Moisture Cycle of the Madden-Julian Oscillation, convectively-coupled Kelvin waves, and a subset of waves in between

The relationship between columnar water vapor and rain rate are analyzed for the buildup and suppression of enhanced convection during the Madden-Julian Oscillation (MJO), convectively coupled Kelvin waves, and a subset of slow, zonally narrow eastward propagating waves with temporal and spatial scales in between the two. Phases are identified by the Realtime Multivariable MJO Indices (RMM) from Wheeler and Hendon (2004) for the MJO and by indices created by Roundy for the Kelvin waves and slow, zonally narrow signals. Columnar atmospheric water vapor and rain rate from the Tropical Rainfall Measuring Mission Microwave Imager are used to demonstrate rainfall as a function of water vapor.

In composites of days before and after the different phases, water vapor and precipitation increase and decrease together along different pathways forming a cycle. In these moisture cycles, the ratio of precipitation to water vapor varies based on time lag and location relative to enhanced convection. Analysis shows a statistically significant difference between the ratios of precipitation to water vapor for days before and days after different phases of the MJO and zonally narrow signals for most locations over the Indian and west Pacific Ocean warm pool, with a preference for more columnar water vapor per similar amounts of precipitation as convection builds up. Moisture cycles for convectively coupled Kelvin waves show less clarity with a potential tendency for more water vapor per a similar amount of precipitation after the peak in convection.