An Oceanic Heat Content–Based Definition for the Pacific Decadal Oscillation

Abstract Based on the variability of heat content in the upper 300 m of the ocean (HC300), the feasibility of defining an index of Pacific decadal oscillation (PDO) is explored. The motivation for defining the PDO index on HC300 stems from the following considerations: (i) a need to accentuate lower-frequency variations in the monitoring of PDO and (ii) to take into account variations in the temperatures associated with the PDO that extend throughout the upper ocean (and are modulated by the seasonal cycle of mixed layer variability). It is demonstrated that an HC300-based definition is better suited to encapsulate these characteristics in the PDO variability. The variability in an HC300-based definition is also contrasted with the traditional definition of the PDO based on SSTs.