Mean (top) and anomalous
(bottom) depth of the 20C isotherm. Data are derived from the NCEP's global ocean data
assimilation system which assimilates oceanic observations into an
oceanic GCM (Behringer, D. W., and Y. Xue, 2004: Evaluation of the global ocean data
assimilation system at NCEP:
The Pacific Ocean. AMS 84th Annual Meeting, Seattle, Washington, 11-15). Anomalies
are departures from the 1981-2010 base period means.