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The Madden-Julian oscillation (MJO) is the principal source of tropical intraseasonal variability, yet challenges remain to accurately simulate its observed convective behavior and eastward propagation. There is specific need for evaluating the role of water within the MJO, including evaporation, vertical transport, precipitation, and latent heating of the coupled atmosphere-ocean system. Hydrogen isotope ratios are particularly useful for investigating these aspects of the water cycle. This study complements previous characterization of MJO joint distributions for water vapor and isotopologue concentrations (D) with consideration of moist entropy in the tropical zonal overturning circulation framework of the MJO. The goals are to distinguish the roles of convective and large-scale dynamic processes through the life cycle of the MJO and identify shortcomings for modeling MJO humidity, clouds, and convection. From MJO composite analyses, wet equivalent potential temperature ((q)) anomalies are largest at 500hPa and tilt westward with altitude. A positive (q) anomaly co-occurs with the precipitation maxima, and negative (q) anomalies co-occur with subsidence both trailing and leading the convective center. Out of phase with (q), D anomalies are positive east and negative west of the convective center, coherent with the regional zonal overturning stream function. These results point to a decoupling in the MJO between midtroposphere water vapor, which is tied to convective processes, and the isotopologue ratios, which are tied to the large-scale circulation. A conceptual model is presented to describe the physical processes that explain the MJO life-cycle for joint distributions of humidity (q) and water vapor D.

Plain Language Summary The Madden-Julian Oscillation refers to a tropical weather pattern centered over the Indian Ocean that influences weather and climate around the globe. We do not fully understand how it works. To better understand this weather system, we studied the chemistry of the water in the air using measurements taken by satellites that orbit the Earth. We learned water distributions in the air around the weather system are controlled by rain patterns, while the chemistry of the water itself is determined by wind patterns. An improved explanation or model for how this weather system works should include the patterns that we have here identified.