An Adiabatic Mechanism for the Reduction of Jet Meander Amplitude by Potential Vorticity Filamentation

Abstract The amplitude of ridges in large-amplitude Rossby waves has been shown to decrease systematically with lead time during the first 1–5 days of operational global numerical weather forecasts. These models also exhibit a rapid reduction in the isentropic gradient of potential vorticity (PV) at the tropopause during the first 1–2 days of forecasts. This paper identifies a mechanism linking the reduction in large-scale meander amplitude on jet streams to declining PV gradients. The mechanism proposed is that a smoother isentropic transition of PV across the tropopause leads to excessive PV filamentation on the jet flanks and a more lossy waveguide. The approach taken is to analyze Rossby wave dynamics in a single-layer quasigeostrophic model. Numerical simulations show that the amplitude of a Rossby wave propagating along a narrow but smooth PV front does indeed decay transiently with time. This process is explained in terms of the filamentation of PV from the jet core and associated absorption of wave activity by the critical layers on the jet flanks, and a simple method for quantitatively predicting the magnitude of the amplitude reduction without simulation is presented. Explicitly diffusive simulations are then used to show that the combined impact of diffusion and the adiabatic rearrangement of PV can result in a decay rate of Rossby waves that is 2–4 times as fast as could be expected from diffusion acting alone. This predicted decay rate is sufficient to explain the decay observed in operational weather forecasting models.

Download Full-text

Rossby wave propagation on potential vorticity fronts with finite width

Journal of Fluid Mechanics ◽

10.1017/jfm.2016.180 ◽

2016 ◽

Vol 794 ◽

pp. 775-797 ◽

Cited By ~ 13

Author(s):

B. J. Harvey ◽

J. Methven ◽

M. H. P. Ambaum

Keyword(s):

Wave Propagation ◽

Rossby Wave ◽

Potential Vorticity ◽

Rossby Waves ◽

Phase Speed ◽

Single Layer ◽

Horizontal Gradient ◽

Finite Width ◽

Numerical Weather ◽

Rossby Wave Propagation

The horizontal gradient of potential vorticity (PV) across the tropopause typically declines with lead time in global numerical weather forecasts and tends towards a steady value dependent on model resolution. This paper examines how spreading the tropopause PV contrast over a broader frontal zone affects the propagation of Rossby waves. The approach taken is to analyse Rossby waves on a PV front of finite width in a simple single-layer model. The dispersion relation for linear Rossby waves on a PV front of infinitesimal width is well known; here, an approximate correction is derived for the case of a finite-width front, valid in the limit that the front is narrow compared to the zonal wavelength. Broadening the front causes a decrease in both the jet speed and the ability of waves to propagate upstream. The contribution of these changes to Rossby wave phase speeds cancel at leading order. At second order the decrease in jet speed dominates, meaning phase speeds are slower on broader PV fronts. This asymptotic phase speed result is shown to hold for a wide class of single-layer dynamics with a varying range of PV inversion operators. The phase speed dependence on frontal width is verified by numerical simulations and also shown to be robust at finite wave amplitude, and estimates are made for the error in Rossby wave propagation speeds due to the PV gradient error present in numerical weather forecast models.

Download Full-text

Method for Identifying and Clustering Rossby Wave Breaking Events in the Northern Hemisphere

Meteorologiya i Gidrologiya ◽

10.52002/0130-2906-2021-1-17-28 ◽

2021 ◽

pp. 17-28

Author(s):

A. V. Gochakov ◽

◽

O. Yu. Antokhina ◽

V. N. Krupchatnikov ◽

Yu. V. Martynova ◽

...

