Tropical Instability Waves (TIWs) are westward-traveling waves associated with shear instabilities of the equatorial current system, and are observed at the edges of the equatorial cold tongues in the Pacific and Atlantic Oceans. TIWs have average wavelengths of 1000-2000 kilometers, periods of 20-40 days, and phase speeds of 0.3-0.5 m/s. These waves redistribute various ocean properties, including temperature, salinity, and nutrients. They interact with ocean currents and large-scale climate variability, such as the El Niño-Southern Oscillation, and influence marine ecosystems and the carbon cycle.

TIWs have previously been observed by satellite observations of sea surface temperature, sea level, ocean surface wind, and ocean surface chlorophyll-a and sparse direct ocean measurements. Salinity has been found to play an important role in the physics of these waves, and observations of the salinity structure are important to understanding TIWs and their impact on climate variability and biogeochemistry. However, until now salinity observations of TIWs have been limited to very sparse direct ocean measurements. The Aquarius instrument onboard the Aquarius/Satélite de Aplicaciones Científicas (SAC)-D satellite provides an unprecedented opportunity to observe the salinity response to these waves.

A recent Bulletin of the American Meteorological Society article lead-authored by Gary Lagerloef of Earth and Space Research, Aquarius Principal Investigator, noted a wave-like pattern in salinity in the tropical Pacific Ocean (Lagerloef et al., 2012). The salinity signature was revealed to be associated with TIWs in a recent Geophysical Research Letters article lead-authored by Tong Lee of NASA's Jet Propulsion Laboratory (Lee et al., 2012).