The MJO problem in GCMs: What are the missing physics?

The Madden-Julian Oscillation (MJO) is well recognized as a key source of untapped predictability in the tropics. It affects a wide range of tropical weather such as the onset and breaks of monsoons and the formation of tropical cyclones. Being a strong tropical heating source, it also drives teleconnections to extratropics and affects precipitation events in western United States and South America. However, the MJO is poorly simulated in current general circulation models (GCMs). The simulated signals are generally too weak and propagate too fast. This constitutes one of the major tropical biases in current GCMs, and is detrimental to both weather prediction and climate prediction.

Because the MJO problem is a common problem in many GCMs, our hypothesis is: The MJO problem is caused by some missing physics in current GCMs. I will discuss about a framework to synthesize the existing MJO theories, and to guide our search for the missing physical processes important for the MJO. Our parallel diagnostics of observational data (satellite, field experiment, and reanalyses) and GCM simulations have revealed three missing physical processes that are likely important for the MJO. They include:

(1) Convective downdrafts (especially unsaturated); (2) Mesoscale updrafts/downdrafts; (3) Control of deep convection by lower tropospheric moisture; and (4) Convective momentum transport by shallow convection

It would be interesting to install these missing physics into GCMs and test their impacts on the MJO simulation. Some improvements are demonstrated using GCM sensitivity experiments.