A more complete Rossby wave source

2020 ◽  
Author(s):  
Wolfgang Wicker ◽  
Richard Greatbatch
Keyword(s):  
Rossby Wave ◽  
Source Region ◽  
Absolute Vorticity ◽  
Wave Source ◽  
Upper Troposphere ◽  
Rossby Wave Source ◽  
Vorticity Advection ◽  
Order Of Magnitude ◽  
Wave Trains ◽  
The Tropics

<p>Tropical convection drives extratropical variability on subseasonal to interannual time-scales by exciting Rossby wave trains in the upper troposphere. Traditionally the relevant Rossby wave source is considered to be the sum of vortex stretching and vorticity advection by the divergent horizontal flow ( - ∇·<strong>u</strong><sub>χ</sub> (ζ+f) - <strong>u</strong><sub>χ</sub>·∇ (ζ+f)). Since absolute vorticity is very small at the equator, the equatorward flanks of the upper tropospheric jets have been regarded the source region of Rossby wave trains. In these considerations vertical momentum advection is neglected, although, it is an important source for westerly momentum at the equator. The curl of vertical momentum advection is the sum of vertical vorticity advection and vortex tilting ( -  ω ζ<sub>p</sub> - ω<sub>x</sub> v<sub>p</sub> + ω<sub>y</sub> u<sub>p</sub>). These contributions are smaller than the traditional Rossby wave source in midlatidues by about one order of magnitude but they are of similar size in the tropics.</p>

Teleconnections from Tropics to Northern Extratropics through a Southerly Conveyor

2005 ◽  
Vol 62 (11) ◽  
pp. 4057-4070 ◽  
Author(s):  
Zhuo Wang ◽  
C-P. Chang ◽  
Bin Wang ◽  
Fei-Fei Jin
Keyword(s):  
Wave Propagation ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Propagation Theory ◽  
Wave Source ◽  
Tropical Forcing ◽  
Rossby Wave Source ◽  
Rossby Wave Response ◽  
Rossby Wave Propagation ◽  
The Tropics

Abstract Rossby wave propagation theory predicts that Rossby waves in a tropical easterly flow cannot escape from the Tropics to the extratropics. Here the authors show that a southerly flow component in the basic state (a southerly conveyor) may transfer a Rossby wave source northward; thus, a forcing embedded in the deep tropical easterlies may excite a Rossby wave response in the extratropical westerlies. It is shown that the southerly conveyor determines the location of the effective Rossby wave source and that the extratropical response is relatively insensitive to the location of the tropical forcing, provided that the tropical response can reach the southerly conveyor. A stronger southerly flow favors a stronger extratropical response, and the spatial structure of the extratropical response is determined by the extratropical westerly basic flows.

Variability patterns of Rossby wave source

2010 ◽  
Vol 37 (3-4) ◽  
pp. 441-454 ◽  
Author(s):  
Marília Harumi Shimizu ◽  
Iracema Fonseca de Albuquerque Cavalcanti
Keyword(s):  
Rossby Wave ◽  
Wave Source ◽  
Rossby Wave Source

scholarly journals Tropical and subtropical forcing of future southern hemisphere stationary wave changes

2021 ◽  
pp. 1-48
Author(s):  
Matthew Patterson ◽  
Tim Woollings ◽  
Thomas J. Bracegirdle
Keyword(s):  
Climate Change ◽  
Southern Hemisphere ◽  
Rossby Wave ◽  
Regional Climate ◽  
Stationary Wave ◽  
Hadley Cell ◽  
Cmip5 Models ◽  
Wave Source ◽  
Barotropic Model ◽  
Rossby Wave Source

AbstractStationary wave changes play a significant role in the regional climate change response in Southern Hemisphere (SH) winter. In particular, almost all CMIP5 models feature a substantial strengthening of the westerlies to the south of Australia and enhancement of the subtropical jet over the eastern Pacific in winter. In this study we investigate the mechanisms behind these changes, finding that the stationary wave response can largely be explained via reductions in the magnitude of the upper level Rossby wave source over the tropical / subtropical East Pacific. The Rossby wave source changes in this region are robust across the model ensemble and are strongly correlated with changes to low latitude circulation patterns, in particular, the projected southward migration of the Hadley cell and weakening of the Walker circulation. To confirm our mechanism of future changes, we employ a series of barotropic model experiments in which the barotropic model is given a background state identical to a particular CMIP5 model and an anomalous Rossby wave source is imposed. This simple approach is able to capture the primary features of the ensemble mean change, including the cyclonic anomaly south of Australia, and is also able to capture many of the inter-model differences. These findings will help to advance our understanding of the mechanisms underpinning SH extratropical circulation changes under climate change.