Keyword(s):

Rossby Wave ◽

Potential Vorticity ◽

Wave Breaking ◽

Large Scale ◽

Method Development ◽

Spatial Clustering ◽

Potential Temperature ◽

Reanalysis Data ◽

Rossby Wave Breaking ◽

Dynamic Phenomena

Many large-scale dynamic phenomena in the Earth’s atmosphere are associated with the processes of propagation and breaking of Rossby waves. A new method for identifying the Rossby wave breaking (RWB) is proposed. It is based on the detection of breakings centers by analyzing the shape of the contours of potential vorticity or temperature on quasimaterial surfaces: isentropic and iserthelic (surfaces of constant Ertel potential vorticity (PV)), with further RWB center clustering to larger regions. The method is applied to the set of constant PV levels (0.3 to 9.8 PVU with a step of 0.5 PVU) at the level of potential temperature of 350 K for 12:00 UTC. The ERA-Interim reanalysis data from 1979 to 2019 are used for the method development. The type of RWB (cyclonic/anticyclonic), its area and center are determined by analyzing the vortex geometry at each PV level for every day. The RWBs obtained at this stage are designated as elementary breakings. Density-Based Spatial Clustering of Applications with Noise algorithm (DBSCAN) was applied to all elementary breakings for each month. As a result, a graphic dataset describing locations and dynamics of RWBs for every month from 1979 to 2019 is formed. The RWB frequency is also evaluated for each longitude, taking into account the duration of each RWB and the number of levels involved, as well as the anomalies of these parameters.

Download Full-text

On the Arrest of Inverse Energy Cascade and the Rhines Scale

Journal of the Atmospheric Sciences ◽

10.1175/jas4013.1 ◽

2007 ◽

Vol 64 (9) ◽

pp. 3312-3327 ◽

Cited By ~ 82

Author(s):

Semion Sukoriansky ◽

Nadejda Dikovskaya ◽

Boris Galperin

Keyword(s):

Rossby Wave ◽

Large Scale ◽

Rossby Waves ◽

Characteristic Length ◽

Unsteady Flows ◽

Energy Propagation ◽

Dimensional Parameter ◽

Inverse Energy Cascade ◽

Energy Sink ◽

Spectral Ranges

Abstract The notion of the cascade arrest in a β-plane turbulence in the context of continuously forced flows is revised in this paper using both theoretical analysis and numerical simulations. It is demonstrated that the upscale energy propagation cannot be stopped by a β effect and can only be absorbed by friction. A fundamental dimensional parameter in flows with a β effect, the Rhines scale, LR, has traditionally been associated with the cascade arrest or with the scale that separates turbulence and Rossby wave–dominated spectral ranges. It is shown that rather than being a measure of the inverse cascade arrest, LR is a characteristic of different processes in different flow regimes. In unsteady flows, LR can be identified with the moving energy front propagating toward the decreasing wavenumbers. When large-scale energy sink is present, β-plane turbulence may attain several steady-state regimes. Two of these regimes are highlighted: friction-dominated and zonostrophic. In the former, LR does not have any particular significance, while in the latter, the Rhines scale nearly coincides with the characteristic length associated with the large-scale friction. Spectral analysis in the frequency domain demonstrates that Rossby waves coexist with turbulence on scales smaller than LR thus indicating that the Rhines scale cannot be viewed as a crossover between turbulence and Rossby wave ranges.

Download Full-text

On the correlation between ozone and potential vorticity for large-scale Rossby waves

Journal of Geophysical Research Atmospheres ◽

10.1029/96jd03059 ◽

1997 ◽

Vol 102 (D7) ◽

pp. 8793-8804 ◽

Cited By ~ 11

Author(s):

Lars Peter Riishøjgaard ◽

Erland Källén

Keyword(s):

Potential Vorticity ◽

Large Scale ◽

Rossby Waves

Download Full-text

Jets and Orography: Idealized Experiments with Tip Jets and Lighthill Blocking

Journal of the Atmospheric Sciences ◽

10.1175/jas4008.1 ◽

2007 ◽

Vol 64 (10) ◽

pp. 3627-3639 ◽

Cited By ~ 21

Author(s):

P. B. Rhines

Keyword(s):

