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

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.

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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0145.1 ◽

2015 ◽

Vol 72 (2) ◽

pp. 660-681 ◽

Cited By ~ 12

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.

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Teleconnections from Tropics to Northern Extratropics through a Southerly Conveyor

Journal of the Atmospheric Sciences ◽

10.1175/jas3600.1 ◽

2005 ◽

Vol 62 (11) ◽

pp. 4057-4070 ◽

Cited By ~ 13

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.

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A more complete Rossby wave source

10.5194/egusphere-egu2020-10398 ◽

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

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 ( - &#8711;&#183;u&#967; (&#950;+f) - u&#967;&#183;&#8711; (&#950;+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 ( -&#160; &#969; &#950;p - &#969;x vp + &#969;y up). 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.

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Variability patterns of Rossby wave source

Climate Dynamics ◽

10.1007/s00382-010-0841-z ◽

2010 ◽

Vol 37 (3-4) ◽

pp. 441-454 ◽

Cited By ~ 31

Author(s):

Marília Harumi Shimizu ◽

Iracema Fonseca de Albuquerque Cavalcanti

Keyword(s):

Rossby Wave ◽

Wave Source ◽

Rossby Wave Source

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Tropical and subtropical forcing of future southern hemisphere stationary wave changes

Journal of Climate ◽

10.1175/jcli-d-21-0075.1 ◽

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.

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

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0053.1 ◽

2016 ◽

Vol 73 (12) ◽

pp. 4989-5002 ◽

Cited By ~ 6

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.

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The Consistency of MJO Teleconnection Patterns on Interannual Time Scales

Journal of Climate ◽

10.1175/jcli-d-19-0510.1 ◽

2020 ◽

Vol 33 (9) ◽

pp. 3471-3486 ◽

Cited By ~ 2

Author(s):

Kai-Chih Tseng ◽

Eric Maloney ◽

Elizabeth A. Barnes

Keyword(s):

Time Scales ◽

Rossby Wave ◽

El Niño ◽

El Nino ◽

Reanalysis Data ◽

La Niña ◽

Wave Source ◽

Teleconnection Patterns ◽

La Nina ◽

Wave Ray

AbstractThe Madden–Julian oscillation (MJO) excites strong variations in extratropical geopotential heights that modulate extratropical weather, making the MJO an important predictability source on subseasonal to seasonal time scales (S2S). Previous research demonstrates a strong similarity of teleconnection patterns across MJO events for certain MJO phases (i.e., pattern consistency) and increased model ensemble agreement during these phases that is beneficial for extended numerical weather forecasts. However, the MJO’s ability to modulate extratropical weather varies greatly on interannual time scales, which brings extra uncertainty in leveraging the MJO for S2S prediction. Few studies have investigated the mechanisms responsible for variations in the consistency of MJO tropical–extratropical teleconnections on interannual time scales. This study uses reanalysis data, ensemble simulations of a linear baroclinic model, and a Rossby wave ray tracing algorithm to demonstrate that two mechanisms largely determine the interannual variability of MJO teleconnection consistency. First, the meridional shift of stationary Rossby wave ray paths indicates increases (decreases) in the MJO’s extratropical modulation during La Niña (El Niño) years. Second, a previous study proposed that the constructive interference of Rossby wave signals caused by a dipole Rossby wave source pattern across the subtropical jet during certain MJO phases produces a consistent MJO teleconnection. However, this dipole feature is less clear in both El Niño and La Niña years due to the extension and contraction of MJO convection, respectively, which would decrease the MJO’s influence in the extratropics. Hence, considering the joint influence of the basic state and MJO forcing, this study suggests a diminished potential to leverage the MJO for S2S prediction in El Niño years.

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Mechanisms for a PNA-Like Teleconnection Pattern in Response to the MJO

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0343.1 ◽

2017 ◽

Vol 74 (6) ◽

pp. 1767-1781 ◽

Cited By ~ 40

Author(s):

Kyong-Hwan Seo ◽

Hyun-Ju Lee

Keyword(s):

Wave Propagation ◽

Indian Ocean ◽

Rossby Wave ◽

General Circulation ◽

Circulation Model ◽

Wave Theory ◽

Teleconnection Pattern ◽

Western Pacific ◽

Wave Source ◽

Divergent Wind

Abstract Kinematic mechanisms of the Pacific–North America (PNA)-like teleconnection pattern induced by the Madden–Julian oscillation (MJO) is examined using an atmospheric general circulation model (GCM) and a barotropic Rossby wave theory. Observation shows that a negative PNA-like teleconnection pattern emerges in response to MJO phase-2 forcing with enhanced (suppressed) convection located over the Indian (western Pacific) Ocean. The GCM simulations show that both forcing anomalies contribute to creating the PNA-like pattern. Indian Ocean forcing induces two major Rossby wave source (RWS) regions: a negative region around southern Asia and a positive region over the western North Pacific (WNP). The negative RWS to the north of the enhanced convection in the Indian Ocean arises from southerly MJO-induced divergent wind crossing the Asian jet. Unexpectedly, another significant RWS region develops over the WNP owing to refracted northerly divergent wind. A ray-tracing method demonstrates three different ways of wave propagation emanating from the RWS to the PNA region: 1) direct arclike propagation from the negative RWS to the PNA region occurs in the longest waves, 2) shorter waves are displaced first downstream by the jet waveguide effect and then emanate at the jet exit to the PNA region, and 3) waves with zonal wavenumbers 1 and 2 exhibit canonical wave propagation from the positive RWS at the jet exit to the PNA region. On the other hand, the positive RWS induced by western Pacific forcing shows similar characteristics to feature 3 described above, with some relaxation such that much shorter waves also contribute to the formation of the southern cells.

