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Darryn W Waugh - One of the best experts on this subject based on the ideXlab platform.
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tropospheric Rossby Wave breaking and variability of the latitude of the eddy driven jet
Journal of Climate, 2014Co-Authors: Chaim I Garfinkel, Darryn W WaughAbstract:A dry general circulation model is used to investigate the connections between Rossby Wave breaking and the latitude of the midlatitude tropospheric eddy-driven jet. An ensemble of experiments is constructed in which the jet latitude is influenced by a midlatitude tropospheric temperature anomaly that resembles observed climate change and by the imposition of a stratospheric polar vortex, and the distribution of Rossby Wave breaking frequency is examined for each experiment. The shift in Wave breaking per degree latitude of jet shift is then compared for three different sources of jet movement: the tropospheric baroclinic forcing imposed in midlatitudes, the imposition of a stratospheric polar vortex, and the internal variability of the midlatitude eddy-driven jet. It is demonstrated that all three sources of jet movement produce a similar change in Rossby Wave breaking frequency per degree of jet shift. Hence, it is difficult (if not impossible) to isolate the ultimate cause behind the shift in Rossby Wave breaking in response to the two external forcings.
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impact of Rossby Wave breaking on u s west coast winter precipitation during enso events
Journal of Climate, 2013Co-Authors: Jumee Ryoo, Darryn W Waugh, Yohai Kaspi, George N Kiladis, Duane E Waliser, Eric J FetzerAbstract:AbstractThis study demonstrates that water vapor transport and precipitation are largely modulated by the intensity of the subtropical jet, transient eddies, and the location of Wave breaking events during the different phases of ENSO. Clear differences are found in the potential vorticity (PV), meteorological fields, and trajectory pathways between the two different phases. Rossby Wave breaking events have cyclonic and anticyclonic regimes, with associated differences in the frequency of occurrence and the dynamic response. During La Nina, there is a relatively weak subtropical jet allowing PV to intrude into lower latitudes over the western United States. This induces a large amount of moisture transport inland ahead of the PV intrusions, as well as northward transport to the west of a surface anticyclone. During El Nino, the subtropical jet is relatively strong and is associated with an enhanced cyclonic Wave breaking. This is accompanied by a time-mean surface cyclone, which brings zonal moisture tran...
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antarctic ozone depletion and trends in tropopause Rossby Wave breaking
Atmospheric Science Letters, 2012Co-Authors: Darryn W Waugh, Thando Ndarana, Lorenzo M Polvani, Gustavo Correa, Edwin P GerberAbstract:Trends in summer tropopause Rossby Wave breaking (RWB) are examined using meteorological reanalyses and model integrations. The reanalyses for the last 30 years show large increases in RWB on the equatorward side of the tropospheric jet and weak decreases on the poleward side. Comparable changes in RWB are found in general circulation model integrations whose stratospheric ozone differs between 1960 and 2000 levels, but not in integrations that differ only in their greenhouse gas concentrations and sea-surface temperatures. These results indicate that the formation of the ozone hole has led to changes in RWB frequency during southern summer. Copyright 2012 Royal Meteorological Society
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a climatology of Rossby Wave breaking on the southern hemisphere tropopause
Journal of the Atmospheric Sciences, 2011Co-Authors: Thando Ndarana, Darryn W WaughAbstract:AbstractA 30-yr climatology of Rossby Wave breaking (RWB) on the Southern Hemisphere (SH) tropopause is formed using 30 yr of reanalyses. Composite analysis of potential vorticity and meridional fluxes of Wave activity show that RWB in the SH can be divided into two broad categories: anticyclonic and cyclonic events. While there is only weak asymmetry in the meridional direction and most events cannot be classified as equatorward or poleward in terms of the potential vorticity structure, the position and structure of the fluxes associated with equatorward breaking differs from those of poleward breaking. Anticyclonic breaking is more common than cyclonic breaking, except on the lower isentrope examined (320 K). There are marked differences in the seasonal variations of RWB on the two surfaces, with a winter minimum for RWB around 350 K but a summer minimum for RWB around 330 K. These seasonal variations are due to changes in the location of the tropospheric jets and dynamical tropopause. During winter the...
