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

Papin, Philippe; Bosart, Lance F.; Torn, Ryan D.

doi:10.1175/jcli-d-19-0812.1

Cited by 19 publications

(16 citation statements)

References 55 publications

(98 reference statements)

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“…The simulation is performed with explicit convection at a horizontal grid spacing of 0.125 • (in rotated coordinates, corresponding to approximately 14 km) and with 60 hybrid levels in the vertical. Marsham et al (2013b), Pearson et al (2014, and Pante and Knippertz (2019) showed that explicit convection leads to a more realistic representation of the West African Monsoon already with a relatively coarse model resolution on the order of 10 km. Initial and lateral boundary conditions are provided every 6 h by the isotope-enabled global climate model ECHAM5-wiso (Werner et al, 2011) at a spectral resolution of T106 (corresponding to a horizontal grid spacing of approximately 1 • ) and on 31 vertical levels.…”

Section: Cosmo Isomentioning

confidence: 99%

“…This section focuses on investigating the large-scale flow conditions associated with the four transport pathways. Previous work has shown that even during the warm season the investigation region is frequently affected by positively tilted upper-level intrusions of high potential vorticity (PV) from higher latitudes, usually associated with Rossby wave breaking over the North Atlantic (Fröhlich and Knippertz, 2008;Papin et al, 2020). Ahead of these troughs, moist mid-level air can be transported northwards around the western flank of the anticyclone overlaying the low-level SHL and lead to precipitation in north-western Africa (Knippertz et al, 2003;Knippertz, 2003).…”

Section: Associated Large-scale Flow Conditionsmentioning

confidence: 99%

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Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

et al. 2021

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Abstract. Due to its dryness, the subtropical free troposphere plays a critical role in the radiative balance of the Earth's climate system. But the complex interactions of the dynamical and physical processes controlling the variability in the moisture budget of this sensitive region of the subtropical atmosphere are still not fully understood. Stable water isotopes can provide important information about several of the latter processes, namely subsidence drying, turbulent mixing, and dry and moist convective moistening. In this study, we use high-resolution simulations of the isotope-enabled version of the regional weather and climate prediction model of the Consortium for Small-Scale Modelling (COSMOiso) to investigate predominant moisture transport pathways in the Canary Islands region in the eastern subtropical North Atlantic. Comparison of the simulated isotope signals with multi-platform isotope observations (aircraft, ground- and space-based remote sensing) from a field campaign in summer 2013 shows that COSMOiso can reproduce the observed variability of stable water vapour isotopes on timescales of hours to days, thus allowing us to study the mechanisms that control the subtropical free-tropospheric humidity. Changes in isotopic signals along backward trajectories from the Canary Islands region reveal the physical processes behind the synoptic-scale isotope variability. We identify four predominant moisture transport pathways of mid-tropospheric air, each with distinct isotopic signatures: air parcels originating from the convective boundary layer of the Saharan heat low (SHL) – these are characterised by a homogeneous isotopic composition with a particularly high δD (median mid-tropospheric δD=-122‰), which results from dry convective mixing of low-level moisture of diverse origin advected into the SHL; air parcels originating from the free troposphere above the SHL – although experiencing the largest changes in humidity and δD during their subsidence over West Africa, these air parcels typically have lower δD values (median δD=-148‰) than air parcels originating from the boundary layer of the SHL; air parcels originating from outside the SHL region, typically descending from tropical upper levels south of the SHL, which are often affected by moist convective injections from mesoscale convective systems in the Sahel – their isotopic composition is much less enriched in heavy isotopes (median δD=-175‰) than those from the SHL region; air parcels subsiding from the upper-level extratropical North Atlantic – this pathway leads to the driest and most depleted conditions (median δD=-255‰) in the middle troposphere near the Canary Islands. The alternation of these transport pathways explains the observed high variability in humidity and δD on synoptic timescales to a large degree. We further show that the four different transport pathways are related to specific large-scale flow conditions. In particular, distinct differences in the location of the North African mid-level anticyclone and of extratropical Rossby wave patterns occur between the four transport pathways. Overall, this study demonstrates that the adopted Lagrangian isotope perspective enhances our understanding of air mass transport and mixing and offers a sound interpretation of the free-tropospheric variability of specific humidity and isotope composition on timescales of hours to days in contrasting atmospheric conditions over the eastern subtropical North Atlantic.