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Effect of the North Pacific Tropospheric Waveguide on the Fidelity of Model El Niño Teleconnections

Journal of Climate ◽

10.1175/jcli-d-19-0156.1 ◽

2020 ◽

Vol 33 (12) ◽

pp. 5223-5237 ◽

Cited By ~ 1

Author(s):

Ronald K. K. Li ◽

Tim Woollings ◽

Christopher O’Reilly ◽

Adam A. Scaife

Keyword(s):

Rossby Wave ◽

North Atlantic ◽

El Niño ◽

North Pacific ◽

El Nino ◽

Wave Source ◽

The North ◽

The Caribbean ◽

The North Atlantic ◽

The North Pacific

AbstractIn a free-running climate model, DJF tropical–extratropical teleconnections are assessed and compared to observed teleconnections in reanalysis data. From reanalysis, the leading mode of covariability between tropical outgoing longwave radiation (OLR) and Northern Hemisphere extratropical geopotential height (Z500) is identified using maximum covariance analysis (MCA). This mode relates closely to the El Niño pattern. The GCM captures the tropical OLR well but the associated extratropical Z500 less well. The GCM climatology has an equatorward shifted North Pacific jet bias. We examine whether the difference in the teleconnection pattern is related to the GCM’s jet bias. In both a ray-tracing analysis and a barotropic model, this jet bias is shown to affect the Rossby wave propagation from the tropical Pacific into the North Pacific. These idealized model results suggest qualitatively that the MCA difference is largely consistent with linear Rossby wave dynamics. While the basic state has a larger effect on the North Pacific MCA, a Rossby wave source (RWS) bias in the Caribbean has a larger effect on the North Atlantic MCA. The North Pacific jet bias is also proposed to affect the downstream propagation of waves from North America into the Caribbean, where it affects tropical RWS and the triggering of secondary waves into the North Atlantic. We propose that climatological biases in the tropics are one underlying cause of the jet bias. Our study may also help understand the results of other climate models with similar jet biases.

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Multi-model assessment of the late-winter tropospheric response to El Niño and La Niña

10.5194/ems2021-265 ◽

2021 ◽

Author(s):

Bianca Mezzina ◽

Javier García-Serrano ◽

Ileana Bladé ◽

Froila M. Palmeiro ◽

Lauriane Batté ◽

...

Keyword(s):

Rossby Wave ◽

North Atlantic ◽

Large Scale ◽

Southern Oscillation ◽

Late Winter ◽

Model Assessment ◽

Wave Source ◽

Enso Events ◽

The North ◽

The North Atlantic

El Ni&#241;o-Southern Oscillation (ENSO) is known to affect the Northern Hemisphere tropospheric circulation in late-winter (January&#8211;March), but whether El Ni&#241;o and La Ni&#241;a lead to symmetric impacts and with the same underlying dynamics remains unclear, particularly in the North Atlantic. Three state-of-the-art atmospheric models forced by symmetric anomalous sea surface temperature (SST) patterns, mimicking strong ENSO events, are used to robustly diagnose symmetries and asymmetries in the extra-tropical ENSO response. Asymmetries arise in the sea-level pressure (SLP) response over the North Pacific and North Atlantic, as the response to La Ni&#241;a tends to be weaker and shifted westward with respect to that of El Ni&#241;o. The difference in amplitude can be traced back to the distinct energy available for the two ENSO phases associated with the non-linear diabatic heating response to the total SST field. The longitudinal shift is embedded into the large-scale Rossby wave train triggered from the tropical Pacific, as its anomalies in the upper troposphere show a similar westward displacement in La Ni&#241;a compared to El Ni&#241;o. To fully explain this shift, the response in tropical convection and the related anomalous upper-level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet, i.e. diagnosing the tropical Rossby wave source. In the North Atlantic, the ENSO-forced SLP signal is a well-known dipole between middle and high latitudes, different from the North Atlantic Oscillation, whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for El Ni&#241;o and La Ni&#241;a.The multi-model assessment, with 50 members for each experiment, contributes to the ERA4CS-funded MEDSCOPE project and includes: EC-EARTH/IFS (L91, 0.01hPa), CNRM/ARPEGE (L91, 0.01hPa), CMCC/CAM (L46, 0.3hPa).

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