Seasonal to Interannual Variations in the North Subsurface Countercurrent of the Equatorial Pacific

While the presence of the Pacific subsurface countercurrents (or Tsuchiya Jets) have been known for over 30 years, their dynamics have only recently been elucidated, as has their importance to local and global circulations. To date very little work has gone into characterizing their variability and its sources, principally due to a dearth of observational data. Now with the development of observationally-constrained ocean reanalysis spanning many decades, there is the opportunity to study these features in more detail. In this talk we focus on the seasonal to interannual variations in the north Pacific subsurface countercurrent, or Northern Tsuchiya Jet. Our interest is in characterizing the intensity and location of the jet, and determining the dynamic underpinnings of variations in these characteristics. Overall, we find that the seasonal variation in the jet strength is on the order of 33% of the mean, reaching a maximum in boreal winter. Further the interannual variations are equally as large. While some of the interannual variability is related in part to the large-scale circulation features that accompany the El Nino/Southern Oscillation, ENSO only explains about 25% of the jet's variance. In this talk we highlight other possible drivers for the year-to-year variability in the jet strength, including variations in the upwelling in the eastern north equatorial Pacific and in its recirculation as part of the north equatorial current.