We propose to synthesize spurs-2 atmospheric and oceanic measurements to study the mechanisms connecting the spatial and temporal patterns in rainfall to the upper-ocean salinity structure on scales…

This is a grant award from the National Aeronautics and Space Administration (NASA) Shared Services Center to the University of Washington (UW) to analyze the relationship between rainfall patterns and upper-ocean salinity structure in the Tropical Eastern Pacific. The $447,058.73 research project will develop unified datasets of precipitation, salinity, and ocean turbulence measurements collected during the SPURS-2 field campaign. This work aims to quantify the physical processes that create the Eastern Pacific Fresh Pool and the multi-scale variability of salinity, to inform ocean modeling efforts. The award has no set-aside designation. UW is a leading public research university that has received numerous prime and sub-contracts across federal agencies for research, healthcare, and technical services in support of various missions.

We propose to synthesize spurs-2 atmospheric and oceanic measurements to study the mechanisms connecting the spatial and temporal patterns in rainfall to the upper-ocean salinity structure on scales of 0.1 to 100 KM and minutes to days. The tropical eastern pacific fresh pool (epfp) is created in part by frequent precipitation under the intertropical convergence zone (itcz). Itcz precipitation varies on a broad range of spatial and temporal scales, introducing strong episodic freshwater forcing into the upper ocean. The freshwater input is redistributed within the ocean mixed layer and integrated into the eastern pacific water mass structure via a range of multi-scale advection and mixing processes, which are still not well understood. The spatio-temporal distribution of rainfall, along with the horizontal variability and vertical structure of salinity observed during spurs-2, can be used to identify the processes controlling freshwater integration and their relative importance. To quantify the links between atmospheric forcing and ocean response, we will first statistically characterize the spatio-temporal variability of rainfall in the itcz using the available multi-scale measurements of precipitation collected during spurs-2: insitu observations, shipboard radars, and satellite products. In parallel, variability of upper-ocean salinity and turbulence will be characterized using the moored records, underway data, and observations collected by the constellation of spurs-2 autonomous assets. Finally, we will connect the two through 1-d numerical simulations that will explore the impacts of the temporal variability of rain forcing on the vertical structure of ocean salinity. The proposed work responds to the research questions identified in the NASA spurs-2 synthesis solicitation. The physical processes responsible for creating the epfp (Q1) will be investigated by carrying out observational analysis and 1-d model simulations to quantify how the properties of surface forcing, ocean mixing, and ocean stratification modulate the depth and timescales over which rain water is integrated vertically into the water column. The nature of the salinity variance cascade (Q3) will be examined by statistically characterizing the multi-scale variability of precipitation and in situ salinity. We will also investigate the spatiotemporal resolution of precipitation and wind forcing required in order for ocean models to reproduce the observed variability of the upperocean salinity over timescales of minutes to days (Q4). This project will produce: (1) a unified precipitation dataset for spurs-2, comprised of the c-band (sea-POL) and x-band radar data, shipboard and moored precipitation gauge measurements, underwater acoustic measurements from floats, gliders, and moorings, and satellite remote sensing; (2) a unified upper-ocean salinity dataset comprised of the observations made with the vessel-based underway thermosalinographs, the towed surface salinity profiler (SSP), moorings, wave gliders, SVP-s drifters, seagliders, profiling apex floats, mixed-layer float, and saildrones; and (3) an upper-ocean turbulence dissipation dataset comprised of SSP-based microstructure and acoustic doppler current measurements as well as seaglider and mixed-layer float estimates. These three unified data sets will be compiled, documented, and made available to the national and international scientific community as part of the curated spurs-2 data library. Since these three datasets of precipitation, salinity, and mixing will also be critical for the completion of the other proposed spurs-2 synthesis tasks, the datasets will be created and disseminated in close collaboration with the fellow synthesis teams. This proposal will primarily support one early career researcher, one postdoc, and one graduate student. All spurs-2 investigators are committed to providing guidance, expertise, and full access to the data to this team of young investigators.