The Madden Julian Oscillation and Global Atmospheric Predictability

The leading mode of intraseasonal variability in the tropical atmosphere, the Madden Julian Oscillation (MJO), has significant impacts on weather and climate around the world. One important impact, which has received very little attention in the literature, is the MJO's influence on global atmospheric predictability. In this study, we explore this important connection using geopotential height data from the new GFS reforecast ensemble.

Sensitivity to initial conditions, the defining condition of a chaotic system, is an intrinsic property of the atmosphere. Ensemble spread is a proxy for the sensitivity of the atmosphere to its initial state. In this study, we calculate ensemble spread, relative to climatology, as well as its growth rate during each phase of the MJO. These calculations are performed globally to gain insight into the MJO's regional and global impacts on atmospheric predictability.

It will be shown that the MJO has statistically significant global impacts on predictability, even at locations that are well removed from the tropics. This is consistent with the view that the MJO has significant extratropical implications which can be either a response to, or a forcing for, the strong convection that often characterizes an MJO event. The strong relationship between the MJO and intrinsic predictability suggests that numerical weather models must struggle more during certain phases of the MJO in certain parts of the world.