Intraseasonal Sea Surface Salinity Variations in the Northeastern Tropical Pacific Fresh Pool

Sea Surface Salinity (SSS) is one of the key factors influencing the ocean circulation but is also an important indicator of the hydrologic cycle. Understanding processes associated with various SSS regimes is thus crucial to the knowledge of ocean dynamics and of the connection between the ocean and the water cycle. In-situ measurements from NASA’s Salinity Processes in the Upper Ocean Regional Study (SPURS) have greatly enhanced the understanding of the processes controlling the SSS in the subtropical North Atlantic, a high SSS regime associated with strong evaporation and low precipitation. SPURS-2 is slated to take place in the northeastern equatorial Pacific, around a low SSS regime associated with high precipitation and low evaporation. Satellite SSS from Aquarius and SMOS provide a large-scale context to understand salinity processes in both regions in combination with the in-situ observations collected by these field experiments. As part of the effort in preparation for SPURS-2, we examine the dominant temporal and spatial scales of SSS around 10ºN and 125ºW using Aquarius and SMOS SSS measurements together with a 0.25ºx0.25º resolution ECCO (Estimating the Circulation and Climate Experiment of the Ocean) ocean circulation model simulation. This study focuses on sub-seasonal variability. A 2D Fast Fourier Transform analysis of SSS reveals a dominant time scale of 50-150 days and spatial scale of 8-20 degrees of longitude during the period of 2011 to 2014. This intraseasonal SSS signal shows a westward propagating tendency of about 17 cm/s. Moreover, observed and modeled sea surface temperature, sea level anomaly and mixed layer depth are discussed in relation to the SSS features. The nature of the observed propagating signal is examined by the study of advection by the time-varying zonal current system, Ekman pumping, wave propagation and precipitation forcing associated with the ITCZ movement.