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ABSTRACT. The spatial and temporal variability of energy exchange in Tropical Instability Waves (TIWs) in the Atlantic 15Ocean were investigated. A spectral analysis was used to filter the 5-day mean results from Simple Ocean Data Assimilation reanalysis spanning from 1958 to 2008. TIWs were filtered over periods of 15 to 60 days and between wavelengths of 4 and 20 longitude degrees. The main approach of this study was the use of bidirectionally filtered TIW time series as the perturbation fields, and the difference in these time series from the SODA total results was considered to be the basic state for energetics analysis. The main result was that the annual cycle (period of ~360 days) was the main source of variability of 20 the waves, and the semi-annual cycle (period of ~180 days) was a secondary variation, which indicated that TIWs occurred throughout the year but with intensity that varies seasonally. Barotropic instability acts as the mechanism that feeds and extracts energy to/from TIWs as alternate zonal bands at equatorial Atlantic. Baroclinic instability is the main mechanism that extracts energy from TIWs to the equatorial circulation north of Equator. All TIW patterns of variability were observed at west of ~10ºW. The present study reveals new evidences regarding TIW variability and suggests that future investigations 25 should include a detailed description of TIW dynamics as part of Atlantic Ocean equatorial circulation. IntroductionA Tropical Instability Wave (TIW) is defined as a cusp-shaped oscillation of the equatorial thermal front that propagates westward. These waves are associated with the seasonal variability of the 30 equatorial current system, and they are observed when the cold tongue ( Figure 1) is well established (Chelton et al., 2000; Jochum et al., 2004a, Legeckis andReverdin, 1987;Philander et al., 1986;Steger and Carton, 1991;Weisberg and Horigan, 1981). These westward waves have wavelengths ranging from 600 km to 2600 km and periods varying between 15 and 37 days in the Atlantic Ocean (Caltabiano et al., 2005;Chelton et al., 2000;Düing et al., 1975;Jochum et al., 2004b; Legeckis and Reverdin, 35 1987;Pezzi and Richards, 2003;Weisberg, 1984), and Athie and Marin (Athie and Marin, 2008) describes a wider range (periods of 15-50 days). The formation process is the naturally generated instability of the equatorial zonal current system with alternating bands of eastward and westward flows 1 Ocean Sci. Discuss., doi:10.5194/os-2016Discuss., doi:10.5194/os- -84, 2016 Manuscript under review for journal Ocean Sci. Published: 15 November 2016 c Author(s) 2016. CC-BY 3.0 License. (Philander, 1976). In the Atlantic, the zonal flows at the top ocean layers are modulated by the coupled air-sea dynamics and have a strong seasonal cycle, as presented by Stramma and Schott (Stramma and 40 Schott, 1999). The authors described the westward South Equatorial Current (SEC) as divided by three bands composed of northern, central and southern regions (the schematic surface circulation and its ...