Afro-Eurasian Intermediate-Frequency Teleconnection and Modulation by ENSO

2018 ◽  
Vol 31 (19) ◽  
pp. 8121-8139 ◽  
Author(s):  
Shan He ◽  
Song Yang ◽  
Mengmeng Lu ◽  
Zhenning Li
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Storm Track ◽  
Intermediate Frequency ◽  
Interactive Systems ◽  
Atmospheric Variability ◽  
Atmospheric Teleconnection ◽  
Waveguide Effect

The Afro-Eurasian intermediate-frequency atmospheric teleconnection conveys meteorological signals zonally, leads to various atmospheric variations, and causes extreme events along its path. This study, aimed at demonstrating the characteristics of the teleconnection, reveals that the teleconnection accounts for nearly half of the atmospheric variability and significantly influences different meteorological fields. With the propagation of signals associated with the teleconnection, local weather varies from prolonged dry and warm days to extended wet and cold days. El Niño–Southern Oscillation (ENSO) modulates the interannual variation of the teleconnection: it becomes more active and its downstream pattern shifts southward during El Niño events. Two responsible mechanisms are proposed for the ENSO modulation: the eddy-to-eddy interaction that leads to the change in the activeness of the teleconnection and the waveguide effect that accounts for the shift of the teleconnection. First, the El Niño–related Atlantic anomalies of the Rossby wave train and storm track amplify the Atlantic disturbances of the intermediate frequency and thus the activeness of the teleconnection. Second, during El Niño years, the East Asian jet stream shifts southward, resulting in the southward shifts of the downstream waveguide effect and thus the downstream pattern. This study also demonstrates that when investigating an atmospheric mode or its impacts, the signals of different time scales should be separated and the cross-frequency interactive systems necessitate examinations.

scholarly journals Interannual Relationship between ENSO and Atlantic Storm Track in Spring Modulated by the Atlantic Multidecadal Oscillation

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 419 ◽  
Author(s):  
Chenfei Liao ◽  
Haiming Xu ◽  
Jiechun Deng ◽  
Leying Zhang
Keyword(s):  
North America ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Storm Track ◽  
Atlantic Multidecadal Oscillation ◽  
Upstream Region ◽  
Short Term ◽  
Easterly Wind

It has been well documented that storm track activity are closely related to the weather and short-term climate variability in the extratropics, which is affected by sea surface temperature anomalies over the tropical eastern Pacific Ocean. Interannual relationship between the El Niño-Southern Oscillation (ENSO) and the Atlantic storm track (AST) in spring modulated by the Atlantic multidecadal oscillation (AMO) was investigated using reanalysis data and model simulations in this study. The meridional displacement of the AST is significantly correlated with ENSO during negative AMO phase, while no significant relationship is found during positive AMO phase. This may be due to the difference of 500-hPa geopotential height anomalies induced by ENSO in different AMO phases. For an El Niño event during the negative AMO phase, an anomalous 500-hPa wave train propagates eastward across the North American continent, with positive height anomalies at the high latitudes, extending from South Canada to Newfoundland. Thus, easterly wind anomalies appear over central North America, upstream of the negative AST anomaly. Accordingly, the local eddy growth rate (EGR) and baroclinic energy conversion (BC) are obviously reduced, which weaken (strengthen) the southern (northern) part of the climatological AST. As a result, the AST is shifted northward significantly. During the positive AMO phase, the ENSO-related anomalous wave train at 500 hPa only propagates northeastward and is largely suppressed over Northwest Canada, with positive height anomalies confined to the northwest of North America. Therefore, no significant changes of the westerly jet, EGR and BC are found in the upstream region of the AST, and the meridional location of the AST generally remains unchanged. Most previous studies investigate AST variabilities in winter, and few focus on AST in spring. This work may be helpful in understanding more about the interannual and interdecadal variations of springtime AST and in further studying the weather and short-term climate changes caused by AST.

scholarly journals An Asymmetry in the IOD and ENSO Teleconnection Pathway and Its Impact on Australian Climate

2012 ◽  
Vol 25 (18) ◽  
pp. 6318-6329 ◽  
Author(s):  
Wenju Cai ◽  
Peter van Rensch ◽  
Tim Cowan ◽  
Harry H. Hendon
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Austral Spring ◽  
Southeast Australia ◽  
Unit Change ◽  
The Impact ◽  
Sst Anomalies

