North Pacific mode waters : Their climatology and variability
Toshio Suga
Tohoku University
Three different types of mode waters in the subtropical North Pacific have been recognized : North Pacific Subtropical Mode Water (NPSTMW), North Pacific Central Mode Water (NPCMW) and Eastern North Pacific Subtropical Mode Water (Eastern NPSTMW). Climatology and variability of these mode waters are reviewed mostly based on observational work during the last pentad. NPSTMW is formed mainly in the Kuroshio Extension area east / southeast of Japan, and is advected out from its wintertime formation area widely in the Kuroshio recirculation region. Both year-to-year and decadal variations of properties and inventory of NPSTMW were described, which are related to the variation in strength of the East Asian wintertime monsoon and the climate shift in mid-1970s, respectively. NPCMW is proposed to be formed between the Kuroshio Extension and the Kuroshio bifurcation front in the central North Pacific centered around the international date line. Hydrographic climatology suggests that NPCMW is advected around the subtropical gyre. Significant changes in its properties and inventory were detected associated with the mid-1970s' climate shift. Eastern NPSTMW is recently identified in the North Pacific Basin east of Hawaii. It is proposed that Eastern NPSTMW is formed as a relatively deep mixed layer associated with the subtropical / subpolar water mass boundary. Several notes on its temporal variability have been made based on the repeat XBT section between San Francisco and Honolulu.