Eliashiv, J., A. C. Subramanian and A. J. Miller, 2020:
A Reliability Budget analysis of CESM-DART
Journal of Advances in Modeling Earth Systems, 12, e2019MS001678.
Abstract.
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 sucient 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 ect 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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