The Pacific Upwelling and Mixing Physics (PUMP) Experiment

Bill Kessler



The PUMP experiment is a process study to observe and model the complex of mechanisms that connect the thermocline to the surface in the equatorial Pacific cold tongue. Its premise is that climate-scale ocean models are ready to exploit realistic vertical exchange processes, but need adequate observational guidance. The convolution of surface fluxes, upwelling and mixing that determines equatorial SST has previously been measured only in isolation, and the results have not yielded an understanding of the mechanisms of vertical exchange that can be distilled into model parameterizations. Further, existing observations have not been able to provide a description of the meridional circulation that would let us evaluate the realism of these structures in modern OGCMs, whose develoment has focused primarily on the
equatorial zonal currents. PUMP will observe the transition from the Ekman-geostrophic regime at +-5 degrees to the equator, and provide a quantitative model and observational diagnosis of the meridional circulation. The proposed surface flux, turbulence and velocity measurements are complementary checks on one another, and will serve as a testable challenge to the models.