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the link between cut off lows and Rossby Wave breaking in the southern hemisphere
Quarterly Journal of the Royal Meteorological Society, 2010Co-Authors: Thando Ndarana, Darryn W WaughAbstract:The climatological link between cut-off low (COL) pressure systems that occur from 20 to 50°S and Rossby Wave breaking (RWB) in the Southern Hemisphere (SH) is examined for 1979–2008. It is shown that COLs are associated with either RWB events (89%) or with potential vorticity (PV) intrusions where there is north–south advection of high-PV air (11%). In the vast majority of COLs, the RWB events occur upstream, on or before the day of the COL formation. The evolution of the PV, geopotential heights, static stability, absolute vorticity and temperature advection fields during the COLs are consistent with the formation of high-PV anomalies that induce cyclonic circulations as predicted by theory. RWB plays a key role in producing the split flow associated with COLs in the SH, which in turn produces absolute vorticity anomalies by shear-curvature vorticity conversion, and creates static stability anomalies. The COLs associated with RWB at 330 K are deeper and more persistent than those associated with 350 K RWB and surface processes differ depending on the isentropic surface on which the associated RWB occurs. The seasonality of the RWB and COLs are similar, and is linked to the seasonal march of the westerly jets. Copyright © 2010 Royal Meteorological Society
Gudrun Magnusdottir - One of the best experts on this subject based on the ideXlab platform.
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characteristics and impacts of extratropical Rossby Wave breaking during the atlantic hurricane season
Journal of Climate, 2017Co-Authors: Gan Zhang, Zhuo Wang, Melinda S Peng, Gudrun MagnusdottirAbstract:AbstractThis study investigates the characteristics of extratropical Rossby Wave breaking (RWB) during the Atlantic hurricane season and its impacts on Atlantic tropical cyclone (TC) activity. It was found that RWB perturbs the wind and moisture fields throughout the troposphere in the vicinity of a breaking Wave. When RWB occurs more frequently over the North Atlantic, the Atlantic main development region (MDR) is subject to stronger vertical wind shear and reduced tropospheric moisture; the basinwide TC counts are reduced, and TCs are generally less intense, have a shorter lifetime, and are less likely to make landfalls. A significant negative correlation was found between Atlantic TC activity and RWB occurrence during 1979–2013. The correlation is comparable to that with the MDR SST index and stronger than that with the Nino-3.4 index. Further analyses suggest that the variability of RWB occurrence in the western Atlantic is largely independent of that in the eastern Atlantic. The RWB occurrence in the...
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the shift of the northern node of the nao and cyclonic Rossby Wave breaking
Journal of Climate, 2012Co-Authors: Yihui Wang, Gudrun MagnusdottirAbstract:AbstractSeveral studies have found an eastward shift in the northern node of the North Atlantic Oscillation (NAO) during the winters of 1978–97 compared to 1958–77. This study focuses on the connection between this shift of the northern node of the NAO and Rossby Wave breaking (RWB) for the period 1958–97. It is found that the region of frequent cyclonic RWB underwent a northeastward shift at high latitudes in the latter 20-yr period. On a year-to-year basis, the cyclonic RWB region moves along a southwest–northeast (SW–NE)-directed axis. Both latitude and longitude of the winter maximum frequency of cyclonic RWB occurrence are positively correlated with the NAO index.To investigate the role of location of cyclonic RWB in influencing the NAO pattern, the geographical location of frequent cyclonic RWB is divided into two subdomains located along the SW–NE axis, to the south (SW domain) and east (NE domain) of Greenland. Two composites are assembled as one cyclonic RWB occurrence is detected in one of the t...
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the role of tropospheric Rossby Wave breaking in the pacific decadal oscillation
Journal of Climate, 2009Co-Authors: Courtenay Strong, Gudrun MagnusdottirAbstract:Abstract The leading pattern of extratropical Pacific sea surface temperature variability [the Pacific decadal oscillation (PDO)] is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby Wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic (cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. The RWB patterns that are relevant to the PDO are closely tied to El Nino–Southern Oscillation, the Pacific–North American pattern, and the northern annular mode. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Nino anomalies eme...
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tropospheric Rossby Wave breaking and the nao nam
Journal of the Atmospheric Sciences, 2008Co-Authors: Courtenay Strong, Gudrun MagnusdottirAbstract:Objective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby Waves is performed for the Northern Hemisphere (NH) winters of 1958–2006. A winter climatology of both anticyclonic and cyclonic Rossby Wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective Wave-breaking analysis method are provided in the appendix.
Hui Li - One of the best experts on this subject based on the ideXlab platform.
