A Reliability Budget Analysis of CESM‐DART

摘要

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. Plain Language Summary A reliability budget is used to diagnose error 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). Although the bias term was low, the residual term was often the largest contributor to the budget, indicating improper observational error statistics and inadequately represented ensemble variance statistics. During periods when the Madden‐Julian Oscillation was active, the error was lower, especially in the western equatorial Pacific during Madden‐Julian Oscillation phases with reduced convection, suggesting a controlling effect of the convection parameterization.