scholarly journals Multidecadal Modulation of ENSO Teleconnection with Europe in Late Winter: Analysis of CMIP5 Models

2016 ◽  
Vol 29 (22) ◽  
pp. 8067-8081 ◽  
Author(s):  
Jorge López Parages ◽  
Belén Rodríguez de Fonseca ◽  
Elsa Mohino ◽  
Teresa Losada
Keyword(s):  
Rossby Wave ◽  
Coupled System ◽  
Cmip5 Models ◽  
Late Winter ◽  
Jet Streams ◽  
Multidecadal Variability ◽  
The North ◽  
Ocean Atmosphere ◽  
Variable Feature ◽  
Wave Trains

Abstract Many studies point to a robust ENSO signature on the North Atlantic–European (NAE) sector associated with a downstream effect of Rossby wave trains. Some of these works also address a nonstationary behavior of the aforementioned link, but only few have explored the possible modulating factors. In this study the internal causes within the ocean–atmosphere coupled system influencing the tropospheric ENSO–Euro-Mediterranean rainfall teleconnection have been analyzed. To this aim, unforced long-term preindustrial control simulations from 18 different CMIP5 models have been used. A nonstationary impact of ENSO on Euro-Mediterranean rainfall, being spatially consistent with the observational one, is found. This variable feature is explained by a changing ENSO-related Rossby wave propagation from the tropical Pacific to the NAE sector, which, in turn, is modulated by multidecadal variability of the climatological jet streams associated with the underlying sea surface temperature (SST). The results, therefore, indicate a modulation of the ENSO–Euro-Mediterranean rainfall teleconnection by the internal (and multidecadal) variability of the ocean–atmosphere coupled system.

scholarly journals Modeled and Observed Multidecadal Variability in the North Atlantic Jet Stream and Its Connection to Sea Surface Temperatures

2018 ◽  
Vol 31 (20) ◽  
pp. 8313-8338 ◽  
Author(s):  
Isla R. Simpson ◽  
Clara Deser ◽  
Karen A. McKinnon ◽  
Elizabeth A. Barnes
Keyword(s):  
North Atlantic ◽  
Sea Surface ◽  
Late Winter ◽  
Jet Stream ◽  
Sea Surface Temperatures ◽  
Multidecadal Variability ◽  
The North ◽  
Surface Temperatures ◽  
The North Atlantic ◽  
North Atlantic Jet

Multidecadal variability in the North Atlantic jet stream in general circulation models (GCMs) is compared with that in reanalysis products of the twentieth century. It is found that almost all models exhibit multidecadal jet stream variability that is entirely consistent with the sampling of white noise year-to-year atmospheric fluctuations. In the observed record, the variability displays a pronounced seasonality within the winter months, with greatly enhanced variability toward the late winter. This late winter variability exceeds that found in any GCM and greatly exceeds expectations from the sampling of atmospheric noise, motivating the need for an underlying explanation. The potential roles of both external forcings and internal coupled ocean–atmosphere processes are considered. While the late winter variability is not found to be closely connected with external forcing, it is found to be strongly related to the internally generated component of Atlantic multidecadal variability (AMV) in sea surface temperatures (SSTs). In fact, consideration of the seasonality of the jet stream variability within the winter months reveals that the AMV is far more strongly connected to jet stream variability during March than the early winter months or the winter season as a whole. Reasoning is put forward for why this connection likely represents a driving of the jet stream variability by the SSTs, although the dynamics involved remain to be understood. This analysis reveals a fundamental mismatch between late winter jet stream variability in observations and GCMs and a potential source of long-term predictability of the late winter Atlantic atmospheric circulation.

