Aspects of modeling the North Pacific Ocean

Three aspects of the problem of modeling North Pacific Ocean climate are investigated: the effect of viscosity on effective model resolution, the effect of ocean surface currents on air-sea heat and momentum flux, and the response of the midlatitude ocean to decadal atmospheric forcing.; A 2°-resolution isopycnal model of the North Pacific is shown to produce anomalies that propagate around the subtropical gyre on the decadal-timescale that do not appear in a 1°-resolution version of the same model. A linearized quasi-geostrophic mode analysis shows that the anomalies are generated by flow instability in the region of the STCC. The instability disappears in the 1° model due to changes in the horizontal viscosity. A criterion for model resolution of an instability of a given length and time scale damped by biharmonic viscosity is derived.; The effect of ocean surface currents on bulk algorithm calculations of wind stress and heat flux in a 1/5° resolution model of the North Pacific is investigated. Localized flux reductions of ∼10% were found in the tropics and in the Kuroshio current system, and basin average power input by the wind to the general circulation was reduced by 27%, when ocean surface currents were included.; Heat and temperature budget changes in a 1/3rd degree model of the North Pacific driven by an idealized Pacific Decadal Oscillation (PDO) atmospheric forcing are diagnosed. Changes in MLT and heat content during the transition between negative and positive PDO are driven by atmospheric heat fluxes. Once the new PDO state is established, atmospheric heat flux in the central North Pacific works to mitigate the MLT change while vertical entrainment and ageostrophic advection act to enhance it. At the same time, wind-driven circulation changes cause a large increase in the geostrophic advective heat flux in the Kuroshio region. This increase results in more heat being fluxed to the atmosphere, demonstrating an active role for ocean dynamics in the upper-ocean heat budget. Eddy heat flux divergence along the Kuroshio Extension doubles after the transition, due to stronger eddy activity related to increased Kuroshio transport.