North African climate variability. Part 1: Tropical thermocline coupling |
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| Authors: | A Yeshanew M R Jury |
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| Institution: | (1) National Meteorological Services Agency, Addis Ababa, Ethiopia;(2) Environmental Studies Department, University of Zululand, KwaDlangezwa, South Africa |
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| Abstract: | Summary Tropical ocean thermocline variability is studied using gridded data assimilated by an ocean model in the period 1950–2000.
The dominant patterns and variability are identified using EOF analysis applied to E–W depth slices of sea temperatures averaged
over the tropics. After removing the annual cycle, an east–west ‘see-saw’ with an interannual to decadal rhythm is the leading
mode in each of the tropical basins. In the case of the leading mode in the Pacific, the thermocline oscillation forms a dipole
structure, but in the (east) Atlantic and (southwest) Indian Ocean there is a single center of action. The interaction of
the ocean thermocline and atmospheric Walker circulations is studied through cross-modulus analysis of wavelet-filtered EOF
time scores.
Our study demonstrates how tropical ocean thermocline variability contributes to zonal circulation anomalies in the atmosphere.
The equatorial Pacific thermocline oscillation explains 62 and 53% of the variability of the Pacific and Atlantic zonal overturning
circulations, the latter driving convective polarity between North Africa and South America. The Pacific sea-saw leads the
Atlantic zonal circulation by a few months. |
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