Environmental Sources of Error in the Navy ESPC MJO Forecasts and MJO-Teleconnections

The Navy Earth System Prediction Capability (ESPC) is the Navy’s coupled ocean-atmosphere-sea ice model. The current version of the Navy ESPC has 16 ensemble members and been operational since August 2020. The Navy ESPC has known biases in the Madden-Julian Oscillation (MJO), during boreal winter, the MJO in the Navy ESPC is too strong due to biases in the vertical motion, which supports larger vertical moisture advection, and the MJO is too fast due to excessive evaporation in the western Pacific supporting moistening to the east of the MJO convective center. In this study, we examine environmental conditions that lead to well and poorly predicted MJO events.

MJO forecasts are split into those that are well predicted and those that are poorly predicted. Individual MJO events are tracked following Chikira (2014), using Hovmöllers of MJO filtered OLR averaged between 10N and 10S. The good and poor MJO forecasts have similar structure to the observed MJO, the determining factor in the good or poor MJO forecasts is largely due to timing and location of the forecasted MJO. The good forecasts well capture the mean state moisture and low-level winds, as well as the intraseasonal moisture budget. Poor MJO forecasts do not build sufficient moisture anomalies to support the MJO’s amplifications and propagation, evidenced by weak moisture tendency. The poor forecasts struggle to simulate the horizontal advection, with the biggest differences occurring in the zonal advection, and the evaporation term, which is largely driven by mean state and MJO scale wind biases. The intraseasonal horizontal advection is examined in more detail by decomposing them into the mean, intraseasonal, and high frequency contributions.

Finally, we examine the impact that the good and poor MJO forecasts have on the extratropical teleconnections. There is a poleward and retracted bias in the Subtropical jet in the Navy ESPC, which impacts the propagation of Rossby Wave Trains. The Navy ESPC has the best MJO-teleconnection pattern in the North Pacific when the MJO is over the Maritime Continent, but there are strong biases in both the good and poor MJO forecasts. The good and poor MJO forecasts fail to simulate the teleconnection patterns in the Northern Pacific when the MJO is in the Indian Ocean and West Pacific.