Baroclinic-to-Barotropic Pathway in El Niño–Southern Oscillation Teleconnections from the Viewpoint of a Barotropic Rossby Wave Source

2016 ◽  
Vol 73 (12) ◽  
pp. 4989-5002 ◽  
Author(s):  
Xuan Ji ◽  
J. David Neelin ◽  
C. Roberto Mechoso
Keyword(s):  
Flow Pattern ◽  
Rossby Wave ◽  
Zonal Wind ◽  
Southern Oscillation ◽  
Atmospheric Model ◽  
Surface Drag ◽  
Wave Source ◽  
Vertical Advection ◽  
Rossby Wave Source ◽  
Enso Teleconnections

Abstract The baroclinic-to-barotropic pathway in ENSO teleconnections is examined from the viewpoint of a barotropic Rossby wave source that results from decomposition into barotropic and baroclinic components. Diagnoses using the NCEP–NCAR reanalysis are supplemented by analysis of the response of a tropical atmospheric model of intermediate complexity to the NCEP–NCAR barotropic Rossby wave source. Among the three barotropic Rossby wave source contributions (shear advection, vertical advection, and surface drag), the leading contribution is from shear advection and, more specifically, the mean baroclinic zonal wind advecting the anomalous baroclinic zonal wind. Vertical advection is the smallest term, while surface drag tends to cancel and reinforce the shear advection in different regions through damping on the baroclinic mode, which spins up a barotropic response. There are also nontrivial impacts of transients in the barotropic wind response to ENSO. Both tropical and subtropical baroclinic vorticity advection contribute to the barotropic component of the Pacific subtropical jet near the coast of North America, where the resulting barotropic wind contribution approximately doubles the zonal jet anomaly at upper levels, relative to the baroclinic anomalies alone. In this view, the barotropic Rossby wave source in the subtropics simply arises from the basic-state baroclinic flow acting on the well-known baroclinic ENSO flow pattern that spreads from the deep tropics into the subtropics over a scale of equatorial radius of deformation. This is inseparably connected to the leading deep tropical Rossby wave source that arises from eastern Pacific climatological baroclinic winds advecting the tropical portion of the same ENSO flow pattern.

scholarly journals The Consistency of MJO Teleconnection Patterns: An Explanation Using Linear Rossby Wave Theory

2018 ◽  
Vol 32 (2) ◽  
pp. 531-548 ◽  
Author(s):  
Kai-Chih Tseng ◽  
Eric Maloney ◽  
Elizabeth Barnes
Keyword(s):  
Rossby Wave ◽  
Wave Theory ◽  
Warm Pool ◽  
Source Analysis ◽  
Destructive Interference ◽  
Wave Source ◽  
Teleconnection Patterns ◽  
The North ◽  
Rossby Wave Source ◽  
Tropical Heating

Abstract The Madden–Julian oscillation (MJO) excites strong variations in extratropical atmospheric circulations that have important implications for subseasonal-to-seasonal (S2S) prediction. A previous study showed that particular MJO phases are characterized by a consistent modulation of geopotential heights in the North Pacific and adjacent regions across different MJO events, and demonstrated that this consistency is beneficial for extended numerical weather forecasts (i.e., lead times of two weeks to one month). In this study, we examine the physical mechanisms that lead some MJO phases to have more consistent teleconnections than others using a linear baroclinic model. The results show that MJO phases 2, 3, 6, and 7 consistently generate Pacific–North American (PNA)-like patterns on S2S time scales while other phases do not. A Rossby wave source analysis is applied and shows that a dipole-like pattern of Rossby wave source on each side of the subtropical jet can increase the pattern consistency of teleconnections due to the constructive interference of similar teleconnection signals. On the other hand, symmetric patterns of Rossby wave source can dramatically reduce the pattern consistency due to destructive interference. A dipole-like Rossby wave source pattern is present most frequently when tropical heating is found in the Indian Ocean or the Pacific warm pool, and a symmetric Rossby wave source is present most frequently when tropical heating is located over the Maritime Continent. Thus, the MJO phase-dependent pattern consistency of teleconnections is a special case of this mechanism.

