saenko ◽  
Mark A. Cane ◽  
Paul J. Kushner
Keyword(s):  
Interannual Variability ◽  
Large Scale ◽  
Southern Oscillation ◽  
Meridional Overturning Circulation ◽  
Ekman Transport ◽  
Prominent Feature ◽  
Overturning Circulation ◽  
Near Surface ◽  
The Pacific ◽  
Meridional Overturning

AbstractThe most prominent feature of the time-mean global meridional overturning circulation (MOC) is the Atlantic MOC (AMOC). However, interannual variability of the global MOC is shown here to be dominated by Pacific MOC (PMOC) variability over the full depth of the ocean at most latitudes. This dominance of interannual PMOC variability is robust across modern climate models and an observational state estimate. PMOC interannual variability has large-scale organization, its most prominent feature being a cross-equatorial cell spanning the tropics. Idealized experiments show that this variability is almost entirely wind driven. Interannual anomalies of zonal mean zonal wind stress produce zonally integrated Ekman transport anomalies that are larger in the Pacific Ocean than in the Atlantic Ocean, simply because the Pacific is wider than the Atlantic at most latitudes. This contrast in Ekman transport variability implies greater variability in the near-surface branch of the PMOC when compared with the near-surface branch of the AMOC. These near-surface variations in turn drive compensating flow anomalies below the Ekman layer. Because the baroclinic adjustment time is longer than a year at most latitudes, these compensating flow anomalies have baroclinic structure spanning the full depth of the ocean. Additional analysis reveals that interannual PMOC variations are the dominant contribution to interannual variations of the global meridional heat transport. There is also evidence of interaction between interannual PMOC variability and El Niño–Southern Oscillation.

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