The Madden–Julian Oscillation (MJO) and Its Teleconnections Analyzed with the NCEP–NCAR Reanalysis Dataset

This study aims to understand and diagnose the teleconnection pattern associated with the Madden-Julian Oscillation (MJO) from Rossby wave forcing. “Active” MJO periods are defined using multivariate empirical orthogonal functions (EOF) of daily OLR and zonal wind vectors at 850mb and 200mb obtained from the NCAR-NCEP Reanalysis data set. Upper-level divergent flow from deep convection produces stationary Rossby waves which can extend into higher latitudes. Thus, a teleconnection associated with the tropical rainfall of the MJO is determined by a signal in the subsidence region, the subtropics. Composite analysis shows a rainfall perturbation in the United States, which indicates that the tropical-extratropical coupling has an influence in the North American region.

ENSO and other low-frequency variability are strategically removed to highlight the teleconnection produced solely from the MJO, and the physical processes driving this are investigated and compared to those of ENSO. The Rossby source term, derived from the single layer potential vorticity equation, shows how Rossby waves can be excited by tropical heating even in small vorticity regions. The Rossby wave source term is the first step towards understanding the dynamical processes of the teleconnection and is evaluated through composite and regression analyses. The MJO is further broken down by phase according to the Wheeler and Hendon (2004) Index, and the response associated with different phases is explored.