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Role of Small-scale Variability in the Tropical Pacific Ocean Data Assimilation

Tuesday, April 30, 2002 - 11:30am - 11:50am
Keller 3-180
Alexey Kaplan (Columbia University)
Use of observations in the climate research normally requires data records substantially longer than most of currently available sets of satellite data. Detailed analyses of the global surface ocean are available for the period after 1992 (because of the high-quality and spatially expansive data coverage of the Topex/Poseidon (T/P) altimetry), but existing analyses of the earlier period are less well validated and arguably of lower quality. Use of the error and signal statistics derived from the satellite data for the optimal tuning of in situ data assimilation systems has a potential for extending the climatologically important data sets back into the pre-satellite era.

Our comparison of tropical Pacific sea level height anomaly from the Topex/Poseidon altimetry with those from a few simulation and assimilation systems differing greatly in their level of complexity showed error patterns with major similarities. We trace these similarity features to the spatial energy distribution in the small-scale variability of the ocean sea level height. This interpretation is supported by cross-data comparisons and Monte Carlo experiments. Small-scale variability affecting state-of-the-art ocean analyses represents the subgrid-scale noise for most ocean models, and thus is not properly simulated. This kind of systematic model bias has to be taken into account in optimal data assimilation systems.