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.

The Combined Influence of the Stratospheric Polar Vortex and ENSO on Zonal Asymmetries in the Southern Hemisphere Upper Tropospheric Circulation during Austral Spring and Summer

2021 ◽  
Author(s):  
Marisol Osman ◽  
Theodore Shepherd ◽  
Carolina Vera
Keyword(s):  
Southern Hemisphere ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Austral Spring ◽  
Stratospheric Polar Vortex ◽  
Wave Source ◽  
Weather Forecasts ◽  
Rossby Wave Source ◽  
Enso Teleconnections ◽  
Tropospheric Circulation

<p>The influence of El Niño Southern Oscillation (ENSO) and the Stratospheric Polar Vortex (SPV) on the zonal asymmetries in the Southern Hemisphere atmospheric circulation during spring and summer is examined. The main objective is to explore if the SPV can modulate the ENSO teleconnections in the extratropics. We use a large ensemble of seasonal hindcasts from the European Centre for Medium-Range Weather Forecasts Integrated Forecast System to provide a much larger sample size than is possible from the observations alone.</p><p>We find a small but statistically significant relationship between ENSO and the SPV, with El Niño events occurring with weak SPV and La Niña events occurring with strong SPV more often than expected by chance, in agreement with previous works. We show that the zonally asymmetric response to ENSO and SPV can be mainly explained by a linear combination of the response to both forcings, and that they can combine constructively or destructively. From this perspective, we find that the tropospheric asymmetries in response to ENSO are more intense when El Niño events occur with weak SPV and La Niña events occur with strong SPV, at least from September through December. In the stratosphere, the ENSO teleconnections are mostly confounded by the SPV signal. The analysis of Rossby Wave Source and of wave activity shows that both are stronger when El Niño events occur together with weak SPV, and when La Niña events occur together with strong SPV.</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.

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>

Indian Ocean mediates the ENSO teleconnections to the Central Southwest Asia during the wet season 

2021 ◽  
Author(s):  
Muhammad Adnan Abid ◽  
Moetasim Ashfaq ◽  
Fred Kucharski ◽  
Katherine J. Evans ◽  
Mansour Almazroui
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
Southern Oscillation ◽  
Intraseasonal Variability ◽  
Tropical Indian Ocean ◽  
Polar Regions ◽  
Southwest Asia ◽  
Wet Season ◽  
Enso Teleconnections ◽  
Hydroclimate Variability

<p>Central Southwest Asia (CSWA) is a region with the largest number of glaciers, outside the polar regions in its northeast and the Arabian desert to its southwest. The region receives precipitation from November to April period also known as the wet season, which contributes to the regional freshwater resources. Mainly, El Niño–Southern Oscillation (ENSO) modulates the wet season precipitation over CSWA, with a positive relationship. However, the intraseasonal characteristics of ENSO influence are largely unknown, which may be important to understand the regional sub-seasonal to seasonal hydroclimate variability. We noted that the ENSO‐CSWA teleconnection varies intraseasonally and is a combination of direct and indirect positive influences. The ENSO direct influence is through a Rossby wave‐like pattern in the tail months of the wet season, while the indirect influence is noted through an ENSO‐forced atmospheric dipole of diabatic heating anomalies in the tropical Indian Ocean (TIO), which also generates a Rossby wave‐like forcing and persists throughout the wet season. The stronger ENSO influence is found when both direct and indirect modes are in phase, while the relationship breaks down when the two modes are out of phase. Moreover, the idealized numerical simulations confirm and reproduce the observed circulation patterns. This suggests that improvements in sub-seasonal to seasonal scale predictability requires the better representation of intraseasonal variability of ENSO teleconnection, as well as the role of interbasin interactions in its propagation.</p>

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.

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

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

<p>El Niño-Southern Oscillation (ENSO) is known to affect the Northern Hemisphere tropospheric circulation in late-winter (January–March), but whether El Niño and La Niña 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 Niña tends to be weaker and shifted westward with respect to that of El Niño. 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 Niña compared to El Niño. 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 Niño and La Niña.</p><p>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).</p>

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.

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