Impact of Sea Ice Reduction in the Barents and Kara Seas on the Variation of the East Asian Trough in Late Winter

2021 ◽  
Vol 34 (3) ◽  
pp. 1081-1097
Author(s):  
Mian Xu ◽  
Wenshou Tian ◽  
Jiankai Zhang ◽  
Tao Wang ◽  
Kai Qie
Keyword(s):  
Sea Ice ◽  
Rossby Wave ◽  
North Pacific ◽  
East Asian ◽  
Late Winter ◽  
East Asian Trough ◽  
The North ◽  
Wave Ray ◽  
The North Pacific ◽  
Sea Ice Reduction

AbstractUsing the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) dataset and the Specified Chemistry Whole Atmosphere Community Climate Model (WACCM-SC), the impacts of sea ice reduction in the Barents–Kara Seas (BKS) on the East Asian trough (EAT) in late winter are investigated. Results from both reanalysis data and simulations show that the BKS sea ice reduction leads to a deepened EAT in late winter, especially in February, while the EAT axis tilt is not sensitive to the BKS sea ice reduction. Further analysis shows that the BKS sea ice reduction influences the EAT through the tropospheric and stratospheric pathways. For the tropospheric pathway, the results from a linearized barotropic model and Rossby wave ray tracing model reveal that long Rossby wave trains stimulated by the BKS sea ice loss propagate downstream to the North Pacific, strengthening the EAT. For the stratospheric pathway, the upward planetary waves enhanced by the BKS sea ice reduction shift the subpolar westerlies near the tropopause southward. With the critical lines displaced equatorward, the poleward transient eddies break at lower latitudes, shifting the eddy momentum deposit throughout the troposphere equatorward. Tropospheric westerlies maintained by eddy momentum deposit are also shifted southward, inducing the cyclonic anomalies over the North Pacific and deepening the EAT in late winter. Nudging experiments show that the tropospheric pathway only contributes to around 29.7% of the deepening of the EAT in February induced by the BKS sea ice loss, while the remaining 70.3% is caused by stratosphere–troposphere coupling.

scholarly journals Simulated Response to Recent Freshwater Flux Change over the Gulf Stream and Its Extension: Coupled Ocean–Atmosphere Adjustment and Atlantic–Pacific Teleconnection

2011 ◽  
Vol 24 (15) ◽  
pp. 3971-3988 ◽  
Author(s):  
Liping Zhang ◽  
Lixin Wu ◽  
Jiaxu Zhang
Keyword(s):  
North Atlantic ◽  
Gulf Stream ◽  
Tropical Pacific ◽  
Late Winter ◽  
Freshwater Flux ◽  
The North ◽  
Flux Change ◽  
Ocean Atmosphere ◽  
The North Atlantic ◽  
The Tropical Pacific

Abstract Recent observation has shown that the dominant mode of the net freshwater flux variations over the North Atlantic Ocean is the significant trend of freshwater loss over the Gulf Stream region and its extension. In this paper, the coupled ocean–atmosphere response to this freshwater flux change is investigated based on a series of the Fast Ocean–Atmosphere Model coupled-model experiments. The model demonstrates that the freshwater loss over the Gulf Stream and its extension region directly forces an anomalous cyclonic gyre and triggers a SST dipole with cooling in the western subtropical and warming in the eastern subpolar North Atlantic. The freshwater loss also forces a significant response in the atmosphere with a negative NAO-like response in early winter and a basin-scale ridge resembling the eastern Atlantic mode (EAM) in late winter. The salinification also strengthens the Atlantic meridional overturning circulation and thus the poleward heat transport, leading to tropical cooling. The freshwater loss over the Gulf Stream and its extension also leads to an El Niño–like warming in the tropical Pacific and cooling in the North Pacific, similar to the responses in previous water-hosing experiments with an input of freshwater in the subpolar North Atlantic. The tropical Pacific responses subsequently strengthen the Northern Hemispheric atmospheric anomalies in early winter, but reverse them in late winter through an emanation of Rossby wave trains. Overall, the tropical Pacific air–sea coupling plays a damping role, while local air–sea coupling tends to enhance the ocean and atmospheric responses over the North Atlantic.

