scholarly journals A Description and Evaluation of an Automated Approach for Feature-Based Tracking of Rossby Wave Packets

2014 ◽  
Vol 142 (10) ◽  
pp. 3505-3527 ◽  
Author(s):  
Matthew B. Souders ◽  
Brian. A. Colle ◽  
Edmund K. M. Chang
Keyword(s):  
Rossby Wave ◽  
Wave Packets ◽  
Cost Optimization ◽  
Hybrid Approach ◽  
Storm Track ◽  
Meridional Wind ◽  
Hybrid Technique ◽  
Local Maxima ◽  
Temporal Smoothing ◽  
Feature Based

Abstract This paper describes an automated approach to track Rossby wave packets (RWPs), and the sensitivity of various tracking parameters and methods used in filtering the raw data in the feature-based tracking. The NCEP–NCAR reanalysis meridional wind and geopotential height data at 300 hPa every 6 h were spectrally filtered using a Hilbert transform technique under the assumption that RWPs propagate along a waveguide defined by the 14-day running average of the 300-hPa wind. After some spatial and temporal smoothing, the local maxima in RWP amplitude (WPA) were tracked using two objective techniques: a point-based cost optimization routine and a hybrid approach using point identification and object-based tracking following rules. A variation of the total energy flux term of the eddy kinetic energy equation was used to subjectively verify RWP tracks in order to compare the performance of each tracking method. When tracking methods are verified over two winter seasons, the hybrid technique outperformed point-based tracking, particularly for track duration and propagation. Problems with tracking were found to be most common during periods when two RWPs merge, one RWP splits into multiple packets, or an RWP moves from one storm track to another. RWPs are found to move irregularly rather than linearly, with their motion and intensity best described as pulse like. The sensitivity to some of the parameters used in the tracking was also explored.

An Integrated Geometric and Topological Approach for the Identification and Visual Analysis of Rossby Wave Packets

2020 ◽  
Vol 148 (8) ◽  
pp. 3139-3155
Author(s):  
Karran Pandey ◽  
Joy Merwin Monteiro ◽  
Vijay Natarajan
Keyword(s):  
Rossby Wave ◽  
Wind Field ◽  
Visual Analysis ◽  
Wave Packets ◽  
Dual Graph ◽  
Meridional Wind ◽  
Local Maxima ◽  
Hourly Data ◽  
Gradient Based ◽  
Association Graph

Abstract A new method for identifying Rossby wave packets (RWPs) using 6-hourly data from the ERA-Interim is presented. The method operates entirely in the spatial domain and relies on the geometric and topological properties of the meridional wind field to identify RWPs. The method represents RWPs as nodes and edges of a dual graph instead of the more common envelope representation. This novel representation allows access to both RWP phase and amplitude information. Local maxima and minima of the meridional wind field are collected into groups. Each group, called a υ-max cluster or υ-min cluster of the meridional wind field, represents a potential wave component. Nodes of the dual graph represent a υ-max cluster or υ-min cluster. Alternating υ-max clusters and υ-min clusters are linked by edges of the dual graph, called the RWP association graph. Amplitude and discrete gradient-based filtering applied on the association graph helps identify RWPs of interest. The method is inherently robust against noise and does not require smoothing of the input data. The main parameters that control the performance of the method and their impact on the identified RWPs are discussed. All filtering and RWP identification operations are performed on the association graph as opposed to directly on the wind field, leading to computational efficiency. Advantages and limitations of the method are discussed and are compared against (transform-based) envelope methods in a series of experiments.

Local Finite-Amplitude Wave Activity as a Diagnostic for Rossby Wave Packets

2018 ◽  
Vol 146 (12) ◽  
pp. 4099-4114 ◽  
Author(s):  
Paolo Ghinassi ◽  
Georgios Fragkoulidis ◽  
Volkmar Wirth
Keyword(s):  
Rossby Wave ◽  
Model Simulation ◽  
Wave Packets ◽  
Meridional Wind ◽  
Finite Amplitude ◽  
Wave Activity ◽  
Amplitude Wave ◽  
High Impact Weather ◽  
Finite Amplitude Wave Activity ◽  
Isentropic Coordinates

AbstractUpper-tropospheric Rossby wave packets (RWPs) are important dynamical features, because they are often associated with weather systems and sometimes act as precursors to high-impact weather. The present work introduces a novel diagnostic to identify RWPs and to quantify their amplitude. It is based on the local finite-amplitude wave activity (LWA) of Huang and Nakamura, which is generalized to the primitive equations in isentropic coordinates. The new diagnostic is applied to a specific episode containing large-amplitude RWPs and compared with a more traditional diagnostic based on the envelope of the meridional wind. In this case, LWA provides a more coherent picture of the RWPs and their zonal propagation. This difference in performance is demonstrated more explicitly in the framework of an idealized barotropic model simulation, where LWA is able to follow an RWP into its fully nonlinear stage, including cutoff formation and wave breaking, while the envelope diagnostic yields reduced amplitudes in such situations.

