The Pacific decadal oscillation as a modulator of summertime North Atlantic Rossby wave breaking

2020 ◽  
Author(s):  
Breanna L. Zavadoff ◽  
Ben P. Kirtman
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Pacific Decadal Oscillation ◽  
Wave Breaking ◽  
Rossby Wave Breaking ◽  
The Pacific

scholarly journals The Role of Tropospheric Rossby Wave Breaking in the Pacific Decadal Oscillation

2009 ◽  
Vol 22 (7) ◽  
pp. 1819-1833 ◽  
Author(s):  
Courtenay Strong ◽  
Gudrun Magnusdottir
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Rossby Wave ◽  
Pacific Decadal Oscillation ◽  
Wave Breaking ◽  
El Nino ◽  
Sea Surface ◽  
Rossby Wave Breaking ◽  
The Pacific ◽  
Circulation Patterns

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 Niño–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 Niño anomalies emerge in summer and modify circulation patterns that act over several months to force sea surface temperature anomalies in the extratropical Pacific during late winter or early spring. Leading patterns of RWB account for a significant fraction of PDO interannual variability for any month of the year. A multilinear model is developed in which the January mean PDO index for 1958–2006 is regressed upon the leading principal components of cyclonic and anticyclonic RWB from the immediately preceding winter and summer months (four indexes in all), accounting for more than two-thirds of the variance.

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 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 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.

scholarly journals Characteristics and Impacts of Extratropical Rossby Wave Breaking during the Atlantic Hurricane Season

2017 ◽  
Vol 30 (7) ◽  
pp. 2363-2379 ◽  
Author(s):  
Gan Zhang ◽  
Zhuo Wang ◽  
Melinda S. Peng ◽  
Gudrun Magnusdottir
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Vertical Wind Shear ◽  
Breaking Wave ◽  
Western Basin ◽  
Western Atlantic ◽  
Rossby Wave Breaking ◽  
Atlantic Hurricane ◽  
Hurricane Season

This 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 Niño-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 western basin is more closely tied to the environmental variability of the tropical North Atlantic and is more likely to hinder TC intensification or reduce the TC lifetime because of its proximity to the central portion of TC tracks. Consequently, the basinwide TC counts and the accumulated cyclone energy have a strong correlation with western-basin RWB occurrence but only a moderate correlation with eastern-basin RWB occurrence. The results highlight the extratropical impacts on Atlantic TC activity and regional climate via RWB and provide new insights into the variability and predictability of TC activity.

Tropical Cyclones in Reduced Rossby Wave Breaking Environments

2021 ◽  
Author(s):  
Bernhard Enz ◽  
David Neubauer ◽  
Michael Sprenger ◽  
Ulrike Lohmann
Keyword(s):  
Boundary Conditions ◽  
Tropical Cyclones ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Breaking ◽  
Tropical Cyclone Activity ◽  
Cyclone Activity ◽  
Rossby Wave Breaking ◽  
The North ◽  
The North Atlantic

<p><span>Tropical cyclones are a weather phenomenon that can devastate coastlines and cause substantial harm to human life and infrastructure every year. Their seasonal prediction is an effort that has been undertaken for several decades. These predictions are generally useful and have skill. The 2013 season was predicted as above average in activity by all forecasting agencies, but was one of the least active on record. A previously proposed reason for this is the abundance of Rossby wave breaking in the north Atlantic, which dries and cools the tropics by mixing in extratropical air. While the existence of this mechanism is not disputed, other pathways linked to the interactions between tropical and extratropical air masses are suggested and evaluated in this study</span></p><p>The numerical model ICON is used in Limited Area Mode (~13 km horizontal resolution) to simulate the north Atlantic, using ERA5 data for the hurricane season of 2013 to prescribe initial and boundary conditions. To influence Rossby wave breaking, a set of simulations uses 30 day running mean boundary conditions in the northern part of the domain, while a reference set uses regular boundary conditions everywhere along the boundary. Though the results do not falsify the aforementioned hypothesis of the abundance of Rossby wave breaking influencing tropical cyclone activity, they suggest that other mechanisms, such as changes in steering flow, tropopause temperature and wind shear, could also be responsible for changes in tropical cyclone activity. Furthermore, the accumulated cyclone energy seems to be rather closely related to the mean latitude of the 2 potential vorticity unit contour on the 350 K isentropic surface within a small longitudinal window in the western Atlantic.</p>

Supplementary material to "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 ◽  
Trade Wind ◽  
Rossby Wave Breaking ◽  
Atlantic Trade ◽  
The North ◽  
Supplementary Material ◽  
The North Atlantic

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

2021 ◽  
Vol 2 (1) ◽  
pp. 281-309
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 ◽  
North East ◽  
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 d measurement campaign (isoTrades, 25 January to 17 February 2018). These data are 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 d 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 1 d 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 determine 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 occur 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 north-east, 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 north-east 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 cut-off 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 are 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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