Science Meetings

Aquarius Brings New Understanding to Tropical Instability Waves (TIWs)
Lee, T., Lagerloef, G.S.E., Gierach, M.M. Kao, H-Y., Yueh, S., and Dohan, K. (17-Apr-13)

Sea surface salinity (SSS) measurements from Aquarius/SAC-D satellite provide the first satellite observations of the salinity structure of tropical instability waves (TIWs) in the Pacific and Atlantic Oceans. In the tropical Pacific, the associated 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 the strongest near the equator in the eastern equatorial Pacific. This is because the salty South Pacific water meets the fresher Inter-tropical Convergence Zone water near the equator to create a large meridional gradient of background SSS. In contrast, the meridional gradient of background SST is the largest at the edge of the cold tongue a few degrees away the equator (but is smaller near the equator because of the relatively uniform SST in the center of the cold tongue). 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 in the past few decades, 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 difference of TIW speed at and off the equator has important implications to eddy-mean flow interaction. Moreover, the stronger SSS signature of TIWs at the equator suggests that salinity may play a more important role in energy conversion between eddies and mean flow there than temperature. The structure of TIWs in the tropical Atlantic observed by Aquarius will also be presented.