scholarly journals On the Seasonality of the El Niño Teleconnection to the Amundsen Sea Region

2019 ◽  
Vol 32 (15) ◽  
pp. 4829-4845 ◽  
Author(s):  
Yu Yeung Scott Yiu ◽  
Amanda C. Maycock
Keyword(s):  
Rossby Wave ◽  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
Austral Summer ◽  
South Pacific ◽  
Austral Winter ◽  
Amundsen Sea ◽  
Wave Source ◽  
Rossby Wave Source

Abstract The Amundsen Sea low (ASL) is a quasi-stationary low pressure system that affects climate in West Antarctica. Previous studies have shown that El Niño–Southern Oscillation (ENSO) modulates the position and strength of the ASL with the strongest teleconnection found in austral winter despite the amplitude of ENSO events generally being largest in austral autumn/summer. This study investigates the mechanisms behind the seasonality of the El Niño teleconnection to the Amundsen Sea region (ASR) using experiments with the HadGEM3 climate model forced with an idealized fixed El Niño sea surface temperature anomaly present throughout the year. The seasonality of the El Niño–ASR teleconnection is found to originate from seasonal differences in the large-scale zonal winds in the South Pacific sector. In austral winter, the region of strong absolute vorticity near ~30°S associated with the subtropical jet, in combination with the changes to upper-tropospheric divergence due to the El Niño perturbation, acts as an anomalous Rossby wave source that is largely absent in austral summer. Furthermore, in austral summer the poleward propagation of tropically sourced Rossby waves into the ASR is inhibited by the strong polar front jet in the South Pacific sector, which leads to Rossby wave reflection away from the ASR. In austral winter, Rossby waves are able to propagate into the ASR, forming part of the Pacific South America pattern. The lack of the Rossby wave source in the tropical Pacific and the absence of favorable conditions for wave propagation explains the weaker El Niño–ASR teleconnection in austral summer compared to austral winter.

scholarly journals Upscale Effects of Deep Convection during the North American Monsoon

2013 ◽  
Vol 70 (9) ◽  
pp. 2681-2695 ◽  
Author(s):  
David J. Stensrud
Keyword(s):  
Numerical Model ◽  
Ray Tracing ◽  
Rossby Wave ◽  
North American ◽  
Wave Train ◽  
Deep Convection ◽  
Source Region ◽  
North American Monsoon ◽  
Low Level ◽  
Wave Trains

Abstract The ability of deep monsoon convection to influence the larger-scale circulation over North America is investigated for a 6-day-long case study during the 2006 North American monsoon. Results from Rossby wave ray tracing and numerical simulations using the Advanced Research Weather Research and Forecasting model indicate that North American monsoon convection provides a source region for stationary Rossby waves. Two wave trains are seen in the numerical model simulations, with behaviors that agree well with expectations from theory and ray tracing. The shorter and faster-moving wave train moves eastward from the source region in Mexico and reaches the western Atlantic within 4 days. The longer and slower-moving wave train travels northeastward and reaches the coastal New England region within 6 days. An upstream tail of anticyclonic vorticity extends westward from the source region into the central Pacific Ocean. The monsoon convection appears to help cut off the low-level anticyclonic flow by developing low-level southerly flow in the Gulf of Mexico and northerly flow in the eastern Pacific, as suggested in earlier global model studies. However, the stationary Rossby wave trains further alter the location and intensity of deep convection in locations remote from the monsoon. These results suggest that unless a numerical model can correctly predict monsoon convection, the ability of the model to produce accurate forecasts of the large-scale pattern and associated convective activity beyond a few days is in question. This result may be important for global climate modeling, since an inaccurate prediction of monsoon convection would lead to an inaccurate Rossby wave response.

