Transient Response of MJO Precipitation and Circulation to Greenhouse Gas Forcing

Abstract

AbstractRecent studies have shown that Madden‐Julian oscillation (MJO) precipitation anomaly amplitude tends to increase while associated circulations weaken at the end of 21st century in Coupled Model Intercomparison Project phase 5 models under Representative Concentration Pathway 8.5. Transient changes of MJO characteristics earlier in the 21st century have received less attention. In this study, changes of MJO precipitation and circulation amplitude during these interim time periods under Representative Concentration Pathway 8.5 are examined in Coupled Model Intercomparison Project phase 5 models. Multimodel mean changes in MJO precipitation and circulation amplitude are not individually detectable in the early and middle 21st century relative to the historical period (1986–2005). However, robust multimodel mean decreases in the ratio of MJO wind to precipitation anomalies occur even early in the 21st century. This decreased ratio is explained by increasingly large tropical static stability as the climate warms, which under weak temperature gradient balance mandates that a diabatic heating anomaly is balanced by an increasingly weaker circulation anomaly. These results suggest the robustness of weak temperature gradient theory for explaining MJO dynamics, not only in an equilibrium climate but also in the transient response.