scholarly journals Implications of the Semigeostrophic Nature of Rossby Waves for Rossby Wave Packet Detection

2015 ◽  
Vol 143 (1) ◽  
pp. 26-38 ◽  
Author(s):  
Gabriel Wolf ◽  
Volkmar Wirth
Keyword(s):  
Wave Packet ◽  
Rossby Wave ◽  
Hilbert Transform ◽  
Wave Packets ◽  
Meridional Wind ◽  
Coordinate Space ◽  
Single Wave ◽  
Planetary Scale ◽  
Complex Demodulation ◽  
The Hilbert Transform

Abstract Upper-tropospheric Rossby wave packets have received increased attention recently. In most previous studies wave packets have been detected by computing the envelope of the meridional wind field using either complex demodulation or a Hilbert transform. The latter requires fewer choices to be made and appears, therefore, preferable. However, the Hilbert transform is fraught with a significant problem, namely, a tendency that fragments a single wave packet into several parts. The problem arises because Rossby wave packets show substantial deviations from the almost-plane wave paradigm, a feature that is well represented by semigeostrophic dynamics. As a consequence, higher harmonics interfere with the reconstruction of the wave envelope leading to undesirable wiggles. A possible cure lies in additional smoothing (e.g., by means of a filter) or resorting to complex demodulation (which implies smoothing, too). Another possibility, which does not imply any smoothing, lies in applying the Hilbert transform in semigeostrophic coordinate space. It turns out beneficial to exclude planetary-scale wavenumbers from this transformation in order to avoid problems in cases when the wave packet travels on a low wavenumber quasi-stationary background flow.

scholarly journals The Climatology and Characteristics of Rossby Wave Packets Using a Feature-Based Tracking Technique

2014 ◽  
Vol 142 (10) ◽  
pp. 3528-3548 ◽  
Author(s):  
Matthew B. Souders ◽  
Brian A. Colle ◽  
Edmund K. M. Chang
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
Large Scale ◽  
Arctic Oscillation ◽  
Southern Oscillation ◽  
Wave Packets ◽  
The Arctic ◽  
Average Intensity ◽  
Feature Based ◽  
The Arctic Oscillation

Abstract This paper describes an objective, track-based climatology of Rossby wave packets (RWPs). NCEP–NCAR reanalysis wind and geopotential height data at 300 hPa every 6 h were spectrally filtered using a Hilbert transform technique under the assumption that RWPs propagate along a waveguide defined by the 14-day running average of the 300-hPa wind. Track data and feature-based descriptive statistics, including area, average intensity, intensity volume (intensity multiplied by area), intensity-weighted centroid position, and velocity, were gathered to describe the interannual, annual, seasonal, and regime-based climatology of RWPs. RWPs have a more pronounced seasonal cycle in the Northern Hemisphere (NH) than the Southern Hemisphere (SH). RWPs are nearly nonexistent in the summer months (June–August; JJA) in the NH, while there is nearly continuous RWP activity downstream of South Africa during austral summer (December–February; DJF). Interannual variability in RWP frequency and intensity in the Northern Hemisphere is found to be strongly connected with the large-scale flow regimes such as El Niño–Southern Oscillation and the Arctic Oscillation. Enhanced RWP activity is also found to coherently propagate from the Pacific into the Atlantic on average when the Arctic Oscillation switches from a positive to a negative phase. No significant long-term (~30 yr) trend in RWP frequency, activity, or amplitude is found.

scholarly journals Recurrent Synoptic-Scale Rossby Wave Patterns and Their Effect on the Persistence of Cold and Hot Spells

2019 ◽  
Vol 32 (11) ◽  
pp. 3207-3226 ◽  
Author(s):  
Matthias Röthlisberger ◽  
Linda Frossard ◽  
Lance F. Bosart ◽  
Daniel Keyser ◽  
Olivia Martius
Keyword(s):  
Rossby Wave ◽  
Wave Packets ◽  
Meridional Wind ◽  
Wave Pattern ◽  
High Impact ◽  
Synoptic Scale ◽  
Transient Wave ◽  
Impact Surface ◽  
Surface Weather ◽  
Hot Spells

