scholarly journals The Shift of the Northern Node of the NAO and Cyclonic Rossby Wave Breaking

2012 ◽  
Vol 25 (22) ◽  
pp. 7973-7982 ◽  
Author(s):  
Yi-Hui Wang ◽  
Gudrun Magnusdottir
Keyword(s):  
Rossby Wave ◽  
Wave Breaking ◽  
Geographical Location ◽  
Mean Flow ◽  
Decadal Time Scale ◽  
Rossby Wave Breaking ◽  
The North ◽  
The Mean ◽  
The Difference ◽  
The North Atlantic Oscillation

Abstract Several 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 two subdomains in 6-hourly instantaneous data. The forcing of the mean flow due to cyclonic RWB within individual subdomains is found to be locally restricted to where the breaking occurs, which is usually near the jet exit region and far removed from the jet core. The difference in the jet between the NE and SW composites resembles the difference in the mean jet between the 1978–97 and 1958–77 periods, which suggests that the change in cyclonic RWB occurrence in the two subdomains is associated with the wobbling of the jet on the decadal time scale.

scholarly journals Tropospheric Rossby Wave Breaking and the NAO/NAM

2008 ◽  
Vol 65 (9) ◽  
pp. 2861-2876 ◽  
Author(s):  
Courtenay Strong ◽  
Gudrun Magnusdottir
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
Wave Breaking ◽  
Time Lag ◽  
Zonal Flow ◽  
Sea Level Pressure ◽  
Rossby Wave Breaking ◽  
The North ◽  
Nao Index ◽  
The North Atlantic Oscillation

Abstract 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.

North Atlantic Summertime Anticyclonic Rossby Wave Breaking: Climatology, Impacts, and Connections to the Pacific Decadal Oscillation

2018 ◽  
Vol 32 (2) ◽  
pp. 485-500 ◽  
Author(s):  
Breanna L. Zavadoff ◽  
Ben P. Kirtman
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Pacific Decadal Oscillation ◽  
Wave Breaking ◽  
Reanalysis Data ◽  
Tropical Cyclogenesis ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Anticyclonic Rossby wave breaking (RWB) is characterized by the rapid and irreversible deformation of potential vorticity (PV) contours on isentropic surfaces manifesting as a pair of meridionally elongated high- and low-PV tongues that transport extratropical stratospheric air equatorward and tropical tropospheric air poleward, respectively. Previous studies have noted connections between different types of RWB and the modulation of localized atmospheric phenomena such as the North Atlantic Oscillation (NAO) and tropical cyclogenesis. Despite being the season in which anticyclonic RWB events are most prevalent, no work has focused solely on the frequency, genesis, or variability of the synoptic environment surrounding the equatorward branch of anticyclonic RWB events during the North Atlantic summertime, providing motivation for this study. Using 58 years (1960–2017) of NCEP–NCAR reanalysis data, a comprehensive spatiotemporal climatology of North Atlantic equatorward anticyclonic RWB identified on the 350-K isentropic surface is developed and the synoptic environment surrounding these events from time- and high-PV-tongue centroid-relative perspectives is investigated. Consistent with previous studies, composites suggest that high-PV tongues associated with equatorward anticyclonic RWB introduce anomalously dry, stable extratropical air into the tropical environment, subsequently inhibiting convection there. Additionally, a connection between atmospheric responses to Pacific decadal oscillation (PDO) sea surface temperature (SST) anomalies and the intrabasin frequency of anticyclonic RWB events is uncovered and explored. Results from this study may aid short- to medium-range forecasts of North Atlantic tropical convection, with applications extending into the field of tropical cyclogenesis forecasting.

scholarly journals A New Perspective toward Cataloging Northern Hemisphere Rossby Wave Breaking on the Dynamic Tropopause

2019 ◽  
Vol 147 (2) ◽  
pp. 409-431 ◽  
Author(s):  
Kevin A. Bowley ◽  
John R. Gyakum ◽  
Eyad H. Atallah
Keyword(s):  
Rossby Wave ◽  
North Pacific ◽  
Wave Breaking ◽  
Potential Temperature ◽  
Low Frequency ◽  
The Arctic ◽  
Rossby Wave Breaking ◽  
Modes Of Variability ◽  
The North ◽  
The North Atlantic Oscillation

