Representation of MJO variability in the NCEP Climate Forecast System

The Madden Julian Oscillation (MJO) is an eastward propagating intraseasonal mode of tropical coupled ocean-atmosphere variability. Many observational studies suggest that MJO variability has significant impacts on the evolution of both the tropical and extratropical subseasonal climate variability. Accurate simulations of MJO variability and its related climate impacts are thus a necessary prerequisite for improving subseasonal climate prediction. While many GCM's have difficulty in simulating some aspects of MJO variability there has been recent progress in the modeling arena. However, it is difficult to assess the relative strengths/weaknesses and model improvements because model evaluations typically use varied diagnostics to assess the veracity of their MJO simulations. In response, the U.S. CLIVAR MJO working group established a standardized set of diagnostics to facilitate uniform MJO model evaluation and comparisons.

Following the recommendations of the MJO working group, MJO variability is analyzed in a set of 27-year hindcasts generated from two versions of the NCEP coupled atmosphere-ocean model. The simulated MJO characteristics are benchmarked through comparisons to atmospheric circulation fields from the Reanalysis, observed precipitation, and NOAA outgoing longwave radiation (OLR) data. The analysis includes an assessment of intraseasonal variability and propagation of anomalies of zonal winds at 850 hPa and 200 hPa, OLR, and precipitation in observations and simulations. The discussion will focus on model intercomparison and comparisons to the observations including the implications for global MJO climate impacts.