Award: OCE-1232971

The overarching goal of Repeat Observations by Gliders in the Equatorial Region (ROGER) is to quantify the thermohaline and velocity structure of the equatorial ocean, particularly the equatorial front and equatorial undercurrent. Our observational program involved Spray underwater gliders deployed from the Galapagos Islands continuously for two years to make three repeated sections, two from the southern and northern coasts of the Galapagos to the ends of a third section along 93°W between 2°S and 2°N. Analyses of the data quantifedvariability in the equatorial front and equatorial undercurrent and partitioning of flow around the Galapagos for periods between 20 days and 1 year, and down to horizontal scales of 10 km. We focused on quantifying the following three metrics: The position and strength of the equatorial front The position and strength of the equatorial undercurrent (EUC) The partitioning of transport around the Galapagos The project was augmented with funding from NOAA to deploy a gider on 95°W. The significant technical results of this program were: 1. We pioneered the use of ADCPs on gliders with what we hope was a definitive paper on the subject this past year. 2. We demonstrated that glider observations across the equatorial current system can be sustained, addressing the doubts of many reviewers of this proposal. The most significant scientific results were: 1. A succession of Kelvin waves were observed in 2014 and 2015 through their expression in the EUC off Galapagos. In early spring 2014, a downwelling Kelvin wave, and associated strong EUC led to some forecasts of an El Ni?o. This was followed by an upwelling Kelvin wave and weak EUC. In late winter and early spring 2015, the first of a succession of downwelling Kelvin waves, with strong EUC bursts led to the establishment of the 2015-2016 El Ni?o. 2. The EUC was observed to have a strong salinity front embedded in the eastward flowing current. The core of the EUC has high salinity water whose origins are south of the equator. The northern side of the EUC has fresher water that originates north of the equator. Concurrent glider measurements in the Solomon Sea and Mindanao Current, which feed the EUC, support the notion that the primary source of EUC water is from the south. 3. The strongest eastward transport in the EUC upper 200 m, occurred during the spring of 2014 and 2015 at about 20-30 Sv. The arrival of an El Ni?o is of intense interest in the western US because it brings the possibility of increased precipitation. There have been a number of stories in the press about our work. Last Modified: 11/29/2018 Submitted by: Daniel Rudnick