Decadal variability in the midlatitude North Pacific Ocean has received considerable attention in recent years because of its impact upon the marine ecosystems and the weather anomalies over the North America continent. While scattered evidence exists suggesting the ocean dynamics works to contribute to an increase in variance and persistence of the North Pacific midlatitude ocean-atmosphere system on decadal timescales, a detailed understanding of how the system works is still lacking. In order to improve our ability to predict the midlatitude Pacific climate variability, a better understanding of how the upper ocean dynamic and thermodynamic processes interact is of fundamental importance. The mid-latitude North Pacific Ocean is subject to both buoyancy and momentum flux forcing at the sea surface. Because of the planetary beta effect, the wind stress-induced upper ocean anomalies tend to propagate westward and accumulate in the Kuroshio Extension region. By transporting warmer tropical-origin water to the mid-latitudes, the Kuroshio Extension is also where the largest air-sea heat exchange and its variability take place. The non-linear nature of the western boundary current circulation variability can further complicate the time-varying upper ocean signals. In this study, Dr Qiu and colleagues examine the processes underlying the observed upper ocean variability based on available in-situ/satellite observations and a high-resolution OGCM hindcast output. The scientific goals of the proposal are (1) to provide a comprehensive description of the decadal variability in the midlatitude North Pacific from the perspective of the upper ocean dynamic and thermodynamic process interaction, (2) to develop testable hypotheses about the role of ocean dynamics in determining the sea surface temperature changes, and (3) to explore whether the long memory of the ocean dynamics can be utilized for improved prediction.
The Kuroshio Extension system is an important component of the earth's climate system, particularly in the North Pacific basin. Its influence upon the intensity and tracks of the midlatitude storms and the North Pacific marine ecosystems, as well as its impact on the weather patterns of the U.S. northwest coast, are of important societal relevance. This study aims to gain a better understanding of the roles of ocean dynamics in determining the decadal and longer timescale variability in the North Pacific climate system. This improved understanding could potentially expand our capacity to predict the decadal oceanic state. While the focus of the study is on the KE system specifically, many of the scientific questions, such as the roles of the oceanic adjustment through baroclinic Rossby waves, the intrinsic recirculation gyre variations, the interaction between the western boundary outflow and the bottom topography, and the impact of the upper ocean circulation changes upon the regional SSTs, apply to the other western boundary current systems as well. A better understanding of the KE system variability could serve as a useful step in elucidating the ocean's roles in the midlatitude air-sea coupling in general.