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>

The Linkage between the Eastern Pacific Teleconnection Pattern and Convective Heating over the Tropical Western Pacific

2015 ◽  
Vol 28 (14) ◽  
pp. 5783-5794 ◽  
Author(s):  
Benkui Tan ◽  
Jiacan Yuan ◽  
Ying Dai ◽  
Steven B. Feldstein ◽  
Sukyoung Lee
Keyword(s):  
Rossby Wave ◽  
Southern China ◽  
Wave Train ◽  
Gulf Of Alaska ◽  
Teleconnection Pattern ◽  
Eastern Pacific ◽  
Late Winter ◽  
Convective Heating ◽  
Central Pacific ◽  
Wave Trains

Abstract The eastern Pacific (EP) pattern is a recently detected atmospheric teleconnection pattern that frequently occurs during late winter. Through analysis of daily ERA-Interim data and outgoing longwave radiation data for the period of 1979–2011, it is shown here that the formation of the EP is preceded by an anomalous tropical convection dipole, with one extremum located over the eastern Indian Ocean–Maritime Continent and the other over the central Pacific. This is followed by the excitation of two quasi-stationary Rossby wave trains. Departing from the subtropics, north of the region of anomalous convection, one Rossby wave train propagates eastward along the East Asian jet from southern China toward the eastern Pacific. The second wave train propagates northward from east of Japan toward eastern Siberia and then turns southeastward to the Gulf of Alaska. Both wave trains are associated with wave activity flux convergence where the EP pattern develops. The results from an examination of the E vector suggest that the EP undergoes further growth with the aid of positive feedback from high-frequency transient eddies. The frequency of occurrence of the dipole convection anomaly increases significantly from early to late winter, a finding that suggests that it is the seasonal change in the convection anomaly that accounts for the EP being more dominant in late winter.

scholarly journals Indo-Pacific–Induced Wave Trains during Austral Autumn and Their Effect on Australian Rainfall

2014 ◽  
Vol 27 (9) ◽  
pp. 3208-3221 ◽  
Author(s):  
Peter van Rensch ◽  
Wenju Cai
Keyword(s):  
Indian Ocean ◽  
Rossby Wave ◽  
Wave Train ◽  
Tropical Indian Ocean ◽  
The North ◽  
Eastern Australia ◽  
Wave Trains ◽  
The Impact ◽  
Austral Autumn ◽  
Australian Rainfall

Abstract During austral winter and spring, the El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD), individually or in combination, induce equivalent-barotropic Rossby wave trains, affecting midlatitude Australian rainfall. In autumn, ENSO is at its annual minimum, and the IOD has usually not developed. However, there is still a strong equivalent-barotropic Rossby wave train associated with tropical Indian Ocean sea surface temperature (SST) variability, with a pressure anomaly to the south of Australia. This wave train is similar in position, but opposite in sign, to the IOD-induced wave train in winter and spring and has little effect on Australian rainfall. This study shows that the SST in the southeastern tropical Indian Ocean (SETIO) displays a high variance during austral autumn, with a strong influence on southeast and eastern Australian rainfall. However, this influence is slightly weaker than that associated with SST to the north of Australia, which shares fluctuations with SST in the SETIO region. The SST north of Australia is coherent with a convective dipole in the tropical Pacific Ocean, which is the source of a wave train to the east of Australia influencing rainfall in eastern Australia. ENSO Modoki is a contributor to the convective dipole and as a result it exerts a weak influence on eastern Australian rainfall through the connecting north Australian SST relationship. Thus, SST to the north of Australia acts as the main agent for delivering the impact of tropical Indo-Pacific variability to eastern Australia.

scholarly journals The Atlantic Multidecadal Variability phase-dependence of teleconnection between the North Atlantic Oscillation in February and the Tibetan Plateau in March

2021 ◽  
pp. 1-40
Author(s):  
Jingyi Li ◽  
Fei Li ◽  
Shengping He ◽  
Huijun Wang ◽  
Yvan J Orsolini
Keyword(s):  
Tibetan Plateau ◽  
Rossby Wave ◽  
North Atlantic ◽  
Wave Train ◽  
The Tibetan Plateau ◽  
Atlantic Multidecadal Variability ◽  
Multidecadal Variability ◽  
The North ◽  
Rossby Wave Train ◽  
The North Atlantic

