The Dynamics of the ENSO–Atlantic Hurricane Teleconnection: ENSO-Related Changes to the North African–Asian Jet Affect Atlantic Basin Tropical Cyclogenesis

2009 ◽  
Vol 22 (9) ◽  
pp. 2458-2482 ◽  
Author(s):  
Jeffrey Shaman ◽  
Steven K. Esbensen ◽  
Eric D. Maloney
Keyword(s):  
Zonal Wind ◽  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
Tropical Storm ◽  
Tropical Cyclogenesis ◽  
Tropical Atlantic ◽  
North African ◽  
Atlantic Basin ◽  
The North

Abstract The nature of the teleconnection linking ENSO variability with Atlantic basin tropical storm formation is investigated. Solutions of the linearized barotropic vorticity equation forced with August–October El Niño event divergence produce upper-tropospheric vorticity anomalies over the Sahel and at the mouth of the North African–Asian (NAA) jet over the tropical Atlantic. These responses are similar in magnitude and orientation to observed ENSO vorticity variability for this region. Further investigation reveals that the vorticity anomalies over the subtropical Atlantic develop primarily in response to very low wavenumber, westward-propagating stationary Rossby waves excited by El Niño–related convective activity over the equatorial Pacific Ocean. However, the dynamics of this teleconnection change as the Atlantic basin hurricane season progresses. In August and September the response is dominated by the westward-propagating stationary Rossby waves that alter vorticity within the NAA jet and to its south. The upper-tropospheric nondivergent zonal wind anomalies produced by these vorticity anomalies are similar in pattern to observed zonal wind and vertical zonal wind shear anomalies, which suppress Atlantic basin tropical cyclogenesis. By October, eastward-propagating signals also develop over the tropical Atlantic Ocean in response to El Niño conditions. Over the main development region of Atlantic basin tropical cyclogenesis, these eastward-propagating Rossby waves appear to destructively interfere with the vorticity changes produced by the westward-propagating Rossby waves within the NAA jet. In addition, the NAA jet has shifted south by October. Consequently, the resultant upper-tropospheric nondivergent zonal wind perturbations for October are weak and suggest that ENSO should have little effect on rates of Atlantic basin tropical cyclogenesis during October. Statistical analyses of monthly ENSO-related changes in Atlantic basin tropical storm formation support this hypothesis.

scholarly journals Spurious North Tropical Atlantic precursors to El Niño

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Wenjun Zhang ◽  
Feng Jiang ◽  
Malte F. Stuecker ◽  
Fei-Fei Jin ◽  
Axel Timmermann
Keyword(s):  
El Niño ◽  
Cross Correlation ◽  
El Nino ◽  
Southern Oscillation ◽  
Global Climate ◽  
Tropical Atlantic ◽  
The North ◽  
Sst Variability ◽  
Primary Driver ◽  
North Tropical Atlantic

AbstractThe El Niño-Southern Oscillation (ENSO), the primary driver of year-to-year global climate variability, is known to influence the North Tropical Atlantic (NTA) sea surface temperature (SST), especially during boreal spring season. Focusing on statistical lead-lag relationships, previous studies have proposed that interannual NTA SST variability can also feed back on ENSO in a predictable manner. However, these studies did not properly account for ENSO’s autocorrelation and the fact that the SST in the Atlantic and Pacific, as well as their interaction are seasonally modulated. This can lead to misinterpretations of causality and the spurious identification of Atlantic precursors for ENSO. Revisiting this issue under consideration of seasonality, time-varying ENSO frequency, and greenhouse warming, we demonstrate that the cross-correlation characteristics between NTA SST and ENSO, are consistent with a one-way Pacific to Atlantic forcing, even though the interpretation of lead-lag relationships may suggest otherwise.

scholarly journals Decadal Shift in El Niño Influences on Indo–Western Pacific and East Asian Climate in the 1970s*

2010 ◽  
Vol 23 (12) ◽  
pp. 3352-3368 ◽  
Author(s):  
Shang-Ping Xie ◽  
Yan Du ◽  
Gang Huang ◽  
Xiao-Tong Zheng ◽  
Hiroki Tokinaga ◽  
...  
Keyword(s):  
Indian Ocean ◽  
El Niño ◽  
Rossby Waves ◽  
El Nino ◽  
East Asian ◽  
North Indian Ocean ◽  
Ocean Warming ◽  
Interdecadal Change ◽  
Wind Pattern ◽  
The North