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identifying anticyclonic vortex features produced by the Rossby Wave instability in protoplanetary disks
The Astrophysical Journal, 2018Co-Authors: Hui Li, Pinghui Huang, Andrea Isella, Shengtai Li, Jianghui JiAbstract:Several nearby protoplanetary disks have been observed to display large-scale crescents in the (sub) millimeter dust continuum emission. One interpretation is that these structures correspond to anticyclonic vortices generated by the Rossby Wave instability within the gaseous disk. Such vortices have local gas overdensities and are expected to concentrate dust particles with a Stokes number around unity. This process might catalyze the formation of planetesimals. Whereas recent observations showed that dust crescents are indeed regions where millimeter-size particles have abnormally high concentration relative to the gas and smaller grains, no observations have yet shown that the gas within the crescent region counterrotates with respect to the protoplanetary disk. Here we investigate the detectability of anticyclonic features through measurement of the line-of-sight component of the gas velocity obtained with ALMA. We carry out 2D hydrodynamic simulations and 3D radiative transfer calculations of a protoplanetary disk characterized by a vortex created by the tidal interaction with a massive planet. As a case study, the disk parameters are chosen to mimic the IRS. 48 system, which has the most prominent crescent observed to date. We generate synthetic ALMA observations of both the dust continuum and (CO)-C-12 emission around the frequency of 345 GHz. We find that the anticyclonic features of the vortex are weak but can be detected if both the source and the observational setup are properly chosen. We provide a recipe for maximizing the probability of detecting such vortex features and present an analysis procedure to infer their kinematic properties.
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Rossby Wave instability of thin accretion disks iii nonlinear simulations
The Astrophysical Journal, 2001Co-Authors: Hui Li, S A Colgate, Burton Wendroff, R LiskaAbstract:We study the nonlinear evolution of the Rossby Wave instability in thin disks using global two-dimensional hydrodynamic simulations. The detailed linear theory of this nonaxisymmetric instability was developed earlier by Lovelace et al. and Li et al., who found that the instability can be excited when there is an extremum in the radial profile of an entropy-modified version of potential vorticity. The key questions we are addressing in this paper are the following: (1) What happens when the instability becomes nonlinear? Specifically, does it lead to vortex formation? (2) What is the detailed behavior of a vortex? (3) Can the instability sustain itself and can the vortex last a long time? Among various initial equilibria that we have examined, we generally find that there are three stages of the disk evolution: (1) The exponential growth of the initial small amplitude perturbations. This is in excellent agreement with the linear theory; (2) The production of large-scale vortices and their interactions with the background flow, including shocks. Significant accretion is observed owing to these vortices. (3) The coupling of Rossby Waves/vortices with global spiral Waves, which facilitates further accretion throughout the whole disk. Even after more than 20 revolutions at the radius of vortices, we find that the disk maintains a state that is populated with vortices, shocks, spiral Waves/shocks, all of which transport angular momentum outward. We elucidate the physics at each stage and show that there is an efficient outward angular momentum transport in stages (2) and (3) over most parts of the disk, with an equivalent Shakura-Sunyaev angular momentum transport parameter α in the range from 10-4 to 10-2. By carefully analyzing the flow structure around a vortex, we show why such vortices prove to be almost ideal "units" in transporting angular momentum outward, namely by positively correlating the radial and azimuthal velocity components. In converting the gravitational energy to the internal energy, we find some special cases in which entropy can remain the same while angular momentum is transported. This is different from the classical α-disk model, which results in the maximum dissipation (or entropy production). The dependence of the transport efficiency on various physical parameters are examined and effects of radiative cooling are briefly discussed as well. We conclude that Rossby Wave/vortex instability is an efficient, purely hydrodynamic mechanism for angular momentum transport in thin disks, and may find important applications in many astrophysical systems.
