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University of Washington
University of Washington
The vertically integrated transport in the Northeast Pacific Basin between western North America and Hawaii shows a large-scale deviation from Sverdrup balance of about 7 Sverdrups magnitude. The anomaly is coincident with a region of weak mode water for mation, the water mass boundary between subtropical and subpolar regimes, and a distinct change in zonal thermocline slope. The goal of this project is to ascertain the underlying causes for the deviation from Sverdrup balance and its relationship to the large-scale heat budget. Our approach has observational and modeling thrusts that are closely related. In collaboration with Dr. Dean Roemmich, we will analyze existing hydrographic and WOCE repeat XBT data to define the mean fields of temperature and transport, the region of mode water formation, and estimate interannual variability in the strength of meridional transport and mode water characteristics. In addition, we have proposed observations for winter 1998 consisting of seasonal hydrographic sur veys across the Northeast Pacific Basin coupled with ADCP and SeaSoar measurements in the vicinity of the front. These measurements will provide the detailed salinity and temperature structure and ageostrophic velocity not available from the XBT data bas e and a detailed description of seasonal mode water preconditioning and formation. The modeling effort will concentrate on examining the effect of wind-stress curl on the thermocline structure and outcrop locations in the subtropical northeast Pacific. Using an isopycnal model, both seasonal and mean wind fields are used as forcing. A second modeling effort utilizes a two-dimensional model to study the role of buoyancy forcing and differential Ekman transport in the formation of mode water near the sub tropical/subpolar water mass boundary. We also plan collaboration with Dr. Kathryn Kelly that will enable us to examine these questions using new data available from earth-observing satellites (see Kelly abstract for this meeting).
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