2000: A simple ocean data assimilation analysis of the global upper ocean 1950–95. Part I: Method

The authors explore the accuracy of a comprehensive 46-year retrospective analysis of upper-ocean temper-ature, salinity, and currents. The Simple Ocean Data Assimilation (SODA) analysis is global, spanning the latitude range 628S–628N. The SODA analysis has been constructed using optimal interpolation data assimilation combining numerical model forecasts with temperature and salinity profiles (MBT, XBT, CTD, and station), sea surface temperature, and altimeter sea level. To determine the accuracy of the analysis, the authors present a series of comparisons to independent observations at interannual and longer timescales and examine the structure of well-known climate features such as the annual cycle, El Niño, and the Pacific–North American (PNA) anomaly pattern. A comparison to tide-gauge time series records shows that 25%–35 % of the variance is explained by the analysis. Part of the variance that is not explained is due to unresolved mesoscale phenomena. Another part is due to errors in the rate of water mass formation and errors in salinity estimates. Comparisons are presented to altimeter sea level, WOCE global hydrographic sections, and to moored and surface drifter velocity. The results of these comparisons are quite encouraging. The differences are largest in the eddy production regions of the western boundary currents and the Antarctic Circumpolar Current. The differences are generally smaller in th