Editorial Type:
Article
Article Type:
Research Article

Seasonal and Interannual Variations of Oceanic Conditions in the Angola Dome

Takeshi Doi Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan

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Tomoki Tozuka Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, Japan

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Hideharu Sasaki Earth Simulator Center/JAMSTEC, Yokohama, Kanagawa, Japan

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Yukio Masumoto Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, and Frontier Research Center for Global Change/JAMSTEC, Yokohama, Kanagawa, Japan

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Toshio Yamagata Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, Tokyo, and Frontier Research Center for Global Change/JAMSTEC, Yokohama, Kanagawa, Japan

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Print Publication:
01 Nov 2007
DOI:
https://doi.org/10.1175/2007JPO3552.1
Page(s):
2698–2713
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Abstract

Using outputs from a high-resolution OGCM, seasonal and interannual variations of the Angola Dome (AD) are revisited. Although the AD was previously considered to be one large cold tongue extending from the West African coast, it is shown that two cold domes exist. These two domes have remarkably different mechanisms for their seasonal variation. The weak dome, whose center is located at 6°S, 1°E, develops from May to September owing to the divergence of heat transport associated with upwelling. The strong dome, on the other hand, extends from the west coast of Africa between 20° and 15°S, and develops from April to August by the surface heat flux. The interannual variation of the weak dome is strongly influenced by the Atlantic Niño. An unusual relaxation of easterly wind stress in the central equatorial Atlantic Ocean associated with the Atlantic Niño triggers second baroclinic downwelling equatorial Kelvin waves, which propagate eastward along the equator and poleward along the coast after reaching the African coast as coastal Kelvin waves. Then, downwelling Rossby waves radiate away from the coast and cause significant warming in the weak dome region. The interannual variation of the South Equatorial Undercurrent may be associated with that of the AD; its transport decreases by 0.6 Sv, and its core shifts equatorward by 0.2° when the AD is anomalously weak.

Corresponding author address: Takeshi Doi, Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Email: doitake@eps.s.u-tokyo.ac.jp

Abstract

Using outputs from a high-resolution OGCM, seasonal and interannual variations of the Angola Dome (AD) are revisited. Although the AD was previously considered to be one large cold tongue extending from the West African coast, it is shown that two cold domes exist. These two domes have remarkably different mechanisms for their seasonal variation. The weak dome, whose center is located at 6°S, 1°E, develops from May to September owing to the divergence of heat transport associated with upwelling. The strong dome, on the other hand, extends from the west coast of Africa between 20° and 15°S, and develops from April to August by the surface heat flux. The interannual variation of the weak dome is strongly influenced by the Atlantic Niño. An unusual relaxation of easterly wind stress in the central equatorial Atlantic Ocean associated with the Atlantic Niño triggers second baroclinic downwelling equatorial Kelvin waves, which propagate eastward along the equator and poleward along the coast after reaching the African coast as coastal Kelvin waves. Then, downwelling Rossby waves radiate away from the coast and cause significant warming in the weak dome region. The interannual variation of the South Equatorial Undercurrent may be associated with that of the AD; its transport decreases by 0.6 Sv, and its core shifts equatorward by 0.2° when the AD is anomalously weak.

Corresponding author address: Takeshi Doi, Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. Email: doitake@eps.s.u-tokyo.ac.jp

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