Numerical Simulations ◽

Shallow Water ◽

Rossby Wave ◽

Potential Vorticity ◽

Rossby Waves ◽

Zonal Flow ◽

Flow Acceleration ◽

Westerly Flow ◽

The Mean ◽

Strong Control

Abstract This paper describes qualitative features of the generation of jetlike concentrated circulations, wakes, and blocks by simple mountainlike orography, both from idealized laboratory experiments and shallow-water numerical simulations on a sphere. The experiments are unstratified with barotropic lee Rossby waves, and jets induced by mountain orography. A persistent pattern of lee jet formation and lee cyclogenesis owes its origins to arrested topographic Rossby waves above the mountain and potential vorticity (PV) advection through them. The wake jet occurs on the equatorward, eastern flank of the topography. A strong upstream blocking of the westerly flow occurs in a Lighthill mode of long Rossby wave propagation, which depends on βa2/U, the ratio of Rossby wave speed based on the scale of the mountain, to zonal advection speed, U (β is the meridional potential vorticity gradient, f is the Coriolis frequency, and a is the diameter of the mountain). Mountains wider (north–south) than the east–west length scale of stationary Rossby waves will tend to block the oncoming westerly flow. These blocks are essentially β plumes, which are illustrated by their linear Green function. For large βa2/U, upwind blocking is strong; the mountain wake can be unstable, filling the fluid with transient Rossby waves as in the numerical simulations of Polvani et al. For small values, βa2/U ≪ 1 classic lee Rossby waves with large wavelength compared to the mountain diameter are the dominant process. The mountain height, δh, relative to the mean fluid depth, H, affects these transitions as well. Simple lee Rossby waves occur only for such small heights, δh/h ≪ aβ/f, that the f/h contours are not greatly distorted by the mountain. Nongeostrophic dynamics are seen in inertial waves generated by geostrophic shear, and ducted by it, and also in a texture of finescale, inadvertent convection. Weakly damped circulations induced in a shallow-water numerical model on a sphere by a lone mountain in an initially simple westerly wind are also described. Here, with βa2/U ∼1, potential vorticity stirring and transient Rossby waves dominate, and drive zonal flow acceleration. Low-latitude critical layers, when present, exert strong control on the high-latitude waves, and with no restorative damping of the mean zonal flow, they migrate poleward toward the source of waves. While these experiments with homogeneous fluid are very simplified, the baroclinic atmosphere and ocean have many tall or equivalent barotropic eddy structures owing to the barotropization process of geostrophic turbulence.

Download Full-text

Signatures of midlatitude heat waves in Rossby wave variability spectra

10.5194/dach2022-25 ◽

2021 ◽

Author(s):

Iana Strigunova ◽

Richard Blender ◽

Frank Lunkeit ◽

Nedjeljka Žagar

Keyword(s):

Rossby Wave ◽

Large Scale ◽

Rossby Waves ◽

Heat Waves ◽

Probability Distributions ◽

Physical Space ◽

Mean Flow ◽

Single Wave ◽

Fourier Decomposition ◽

Latitude Belt

This work aims at identifying extreme circulation conditions such as heat waves in modal space which is defined by eigensolutions of the linearized primitive equations. Here, the Rossby waves are represented in terms of Hough harmonics that are an orthogonal and complete expansion set allowing Rossby wave diagnostics in terms of their total (kinetic and available potential) energies. We expect that this diagnostic provides a more clear picture of the Rossby wave variability spectra compared to the common Fourier decomposition along a latitude belt.&#160; The probability distributions of Rossby wave energies are analysed separately for the zonal mean flow, for the planetary and synoptic zonal wavenumbers. The robustness is ensured by considering the four reanalyses ERA5, ERA-Interim, JRA-55 and MERRA. A single wave is characterized by Gaussianity in the complex Hough amplitudes and by a chi-square distribution for the energies. We find that the distributions of the energy anomalies in the wavenumber space are non-Gaussian with almost the same positive skewness in the four reanalyses.&#160; The skewness increases during persistent heat waves for all energy anomaly distributions, in agreement with the recent trend of increased subseasonal variance in large-scale Rossby waves and decreased variance at synoptic scales. The new approach offers a selective filtering to physical space. The reconstructed circulation during heat waves is dominated by large-scale anticyclonic systems in northeastern Europe with zonal wavenumbers 2 and 3, in agreement with previous studies, thereby demonstrating physical meaningfulness of the skewness.&#160; &#160;

Download Full-text

The impact of ENSO and the Atlantic Multidecadal Variability (AMV) on the upper tropospheric large scale flow in the PRIMAVERA models.

