Multi-year satellite observations of instability waves in the Tropical Atlantic Ocean

Abstract

Instability waves in the tropical Atlantic Ocean are analysed by microwave satellite-based data spanning from 1998 to 2001. This is the first multi-year observational study of the sea surface temperature (SST) signature of the Tropical Instability Waves (TIW) in the region. SST data were used to show that the waves spectral characteristics vary from yearto-year. They also vary on each latitude north of the equator, with the region of 1 • N, 15 • W concentrating the largest variability when the time series is averaged along the years. Analyses of wind components show that meridional winds are more affected near the equator and 1 • N, while zonal winds are more affected further north at around 3 • N and 4 • N. Concurrent observations of SST, wind, atmospheric water vapour, liquid cloud water, precipitation rates and wind were used to suggest the possible influence of these waves on the Intertropical Convergence Zone (ITCZ). It seems that these instabilities have a large impact on the ITCZ due to its proximity of the equator, compared to its Pacific counterpart, and the geography of the tropical Atlantic basin. These analyses also suggest that the air-sea coupling mechanism suggested by Wallace et al. (1989) can also be applied to the tropical Atlantic region.

Revisiting Tropical Instability Wave Variability in the Atlantic Ocean using SODA reanalysis

“…This study applied a twofold approach: a bidirectional (period and wavelength) band pass filter was used to extract the TIW signal, and this field 150 was considered as the perturbation, and a transient (time-dependent) basic state was defined, both for energetics. It will be shown that this methodology maintains TIW signal in a manner similar to that reported by Pezzi and Richards (Pezzi and Richards, 2003), Caltabiano et al (Caltabiano et al, 2005) and Pezzi et al (Pezzi et al, 2006). Consistent advancements regarding TIW physics and dynamics will be achieved with the employment of this methodology.…”

“…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.…”

“…Again, this discussion and distinct characteristics might be associated with different methods of filtering data/model results only in time or space frequency bands or high TIW variability. Using a bidirectional filter applied to remotely sensed sea surface temperature (SST), Caltabiano et al (Caltabiano et al, 2005) observed TIW seasonality from 1998 to 2001, which varied from year to year. 140 Perez et al (Perez et al, 2012) also used satellite data with temporal and zonal band-pass filter to study TIW variability in the Atlantic and found peak TIW variance during summer months.…”

“…To filter the data in both dimensions (spatial and temporal), a Fourier 2D directional filter was designed using a twodimensional fast Fourier transform (2DFFT). A band pass filter was applied to the data matrices to 205 retain periods from 15 to 60 days and wavelengths from 4º to 20º of longitude, which was a slightly wider range than Caltabiano et al (Caltabiano et al, 2005) considered. Here, these filtered data will be called TIW data.…”

The influence of salinity on tropical Atlantic instability waves

“…The zonal distributions of @qðTÞ @y and @qðSÞ @y at 1 N where TIWs have been found to be the most energetic for SST [e.g., Chelton et al, 2000;Caltabiano et al, 2005] are shown in Figure 4c. In the east between 19 W and 5 E (the two crossings of the two curves), the ratio of @qðTÞ @y and @qðSÞ @y is 1.6.…”