The Crucial Role of the Initial State in MJO prediction

Lisa Bengtsson

NOAA Physical Sciences Laboratory

Tuesday, Jan 28, 2025, 2:00 pm MT
DSRC Room 2A305

JOIN THE WEBINAR:

Abstract

The Madden Julian Oscillation (MJO) is a dominant mode of tropical variability and a key driver of sub-seasonal to seasonal climate predictability in mid-latitudes through tropical-extratropical teleconnections. Accurately modeling the MJO is challenging due to its complex interactions with atmospheric circulation and sensitivity to initial conditions and unresolved physical processes. Using NOAA’s Unified Forecast System, we explore the impact of initial conditions on MJO forecasts over the Indo-Pacific. Model runs initialized with GEFSv12 reanalysis show a significantly stronger amplitude in the MJO’s circulation index compared to those initialized with UFS replay, a difference that persists over the 15-day forecast period. This is due to a less statically stable initial atmosphere in GEFSv12 initialized runs stemming from a colder upper troposphere, which enhances vertical motion and divergent winds following the Weak Temperature Gradient (WTG) approximation. Notably, the convection-based MJO index shows lower sensitivity to initial conditions, suggesting that variations in convection or diabatic heating are not responsible for the observed differences in MJO circulation.