10.5194/egusphere-egu2020-18113 ◽

2020 ◽

Author(s):

Paolo Ghinassi ◽

Federico Fabiano ◽

Virna L. Meccia ◽

Susanna Corti

Keyword(s):

Rossby Wave ◽

Large Scale ◽

Rossby Waves ◽

Wave Activity ◽

Transient Wave ◽

Weather Regime ◽

Weather Regimes ◽

The Pacific ◽

Large Scale Flow ◽

The Impact

Rossby waves play a fundamental role for both climate and weather. They are in fact associated with heat, momentum and moisture transport across large distances and with different types of weather at the surface. Assessing how they are represented in climate models is thus of primary importance to understand both predictability and the present and future climate. In this study we investigate how ENSO and the AMV affect the large scale flow pattern in the upper troposphere of the Northern Hemisphere, using reanalysis data and data from the PRIMAVERA simulations.The upper tropospheric large scale flow is investigated in terms of the Rossby wave activity associated with persistent and recurrent patterns over the Pacific-North American and Euro-Atlantic regions during winter, the so called weather regimes. In order to quantify the vigour of Rossby wave activity associated with each weather regime we make use of a recently developed diagnostic based on Finite Amplitude Local Wave Activity in isentropic coordinates, partitioning the total wave activity into the stationary and transient components. The former is associated with quasi-stationary, planetary Rossby waves, whereas the latter is associated with synoptic scale Rossby wave packets. This allows one to quantify the contribution from stationary versus transient eddies in the total Rossby wave activity linked to each weather regime.In this study we explore how ENSO and the AMV affect both the weather regimes frequencies and the upper tropospheric waviness in the Pacific and Atlantic storm tracks, respectively. Furthermore we analyse how both the stationary and transient wave activity component modulate the onset and transition between different regimes.

Download Full-text

Rossby Waves and the Interannual and Interdecadal Variability of Temperature and Salinity off California

Journal of Physical Oceanography ◽

10.1175/2009jpo3898.1 ◽

2009 ◽

Vol 39 (10) ◽

pp. 2543-2561 ◽

Cited By ~ 5

Author(s):

Marcelo Dottori ◽

Allan J. Clarke

Keyword(s):

Sea Level ◽

Rossby Wave ◽

Large Scale ◽

Southern California ◽

Rossby Waves ◽

Salinity Gradient ◽

Time Derivative ◽

Temperature Fluctuations ◽

Dynamic Height ◽

The Mean

Abstract Previous work has shown that large-scale interannual Rossby waves, largely remotely generated by equatorial winds, propagate westward from the coast off southern California. These waves have a large-scale anomalous alongshore velocity field that is proportional to the time derivative of the interannual sea level anomaly. Using these results, a theory is developed for interannual perturbations to a mean density field that varies both vertically and alongshore, like that for the California Current region off southern California. Because both the anomalous vertical and alongshore currents are proportional to the time derivative of the interannual sea level, the theory suggests that the anomalous currents associated with the Rossby waves, acting on the mean temperature field, should induce temperature fluctuations proportional to the anomalous dynamic height. The alongshore and vertical advections contribute to the temperature fluctuations in the same sense, a higher-than-normal sea level, for example, resulting in downward and poleward displacement of warmer water and a local higher-than-normal temperature. Near the surface, alongshore advection dominates vertical advection but both contribute comparably near the thermocline and below. The correlation of observed temperature and dynamic height anomalies from the California Cooperative Oceanic Fisheries Investigation (CalCOFI) data is positive, which is consistent with the theory. The correlation is highest (r ≈ 0.8) near 100-m depth in the thermocline. Although the correlation falls toward the surface, it is still between 0.5 and 0.6, suggesting that the advection mechanism is a major contributor to the temperature anomalies there. The anomalous Rossby wave currents, acting on the mean background salinity gradient, also induce salinity anomalies. At halocline depths of 100–200 m, consistent with the theory, the correlation of observed CalCOFI salinity and dynamic height anomalies is negative and large in magnitude (r ≈ −0.8). However, the surface salinity anomaly is not due to Rossby wave dynamics; instead, much of it is driven by the alongshore wind stress, which it lags by 4 months.

