Abstract
Many recent studies have characterized the Madden–Julian Oscillation (MJO) as a moisture mode, suggesting that its amplification and eastward propagation result from processes that build up moisture to the east of the MJO’s convective center, including frictionally driven boundary layer convergence, surface fluxes, and shallow convection. Discussions of MJO moistening under this theory often implicitly assume an Eulerian framework; i.e., that local increases in moisture result from physical processes acting in the same location as the moistening is observed. In this study, the authors examine MJO moistening in a Lagrangian framework using a model that simulates atmospheric circulations by predicting the motions of individual air parcels. Back trajectories are presented for parcels in moist convecting regions of the MJO, and the effects of different physical processes on their moisture and moist static energy budgets are quantified. The Lagrangian MJO simulations suggest that much of the low-level moist air in heavily precipitating regions of the MJO arrives via the mid troposphere, coming from nearby equatorial regions, where it has been moistened largely by convective processes. Consequently, a thorough understanding of MJO moistening requires knowledge of the origin of the moist air and information about remote moisture sources.
Highlights
The Madden–Julian Oscillation (MJO) [1,2,3,4] is a planetary-scale weather disturbance that propagates slowly eastward over the equatorial Indian and west-Pacific Oceans
While the focus of this paper and previous work involving the Lagrangian atmospheric model (LAM) has been on tropical convective systems, we begin by briefly reviewing several aspects of the model’s simulation of the atmosphere’s time-average global state, since this is the first study conducted with the global version of the LAM that includes continents
The LAM’s annual average rainfall (Figure 2a) exhibits many features seen in observationally based estimates (e.g., Figure 2b) including heavy rainfall over the warm waters of the Indian and west Pacific Oceans and the Amazon basin, an intertropical convergence zone (ITCZ) that encircles the tropics and lies to the north of the equator in the east Pacific and Atlantic Oceans, prominent storm tracks to the east of North America and Asia, and dry regions over Northern Africa, continental
Summary
The Madden–Julian Oscillation (MJO) [1,2,3,4] is a planetary-scale weather disturbance that propagates slowly eastward over the equatorial Indian and west-Pacific Oceans. It is the dominant mode of intraseasonal variability in the tropics [5], is coupled to Asian, Australian, and North. One popular way of thinking about the MJO is as a moisture mode [14,21] with many studies seeking to understand its mechanism(s) of moistening and drying [22,23,24]. There is a growing consensus that the low-level Rossby gyres that develop in response to the MJO’s heat source [29,30,31] advect off-equatorial
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
