The Madden-Julian Oscillation, or MJO, is a system of clouds, wind, and precipitation which continuously moves eastward around the globe, varying on a week-to-week basis. The MJO exerts the most important influence on variability within seasons in the tropical climate, affecting monsoon season onset, ENSO initiation, and the locations of tropical cyclone formation. There is well documented variance in the MJO with seasons, showing that MJO is most variable from December to February, but research has not yet fully explained the drivers of this maximum variability. One proposed influence of MJO variability is the relationship between the average state of Earth’s climate and incoming solar radiation, which is largely determined by characteristics of Earth’s orbit. New research, supported in part by the Climate Program Office’s Climate Variability & Predictability (CVP) Program, manipulates the details of Earth’s orbit within a set of global climate models to investigate the drivers of the December to February MJO variability. An international group of researchers, including Daehyun Kim of the University of Washington, used these model experiments to refine our understanding of the relationships between orbital and solar factors and sea-surface temperature, precipitation, westerly winds, and heat flux from Earth’s surface to the atmosphere within the MJO. The results, published in the Journal of Climate, illuminate an important chain of events for the MJO. When mean precipitation increases, there is less time needed to remove excess water vapor from the atmosphere, which causes more precipitation variability. This work contributes to a growing body of work funded by CVP to advance our understanding of changes in the climate system that occur within seasons in systems like the MJO.