AbstractThe Tibetan Plateau (TP), referred to as the “Asian water tower”, contains one of the largest land ice masses on Earth. The local glacier shrinkage and frozen-water storage are strongly affected by variations in surface air temperature over the TP (TPSAT), especially in springtime. This study reveals that the relationship between the February North Atlantic Oscillation (NAO) and March TPSAT is unstable with time and regulated by the phase of the Atlantic Multidecadal Variability (AMV). The significant out-of-phase connection occurs only during the warm phase of AMV (AMV+). The results show that during the AMV+, the negative phase of the NAO persists from February to March, and is accompanied by a quasi-stationary Rossby wave train trapped along a northward-shifted subtropical westerly jet stream across Eurasia, inducing an anomalous adiabatic descent that warms the TP. However, during the cold phase of the AMV, the negative NAO can not persist into March. The Rossby wave train propagates along the well-separated polar and subtropical westerly jets, and the NAO−TPSAT connection is broken. Further investigation suggests that the enhanced synoptic eddy and low frequency flow (SELF) interaction over the North Atlantic in February and March during the AMV+, caused by the enhanced and southward-shifted storm track, help maintain the NAO anomaly pattern via positive eddy feedback. This study provides a new detailed perspective on the decadal variability of the North Atlantic−TP connection in late winter−early spring.

Some aspects of Rossby waves and non-linear dynamics

2021 ◽  
Author(s):  
Brian Hoskins
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Tropical Convection ◽  
Jet Streams ◽  
Linear Dynamics ◽  
Middle Latitudes ◽  
Weather Events ◽  
Wave Trains ◽  
The Impact ◽  
Weather Anomalies

<p>Rossby waves are able to communicate weather anomalies in one region to other regions. There anomalous weather events can follow if the wave is persistent and large amplitude. They can also be caused by breaking of the wave leading to blocking. The impact on the middle latitudes via stationary Rossby wave trains triggered by tropical convection anomalies has been of interest for many years. However, tropical convective events can also interact with higher latitude jet streams and the weather systems on them through a very different mechanism. In this talk, some examples will be given that indicate the flaring of tropical convection can lead to strong upper tropospheric outflows in which filaments of air with near equatorial values of PV interact with higher latitude jet streams and the weather systems on them.</p>

The role of an Indian Ocean heating dipole in the ENSO teleconnection to the North Atlantic in early winter in the 20th century in observations and CMIP5 simulations

2020 ◽  
Author(s):  
Fred Kucharski ◽  
Manish K. Joshi ◽  
Mohammad Adnan Abid
Keyword(s):  
Indian Ocean ◽  
North Atlantic ◽  
Cmip5 Models ◽  
Late Winter ◽  
Early Winter ◽  
Atlantic Region ◽  
The North ◽  
The Indian Ocean ◽  
The North Atlantic

<p>In this study the role of an Indian Ocean heating dipole anomaly in the transition of the North Atlantic circulation response to ENSO from early to late winter is analysed using 20th century observations and simulations from the fifth Coupled Model Intercomparison Project (CMIP5). It is shown that in early winter a warm (cold) ENSO even is connected trough an atmospheric bridge with positive (negative) rainfall anomalies in the western and negative (positive) anomalies in the eastern Indian Ocean. The early winter heating dipole teleconnected to a warm (cold) ENSO event can set up a wavetrain emanating from the south Asian subtropical jet region that reaches the North Atlantic and leads to response that spatially projects onto the positive (negative) phase of the North Atlantic Oscillation (NAO). The Indian Ocean heating dipole is partly forced as an atmospheric teleconnection by ENSO, but can also exist independently and is not related to local Indian Ocean SST forcing. The Indian Ocean heating dipole response to ENSO is much weaker in late winter (February and March) and not able to force significant signals in the North Atlantic region. CMIP5 models reproduce the early winter heating dipole reponse to ENSO and the ENSO response transition in the North Atlantic region to some extend, but with weaker amplitude. Generally models that have a strong early winter ENSO heating dipole teleconnection to the Indian Ocean also reproduce the North Atlantic response. If an Indian Ocean vertical velocity dipole index is defined, overall CMIP5 models are able to reproduce the extratropical responses in early winter reasonably well.</p>

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