Largest SSS Anomalies of the last decade in 2012 and 2014 of the Eastern Tropical Pacific Fresh Pool as detected by SMOS and other EO data

The Eastern Pacific Fresh Pool (EPFP) is a large region of low Sea Surface Salinity (SSS) defined by SSS < 34 that develop east of 180°W. Seasonal SSS variations of the EPFP are the strongest of the tropical Pacific: the fresh pool dynamically responds to strong regional and seasonally varying ocean-atmosphere-land interactions. The freshpool forms in boreal winter in the most eastern part of the tropical Pacific due to strong rain accumulation under the ITCZ and is trapped by eastward flowing currents. The pool then extends westward by about 2000 kms during spring to autumn due to North Equatorial Current (NEC)-driven westward advection on its northern flank and North Equatorial Counter Current (NECC)-driven eastward advection of low SSS patches generated in the central pacific during the ITCZ seasonal migration to form its central and southern flanks. The SSS fronts associated with the fresh pool and the amplitude of its variability are large enough to be well detected by the SSS satellite sensors, such as the SMOS mission. Using five years of SMOS SSS and complementary satellite wind, rain, currents, sea surface temperature together with an historical ensemble of in situ products, the present study explores qualitatively the interannual dynamic of the freshpool zonal extent over the period 2010-2014. Remarkably, it includes the strongest interannual variability of the maximal zonal surface extension of the EPFP over the past decade: from a minimum of ~7x10⁶ km² in Oct 2012 to a maximum of ~12x10⁶ km² reached in Oct 2014. This strong interannual variability in the EPFP zonal extent is found to be mostly driven by the beginning of the year pre-conditioning rain falls and characteristics (strength, direction) of the NECC in the central tropical Pacific, east of the dateline. Connections with a strong ENSO event starting in 2014 will be discussed.