Abstract Rossby wave breaking (RWB) events are a common feature on the dynamic tropopause and act to modulate synoptic-scale jet dynamics. These events are characterized on the dynamic tropopause by an irreversible overturning of isentropes and are coupled to troposphere-deep vertical motions and geopotential height anomalies. Prior climatologies have focused on the poleward streamer, the equatorward streamer, or the reversal in potential temperature gradient between the streamers, resulting in differences in the frequencies of RWB. Here, a new approach toward cataloging these events that captures both streamers is applied to the National Centers for Environmental Prediction Reanalysis-2 dataset for 1979–2011. Anticyclonic RWB (AWB) events are found to be nearly twice as frequent as cyclonic RWB (CWB) events. Seasonal decompositions of the annual mean find AWB to be most common in summer (40% occurrence), which is likely due to the Asian monsoon, while CWB is most frequent in winter (22.5%) and is likely due to the equatorward shift in mean baroclinicity. Trends in RWB from 1980 to 2010 illustrate a westward shift in North Pacific AWB during winter and summer (up to 0.4% yr−1), while CWB in the North Pacific increases in winter and spring (up to 0.2% yr−1). These changes are hypothesized to be associated with localized changes in the two-way interaction between the jet and RWB. The interannual variability of AWB and CWB is also explored, and a notable modality to the frequency of RWB is found that may be attributable to known low-frequency modes of variability including the Arctic Oscillation, the North Atlantic Oscillation, and the Pacific–North American pattern.

scholarly journals Links between Rossby Wave Breaking and the North Atlantic Oscillation–Arctic Oscillation in Present-Day and Last Glacial Maximum Climate Simulations

2010 ◽  
Vol 23 (11) ◽  
pp. 2987-3008 ◽  
Author(s):  
Gwendal Rivière ◽  
Alexandre Laîné ◽  
Guillaume Lapeyre ◽  
David Salas-Mélia ◽  
Masa Kageyama
Keyword(s):  
North Atlantic Oscillation ◽  
Last Glacial Maximum ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Arctic Oscillation ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic ◽  
The North Atlantic Oscillation

Abstract Upper-tropospheric Rossby wave–breaking processes are examined in coupled ocean–atmosphere simulations of the Last Glacial Maximum (LGM) and of the modern era. LGM statistics of the Northern Hemisphere in winter, computed from the Paleoclimate Modeling Intercomparison Project Phase II (PMIP2) dataset, are compared with those from preindustrial simulations and from the 40-yr ECMWF Re-Analysis (ERA-40). Particular attention is given to the role of wave-breaking events in the North Atlantic Oscillation (NAO) for each simulation. Anticyclonic (AWB) and cyclonic (CWB) wave-breaking events during LGM are shown to be less and more frequent, respectively, than in the preindustrial climate, especially in the Pacific. This is consistent with the slight equatorward shift of the eddy-driven jets in the LGM runs. The most remarkable feature of the simulated LGM climate is that it presents much weaker latitudinal fluctuations of the eddy-driven jets. This is accompanied by less dispersion in the wave-breaking events. A physical interpretation is provided in terms of the fluctuations of the low-level baroclinicity at the entrance of the storm tracks. The NAO in the preindustrial simulations and in ERA-40 is characterized by strong latitudinal fluctuations of the Atlantic eddy-driven jet as well as by significant changes in the nature of the wave breaking. During the positive phase, the eddy-driven jet moves to the north with more AWB events than usual and is well separated from the subtropical African jet. The negative phase exhibits a more equatorward Atlantic jet and more CWB events. In contrast, the LGM NAO is less well marked by the latitudinal vacillation of the Atlantic jet and for some models this property disappears entirely. The LGM NAO corresponds more to acceleration–deceleration or extension–retraction of the Atlantic jet. The hemispheric point of view of the Arctic Oscillation exhibits similar changes.

scholarly journals A New Rossby Wave–Breaking Interpretation of the North Atlantic Oscillation

