Evaluating Relationships between the Extratropical Stratospheric Circulation and the MJO in the S2S Models

The Madden Julian Oscillation (MJO) is the leading mode of intraseasonal variability in the tropics, and is a source of predictability for the extratropical Northern Hemisphere atmospheric circulation during the boreal winter. Observational analyses have demonstrated a link between the positive phase of the Arctic Oscillation (AO) and MJO phases characterized by convection in the eastern hemisphere (MJO phases 3-4). The negative phase of the AO tends to be linked to MJO convection in the western hemisphere (MJO phases 7-8). This study seeks to evaluate how well these modes and relationships are represented within selected models from the Subseasonal to Seasonal (S2S) Prediction Project.

Following the S2S project goal of improving forecast skill, initial analysis suggests that both the boreal winter AO and the stratospheric polar vortex are largely captured in the S2S models at leads out to 5-10 days. While the RMM indices that track the MJO are also well represented in the models, the skill of the MJO amplitude, which is used to evaluate the MJO teleconnections, is lower. Composite maps of temperature over North America also demonstrate the influence of the MJO. A few of the models mirror the observations, however, the magnitude and pattern of anomalies vary greatly amongst most of the models.