Numerical and theoretical investigations of North Pacific subtropical mode water with implications to Pacific climate variability

Xujing Jia Davis, University of Rhode Island


An investigation using a combined numerical modeling and theoretical approach is followed to better resolve the role of Subtropical Mode Water (STMW) in the exchange of information between the atmosphere and the ocean linked to climate variability in the North Pacific Ocean. In this, a High resolution MIT General Circulation Model (MITgcm) simulation is analyzed to study the formation, isolation, dispersal of STMW and identify correlations between STMW variations and established climatic signals in the Pacific basin. During a 171-month time period (from January 1992 to March 2006), the seasonal variability is the dominant temporal variation observed. From climatological model fields, STMW exhibits distinct features in time and space. This can be seen more clearly by dividing the cycle into three distinct time periods: the formation, the isolation and the dissipation periods. In addition to seasonality there is also an interannual signal observed in STMW variability. This interannual variation pattern is connected closely to the climate shifts of North Pacific with further investigation showing that there is a high correlation between the STMW variability and the Pacific Decadal Oscillation index. To identify the mechanisms responsible for this interannual STMW variability, classical ocean thermocline theories are reviewed and STMW connections to large scale ocean circulation patterns are explored. A planetary geostrophic ocean model (PGOM) is employed as a theoretical platform for this purpose. Specifically, numerical PGOM experiments are performed to isolate and examine in further detail, the influence of variations of the large scale wind stress pattern and large scale air-sea heat flux on STMW variability. It may be gathered from these experiments that large scale wind stress patterns responsible for Ekman pumping are necessary for the generation of STMW in this ventilated thermocline scheme in the PGOM. Variability in this large scale wind stress is seen to affect the variability pattern of model STMW. Yet, results also indicate that the amplitude of seasonal and interannual variability of STMW volume is primarily dominated by the variability in the air-sea heat flux. ^

Subject Area

Physical Oceanography|Atmospheric Sciences

Recommended Citation

Xujing Jia Davis, "Numerical and theoretical investigations of North Pacific subtropical mode water with implications to Pacific climate variability" (2008). Dissertations and Master's Theses (Campus Access). Paper AAI3328720.