Tropical Atlantic sea level variability from Geosat (1985–1989)

Abstract

Geosat altimeter data between April 1985 and September 1989 are analyzed in the tropical Atlantic Ocean. First, improvements due to the use of new corrections and orbit computations are found to be effective, especially in the Gulf of Guinea, where part of the previously missing signal is recovered. Then, the variability of the ocean is examined using empirical orthogonal functions (EOFs). Only three EOFs are needed to describe 80% of the seasonal variance. The first one describes the meridional tilting of the tropical Atlantic along the mean location of the Intertropical Convergence Zone, with an annual period. The second describes a mass redistribution due to the equatorial upwelling peaking in June-July. The third function presents a clear semiannual signal. Looking at interannual variability, the first EOF reveals a mass redistribution between the equatorial region (10"N to 10"s) and the northern and southern ones (10"N to 30"N, 10"s to 30"s). In the equatorial region the upper layer volume increases from about-1.5 to 1.5 x 1014 m3 between 1987 and 1989. Occurring 1 year after the Pacific El Niño, this phenomenon recalls the 1984 anomaly observed during the Programme Français OcCan et Climat en Atlantique TropicaVSeasonal Equatorial Atlantic experiments.

A Quasi‐Biennial Oscillation in the equatorial Atlantic Ocean

“…Sea surt•tce temperature (SST) anomalies in the equatorial Atlantic Ocean are substantially weaker than E1 Nifio/Southern Oscillation (ENSO) in the Pacific (Harrison and Larkin, 1998). Nevertheless, the interannual variability in the equatorial Atlantic is a significant component of the climate system (Carton and Huang 1994;Arnault and Cheney 1994). During 1900-87 there were nine events in which SST anomalies exceeded 0.5øC for more than one month during the northern spring-summer.…”

An optimized design for a moored instrument array in the tropical Atlantic Ocean

“…Much information has been gained on the dynamics of the tropical Atlantic through analysis of recently available altimetric data [Katz et al, 1995;Canon., 1989;Arnault and Cheney, 1994]. However, there exist very few in situ observations for the tropical Atlantic.…”

Investigation of the Interannual Variability of the Tropical Atlantic Ocean from Satellite Data

“…This is done to remove the seasonal signal which is known to be dominant in the tropical Atlantic Ocean (Merle et al 1979;Arnault and Cheney 1994). The low-frequency variability described hereafter refers to periods longer than 12 months.…”

“…Contrary to the Pacific Ocean, where the dominant mode of variability, the El Niňo-Southern Oscillation (ENSO), occurs on an interannual timescale, the dominant mode of variability in the tropical Atlantic Ocean occurs mainly on annual timescales (Merle et al 1979;Arnault and Cheney 1994;Schouten et al 2005;Ding et al 2010). Moreover, the large scale variability of the Atlantic is much more complex than the Pacific, both in time and space.…”