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.

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 Diagnosing the Horizontal Propagation of Rossby Wave Packets along the Midlatitude Waveguide

2017 ◽  
Vol 145 (8) ◽  
pp. 3247-3264 ◽  
Author(s):  
Gabriel Wolf ◽  
Volkmar Wirth
Keyword(s):  
Wave Packet ◽  
Rossby Wave ◽  
Wave Breaking ◽  
Wave Packets ◽  
Wave Activity ◽  
Severe Weather ◽  
Robust Methods ◽  
Misleading Information ◽  
Individual Wave ◽  
Wave Activity Flux

It has been suggested that upper-tropospheric Rossby wave packets propagating along the midlatitude waveguide may play a role for triggering severe weather. This motivates the search for robust methods to detect and track Rossby wave packets and to diagnose their properties. In the framework of several observed cases, this paper compares different methods that have been proposed for these tasks, with an emphasis on horizontal propagation and on a particular formulation of a wave activity flux previously suggested by Takaya and Nakamura. The utility of this flux is compromised by the semigeostrophic nature of upper-tropospheric Rossby waves, but this problem can partly be overcome by a semigeostrophic coordinate transformation. The wave activity flux allows one to obtain information from a single snapshot about the meridional propagation, in particular propagation from or into polar and subtropical latitudes, as well as about the onset of wave breaking. This helps to clarify the dynamics of individual wave packets in cases where other, more conventional methods provide ambiguous or even misleading information. In some cases, the “true dynamics” of the Rossby wave packet turns out to be more complex than apparent from the more conventional diagnostics, and this may have important implications for the predictability of the wave packet.

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.

scholarly journals Modulation of surface meteorological parameters by extratropical planetary-scale Rossby waves

2016 ◽  
Vol 34 (1) ◽  
pp. 123-132 ◽  
Author(s):  
K. Niranjan Kumar ◽  
D. V. Phanikumar ◽  
T. B. M. J. Ouarda ◽  
M. Rajeevan ◽  
M. Naja ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Rossby Wave ◽  
Meteorological Parameters ◽  
Rossby Waves ◽  
Weather Conditions ◽  
Meridional Wind ◽  
Wave Number ◽  
Study Region ◽  
Upper Troposphere ◽  
Planetary Scale

Abstract. This study examines the link between upper-tropospheric planetary-scale Rossby waves and surface meteorological parameters based on the observations made in association with the Ganges Valley Aerosol Experiment (GVAX) campaign at an extratropical site at Aryabhatta Research Institute of Observational Sciences, Nainital (29.45° N, 79.5° E) during November–December 2011. The spectral analysis of the tropospheric wind field from radiosonde measurements indicates a predominance power of around 8 days in the upper troposphere during the observational period. An analysis of the 200 hPa meridional wind (v200 hPa) anomalies from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) reanalysis shows distinct Rossby-wave-like structures over a high-altitude site in the central Himalayan region. Furthermore, the spectral analysis of global v200 hPa anomalies indicates the Rossby waves are characterized by zonal wave number 6. The amplification of the Rossby wave packets over the site leads to persistent subtropical jet stream (STJ) patterns, which further affects the surface weather conditions. The propagating Rossby waves in the upper troposphere along with the undulations in the STJ create convergence and divergence regions in the mid-troposphere. Therefore, the surface meteorological parameters such as the relative humidity, wind speeds, and temperature are synchronized with the phase of the propagating Rossby waves. Moreover, the present study finds important implications for medium-range forecasting through the upper-level Rossby waves over the study region.

scholarly journals A Budget Equation for the Amplitude of Rossby Wave Packets Based on Finite-Amplitude Local Wave Activity

2019 ◽  
Vol 77 (1) ◽  
pp. 277-296
Author(s):  
Paolo Ghinassi ◽  
Marlene Baumgart ◽  
Franziska Teubler ◽  
Michael Riemer ◽  
Volkmar Wirth
Keyword(s):  
Wave Packet ◽  
Rossby Wave ◽  
Wave Packets ◽  
Finite Amplitude ◽  
Equation Model ◽  
Wave Activity ◽  
Phase Dependence ◽  
Local Wave ◽  
Budget Equation ◽  
Upper Level

Abstract Recently, the authors proposed a novel diagnostic to quantify the amplitude of Rossby wave packets. This diagnostic extends the local finite-amplitude wave activity (LWA) of N. Nakamura and collaborators to the primitive-equations framework and combines it with a zonal filter to remove the phase dependence. In the present work, this diagnostic is used to investigate the dynamics of upper-tropospheric Rossby wave packets, with a particular focus on distinguishing between conservative dynamics and nonconservative processes. For this purpose, a budget equation for filtered LWA is derived and its utility is tested in a hierarchy of models. Idealized simulations with a barotropic and a dry primitive-equation model confirm the ability of the LWA diagnostic to identify nonconservative local sources or sinks of wave activity. In addition, the LWA budget is applied to forecast data for an episode in which the amplitude of an upper-tropospheric Rossby wave packet was poorly represented. The analysis attributes deficiencies in the Rossby wave packet amplitude to the misrepresentation of diabatic processes and illuminates the importance of the upper-level divergent outflow as a source for the error in the wave packet amplitude.