2008 ◽  
Vol 65 (2) ◽  
pp. 609-626 ◽  
Author(s):  
Tim Woollings ◽  
Brian Hoskins ◽  
Mike Blackburn ◽  
Paul Berrisford
Keyword(s):  
North Atlantic Oscillation ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Low Frequency ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic ◽  
Hemisphere Winter ◽  
The North Atlantic Oscillation

Abstract This paper proposes the hypothesis that the low-frequency variability of the North Atlantic Oscillation (NAO) arises as a result of variations in the occurrence of upper-level Rossby wave–breaking events over the North Atlantic. These events lead to synoptic situations similar to midlatitude blocking that are referred to as high-latitude blocking episodes. A positive NAO is envisaged as being a description of periods in which these episodes are infrequent and can be considered as a basic, unblocked situation. A negative NAO is a description of periods in which episodes occur frequently. A similar, but weaker, relationship exists between wave breaking over the Pacific and the west Pacific pattern. Evidence is given to support this hypothesis by using a two-dimensional potential-vorticity-based index to identify wave breaking at various latitudes. This is applied to Northern Hemisphere winter data from the 40-yr ECMWF Re-Analysis (ERA-40), and the events identified are then related to the NAO. Certain dynamical precursors are identified that appear to increase the likelihood of wave breaking. These suggest mechanisms by which variability in the tropical Pacific, and in the stratosphere, could affect the NAO.

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.

scholarly journals A Feature-Based Approach to Classifying Summertime Potential Vorticity Streamers Linked to Rossby Wave Breaking in the North Atlantic Basin

2020 ◽  
Vol 33 (14) ◽  
pp. 5953-5969 ◽  
Author(s):  
Philippe P. Papin ◽  
Lance F. Bosart ◽  
Ryan D. Torn
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Potential Vorticity ◽  
Wave Breaking ◽  
Activity Index ◽  
Static Stability ◽  
Japan Meteorological Agency ◽  
Average Intensity ◽  
Rossby Wave Breaking ◽  
The North

AbstractThis study examines climatological potential vorticity streamer (PVS) activity associated with Rossby wave breaking (RWB), which can impact TC activity in the subtropical North Atlantic (NATL) basin via moisture and wind anomalies. PVSs are identified along the 2-PVU (1 PVU = 10−6 K kg−1 m2 s−1) contour on the 350-K isentropic surface, using a unique identification technique that combines previous methods. In total, 21 149 individual PVS instances are identified from the ERA-Interim (ERAI) climatology during June–November over 1979–2015 with a peak in July–August. The total number of PVSs identified in this study is more than previous PVS climatologies for this region, since the new technique identifies a wider range of cases. Variations in PVS size and intensity prompt the development of a new PVS activity index (PVSI), which provides an integrated measure of PVS activity that can improve comparisons with TC activity. For instance, PVSI has a stronger negative correlation with seasonal TC activity (r = −0.55) relative to PVS frequency, size, or intensity alone. PVSI in June–July is also positively correlated with PVSI in August–November (r = 0.67), suggesting predictive capability. Compared to the ERAI and Japan Meteorological Agency 55-Year Reanalysis (JRA-55) climatology, there are more PVSs in the Climate Forecast System Reanalysis (CFSR) but these have weaker average intensity overall. While no long-term trend in PVSI is observed in the ERAI or JRA-55 climatologies, a negative trend is observed in CFSR, which could be related to differences in near tropopause static stability early in the climatological period (1979–86) between the CFSR and ERAI datasets.

scholarly journals Linking air stagnation in Europe with the synoptic- to large-scale atmospheric circulation

2021 ◽  
Vol 2 (3) ◽  
pp. 675-694
Author(s):  
Jacob W. Maddison ◽  
Marta Abalos ◽  
David Barriopedro ◽  
Ricardo García-Herrera ◽  
Jose M. Garrido-Perez ◽  
...  
Keyword(s):  
Rossby Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Climate Models ◽  
Large Scale Circulation ◽  
Rossby Wave Breaking ◽  
The North ◽  
Northern Regions ◽  
Climatic Impacts ◽  
Large Scale Atmospheric Circulation

