Presented at the 2014 Aquarius/SAC-D Science Team MeetingThe primary objectives of the Aquarius/SAC-D mission are to map month-to-month variability of sea surface salinity (SSS) to facilitate the studies of the relationships between SSS, ocean circulation, climate variability, and the water cycle with an emphasis on seasonal-to-interannual time scales. However, Aquarius SSS measurements have enabled the investigations of intraseasonal variability, especially those on time scales closer to a month. These include the studies of tropical instability waves (TIWs) in the Pacific and Atlantic Oceans and SSS signature associated with the Madden-Julian Oscillation (MJO) in the tropical Indo-Pacific oceans that are important to ocean dynamics, climate variability, and marine ecosystem. This presentation highlights the new understanding of TIWs and MJO enabled by the applications of Aquarius data. For the Pacific, Aquarius data provided a better view of TIW at the equator because of the large meridional gradient of SSS there, and revealed a shorter dominant period and faster propagation of TIWs at the equator than those at off-equatorial latitudes. These features have significant implications to the physics associated with TIWs at and away from the equator and TIW-mean flow interactions. In the Atlantic, SSS is found to play an essential role in TIW-mean flow interaction. Not accounting for the influence of SSS would underestimate the perturbation potential energy at the surface by a factor of three. For MJO-related oceanic response in the Indo-Pacific oceans, SSS is found to be as important as sea surface temperature in regulating the surface density anomalies. This has strong implications to MJO-related modeling and coupled forecast.