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.

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.

scholarly journals The Role of Wave Packets in Wave–Mean Flow Interactions during Southern Hemisphere Summer

2005 ◽  
Vol 62 (7) ◽  
pp. 2467-2483 ◽  
Author(s):  
Edmund K. M. Chang
Keyword(s):  
Life Cycle ◽  
Wave Packet ◽  
Southern Hemisphere ◽  
Wave Packets ◽  
Reanalysis Data ◽  
Heat Fluxes ◽  
Mean Flow ◽  
Single Wave ◽  
Dominant Wave ◽  
Flow Interactions

Abstract In this study, reanalysis data produced by the European Centre for Medium-Range Weather Forecasts for 14 Southern Hemisphere (SH) summer seasons have been analyzed. All cases of hemispheric transient eddy kinetic energy (TEKE) maxima have been identified, and the evolution of the local energetics and planetary-scale flow anomalies accompanying these TEKE growth/decay episodes are composited. The longitude–time evolution of the composite energetics shows the clear signature of a wave packet propagating eastward at a group velocity of about 27° longitude per day and undergoing a life cycle of growth and decay, with the energetics within a volume close to the wave packet center dominating the hemispheric mean energetics. When individual cases are examined, 52% are found to resemble the composite and have the energetics life cycle dominated by the evolution of a single wave packet, and an additional 21% are found to be dominated by the evolution of two wave packets having similar amplitudes. Only the remaining 27% can be regarded as having experienced TEKE growth and decay throughout much of the hemisphere. The zonal mean flow and eddy feedback anomalies (i.e., reduction in the meridional temperature gradient due to the effects of the eddy heat fluxes, as well as increase in the barotropic shear due to a narrowing of the midlatitude jet through the effects of the eddy momentum fluxes) associated with the cases dominated by the evolution of a single wave packet are also found to be dominated by anomalies close to the wave packet center. The fact that hemispheric wave growth/decay is often dominated by the evolution of a single wave packet has interesting dynamical consequences when the climatological basic flow is not zonally symmetric. When a wave packet propagates over regions of enhanced baroclinicity, it can extract more energy from the mean flow via baroclinic conversion, leading to its preferential growth. On the other hand, when a wave packet propagates over regions of weak baroclinicity, baroclinic conversion is suppressed; hence any packet growth must be due to other processes. By examining the location of wave packet peaks when hemispheric TEKE is at a maximum, it is observed that hemispheric mean TEKE peaks much more frequently when the dominant wave packet is located downstream of the region with strongest baroclinicity. In addition, the growth in TEKE for these cases is usually dominated by an increase in baroclinic conversion. In contrast, for the small number of cases in which the hemispheric mean TEKE maximum occurs when the dominant wave packet is located downstream of the region with weakest baroclinicity, the growth of the hemispheric TEKE is instead dominated by a reduction in barotropic dissipation.

Model of multicomponent narrow-band periodical non-stationary random signal

2020 ◽  
Vol 2020 (48) ◽  
pp. 17-24
Author(s):  
I.M. Javorskyj ◽  
◽  
R.M. Yuzefovych ◽  
P.R. Kurapov ◽  
◽  
...  
Keyword(s):  
Time Series ◽  
Real Time ◽  
Hilbert Transform ◽  
Spectral Properties ◽  
Narrow Band ◽  
Analytic Signal ◽  
Random Signal ◽  
Hilbert Transformation ◽  
The Hilbert Transform

The correlation and spectral properties of a multicomponent narrowband periodical non-stationary random signal (PNRS) and its Hilbert transformation are considered. It is shown that multicomponent narrowband PNRS differ from the monocomponent signal. This difference is caused by correlation of the quadratures for the different carrier harmonics. Such features of the analytic signal must be taken into account when we use the Hilbert transform for the analysis of real time series.

A Bayesian View on the Hilbert Transform and the Kramers-Kronig Transform of Electrochemical Impedance Data: Probabilistic Estimates and Quality Scores

2020 ◽  
Author(s):  
Jiapeng Liu ◽  
Ting Hei Wan ◽  
Francesco Ciucci
Keyword(s):  
Power Generation ◽  
Electrochemical Impedance Spectroscopy ◽  
Hilbert Transform ◽  
Electrochemical Impedance ◽  
The Self ◽  
Impedance Data ◽  
The Hilbert Transform ◽  
Validation Tests ◽  
Self Consistency ◽  
Mathematical Relations

<p>Electrochemical impedance spectroscopy (EIS) is one of the most widely used experimental tools in electrochemistry and has applications ranging from energy storage and power generation to medicine. Considering the broad applicability of the EIS technique, it is critical to validate the EIS data against the Hilbert transform (HT) or, equivalently, the Kramers–Kronig relations. These mathematical relations allow one to assess the self-consistency of obtained spectra. However, the use of validation tests is still uncommon. In the present article, we aim at bridging this gap by reformulating the HT under a Bayesian framework. In particular, we developed the Bayesian Hilbert transform (BHT) method that interprets the HT probabilistic. Leveraging the BHT, we proposed several scores that provide quick metrics for the evaluation of the EIS data quality.<br></p>

Sign in / Sign up

Export Citation Format

Share Document