Abstract El Niño’s influence on the subtropical northwest (NW) Pacific climate increased after the climate regime shift of the 1970s. This is manifested in well-organized atmospheric anomalies of suppressed convection and a surface anticyclone during the summer (June–August) of the El Niño decay year [JJA(1)], a season when equatorial Pacific sea surface temperature (SST) anomalies have dissipated. In situ observations and ocean–atmospheric reanalyses are used to investigate mechanisms for the interdecadal change. During JJA(1), the influence of the El Niño–Southern Oscillation (ENSO) on the NW Pacific is indirect, being mediated by SST conditions over the tropical Indian Ocean (TIO). The results here show that interdecadal change in this influence is due to changes in the TIO response to ENSO. During the postregime shift epoch, the El Niño teleconnection excites downwelling Rossby waves in the south TIO by anticyclonic wind curls. These Rossby waves propagate slowly westward, causing persistent SST warming over the thermocline ridge in the southwest TIO. The ocean warming induces an antisymmetric wind pattern across the equator, and the anomalous northeasterlies cause the north Indian Ocean to warm through JJA(1) by reducing the southwesterly monsoon winds. The TIO warming excites a warm Kelvin wave in tropospheric temperature, resulting in robust atmospheric anomalies over the NW Pacific that include the surface anticyclone. During the preregime shift epoch, ENSO is significantly weaker in variance and decays earlier than during the recent epoch. Compared to the epoch after the mid-1970s, SST and wind anomalies over the TIO are similar during the developing and mature phases of ENSO but are very weak during the decay phase. Specifically, the southern TIO Rossby waves are weaker, so are the antisymmetric wind pattern and the North Indian Ocean warming during JJA(1). Without the anchor in the TIO warming, atmospheric anomalies over the NW Pacific fail to develop during JJA(1) prior to the mid-1970s. The relationship of the interdecadal change to global warming and implications for the East Asian summer monsoon are discussed.

scholarly journals Modeling the Dependence of Tropical Storm Counts in the North Atlantic Basin on Climate Indices

2010 ◽  
Vol 138 (7) ◽  
pp. 2681-2705 ◽  
Author(s):  
Gabriele Villarini ◽  
Gabriel A. Vecchi ◽  
James A. Smith
Keyword(s):  
Time Series ◽  
North Atlantic ◽  
Tropical Storm ◽  
Climate Indices ◽  
Tropical Storms ◽  
Tropical Atlantic ◽  
Atlantic Basin ◽  
North Atlantic Basin ◽  
The North ◽  
The North Atlantic

Abstract The authors analyze and model time series of annual counts of tropical storms lasting more than 2 days in the North Atlantic basin and U.S. landfalling tropical storms over the period 1878–2008 in relation to different climate indices. The climate indices considered are the tropical Atlantic sea surface temperature (SST), tropical mean SST, the North Atlantic Oscillation (NAO), and the Southern Oscillation index (SOI). Given the uncertainties associated with a possible tropical storm undercount in the presatellite era, two different time series of counts for the North Atlantic basin are employed: one is the original (uncorrected) tropical storm record maintained by the National Hurricane Center and the other one is with a correction for the estimated undercount associated with a changing observation network. Two different SST time series are considered: the Met Office’s HadISSTv1 and NOAA’s Extended Reconstructed SST. Given the nature of the data (counts), a Poisson regression model is adopted. The selection of statistically significant covariates is performed by penalizing models for adding extra parameters and two penalty functions are used. Depending on the penalty function, slightly different models, both in terms of covariates and dependence of the model’s parameter, are obtained, showing that there is not a “single best” model. Moreover, results are sensitive to the undercount correction and the SST time series. Suggestions concerning the model to use are provided, driven by both the outcomes of the statistical analyses and the current understanding of the underlying physical processes responsible for the genesis, development, and tracks of tropical storms in the North Atlantic basin. Although no single model is unequivocally superior to the others, the authors suggest a very parsimonious family of models using as covariates tropical Atlantic and tropical mean SSTs.

Impact of the North African drought and El Niño on mineral dust in the Barbados trade winds

Nature ◽  
1986 ◽  
Vol 320 (6064) ◽  
pp. 735-738 ◽  
Author(s):  
Joseph M. Prospero ◽  
Ruby T. Nees
Keyword(s):  
El Niño ◽  
Mineral Dust ◽  
El Nino ◽  
North African ◽  
Trade Winds ◽  
The North

scholarly journals The Physical Basis for Predicting Atlantic Sector Seasonal-to-Interannual Climate Variability*

2006 ◽  
Vol 19 (23) ◽  
pp. 5949-5970 ◽  
Author(s):  
Yochanan Kushnir ◽  
Walter A. Robinson ◽  
Ping Chang ◽  
Andrew W. Robertson
Keyword(s):  
Climate Variability ◽  
North Atlantic ◽  
El Niño ◽  
El Nino ◽  
South Atlantic ◽  
Tropical Atlantic ◽  
Coupled Models ◽  
Atlantic Sector ◽  
The North ◽  
The North Atlantic