Abstract Recent research has shown that the climatic impact from El Niño–Southern Oscillation (ENSO) on middle latitudes west of the western Pacific (e.g., southeast Australia) during austral spring (September–November) is conducted via the tropical Indian Ocean (TIO). However, it is not clear whether this impact pathway is symmetric about the positive and negative phases of ENSO and the Indian Ocean dipole (IOD). It is shown that a strong asymmetry does exist. For ENSO, only the impact from El Niño is conducted through the TIO pathway; the impact from La Niña is delivered through the Pacific–South America pattern. For the IOD, a greater convection anomaly and wave train response occurs during positive IOD (pIOD) events than during negative IOD (nIOD) events. This “impact asymmetry” is consistent with the positive skewness of the IOD, principally due to a negative skewness of sea surface temperature (SST) anomalies in the east IOD (IODE) pole. In the IODE region, convection anomalies are more sensitive to a per unit change of cold SST anomalies than to the same unit change of warm SST anomalies. This study shows that the IOD skewness occurs despite the greater damping, rather than due to a breakdown of this damping as suggested by previous studies. This IOD impact asymmetry provides an explanation for much of the reduction in spring rainfall over southeast Australia during the 2000s. Key to this rainfall reduction is the increased occurrences of pIOD events, more so than the lack of nIOD events.

scholarly journals Maximizing ENSO as a source of western US hydroclimate predictability

2019 ◽  
Vol 54 (1-2) ◽  
pp. 351-372 ◽  
Author(s):  
Christina M. Patricola ◽  
John P. O’Brien ◽  
Mark D. Risser ◽  
Alan M. Rhoades ◽  
Travis A. O’Brien ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Wave Train ◽  
Global Climate Model ◽  
Western Us ◽  
El Niño Events ◽  
Fixed Region ◽  
Sst Anomalies ◽  
El Nino Events

Abstract Until recently, the El Niño–Southern Oscillation (ENSO) was considered a reliable source of winter precipitation predictability in the western US, with a historically strong link between extreme El Niño events and extremely wet seasons. However, the 2015–2016 El Niño challenged our understanding of the ENSO-precipitation relationship. California precipitation was near-average during the 2015–2016 El Niño, which was characterized by warm sea surface temperature (SST) anomalies of similar magnitude compared to the extreme 1997–1998 and 1982–1983 El Niño events. We demonstrate that this precipitation response can be explained by El Niño’s spatial pattern, rather than internal atmospheric variability. In addition, observations and large-ensembles of regional and global climate model simulations indicate that extremes in seasonal and daily precipitation during strong El Niño events are better explained using the ENSO Longitude Index (ELI), which captures the diversity of ENSO’s spatial patterns in a single metric, compared to the traditional Niño3.4 index, which measures SST anomalies in a fixed region and therefore fails to capture ENSO diversity. The physically-based ELI better explains western US precipitation variability because it tracks the zonal shifts in tropical Pacific deep convection that drive teleconnections through the response in the extratropical wave-train, integrated vapor transport, and atmospheric rivers. This research provides evidence that ELI improves the value of ENSO as a predictor of California’s seasonal hydroclimate extremes compared to traditional ENSO indices, especially during strong El Niño events.

Ocean dynamics are key to extratropical forcing of El Niño

2021 ◽  
pp. 1-34
Author(s):  
Soumi Chakravorty ◽  
Renellys C. Perez ◽  
Bruce T. Anderson ◽  
Sarah M. Larson ◽  
Benjamin S. Giese ◽  
...  
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Ocean Dynamics ◽  
Positive Phase ◽  
Trade Wind ◽  
Atmospheric Variability ◽  
Central Pacific ◽  
Central Pacific El Niño ◽  
Extratropical Forcing

AbstractThe El Niño/Southern Oscillation (ENSO) has been recently linked with extratropical-Pacific atmospheric variability. The two key mechanisms connecting the atmospheric variability of extratropical-Pacific with ENSO are the heat-flux driven “seasonal footprinting mechanism” (SFM) and the ocean-dynamics driven “trade wind charging” (TWC) mechanism. However, their relative contributions to ENSO are still unknown. Here we present modeling evidence that the positive phase of the SFM generates a weaker, short-lived central Pacific El Niño-like warming pattern in the fall, whereas the TWC positive phase leads to a wintertime eastern Pacific El Niño-like warming. When both mechanisms are active, a strong, persistent El Niño develops. While both mechanisms can trigger equatorial wind anomalies that generate an El Niño, the strength and persistence of the warming depends on the subsurface heat content buildup by the TWC mechanism. These results suggest that while dynamical-coupling associated with extratropical forcing is crucial to maintain an El Niño, thermodynamical-coupling is an extratropical source of El Niño diversity.

Interannual Variation of the Spring and Summer Precipitation over the Three River Source Region in China and the Associated Regimes

2018 ◽  
Vol 31 (18) ◽  
pp. 7441-7457 ◽  
Author(s):  
Bo Sun ◽  
Huijun Wang
Keyword(s):  
Interannual Variability ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Asian Summer Monsoon ◽  
Wave Train ◽  
Summer Precipitation ◽  
Interdecadal Variability ◽  
Water Vapor Transport ◽  
Spring Precipitation

