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A reliability budget analysis of CESM-DART

TitleA reliability budget analysis of CESM-DART
Publication TypeJournal Article
Year of Publication2020
AuthorsEliashiv J., Subramanian AC, Miller AJ
Date Published2020/02
Type of ArticleArticle
Accession NumberWOS:000519728500003
Keywordsbiases; CESM; Data assimilation; Ensemble Kalman filter; madden-julian; Meteorology & Atmospheric Sciences; oscillation; reliability budget; simulation

A reliability budget is used to diagnose potential sources of error (departure from observations) in a new prototype coupled ocean-atmosphere ensemble Kalman filter reanalysis product, the Community Earth System Model using the Data Assimilation Research Testbed (CESM-DART). In areas with sufficient observations, the mean bias in zonal wind was generally very low compared to the spread due to ensemble variance, which did not exhibit patterns associated with Northern Hemisphere jet streams but did have regional enhancement over the Maritime Continent. However, the residual term was often the largest contributor to the budget, which is problematic, suggesting improper observational error statistics and inadequately represented ensemble variance statistics. The departure and residual exhibit significant seasonal variability, with a strong peak in boreal winter months, indicating the model's deficiencies during the energetic Northern Hemisphere winter. Ocean temperature contained large error in areas with eddy production indicating inadequate ensemble variance due to poor model resolution. Periods when the Madden-Julian Oscillation (MJO) was active exhibited lower error, especially in the western equatorial Pacific during MJO phases with reduced convection. In contrast, during MJO phases with enhanced convection in that region, the ensemble variance is increased yet the error is comparable to non-MJO conditions, suggesting a controlling effect of the precipitation parameterization. Further studies evaluating the impact of the coupled assimilation procedure on the reliability budget will be illuminating.

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