Download Full-text

Weak upstream westerly wind attracts western north pacific typhoon tracks to west

Environmental Research Letters ◽

10.1088/1748-9326/ac3aa4 ◽

2021 ◽

Author(s):

Jun-Hyeok Son ◽

Jae-Il Kwon ◽

Ki-Young Heo

Keyword(s):

Tibetan Plateau ◽

Rossby Wave ◽

Large Scale ◽

Rossby Waves ◽

Circulation Pattern ◽

The Tibetan Plateau ◽

Circulation Anomaly ◽

North East ◽

The North ◽

Typhoon Tracks

Abstract The steering flow of the large-scale circulation patterns over the Western North Pacific and North East Asia, constrains typhoon tracks. Westerly winds impinging on the Tibetan Plateau, and the resulting flow uplift along the slope of the mountain, induce atmospheric vortex flow and generate stationary barotropic Rossby waves downstream. The downstream Rossby wave zonal phase is determined by the upstream zonal wind speed impinging on the Tibetan Plateau. Positive anomaly of westerly wind forcing tends to induce an eastward shift of the large-scale Rossby wave circulation pattern, forming a cyclonic circulation anomaly over North East Asia. In this study, we show that the Tibetan Plateau dynamically impacts the tracks of western Pacific typhoons via modulation of downstream Rossby waves. Using the topographically forced stationary Rossby wave theory, the dynamical mechanisms for the formation of the North East Asian cyclonic anomaly and its impact on the typhoon tracks are analyzed. The eastward shift of typhoon tracks, caused by the southwesterly wind anomaly located to the southeast of the North East Asian cyclonic circulation anomaly, is robust in June and September, but it is not statistically significant in July–August. The physical understanding of the large-scale circulation pattern affecting typhoon trajectories has large implications not only at the seasonal prediction of the high impact weather phenomena, but also at the right understanding of the long-term climate change.

Download Full-text

Rossby Wave Initiation by Recurving Tropical Cyclones in the Western North Pacific

Monthly Weather Review ◽

10.1175/mwr-d-17-0219.1 ◽

2018 ◽

Vol 146 (5) ◽

pp. 1283-1301 ◽

Cited By ~ 7

Author(s):

Jacopo Riboldi ◽

Matthias Röthlisberger ◽

Christian M. Grams

Keyword(s):

Ab Initio ◽

Tropical Cyclones ◽

Rossby Wave ◽

North Pacific ◽

Western North Pacific ◽

Large Scale ◽

Rossby Waves ◽

Boreal Summer ◽

Large Scale Flow ◽

Upper Level Jet

Abstract The interaction of recurving tropical cyclones (TCs) with midlatitude Rossby waves during extratropical transition (ET) can significantly alter the midlatitude flow configuration. This study provides a climatological investigation of Rossby wave initiation (RWI) by transitioning TCs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during ET. Recurving TCs interacting with a zonally oriented waveguide in the western North Pacific (WNP) basin from 1979 to 2013 are categorized into cases initiating Rossby waves (TC-RWI) or not (TC-noRWI). Interactions with a zonally oriented waveguide occurred for 22.7% of the recurving TCs, and one-third of these resulted in TC-RWI. In the presence of a TC, the probability of RWI on a zonally oriented waveguide is 3 times larger than in situations without a TC. The occurrence of TC-RWI exhibits a seasonality and is relatively more common during boreal summer than in autumn. We further reveal that a strong preexisting upper-level jet stream, embedded in a deformative large-scale flow pattern, hinders TC-RWI as air from the diabatic outflow of the TC is rapidly advected downstream and does not lead to strong ridge building. In contrast, an enhanced monsoon trough favors TC-RWI as the poleward moisture transport strengthens diabatic outflow and leads to strong ridge building during ET. Thus, we conclude that TC-related ab initio flow amplification over the WNP is governed by characteristics of the large-scale flow more so than by characteristics of the recurving TC.

Download Full-text