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Rossby Wave instability of thin accretion disks ii detailed linear theory
The Astrophysical Journal, 2000Co-Authors: Hui Li, J M Finn, R V E Lovelace, S A ColgateAbstract:In an earlier work we identi—ed a global, nonaxisymmetric instability associated with the presence of an extreme in the radial pro—le of the key function L(r) 4 (&)/i2)S2@! in a thin, inviscid, nonmagnetized accretion disk. Here &(r) is the surface mass density of the disk, )(r) is the angular rotation rate, S(r )i s the speci—c entropy, ! is the adiabatic index, and i(r) is the radial epicyclic frequency. The dispersion relation of the instability was shown to be similar to that of Rossby Waves in planetary atmospheres. In this paper, we present the detailed linear theory of this Rossby Wave instability and show that it exists for a wider range of conditions, speci—cally, for the case where there is a ii jump ˇˇ over some range of r in &(r) or in the pressure P(r). We elucidate the physical mechanism of this instability and its dependence on various parameters, including the magnitude of the ii bump ˇˇ or ii jump,ˇˇ the azimuthal mode number, and the sound speed in the disk. We —nd a large parameter range where the disk is stable to axisym- metric perturbations but unstable to the nonaxisymmetric Rossby Waves. We —nd that growth rates of the Rossby Wave instability can be high, for relative small jumps or bumps. We discuss possible D0.2) K conditions which can lead to this instability and the consequences of the instability. Subject headings: accretion, accretion diskshydrodynamicsinstabilitiesWaves
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Rossby Wave instability of keplerian accretion disks
The Astrophysical Journal, 1999Co-Authors: R V E Lovelace, Hui Li, S A Colgate, Andrew F NelsonAbstract:We find a linear instability of nonaxisymmetric Rossby Waves in a thin nonmagnetized Keplerian disk when there is a local maximum in the radial profile of a key function (r)≡(r)S2/Γ(r), where −1=(∇×v)/Σ is the potential vorticity, S=P/ΣΓ is the entropy, Σ is the surface mass density, P is the vertically integrated pressure, and Γ is the adiabatic index. We consider in detail the special case where there is a local maximum in the disk entropy profile S(r). This maximum acts to trap the Waves in its vicinity if its height-to-width ratio max(S)/Δr is larger than a threshold value. The pressure gradient derived from this entropy variation provides the restoring force for the Wave growth. We show that the trapped Waves act to transport angular momentum outward. A plausible way to produce an entropy variation is when an accretion disk is starting from negligible mass and temperature, therefore, negligible entropy. As mass accumulates by either tidal torquing, magnetic torquing, or Roche-lobe overflow, confinement of heat will lead to an entropy maximum at the outer boundary of the disk. Possible nonlinear developments from this instability include the formation of Rossby vortices and the formation of spiral shocks. What remains to be determined from hydrodynamic simulations is whether or not Rossby Wave packets (or vortices) "hold together" as they propagate radially inward.
Zhuo Wang - One of the best experts on this subject based on the ideXlab platform.
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north atlantic Rossby Wave breaking during the hurricane season association with tropical and extratropical variability
Journal of Climate, 2019Co-Authors: Gan Zhang, Zhuo WangAbstract:AbstractThis study explores the connection of Rossby Wave breaking (RWB) with tropical and extratropical variability during the Atlantic hurricane season. The exploration emphasizes subtropical ant...
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subseasonal variability of Rossby Wave breaking and impacts on tropical cyclones during the north atlantic warm season
Journal of Climate, 2018Co-Authors: Gan Zhang, Zhuo Wang, Weiwei Li, Melinda S Peng, Stanley G Benjamin, Ming ZhaoAbstract:AbstractThis study investigates the subseasonal variability of anticyclonic Rossby Wave breaking (AWB) and its impacts on atmospheric circulations and tropical cyclones (TCs) over the North Atlanti...
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north atlantic extratropical Rossby Wave breaking during the warm season Wave life cycle and role of diabatic heating
Monthly Weather Review, 2018Co-Authors: Gan Zhang, Zhuo WangAbstract:AbstractThis study investigates the life cycle of anticyclonic Rossby Wave breaking during the extended warm season (July–October) over the North Atlantic basin. It was found that upper-tropospheric breaking Waves are coupled with lower-level perturbations and can be traced back to a Wave train that extends from the North Pacific. The overturning of potential vorticity (PV) contours during Wave breaking is associated with the rapid development of an upper-level ridge, which occurs along the east coast of North America and over a warm and moist airstream. The ridge development is investigated using the PV budget analysis and trajectory analysis. The PV budget analysis suggests that the horizontal advection of PV by the perturbed flow dictates the movement and the later decay of the ridge. The ridge amplification, opposed by the horizontal advection of PV, is driven by the vertical advection and the diabatic production of PV, both of which are connected to diabatic heating. The vital role of diabatic heatin...
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linking atmospheric river hydrological impacts on the u s west coast to Rossby Wave breaking
Journal of Climate, 2017Co-Authors: Huancui Hu, Gan Zhang, Zhuo Wang, Francina Dominguez, David A Laversa, Martin F RalphAbstract:AbstractAtmospheric rivers (ARs) have significant hydrometeorological impacts on the U.S. West Coast. This study presents the connection between the characteristics of large-scale Rossby Wave breaking (RWB) over the eastern North Pacific and the regional-scale hydrological impacts associated with landfalling ARs on the U.S. West Coast (36°–49°N). ARs associated with RWB account for two-thirds of the landfalling AR events and >70% of total AR-precipitation in the winter season. The two regimes of RWB—anticyclonic Wave breaking (AWB) and cyclonic Wave breaking (CWB)—are associated with different directions of the vertically integrated water vapor transport (IVT). AWB-ARs impinge in a more westerly direction on the coast whereas CWB-ARs impinge in a more southwesterly direction.Most of the landfalling ARs along the northwestern coast of the United States (states of Washington and Oregon) are AWB-ARs. Because of their westerly impinging angles when compared to CWB-ARs, AWB-ARs arrive more orthogonally to the ...
