Aquarius reveals salinity structure of tropical instability waves

Abstract

Sea surface salinity (SSS) measurements from the Aquarius/SAC‐D satellite during September–December 2011 provide the first satellite observations of the salinity structure of tropical instability waves (TIWs) in the Pacific. The related SSS anomaly has a magnitude of approximately ±0.5 PSU. Different from sea surface temperature (SST) and sea surface height anomaly (SSHA) where TIW‐related propagating signals are stronger a few degrees away from the equator, the SSS signature of TIWs is largest near the equator in the eastern equatorial Pacific where salty South Pacific water meets the fresher Inter‐tropical Convergence Zone water. The dominant westward propagation speed of SSS near the equator is approximately 1 m/s. This is twice as fast as the 0.5 m/s TIW speed widely reported in the literature, typically from SST and SSHA away from the equator. This difference is attributed to the more dominant 17‐day TIWs near the equator that have a 1 m/s dominant phase speed and the stronger 33‐day TIWs away from the equator that have a 0.5 m/s dominant phase speed. The results demonstrate the important value of Aquarius in studying TIWs.

SMOSSea Surface Salinity signals of tropical instability waves

“…TIWs have been detected in the atmospheric boundary layer and modulations of ocean surface wind stress as observed by scatterometers [Liu et al, 2000;Polito et al, 2001;Yu and Liu, 2003]. The TIW pattern is also identifiable in chlorophyll a (chl a) [Strutton et al, 2001;McClain et al, 2002;Lee et al, 2012].…”

“…The spatial and temporal variabilities of ocean surface salinity in the tropical eastern and central Pacific Ocean are poorly known mostly because in situ salinity observations are sparse. With the advent of satellite salinity measurements, it is now possible to analyze the salinity signal associated with TIWs [Lee et al, 2012]. This provides a significant new capability to the scope of TIW observations that has important implications to ocean circulation and climate [Lagerloef, 2008].…”

“…This provides a significant new capability to the scope of TIW observations that has important implications to ocean circulation and climate [Lagerloef, 2008]. Lee et al [2012] have studied the TIWs from September to December 2012 using Aquarius Sea Surface Salinity (SSS). Major results in that study are: (1) Different from SST and sea surface height anomaly, where the largest signals of TIWs are found a few degrees north of the equator, the SSS signature of TIWs is strongest near the equator.…”

The influence of salinity on tropical Atlantic instability waves

“…Aquarius, launched in June 2011, has been providing SSS measurements since September 2011 with 7 day global coverage. Lee et al [2012] demonstrated the advantage of Aquarius' SSS in improving the understanding of Pacific TIWs. In particular, Aquarius SSS data captured the dominant 17 day TIWs near the equator that were not well observed by SST and SSH.…”

“…Thousand kilometer zonal scale propagating waves with typical periods of tens of days have been observed in the tropical Pacific and Atlantic Oceans, affecting the physical and biogeochemical properties of the ocean and its interaction with the atmosphere [e.g., Legeckis, 1977;Legeckis and Reverdin, 1983;McPhaden et al, 1984;Hayes et al, 1989;Luther and Johnson, 1990;Yoder et al, 1994;Qiao and Weisberg, 1995;McPhaden, 1996;Xie et al, 1998;Chelton et al, 2000;Liu et al, 2000;Polito et al, 2001;Lee et al, 2012]. These tropical instability waves (TIWs) are generated from barotropic and baroclinic instabilities associated with the horizontal and vertical shear of equatorial current systems and related density gradients [e.g., Philander, 1978;Weisberg and Weingartner, 1988;McCreary and Yu, 1992;Masina et al, 1999;Grodsky et al, 2005;Jochum et al, 2004;Lyman et al, 2007;von Schuckmann et al, 2008].…”