An Evaluation of the National Meteorological Center Weekly Hindcast of Upper-Ocean Temperature along the Eastern Pacific Equator in January 1992

Abstract

The upper-ocean temperature distribution along the Pacific equator from 139° to 103°W was observed in January 1992 with temperature profiles recorded from a ship and inferred from an ocean general circulation model calculation involving data assimilation (i.e., hindcast). An El Niño episode was in progress. The 100-m-thick mixed layer depth, the mixed-layer temperature, and the depth-averaged temperature below the thermocline were similar in both data products. Considerable differences occurred in the representation of the 15°?25°C thermocline, such as the depth-averaged temperatures above and below the 20°C isotherm, the cast-west slope of the 20°C isotherm, and a 1000-km-wide depression. The longitudinal-averaged root-mean-square difference between the hindcast and observed depths of the center of the thermocline was 17 m. Most of the disparities could be attributed to a high wavenumber transient event that the model-based assimilation system was not intended to resolve.