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characteristics and impacts of extratropical Rossby Wave breaking during the atlantic hurricane season
Journal of Climate, 2017Co-Authors: Gan Zhang, Zhuo Wang, Melinda S Peng, Gudrun MagnusdottirAbstract:AbstractThis study investigates the characteristics of extratropical Rossby Wave breaking (RWB) during the Atlantic hurricane season and its impacts on Atlantic tropical cyclone (TC) activity. It was found that RWB perturbs the wind and moisture fields throughout the troposphere in the vicinity of a breaking Wave. When RWB occurs more frequently over the North Atlantic, the Atlantic main development region (MDR) is subject to stronger vertical wind shear and reduced tropospheric moisture; the basinwide TC counts are reduced, and TCs are generally less intense, have a shorter lifetime, and are less likely to make landfalls. A significant negative correlation was found between Atlantic TC activity and RWB occurrence during 1979–2013. The correlation is comparable to that with the MDR SST index and stronger than that with the Nino-3.4 index. Further analyses suggest that the variability of RWB occurrence in the western Atlantic is largely independent of that in the eastern Atlantic. The RWB occurrence in the...
Courtenay Strong - One of the best experts on this subject based on the ideXlab platform.
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the role of tropospheric Rossby Wave breaking in the pacific decadal oscillation
Journal of Climate, 2009Co-Authors: Courtenay Strong, Gudrun MagnusdottirAbstract:Abstract The leading pattern of extratropical Pacific sea surface temperature variability [the Pacific decadal oscillation (PDO)] is shown to depend on observed variability in the spatiotemporal distribution of tropospheric Rossby Wave breaking (RWB), where RWB is the irreversible overturning of potential vorticity on isentropic surfaces. Composite analyses based on hundreds of RWB cases show that anticyclonic (cyclonic) RWB is associated with a warm, moist (cool, dry) column that extends down to a surface anticyclonic (cyclonic) circulation, and that the moisture and temperature advection associated with the surface circulation patterns force turbulent heat flux anomalies that project onto the spatial pattern of the PDO. The RWB patterns that are relevant to the PDO are closely tied to El Nino–Southern Oscillation, the Pacific–North American pattern, and the northern annular mode. These results explain the free troposphere-to-surface segment of the atmospheric bridge concept wherein El Nino anomalies eme...
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tropospheric Rossby Wave breaking and the nao nam
Journal of the Atmospheric Sciences, 2008Co-Authors: Courtenay Strong, Gudrun MagnusdottirAbstract:Objective analysis of several hundred thousand anticyclonic and cyclonic breaking Rossby Waves is performed for the Northern Hemisphere (NH) winters of 1958–2006. A winter climatology of both anticyclonic and cyclonic Rossby Wave breaking (RWB) frequency and size (zonal extent) is presented for the 350-K isentropic surface over the NH, and the spatial distribution of RWB is shown to agree with theoretical ideas of RWB in shear flow. Composites of the two types of RWB reveal their characteristic sea level pressure anomalies, upper- and lower-tropospheric velocity fields, and forcing of the upper-tropospheric zonal flow. It is shown how these signatures project onto the centers of action and force the velocity patterns associated with the North Atlantic Oscillation (NAO) and Northern Hemisphere annular mode (NAM). Previous studies have presented evidence that anticyclonic (cyclonic) breaking leads to the positive (negative) polarity of the NAO, and this relationship is confirmed for RWB over the midlatitudes centered near 50°N. However, an opposite and statistically significant relationship, in which cyclonic RWB forces the positive NAO and anticyclonic RWB forces the negative NAO, is shown over regions 20° to the north and south, centered at 70° and 30°N, respectively. On a winter mean basis, the frequency of RWB over objectively defined regions covering 12% of the area of the NH accounts for 95% of the NAO index and 92% of the NAM index. A 6-hourly analysis of all the winters indicates that RWB over the objectively defined regions affects the NAO/NAM without a time lag. Details of the objective Wave-breaking analysis method are provided in the appendix.
