Aquarius Data Are Valuable for El Niño Forecasts T. Qu , Y. T. Song, and C. Maes 34.8 psu At the eastern edge of the western Pacific warm pool is a sea surface salinity (SSS) front along the equator. The front’s zonal displacement is a key feature of the El Niño- Southern Oscillation (ENSO). The new SSS observations from the satellite instrument of Aquarius are consistent with Argo observations, but depict this SSS front much more precisely than Argo (Fig.1). In both the Aquarius and Argo data, the zonal displacements of the eastern edge of the warm pool (29 C isotherm) and the SSS front (34.8 psu isohaline) correspond well to ENSO phases, the correlation with the Southern Oscillation Index (SOI) exceeding 0.8 (Fig. 2). Since at the eastern edge of the warm pool, the east-west SSS gradient is more clearly defined than the sea surface temperature gradient, the Aquarius observations could become a valuable tool for monitoring El Niño and for improving predictions of El Niño onset. Fig. 1. Time-longitude distribution of SSS along the equator from a) Aquarius and b) Argo Aquarius 29C SOI 34.8 psu Fig. 2. Zonal displacement of 29 C isotherm (black) and 34.8 psu isohaline (red) compared with SOI (green).