Mechanisms Controlling Variability of the Interhemispheric Sea Surface Temperature Gradient in the Tropical Atlantic

Wagner, Regina L.

doi:10.1175/1520-0442(1996)009<2010:mcvoti>2.0.co;2

Cited by 40 publications

(31 citation statements)

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“…2 Cross-equatorial gradient index and tropical index The strength of the cross-equatorial SST gradient in the tropical Atlantic and its impact on adjoining land areas climate have been investigated based on its temporal evolution (e.g., Wagner, 1996;Nobre and Shukla, 1996). To obtain a long time series of the tropical SST gradient, we define a gradient index similar to the dipole index in Servain (1991) by taking the difference between northern (10-20°N) and southern (10-20°S) tonal means of normalized annual-mean SST anomalies from coast to coast.…”

Section: Data and Analysis Proceduressupporting

confidence: 88%

“…In the tropical Atlantic, a dipole mode where SST and sea level pressure (SLP) in the Northern and Southern Hemispheres oscillate like a seesaw (Chang et al, 1997) is believed to have strong direct and remote impacts on the precipitation and other climate variables' pattern over the northeastern part of Brazil (Wagner, 1996;Nobre and Shukla, 1996) and Sahel (Folland et al, 1986). This paper examines decadal variability over the whole Atlantic basin with a focus on the interaction of the tropics and extratropics.…”

Section: Introductionmentioning

confidence: 99%

“…The Golions force turns cross-equatorial southerly wind anomalies into the southwesterly anomalies in the Northern Hemisphere, weakening the climatological northeast trades, suppressing latent heat release from the ocean, and acting to further warm the northern tropical SST anomalies (Huang and Shukla, 1997). Meridional profiles of the zonal-mean latent heat flux forcing on SST anomalies (Wagner, 1996) suggest that flux anomalies are capable of maintaining dipole structure in the presence of the decay process by Ekman pumping. In fact, the numerical study by Carton et al (1996) showed that decadal SST variations in the tropical Atlantic were not well simulated without incorporating the latent heat loss process.…”

Section: Introductionmentioning

confidence: 99%

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Ocean-Atmosphere Variability over the Pan-Atlantic Basin

Tanimoto

Xie

1999

Journal of the Meteorological Society of Japan

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Ocean and atmosphere variability is investigated over the whole Atlantic basin in a 51-year record of sea surface temperature (SST). In the tropics, SSTs variations are separated into two time scales: decadal (8-16 years) and interannual (<5 years). A strong cross-equatorial gradient mode dominates decadal SST anomalies with centers of action having opposite polarities at 15N and 15S, while interannual variations are characterized by SST anomalies of the same polarity throughout the tropics. Sea level pressure (SLP) regressions onto the cross-equatorial gradient index reveal extratropical teleconnections associated with the North Atlantic Oscillation (NAO), and with the South Atlantic. At the same time, a Pan-Atlantic spatial pattern is also found in SST regressions. Lagged regressions of SLP on the cross-equatorial SST gradient index shows the extratropical decadal oscillation that is out of phase between hemispheres. These results suggest that an extratropical forcing could excite the tropical Atlantic variability.

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Section: Data and Analysis Proceduressupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ocean-Atmosphere Variability over the Pan-Atlantic Basin

Tanimoto

Xie

1999

Journal of the Meteorological Society of Japan

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“…Wagner, 1996;Carton et al, 1996;Chang et al, 2000). By influencing surface pressure gradients, the SST gradients modulate the location of the marine ITCZ and thereby influence rainfall in Africa and South America Greischar, 1993a, 1993b).…”