Abstract The persistence of surface weather during several recent high-impact weather events has been pivotal in generating their societal impact. Here we examine Hovmöller diagrams of the 250-hPa meridional wind during several periods with particularly persistent surface weather and find a common pattern in these Hovmöller diagrams. This pattern can be characterized as a “recurrent Rossby wave pattern” (RRWP), arising from multiple transient synoptic-scale wave packets. During such RRWP periods, individual troughs and ridges forming the wave packets repeatedly amplify in the same geographical region. We discuss the synoptic evolution of two RRWP periods, in February–March 1987 and July–August 1994, and illustrate how the recurrence of the transient wave packets led to unusually long-lasting cold and hot spells, which occurred simultaneously in several regions, each separated by roughly one synoptic wavelength. Furthermore, a simple index termed R is proposed to identify RRWPs, which is based on both a time and wavenumber filter applied to conventional Hovmöller diagrams. A Weibull regression analysis then shows that large values of R are statistically significantly linked to increased durations of winter cold and summer hot spells in large areas of the Northern Hemisphere midlatitudes. Traditionally, persistent high-impact surface weather has often been linked to the occurrence of proximate atmospheric blocking. In contrast to blocking, RRWPs affect persistent surface temperature anomalies over multiple synoptic wavelengths. We therefore argue that, in addition to blocking, RRWPs should be considered as an important flow feature leading to persistent high-impact surface weather.

Comparison of Wave Packets Associated with Extratropical Transition and Winter Cyclones

2015 ◽  
Vol 143 (5) ◽  
pp. 1782-1803 ◽  
Author(s):  
Ryan D. Torn ◽  
Gregory J. Hakim
Keyword(s):  
Wave Packets ◽  
Storm Track ◽  
Moisture Flux ◽  
Meridional Wind ◽  
Extratropical Transition ◽  
Climate Forecast System Reanalysis ◽  
Atlantic Basin ◽  
Moisture Flux Convergence ◽  
Development Structure ◽  
Midlatitude Cyclones

Abstract Differences in the development of wave packets associated with midlatitude cyclones and the extratropical transition (ET) of tropical cyclones in the western North Pacific (WNP) and Atlantic basins are diagnosed observationally by compositing Climate Forecast System Reanalysis (CFSR) data over a 32-yr period and applying the null hypothesis of no difference in the development, structure, propagation, or downstream extent. While the development of midlatitude cyclones during the fall (August–October) and winter (November–March) amplifies a preexisting wave packet moving through the midlatitude storm track, ET is associated with the quasi-stationary amplification of the midlatitude flow. The ET cases involving the interaction of the decaying TC with a preexisting midlatitude trough are associated with a greater downstream amplitude and longer-lasting downstream response than ET cases that do not involve the interaction with a trough. In the WNP, ET wave packets have greater amplitude than those associated with winter midlatitude cyclones, but are similar to those associated with fall midlatitude cyclones. Moreover, ET events are associated with larger wavelengths and a statistically significant meridional wind anomaly farther downstream. By contrast, ET wave packets in the Atlantic basin have less amplitude and do not reach as far downstream as wave packets associated with fall and winter cyclones. WNP ET is characterized by larger integrated moisture flux convergence and, thus, latent heat release relative to its midlatitude counterpart, while Atlantic basin ET has smaller moisture flux convergence compared to midlatitude cyclones, which could explain why Atlantic ET is associated with less-amplified wave packets.

scholarly journals Hybrid technique of virtual-assisted lung mapping and systemic indocyanine green injection for extended segmentectomy

2020 ◽  
Vol 6 (1) ◽  
Author(s):  
Masahiro Yanagiya ◽  
Noriko Hiyama ◽  
Jun Matsumoto
Keyword(s):  
Indocyanine Green ◽  
Hybrid Approach ◽  
Lung Nodule ◽  
Adenocarcinoma In Situ ◽  
Hybrid Technique ◽  
Medical Checkup ◽  
Resection Line ◽  
Intersegmental Plane ◽  
Computed Tomography Image ◽  
Dye Marking

Abstract Background Various approaches have been used to assist and facilitate segmentectomy with favorable oncological outcomes. We describe a hybrid approach comprising virtual-assisted lung mapping (VAL-MAP), which is a preoperative bronchoscopic dye-marking technique, combined with systemic indocyanine green (ICG) injection. Clinical presentation An asymptomatic 64-year-old man was referred to our department because of a lung nodule detected during his annual medical checkup. The chest computed-tomography image revealed a 16-mm, partly solid, ground-glass nodule in the left segment 4. Because the nodule was hardly palpable and deeply located between the left upper division segment and the left lingular segment, we performed VAL-MAP to facilitate extended left lingulectomy. Five dye markings were undertaken preoperatively. Surgery to remove the nodule was then conducted via complete three-port video-assisted thoracic surgery. The VAL-MAP markings were easily identified intraoperatively and helped locate the nodule. The intersegmental plane was identified by the ICG injection. The resection line was determined based on the intersegmental plane identified by the ICG injection and the site of the nodule suggested by the VAL-MAP markings. Following the resection line, we thoracoscopically achieved extended lingulectomy with sufficient surgical margins. The patient was discharged with no complications. The pathological diagnosis was adenocarcinoma in situ. Conclusion The hybrid technique of VAL-MAP and systemic ICG injection can be useful for accomplishing successful extended segmentectomy.

