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Yu, L. (11-Nov-14)

The concept of using ocean salinity as a rain gauge to detect the change of the global water cycle has long been proposed but yet materialized. The main obstacle is that ocean salinity and the freshwater flux (namely, the E-P flux) are related through complex upper ocean dynamics, and the ocean advective/mixing processes are often found to have a more influential role than the freshwater flux in explaining the observed SSS variability on seasonal and longer timescales. The correlation between the E-P flux and ocean salinity is typically weak and insignificant in most global oceans but with exception for limited regions under the influence of the ITCZ. In this study I will show that the better correlation in the tropical oceans is due to the existence of the intertropical low-salinity converge zone (LSCZ), identified recently from the satellite sea surface salinity (SSS) retrievals and Argo subsurface salinity observations. The LSCZ is a narrow zone band on either side of the equator, with a SSS front as its surface manifestation. I will show that although the LSCZ owes its source to the ITCZ precipitation, its generation and seasonal migration are dictated by the wind-driven Ekman dynamics. One key evidence is that the center of the LSCZ is locked to the poleward edge of the Ekman convergence zone and moves poleward progressively after the LSCZ is formed at the equatorial latitudes in early spring. In the tropical north Pacific, the LSCZ and ITCZ rain band collocate only during August-October, the time that the Ekman convergence aligns with the rain band. Lastly, I will discuss the connection between the ITCZ precipitation and the low salinity in the LSCZ and the potential implications of the findings for the global water study.