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

Abstract

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.

Satellite observations of the Pacific tropical instability wave characteristics and their interannual variability

“…TIW propagation speed (c T ) was calculated by applying the Radon transform technique, as used by Challenor et al (2004), Caltabiano et al (2005), Polito and Cornillon (1997) there is evidence that besides a strong reduction in TIW activity there is also a reduction in TIW propagation speeds, where they are reduced by 10 cm s 21 approximately along of all latitudes between 1 and 4u N.…”

“…In the tropical Atlantic, this year-to-year variability has been recently demonstrated by Caltabiano et al (2005). In the tropical Pacific, they are more active during La Niñ a years when the equatorial trades and cold tongue are stronger and the meridional gradients sharper.…”

“…Although this point has been addressed by other authors, e.g. Baturin and Niiler (1997) and Contreras (2002), there is still ample scope to further explore TIW variability using both modelling and observational approaches, in particular by the exploitation of satellite data such as shown by Caltabiano et al (2005).…”

Assimilating altimetric data to control the tropical instability waves: an observing system simulation experiment study

“…The period from Jan. 1, 1999 to Jan. 1, 2001 was used as an initialization phase to ensure correct adjustment to the boundaries. The period of study is the whole year of 2001, a year of intense TIWs in the Atlantic as reported by Caltabiano et al (2005). Indeed the shape of the SST observed in August 2001 ( Fig.…”

“…They have been extensively studied in the Pacific (e.g., Flament et al 1996) and in the Atlantic (e.g., Jochum et al 2004;Caltabiano et al 2005;Von Schuckmann et al 2008). During wave events, the meridional velocity and the SST front oscillate more intensively at the north side of the equator (between 2°and 4°N), with a 25-30-day period and a westward propagation of 0.4-0.5 m/s.…”