Abstract. The build-up of pollutants to harmful levels can occur when meteorological conditions favour their production or accumulation near the surface. Such conditions can arise when a region experiences air stagnation. The link between European air stagnation, air pollution and the synoptic- to large-scale circulation is investigated in this article across all seasons and the 1979–2018 period. Dynamical indices identifying atmospheric blocking, Rossby wave breaking, subtropical ridges, and the North Atlantic eddy-driven and subtropical jets are used to describe the synoptic- to large-scale circulation as predictors in statistical models of air stagnation and pollutant variability. It is found that the large-scale circulation can explain approximately 60 % of the variance in monthly air stagnation, ozone and wintertime particulate matter (PM) in five distinct regions within Europe. The variance explained by the model does not vary strongly across regions and seasons, apart from for PM when the skill is highest in winter. However, the dynamical indices most related to air stagnation do depend on region and season. The blocking and Rossby wave breaking predictors tend to be the most important for describing air stagnation and pollutant variability in northern regions, whereas ridges and the subtropical jet are more important to the south. The demonstrated correspondence between air stagnation, pollution and the large-scale circulation can be used to assess the representation of stagnation in climate models, which is key for understanding how air stagnation and its associated climatic impacts may change in the future.

scholarly journals How Rossby wave breaking modulates the water cycle in the North Atlantic trade wind region

2020 ◽  
Author(s):  
Franziska Aemisegger ◽  
Raphaela Vogel ◽  
Pascal Graf ◽  
Fabienne Dahinden ◽  
Leonie Villiger ◽  
...  
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Water Cycle ◽  
Cloud Layer ◽  
Trade Wind ◽  
Rossby Wave Breaking ◽  
Atlantic Trade ◽  
The North ◽  
The Caribbean

Abstract. The interaction between low-level tropical clouds and the large-scale circulation is a key feedback element in our climate system, but our understanding of it is still fragmentary. In this paper, the role of upper-level extratropical dynamics for the development of contrasting shallow cumulus cloud patterns in the western North Atlantic trade wind region is investigated. Stable water isotopes are used as tracers for the origin of air parcels arriving in the sub-cloud layer above Barbados, measured continuously in water vapour at the Barbados Cloud Observatory during a 24-day measurement campaign (isoTrades, 25 January to 17 February 2018). This data is combined with a detailed air parcel back-trajectory analysis using hourly ERA5 reanalyses of the European Centre for Medium Range Weather Forecasts. A climatological investigation of the 10-day air parcel history for January and February in the recent decade shows that 55 % of the air parcels arriving in the sub-cloud layer have spent at least one day in the extratropics (north of 35° N) before arriving in the eastern Caribbean at about 13° N. In 2018, this share of air parcels with extratropical origin was anomalously large with 88 %. In two detailed case studies during the campaign, two flow regimes with distinct isotope signatures transporting extratropical air into the Caribbean are investigated. In both regimes, the air parcels descend from the lower part of the midlatitude jet stream towards the equator, at the eastern edge of subtropical anticyclones, in the context of Rossby wave breaking events. The zonal location of the wave breaking, and the surface anticyclone, determines the dominant transport regime. The first regime represents the typical trade wind situation with easterly winds bringing moist air from the eastern North Atlantic into the Caribbean, in a deep layer from the surface up to ∼600 hPa. The moisture source of the sub-cloud layer water vapour is located on average 2000 km upstream of Barbados. In this regime, Rossby wave breaking and the descent of air from the extratropics occurs in the eastern North Atlantic, at about 33° W. The second regime is associated with air parcels descending slantwise by on average 300 hPa (6 d)-1 directly from the northeast, i.e., at about 50° W. These originally dry airstreams experience a more rapid moistening than typical trade wind air parcels when interacting with the subtropical oceanic boundary layer, with moisture sources being located on average 1350 km upstream to the northeast of Barbados. The descent of dry air in the second regime can be steered towards the Caribbean by the interplay of a persistent upper-level cutoff low over the central North Atlantic (about 45° W) and the associated surface cyclone underneath. The zonal location of Rossby wave breaking, and consequently, the pathway of extratropical air towards the Caribbean, is shown to be relevant for the sub-cloud layer humidity and shallow cumulus cloud cover properties of the North Atlantic winter trades. Overall, this study highlights the importance of extratropical dynamical processes for the tropical water cycle and reveals that these processes lead to a substantial modulation of stable water isotope signals in the near-surface humidity.

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