Evolution of MJO-Associated Moist Static Energy over Small Tropical Islands Using in Situ Observations

The moist static energy (MSE) is important for the organization and propagation of the Madden-Julian oscillation (MJO). The evolution of MJO-associated MSE has been investigated in many studies that, for the most part, were confined to the open ocean or large islands, and relied primarily on reanalysis data or model simulations. Here, we present 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: Manus and Nauru. We use 14 years (2000 to 2014) of value-added radiosonde and microwave radiometer products, and routinely measured surface meteorological variables to estimate vertical profiles of MSE during MJO propagation across the western Pacific. We use large-scale precipitation tracking to identify MJO propagation (instead of usual MJO tracking using 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. We will show results related to (i) the relative influence of temperature and humidity in determining the MSE profiles at different MJO phases; (ii) how these profiles change in different seasons and climate regimes (e.g., ENSO and IOD phases); and (iii) the role of free troposphere in modulating the vertically-integrated MSE and stability.