Understanding long-term variability of the Madden-Julian Oscillation leveraging in-situ observations

The Madden-Julian Oscillation (MJO) is a phenomenon characterized by a cloudy planetary scale (~10000 km) coherent structure in the tropical atmosphere that primarily moves from west to east at about 5 m/s,  with a period of about 40 days. The MJO associated convective heating is balanced by upward motion leading to upper level divergent flow. This low latitude divergence anomaly interacts with the subtropical jets through vortex stretching and vorticity advection by the divergent horizontal flow generating Rossby waves. These Rossby waves then propagate away from the tropics  modulating the higher latitude atmospheric flow.  Even though the MJO was discovered over 50 years ago, and much progress has been made in its theoretical understanding as well as MJO global impacts,  both issues remain  significant outstanding problems in climate research. This presentation focuses on understanding potential changes in  the MJO over the last hundred years.

Long-term variability of the MJO is an important topic of research because changes in MJO propagation and amplitude characteristics could alter its role as a source of predictability within the tropics and at higher latitudes via the tropical-to-extratropical teleconnections described above. While there have been a few studies suggesting that the MJO amplitude has been increasing over the last century, there are also substantial uncertainties surrounding these estimates. Understanding long-term variability of the MJO is challenging because characterizing its behavior outside of the satellite era lacks detailed information about its observed state, and or relies on climate models’ typically poor MJO representation.    In this presentation, we discuss the contrast between long-term variability of the MJO derived from (imperfect) climate model products with the MJO behavior inferred from (sparse) tropical in-situ observations during the same period.