The influence of ENSO on the equatorial Atlantic precipitation through the Walker circulation in a CGCM

Sasaki, Wataru; Doi, Takeshi; Richards, Kelvin J; Masumoto, Yukio

doi:10.1007/s00382-014-2133-5

Cited by 47 publications

(25 citation statements)

References 35 publications

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“…2e). As in the tropical Pacific, deviations from the idealized Gill-type solution in the tropical Atlantic are due to the background flow (Lee et al 2009), which are also observed in MAM (Sasaki et al 2015). The focus of this study is the evolution of the secondary Gill-type response in the tropical Atlantic and its link to TNA SST anomalies.…”

Section: Resultsmentioning

confidence: 94%

“…In accordance with Lee et al (2008) and partially in disagreement with Czaja et al (2002), the remote Gill-type mechanism constitutes a regional atmospheric forcing rather than the expression of the WES feedback. The dynamics of the secondary Gill-type response to ENSO in the tropical Atlantic during spring have been recently simulated in a coupled GCM (Sasaki et al 2015), although the focus was the impact on equatorial precipitation, not on TNA SSTs. The results shown here on the transition from a subtropical forcing associated with the extratropical ENSO teleconnection (in winter/late winter; via Rossby wave train and/or Walker-Hadley) into a tropical forcing associated with the remote Gill-type response (in early spring/spring) are consistent with previous studies reporting a similar winter-to-spring evolution in observations (e.g., Chiang et al 2002) and atmosphere-only (e.g., Sutton et al 2000) and coupled (e.g., Huang et al 2002) GCM simulations.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…Previous works have shown that the diabatic heat source during ENSO events perturbs the zonal Walker circulation in such a way that associated branches yield anomalous diabatic heat sources (opposite in sign to the ENSO anomaly) on both sides of the tropical Pacific, that is, over the Maritime Continent and South America (Nigam et al 2000;DeWeaver and Nigam 2002). These zonally compensated heat sources lead to secondary Gill-type responses over those remote tropical basins, inducing twin anomalous circulation centers straddling the equator (DeWeaver and Nigam 2004;Spencer et al 2004;Sasaki et al 2015). This fast, linear mechanism could be acting in the ENSO-TNA teleconnection.…”

Section: Introductionmentioning

confidence: 99%

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Revisiting the ENSO Teleconnection to the Tropical North Atlantic

et al. 2017

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One of the most robust remote impacts of El Niño-Southern Oscillation (ENSO) is the teleconnection to tropical North Atlantic (TNA) sea surface temperature (SST) in boreal spring. However, important questions still remain open. In particular, the timing of the ENSO-TNA relationship lacks understanding. The three previously proposed mechanisms rely on teleconnection dynamics involving a time lag of one season with respect to the ENSO mature phase in winter, but recent results have shown that the persistence of ENSO into spring is necessary for the development of the TNA SST anomalies. Likewise, the identification of the effective atmospheric forcing in the deep TNA to drive the regional air-sea interaction is also lacking. In this manuscript a new dynamical framework to understand the ENSO-TNA teleconnection is proposed, in which a continuous atmospheric forcing is present throughout the ENSO decaying phase. Observational datasets in the satellite era, which include reliable estimates over the ocean, are used to illustrate the mechanism at play. The dynamics rely on the remote Gill-type response to the ENSO zonally compensated heat source over the Amazon basin, associated with perturbations in the Walker circulation. For El Niño conditions, the anomalous diabatic heating in the tropical Pacific is compensated by anomalous diabatic cooling, in association with negative rainfall anomalies and descending motion over northern South America. A pair of anomalous cyclonic circulations is established at upper-tropospheric levels in the tropical Atlantic straddling the equator, displaying a characteristic baroclinic structure with height. In the TNA region, the mirrored anomalous anticyclonic circulation at lower-tropospheric levels weakens the northeasterly trade winds, leading to a reduction in evaporation and of the ocean mixed layer depth, hence to positive SST anomalies. Apart from the dominance of latent heat flux anomalies in the remote response, sensible heat flux and shortwave radiation anomalies also appear to contribute. The ''lagged'' relationship between mature ENSO in winter and peaking TNA SSTs in spring seems to be phase locked with the seasonal cycle in both the location of the mechanism's centers of action and regional SST variance.

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Section: Resultsmentioning

confidence: 94%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Revisiting the ENSO Teleconnection to the Tropical North Atlantic

et al. 2017

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“…According to the standard developed by ENSO monitoring groups, Oceanic Niño Index (ONI) data provided by the US National Oceanic and Atmospheric Administration and a literature search, there are six El Niño years (1991, 1992, 1997, 2002, 2004, and 2009) and six La Niña years (1998, 1999, 2000, 2008, 2010, and 2011) during 1990-2014. Prior studies showed that although the relationship between ENSO and precipitation is nonlinear, global land annual precipitation is less offset in most El Niño years, while it is more offset in La Niña years (Meque and Abiodun 2014;Sasaki et al 2015;Tang and Yuan 2010). Annual frequencies of flood disasters showed several peaks in 1996-2000, 2006-2008, and 2010-2012.…”

Section: Inter-annual Changes and Influencing Factorsmentioning

confidence: 99%

Spatio-temporal distribution of flood disasters and analysis of influencing factors in Africa

Chai

Yang

et al. 2016

Nat Hazards

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To analyse inner-and inter-annual changes, disaster events of 55 countries in Africa from 1990 to 2014 recorded in the International Disaster Database (EM-DAT) were recounted by year and month and were reorganised in five different regions. Thematic maps of flood disasters in Africa between 1990 and 2014 were drawn using ArcGIS 9.3 to research the spatial distribution patterns of average annual flood frequency, total deaths, total affected, and damage. There were eight natural and socio-economic indicators chosen to explore the main factors influencing the spatio-temporal distribution of flood disasters in Africa, including precipitation, ENSO, runoff, forest coverage rate, reservoir capacity, per capita GDP, population, and urbanisation rate. Studies show that seasonal changes of flood disasters in various regions of Africa, except North Africa, are closely related to precipitation. Annual flood frequencies, from 1990 to 2014, showed a fluctuating upward trend and were in good agreement with ENSO years. In terms of spatial distributions, Ethiopia, Kenya, Somalia, Tanzania in eastern Africa, Nigeria in western Africa, and Libya, and Sudan in northern Arica are flood-prone countries, and main factors influencing spatial disparities include runoff, per capita GDP, population, and urbanisation rate.

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“…Generally, perturbations in the Walker cell induced by El Niño events produce anomalous subsidence and increased sea level pressure in the eastern and southern part of the tropical Atlantic, thus enhancing the zonal pressure gradient at the surface. The anomalous subsidence directly reduces convection and inhibits precipitation in the equatorial Atlantic (Sasaki et al 2014). The anomalous surface pressure gradient strengthens the trade winds on and to the south of the equator, intensifying the local Walker circulation Sasaki et al 2014) and giving rise to the Bjerknes feedback mechanism in the Atlantic sector.…”

Section: Introductionmentioning

confidence: 98%