Evaluating Lagrangian Model Simulations of the Madden-Julian Oscillation with Metrics for Balanced Dynamics*

The Madden-Julian Oscillation (MJO) is a planetary-scale disturbance that occurs on intraseasonal time scales and influences weather and climate globally. Predicting the MJO is possible if it is a response to large-scale balanced flow. In the balanced dynamics framework, a large scale horizontal rotation modifies the thermodynamic environment which contributes to the development and maintenance of a secondary circulation associated with the convective system. Observational data suggest that the MJO exhibits characteristics consistent with balanced dynamics. Namely, the mid-tropospheric potential vorticity is strongly correlated with moist atmospheric instability and parameters related to the secondary circulation, including mid- and low-tropospheric convergence. These are also well correlated with precipitation. These correlations can be used to evaluate models which simulate the MJO. We apply this strategy to two simulations using a Lagrangian model. The first simulation has a robust MJO signature, while the second poorly reproduces the MJO. Comparing correlations of parameters relevant to the balanced dynamics can help identify where the correlations break down in the model, and thus identify physical mechanisms important for convective organization on the MJO scale.