scholarly journals The MJO Cycle Forcing of the North Atlantic Circulation: Intervention Experiments with the Community Earth System Model

2015 ◽  
Vol 72 (2) ◽  
pp. 660-681 ◽  
Author(s):  
David M. Straus ◽  
Erik Swenson ◽  
Cara-Lyn Lappen
Keyword(s):  
Rossby Wave ◽  
North Atlantic ◽  
System Model ◽  
Earth System ◽  
Wave Source ◽  
The North ◽  
Rossby Wave Source ◽  
Community Earth System Model ◽  
The North Atlantic ◽  
Vorticity Flux

Abstract A three-dimensional evolution of Madden–Julian oscillation (MJO) diabatic heating for October–March from satellite data is constructed: the heating propagates eastward for three cycles, modulated by the likelihood for a given MJO phase to occur on a given calendar day. This heating is added to the temperature tendencies of each member of an ensemble of 48 (1 October–31 March) simulations with the Community Earth System Model. The leading two most predictable modes of the planetary wave vertically integrated total (added plus model generated) heating capture 81% of the ensemble-mean variance and form an eastward-propagating oscillation with very high signal-to-noise ratio. The two most predictable modes of the extratropical Northern Hemisphere 200-hPa height form an oscillation, as do those of the 300-hPa height tendency due to synoptic vorticity flux convergence, the 200-hPa Rossby wave source, and the envelope transient kinetic energy. The North Atlantic Oscillation (NAO+) occurs 15–25 days after the MJO convection crosses the 90°E meridian, supported by synoptic vorticity flux convergence and a distinct pattern of Rossby wave source. The daily North Atlantic circulation anomalies are categorized into four circulation regimes with a cluster analysis. The NAO+ and NAO− are equally likely in the control model runs, but the NAO+ is 10% more likely in the model runs with heating, compared to a difference of 14% in reanalyses. The daily occurrence of the NAO+ regime in the heating ensemble shows maxima at times when the leading two optimal modes of height also indicate NAO+ but also shows maxima at other times.

scholarly journals Influence of the Background State on Rossby Wave Propagation into the Great Lakes Region Based on Observations and Model Simulations*

2014 ◽  
Vol 27 (24) ◽  
pp. 9302-9322 ◽  
Author(s):  
Kathleen D. Holman ◽  
David J. Lorenz ◽  
Michael Notaro
Keyword(s):  
Great Lakes ◽  
Rossby Wave ◽  
Rossby Waves ◽  
Lake Superior ◽  
Great Lakes Region ◽  
The Pacific ◽  
Wave Trains ◽  
Rossby Wave Propagation ◽  
Upper Level ◽  
The Tropics

Abstract The authors investigate the relationship between hydrology in the Great Lakes basin—namely, overlake precipitation and transient Rossby waves—using the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis data and historical output from phase 3 of the Coupled Model Intercomparison Project (CMIP3). The preferred path of observed Rossby wave trains associated with overlake precipitation on Lake Superior depends strongly on season and appears to be related to the time-mean, upper-level flow. During summer and fall, the Northern Hemisphere extratropical jet is relatively narrow and acts as a waveguide, such that Rossby wave trains traversing the Great Lakes region travel along the extratropical Pacific and Atlantic jets. During other months, the Pacific jet is relatively broad, which allows more wave activity originating in the tropics to penetrate into the midlatitudes and influence Lake Superior precipitation. Analysis is extended to CMIP3 models and is intended to 1) further understanding of how variations in the mean state influence transient Rossby waves and 2) assess models’ ability to capture observed features, such as wave origin and track. Results indicate that Rossby wave train propagation in twentieth-century simulations can significantly differ by model. Unlike observations, some models do not produce a well-defined jet across the Pacific Ocean during summer and autumn. In these models, some Rossby waves affecting the Great Lakes region originate in the tropics. Collectively, observations and model results show the importance of the time-mean upper-level flow on Rossby wave propagation and therefore on the relative influence of the tropics versus the extratropics on the hydroclimate of the Great Lakes region.

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