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Section: Cosmo Isomentioning

confidence: 99%

Section: Associated Large-scale Flow Conditionsmentioning

confidence: 99%

Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

et al. 2021

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“…2) can be applied independently on the number of dimensions and can therefore be used the same way. Existing identification techniques (see an overview of them in Papin et al, 2020) rely on following the 2-PVU boundary, and searching points along this boundary meeting certain criteria. However in 3-D, there is no unique direction to follow the dynamical tropopause, making such techniques not applicable.…”

Section: Strategymentioning

confidence: 99%

“…Recently, combination of state-of-the-art interactive 3-D visualization techniques (Rautenhaus et al, 2018, provide a comprehensive survey) with 3-D detection of atmospheric features opened the door for comprehensive case studies of 3-D atmospheric dynamics (e.g., Rautenhaus et al, 2015a;Kern et al, 2018Kern et al, , 2019Bader et al, 2019). With respect to objective identification of PV structures, Papin et al (2020) recently provided an overview of identification techniques for PVSs. They classified the methods into techniques based on the reversal of the meridional PV gradient, and techniques based on distance thresholds along a 2-PVU contour.…”

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confidence: 99%

A novel method for objective identification of 3-D potential vorticity anomalies

Fischer

Fink

Schömer

et al. 2022

Preprint

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Abstract. Potential vorticity (PV) analysis plays a central role in studying atmospheric dynamics and in particular in studying the life cycle of weather systems. The three-dimensional (3-D) structure and temporal evolution of the associated PV anomalies, however, are not yet fully understood. An automated technique to objectively identify 3-D PV anomalies can help to shed light on 3-D atmospheric dynamics in specific case studies, as well as facilitate statistical evaluations within climatological studies. Such a technique to identify PV anomalies fully in 3-D, however, does not yet exist. This study presents a novel algorithm for the objective identification of PV anomalies in gridded data, as commonly output by numerical simulation models. The algorithm is inspired by morphological image processing techniques and can be applied to both two-dimensional (2-D) and 3-D fields on vertically isentropic levels. The method maps input data to a horizontally stereographic projection and relies on an efficient computation of horizontal distances within the projected field. Candidates for PV anomaly features are filtered according to heuristic criteria, and feature description vectors are obtained for further analysis. The generated feature descriptions are well suited for subsequent case studies of 3-D atmospheric dynamics as represented by the underlying numerical simulation, or for generation of climatologies of feature characteristics. We evaluate our approach by comparison with an existing 2-D technique, and demonstrate the full 3-D perspective by means of a case study of an extreme precipitation event that was dynamically linked to a prominent subtropical PV anomaly. The case study demonstrates variations in the 3-D structure of the detected PV anomalies that would not have been captured by a 2-D method. We discuss further advantages of using a 3-D approach, including elimination of temporal inconsistencies in the detected features due to 3-D structural variation, and elimination of the need to manually select a specific isentropic level on which the anomalies are assumed to be best captured. The method is made available as open-source for straightforward use by the atmospheric community.

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“…It occurs when the background flow is weak and the latitudinal potential vorticity (PV) gradient is small so that the waves become nonlinear and eventually break (Li et al., 2018; McIntyre & Palmer, 1983; Strong & Magnusdottir, 2008a; Tyrlis & Hoskins, 2008). Accompanied by deforming and overturning of the PV contours, the RWB leads to the exchange of heat, momentum and moisture between the tropics and extratropics (e.g., Papin et al., 2020). The occurrence of the RWB can modulate the interaction between high and low latitudes (Li et al., 2018), and it links the mid‐latitude weather systems and the Madden‐Julian oscillation (Cassou, 2008; Li et al., 2018; MacRitchie & Roundy, 2016).…”

Section: Introductionmentioning

confidence: 99%

Two Types of Rossby Wave Breaking Events and Their Influences on East Asian Winter Temperature

Song

2021

JGR Atmospheres

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Manifested as irreversible overturning of potential temperature contours on the tropopause, the Rossby wave breaking (RWB) can impact mid‐latitude weather and climate. Little attention has been paid to the influence of the Rossby wave breaking around East Asia on the East Asian winter climate. The present study reveals that anticyclonic wave breaking (AWB) and cyclonic wave breaking (CWB) events over Siberia and the North Pacific can impact East Asian winter temperature through different dynamical processes. The AWB events are characterized as northeastward intrusion of low‐potential vorticity (PV) air from the subtropics and southwestward extension of high‐PV air from the high latitudes over the western Siberia. The positive Arctic Oscillation (AO) during the AWB is accompanied by a wave train over Eurasia, contributing to the enhancement of the Siberian high, which causes cold anomalies over East Asia. The CWB events are manifested as northwestward intrusion of low‐PV air from the middle latitudes and southeastward extension of high‐PV air from the high latitudes over the western North Pacific. The CWB events are associated with the westward retrogression of the blocking over the North Pacific, leading to intensification of the Siberian high. Furthermore, the CWB forces cyclonic anomalies over East Asia, leading to the deepening of the East Asian trough and cold anomalies there. In addition, the CWB events over the western North Pacific can impact the climate over North America via the Rossby wave train emanating from the CWB region.

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

Cited by 19 publications

References 55 publications

Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

Disentangling different moisture transport pathways over the eastern subtropical North Atlantic using multi-platform isotope observations and high-resolution numerical modelling

A novel method for objective identification of 3-D potential vorticity anomalies

Two Types of Rossby Wave Breaking Events and Their Influences on East Asian Winter Temperature

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