scholarly journals Lifting restrictions on coherence loss when characterizing non-transparent hypersonic phononic crystals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Konrad Rolle ◽  
Dmytro Yaremkevich ◽  
Alexey V. Scherbakov ◽  
Manfred Bayer ◽  
George Fytas
Keyword(s):  
Frequency Domain ◽  
Hybrid Approach ◽  
Three Dimensional ◽  
Phononic Crystals ◽  
Hybrid Technique ◽  
Detection Mechanism ◽  
Pump Probe ◽  
Fabry Perot ◽  
Multilayer Stacks ◽  
Deposition Techniques

AbstractHypersonic phononic bandgap structures confine acoustic vibrations whose wavelength is commensurate with that of light, and have been studied using either time- or frequency-domain optical spectroscopy. Pulsed pump-probe lasers are the preferred instruments for characterizing periodic multilayer stacks from common vacuum deposition techniques, but the detection mechanism requires the injected sound wave to maintain coherence during propagation. Beyond acoustic Bragg mirrors, frequency-domain studies using a tandem Fabry–Perot interferometer (TFPI) find dispersions of two- and three-dimensional phononic crystals (PnCs) even for highly disordered samples, but with the caveat that PnCs must be transparent. Here, we demonstrate a hybrid technique for overcoming the limitations that time- and frequency-domain approaches exhibit separately. Accordingly, we inject coherent phonons into a non-transparent PnC using a pulsed laser and acquire the acoustic transmission spectrum on a TFPI, where pumped appear alongside spontaneously excited (i.e. incoherent) phonons. Choosing a metallic Bragg mirror for illustration, we determine the bandgap and compare with conventional time-domain spectroscopy, finding resolution of the hybrid approach to match that of a state-of-the-art asynchronous optical sampling setup. Thus, the hybrid pump–probe technique retains key performance features of the established one and going forward will likely be preferred for disordered samples.

Recurrent Rossby wave packets and persistent extreme weather

2021 ◽  
Author(s):  
S. Mubashshir Ali ◽  
Olivia Martius ◽  
Matthias Röthlisberger
Keyword(s):  
Southern Hemisphere ◽  
Spatial Patterns ◽  
Rossby Wave ◽  
Wave Packets ◽  
Reanalysis Data ◽  
Synoptic Scale ◽  
Background Flow ◽  
Dry Spell ◽  
Upper Level ◽  
Wet Spells

<p>Upper-level synoptic-scale Rossby wave packets are well-known to affect surface weather. When these Rossby wave packets occur repeatedly in the same phase at a specific location, they can result in persistent hot, cold, dry, and wet conditions. The repeated and in-phase occurrence of Rossby wave packets is termed as recurrent synoptic-scale Rossby wave packets (RRWPs). RRWPs result from multiple transient synoptic-scale wave packets amplifying in the same geographical region over several weeks.</p><p>Our climatological analyses using reanalysis data have shown that RRWPs can significantly modulate the persistence of hot, cold, dry, and wet spells in several regions in the Northern and the Southern Hemisphere.  RRWPs can both shorten or extend hot, cold, and dry spell durations. The spatial patterns of statistically significant links between RRWPs and spell durations are distinct for the type of the spell (hot, cold, dry, or wet) and the season (MJJASO or NDJFMA). In the Northern Hemisphere, the spatial patterns where RRWPs either extend or shorten the spell durations are wave-like. In the Southern Hemisphere, the spatial patterns are either wave-like (hot and cold spells) or latitudinally banded (dry and wet spells).</p><p>Furthermore, we explore the atmospheric drivers behind RRWP events. This includes both the background flow and potential wave-triggers such as the Madden Julian Oscillation or blocking. For 100 events of intense Rossby wave recurrence in the Atlantic, the background flow, the intensity of tropical convection, and the occurrence of blocking are studied using flow composites.</p>

Extracting Envelopes of Rossby Wave Packets

2003 ◽  
Vol 131 (5) ◽  
pp. 1011-1017 ◽  
Author(s):  
Aleksey V. Zimin ◽  
Istvan Szunyogh ◽  
D. J. Patil ◽  
Brian R. Hunt ◽  
Edward Ott
Keyword(s):  
Rossby Wave ◽  
Wave Packets
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