This study analyzes the interannual and interdecadal variability of spring and summer precipitation over the Three River Source (TRS) region in China using four datasets. A general consistency is revealed among the four datasets with regard to the interannual and interdecadal variability of TRS precipitation during 1979–2015, demonstrating a confidence of the four datasets in representing the precipitation variability over the TRS region. The TRS spring and summer precipitation shows distinct interannual and interdecadal variability, with an overall increasing trend in the spring precipitation and an interdecadal oscillation in the summer precipitation. The regimes associated with the interannual variability of TRS spring and summer precipitation are further investigated. The interannual variability of TRS spring precipitation is essentially modulated by an anomalous easterly water vapor transport (WVT) branch associated with the leading mode of Eurasian spring circulation. El Niño–Southern Oscillation (ENSO) may affect the interannual variability of TRS spring precipitation by causing southerly WVT anomalies toward the TRS region. The interannual variability of TRS summer precipitation is essentially modulated by an anomalous southwesterly WVT branch over the TRS region, which is mainly associated with a Eurasian wave train connected with the summer North Atlantic Oscillation. A strong East Asian summer monsoon and an El Niño–decaying summer may also contribute to the southwesterly WVT anomalies over the TRS region.

scholarly journals A New Extratropical Tracer Describing the Role of the Western Pacific in the Onset of El Niño: Implications for ENSO Understanding and Forecasting

2011 ◽  
Vol 24 (5) ◽  
pp. 1425-1437 ◽  
Author(s):  
Joan Ballester ◽  
Miquel Àngel Rodríguez-Arias ◽  
Xavier Rodó
Keyword(s):  
High Latitude ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Function Analysis ◽  
Wave Train ◽  
Tropical Pacific ◽  
Central Pacific ◽  
High Latitude Region ◽  
Southern High Latitude

Abstract A complex empirical orthogonal function analysis was applied to sea surface temperature data in the southern high-latitude Pacific to identify and isolate primary processes related to the onset of El Niño (EN) events. Results were compared to those of a lead–lag composite analysis of a new tracer of EN events in the southern high-latitude Pacific, the Ross–Bellingshausen (RB) dipole. Both techniques successfully isolate the main low-frequency features in the interaction among the tropical and southern extratropical Pacific during the onset of recent eastward-propagating EN events. Particularly, positive RB peaks were followed by EN events around 9 months later, on average. In turn, RB maxima were anticipated by local warm anomalies in the western tropical Pacific a year in advance, which enhance local convection and upper-troposphere divergence and generate an anomalous wave train extending eastward and poleward in the southern extratropics. In addition, circulation changes lead to a warm SST region in the central tropical Pacific, which is then strengthened by suppressed equatorial easterlies. Convection thus starts to move to the central Pacific and so the Walker circulation weakens, activating the positive Bjerknes feedback that ultimately leads to the development of an EN event. These results highlight the enormous potential of the interaction between the tropics and this high-latitude region in the Southern Hemisphere to increase El Niño–Southern Oscillation understanding and to improve the long-lead prediction skill of EN phenomenon.

scholarly journals Distinguishing the effects of internal and forced atmospheric variability in climate networks

2014 ◽  
Vol 21 (3) ◽  
pp. 617-631 ◽  
Author(s):  
J. I. Deza ◽  
C. Masoller ◽  
M. Barreiro
Keyword(s):  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Internal Variability ◽  
Equatorial Pacific Ocean ◽  
Atmospheric Variability ◽  
The North ◽  
Ordinal Patterns ◽  
The North Atlantic Oscillation ◽  
Climate Networks

Abstract. The fact that the climate on the earth is a highly complex dynamical system is well-known. In the last few decades great deal of effort has been focused on understanding how climate phenomena in one geographical region affects the climate of other regions. Complex networks are a powerful framework for identifying climate interdependencies. To further exploit the knowledge of the links uncovered via the network analysis (for, e.g., improvements in prediction), a good understanding of the physical mechanisms underlying these links is required. Here we focus on understanding the role of atmospheric variability, and construct climate networks representing internal and forced variability using the output of an ensemble of AGCM runs. A main strength of our work is that we construct the networks using MIOP (mutual information computed from ordinal patterns), which allows the separation of intraseasonal, intra-annual and interannual timescales. This gives further insight to the analysis of climatological data. The connectivity of these networks allows us to assess the influence of two main indices, NINO3.4 – one of the indices used to describe ENSO (El Niño–Southern oscillation) – and of the North Atlantic Oscillation (NAO), by calculating the networks from time series where these indices were linearly removed. A main result of our analysis is that the connectivity of the forced variability network is heavily affected by "El Niño": removing the NINO3.4 index yields a general loss of connectivity; even teleconnections between regions far away from the equatorial Pacific Ocean are lost, suggesting that these regions are not directly linked, but rather, are indirectly interconnected via El Niño, particularly at interannual timescales. On the contrary, on the internal variability network – independent of sea surface temperature (SST) forcing – the links connecting the Labrador Sea with the rest of the world are found to be significantly affected by NAO, with a maximum at intra-annual timescales. While the strongest non-local links found are those forced by the ocean, the presence of teleconnections due to internal atmospheric variability is also shown.

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