Evolution of Moist Static Energy during MJO Using Long-Term in-Situ Observations over Manus in the Tropical Western Pacific.

The evolution in moist static energy (MSE) has been found to be closely linked with the Madden-Julian Oscillation (MJO) and its propagation. We analyze the MSE evolution over the tropical western Pacific (TWP) using a Department of Energy – Atmospheric Radiation Measurement (DOE-ARM) site located over Manus and approximately 14 years (2000 - 2014) of bias-corrected radiosonde data. We also use routinely measured surface meteorological variables to supplement our analysis. Four distinct phases, suppressed, transition, active, and discharge, were defined based on MSE evolution during the MJO events. Consistent with previous studies, observations show that humidity (rather than temperature) dominates the MSE profiles during active MJO phases. Whereas past studies have predominantly focused on the suppressed and active phases of the MJO, here we focus on exploring tropospheric MSE evolution and its drivers during the MJO transition and discharge phases. We show that temperature effects cannot be neglected during the suppressed and transition phases. The possible role of sea surface temperatures in driving the mid-tropospheric MSE (moisture and temperature) anomalies during the transition and discharge phases is also explored.