Using Simplified Linear and Nonlinear Models to Assess ENSO-Modulated MJO Teleconnections

Abstract Some simple dynamical models have proven to be useful tools for understanding tropical-extratropical teleconnections. Here, we use simple linear and non-linear dynamical models to understand how ENSO modulates subseasonal teleconnections associated with the tropical imprint of the MJO. Both a dry linear baroclinic model (LBM) and a dry nonlinear baroclinic model (AGCM) are employed to 1) assess how much of the MJO teleconnection pattern in a particular ENSO phase can be captured by linear and nonlinear dynamics and 2) understand the key driver(s) in differences in Northern Hemisphere MJO teleconnection patterns based on ENSO phase. The modeling experiments reveal that elements of the Northern Hemisphere teleconnection pattern are a direct Rossby wave response to tropical MJO heating. Nonlinear dynamics modestly capture more of the Northern Hemisphere MJO teleconnection pattern than linear dynamics alone, but some key elements of the teleconnection pattern seen in Reanalysis are still missing in the model representations. Both models show that the response is sensitive to the location and domain of the MJO-associated forcing and the month, MJO phase, and ENSO phase of the forcing and background state. Further, ENSO modulates both the spatial structure and magnitude of the MJO teleconnections and results show that the ENSO-modulated MJO forcing is the dominant driver of the mid-latitude response over the background state. The results show evidence for subseasonal variability related to the MJO within the interannual ENSO teleconnections in the North Pacific and North America and so MJO teleconnections must be considered in the context of the ongoing ENSO event