Section: Introductionmentioning

confidence: 99%

A physical basis for the interannual variability of rainfall in the Sahel

Nicholson¹,

Webster²

2007

Quart J Royal Meteoro Soc

108

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A major factor in rainfall variability over Sahelian West Africa is the latitudinal location of the tropical rainbelt. When it is displaced abnormally far northward, the Sahel experiences a wet year. An anomalous southward displacement results in drought. In this paper we examine the question of what controls the location during the boreal summer, hypothesizing that inertial instability plays a role. An analysis of surface pressure and temperature fields, wind fields, divergence and vertical motion show that the criteria for inertial instability are satisfied in wet Augusts but not in dry ones. The key determinant appears to be the surface pressure gradient between the continent and the equatorial Atlantic. When this is large, inertial instability results in the development of a low-level westerly jet. The presence of this jet enhances the horizontal and vertical shear, and displaces the African Easterly Jet northwestward. Associated with this situation is strong vertical motion over the Sahel and subsidence over the Guinea Coast, producing dry conditions over the latter. The result is a rainfall dipole, one of two major modes of variability over West Africa. Important factors include sea surface temperatures (SSTs) in the equatorial Atlantic and pressure in the South Atlantic. The first of these factors suggests a link with the Atlantic Niño mode of tropical Atlantic variability; while the second suggests a possible link with the Pacific and the extratropical South Atlantic. Overall, our study relates the well-known SST influence on Sahel rainfall to atmospheric dynamics over the continent.

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“…Warm (cold) dipole is characterized by the si multaneous occurrences of positive (negative) SST anomalies in the tropi cal North Atlantic and negative (posi tive) SST anomalies in the tropical South Atlantic. As a consequence of the north/south dipole a meridional interhemispheric thermal gradient establishes in the equatorial Atlantic (Wagner, 1996). The related varia tions in the SST, trade winds and SLP are crucial in steering the intensity and positioning of the cloudiness and pre cipitation band associated with the ITCZ.…”

Section: Introductionmentioning

confidence: 99%

On the influences of the El Niño, La niña and Atlantic Dipole Paterni on the Amazonian Rainfall during 1960-1998

et al. 2000

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-The influence of the large-scale climatic variability dominant modes in the tropical Atlantic present values (magnitude and sign) consistent with those found in previous works on the relationship between Amazon rainfall variations and the SST anomalies in the tropical Pacific and Atlantic. However, austral summer and autumn composites for the years with tropical Atlantic show negative precipitation anomalies extending eastward over the Key words: Seasonal rainfall, ENSO, Amazon, SST anomalous north-south dipole in the Atlantic. Sobre a Influência do El Niño, La Niña e Padrão De Dipolo do Atlântico na precipitação da amazônia durante 1960-1998RESUMO -A influência dos modos de variabilidade climática dc grande escala dominantes no Pacifico e Atlântico nas chuvas da Amazônia é investigada. A técnica de compósitos das anomalias de precipitação na Amazônia é usada neste trabalho. Os anos base destes compósitos são aqueles do período 1960-1998 com ocorrências de extremos na Oscilação Sul (El Niño ou La Niña) e de padrão de dipolo norte/sul quente (ou frio) nas anomalias de TSM no Atlântico tropical. Dipolo quente (frio) significa anomalias positivas (negativas) no Atlântico tropical Norte e negativas (positivas) no Atlântico tropical Sul. Compósitos de verão e outono austrais para extremos na Oscilação Sul (El Niño ou La Niña) e independente para padrão de dipolo norte/sul (quente ou frio) de anomalias de TSM no Atlântico tropical, apresentam valores (magnitude e signal) consistentes com aqueles encontrados em trabalhos anteriores sobre a relação entre as variações de precipitação na Amazônia e anomalias de TSM no Pacífico e Atlântico tropicais. No entanto, compósitos dos verões e outonos austrais para os anos com ocorrências simultâneas dc El Niño e dipolo quente norte/sul de anomalias de TSM no Atlântico tropical mostram anomalias negativas de precipitação estendendo-se para leste sobre a Amazônia centro-leste. Este resultado indica o importante papel desempenhado pelo Atlântico tropical na distribuição anômala de precipitação na Amazônia.Palavras-chave: Chuva sazonal, ENOS, Amazônia, Dipolo norte-sul de anomalias de TSM.

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Mechanisms Controlling Variability of the Interhemispheric Sea Surface Temperature Gradient in the Tropical Atlantic

Cited by 40 publications

References 0 publications

Ocean-Atmosphere Variability over the Pan-Atlantic Basin

Ocean-Atmosphere Variability over the Pan-Atlantic Basin

A physical basis for the interannual variability of rainfall in the Sahel

On the influences of the El Niño, La niña and Atlantic Dipole Paterni on the Amazonian Rainfall during 1960-1998

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