Abstract This paper reviews the observational and theoretical basis for the prediction of seasonal-to-interannual (S/I) climate variability in the Atlantic sector. The emphasis is on the large-scale picture rather than on regional details. The paper is divided into two main parts: a discussion of the predictability of the North Atlantic Oscillation (NAO)—the dominant pattern of variability in the North Atlantic—and a review of the tropical Atlantic prediction problem. The remote effects of El Niño are also mentioned as an important factor in Atlantic climate variability. Only a brief discussion is provided on the subject of South Atlantic climate predictability. Because of its chaotic dynamical nature, the NAO and its related rainfall and temperature variability, while highly significant over Europe and North America, are largely unpredictable. This also affects the predictive skill over the tropical Atlantic, because the NAO interferes with the remote influence of El Niño. That said, there appears to be an insufficiently understood, marginal signal in the NAO behavior that may be predictable and thus useful to certain end users. It is manifested in the deviation of the NAO temporal behavior from first-order autoregressive behavior. Tropical Atlantic climate variability centers on the sensitivity of the marine ITCZ to remote forcing from the equatorial Pacific and interactions with underlying sea surface temperature (SST) variability. Both mechanisms are potentially predictable—that is, given the underlying SSTs and the strength of El Niño, one could determine with a high degree of skill the anomalies in ITCZ position and intensity. However, local SSTs are easily affected by largely unpredictable North and South Atlantic phenomena, such as the NAO. In addition, the local ocean–atmosphere coupling in the Atlantic acts on relatively short time scales. Thus, in reality the level of skill indicated by forced model simulations are difficult to achieve. The use of coupled models may improve the prospects of tropical Atlantic prediction.

scholarly journals Studies of El Niño and Interdecadal Variability in Tropical Sea Surface Temperatures Using a Nonnormal Filter

2006 ◽  
Vol 19 (22) ◽  
pp. 5796-5815 ◽  
Author(s):  
Cécile Penland ◽  
Ludmila Matrosova
Keyword(s):  
El Niño ◽  
El Nino ◽  
Equatorial Indian Ocean ◽  
Sea Surface ◽  
Sea Surface Temperatures ◽  
Tropical Atlantic ◽  
The North ◽  
Surface Temperatures ◽  
Parabolic Structure ◽  
Tropical Sea

Abstract A dynamically based filter is used to separate tropical sea surface temperatures (SSTs) into three components: the evolving El Niño signal, the global tropical trend, and the background. The components thus isolated are not independent. On the contrary, this procedure allows us to see the importance of the interdecadal signal to the predictability of El Niño. The data filtered in this way reveal El Niño signals in the equatorial Indian Ocean and in the north tropical Atlantic Ocean that are remarkably similar. A signature of El Niño in the south tropical Atlantic leads Niño-3.4 SST anomalies by about 9 months. The time series of a global tropical trend is found to have a very smooth parabolic structure. In unfiltered data, this trend conspires with El Niño to obscure a meridional tropical Atlantic dipole, which is significant in the filtered background SST data.

scholarly journals Local Coupled Equatorial Variability versus Remote ENSO Forcing in an Intermediate Coupled Model of the Tropical Atlantic

2006 ◽  
Vol 19 (20) ◽  
pp. 5227-5252 ◽  
Author(s):  
Serena Illig ◽  
Boris Dewitte
Keyword(s):  
Mixed Layer ◽  
El Niño ◽  
Time Scale ◽  
El Nino ◽  
Coupled Model ◽  
Tropical Atlantic ◽  
Equatorial Atlantic ◽  
Layer Model ◽  
Intermediate Coupled Model ◽  
Mixed Layer Model

Abstract The relative roles played by the remote El Niño–Southern Oscillation (ENSO) forcing and the local air–sea interactions in the tropical Atlantic are investigated using an intermediate coupled model (ICM) of the tropical Atlantic. The oceanic component of the ICM consists of a six-baroclinic mode ocean model and a simple mixed layer model that has been validated from observations. The atmospheric component is a global atmospheric general circulation model developed at the University of California, Los Angeles (UCLA). In a forced context, the ICM realistically simulates both the sea surface temperature anomaly (SSTA) variability in the equatorial band, and the relaxation of the Atlantic northeast trade winds and the intensification of the equatorial westerlies in boreal spring that usually follows an El Niño event. The results of coupled experiments with or without Pacific ENSO forcing and with or without explicit air–sea interactions in the equatorial Atlantic indicate that the background energy in the equatorial Atlantic is provided by ENSO. However, the time scale of the variability and the magnitude of some peculiar events cannot be explained solely by ENSO remote forcing. It is demonstrated that the peak of SSTA variability in the 1–3-yr band as observed in the equatorial Atlantic is due to the local air–sea interactions and is not a linear response to ENSO. Seasonal phase locking in boreal summer is also the result of the local coupling. The analysis of the intrinsic sustainable modes indicates that the Atlantic El Niño is qualitatively a noise-driven stable system. Such a system can produce coherent interdecadal variability that is not forced by the Pacific or extraequatorial variability. It is shown that when a simple slab mixed layer model is embedded into the system to simulate the northern tropical Atlantic (NTA) SST variability, the warming over NTA following El Niño events have characteristics (location and peak phase) that depend on air–sea interaction in the equatorial Atlantic. In the model, the interaction between the equatorial mode and NTA can produce a dipolelike structure of the SSTA variability that evolves at a decadal time scale. The results herein illustrate the complexity of the tropical Atlantic ocean–atmosphere system, whose predictability jointly depends on ENSO and the connections between the Atlantic modes of variability.

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