Evolution of Moist Static Energy During Madden-Julian Oscillation Using Tropical Western Pacific Atmospheric Radiation Measurement Observations

Authors

Nirmal Alex¹, Pallav Ray¹* (pray@fit.edu), Steven M. Lazarus¹, Michael Splitt¹, Samson Hagos²

Institutions

¹Florida Institute of Technology, Melbourne, FL; ²Pacific Northwest National Laboratory, Richland, WA

Abstract

The evolution of moist static energy (MSE) is intimately associated with the organization and propagation of the Madden-Julian oscillation (MJO). Past studies on MJO-associated MSE, for the most part, were confined to the open ocean or large tropical islands and relied primarily on reanalysis data or model simulations. This research team presents a systematic analysis of the intraseasonal variation in MSE in the tropical western Pacific (TWP) using long-term, high-quality, ground-based observations from two Department of Energy Atmospheric Radiation Measurement (DOE-ARM) sites located over small islands: Manus and Nauru. Researchers use 14 years (2000 to 2014) of value-added radiosonde and microwave radiometer products, and researchers routinely measured surface meteorological variables to estimate vertical profiles of MSE during MJO propagation across the western Pacific. The team used large-scale precipitation tracking to identify MJO propagation (instead of usual MJO tracking using Realtime Multivariate MJO; RMM) since it can provide the exact location of the MJO precipitation centroid (unlike the RMM index). Therefore, composites of MSE vertical structure can be developed as a function of the location of the MJO precipitation centroid, and the distance between the ARM sites and the MJO. The results show (1) the humidity dominates the MSE profiles during active MJO phases, while temperature plays a role in suppressed and transition phases; (2) the mid-tropospheric moistening from the transition to active phases is consistent with the moisture-mode theory; and (3) MJO events propagating closer to the TWP-ARM stations show an abrupt increase in MSE at the beginning of active phases instead of a gradual increase in MSE seen in the composites of all MJO events. This result may reconcile the differences found in past studies that differ from each other related to slow and fast evolution in MSE in the TWP.