The Madden–Julian Oscillation, Forecast Initialization, and Subseasonal Predictability

The Madden-Julian Oscillation (MJO) is recognized as an important source of potential predictability on subseasonal scales. A previous study showed that, when the MJO is active, errors in initial conditions on small scales relative to the large-scale characteristics of the MJO grow quickly, propagate to the extratropics and degrade forecast skill. Here, the boreal 2004-05 winter is used as a case study to conduct potential predictability experiments with the Weather Research and Forecasting (WRF) model. That winter season was characterized by an MJO event during 18 December-20 January 2004-05, weak El Niño, strong North Atlantic Oscillation and extremely wet conditions over the contiguous United States (CONUS). WRF is used on a global domain (1.25 degrees latitude/longitude) and nested grids in the tropics with high spatial resolution to simulate multi-scale variability within the MJO envelope. Different model initialization strategies are tested to investigate forecast error growth on multi-scales and their influence on potential predictability on 2-4 week lead times. The presentation will discuss the implications of model initialization and subseasonal predictability.