Using Observations to Examine the Diurnal Cycle of Moist Static Energy During MJO Events in the Maritime Continent.

The evolution of moist static energy (MSE) is important with respect to the organization and
propagation of the Madden-Julian oscillation (MJO). The evolution of MJO-associated MSE has
been investigated in numerous studies that, for the most part, were confined to the open
ocean, relied primarily on reanalysis data, and did not fully explore the diurnal variation in MSE.
Here, we present a systematic analysis of the MSE diurnal cycle in the Maritime Continent using
ground-based observations from three Department of Energy – Atmospheric Radiation
Measurement (DOE-ARM) sites: Darwin, Manus, and Nauru.

We use 14 years (2000 to 2014) of value-added radiosonde and microwave radiometer
products (INTERPSONDE-ARM) and routinely measured surface meteorological variables with a
composite-based approach that is synced to the passage of the MJO centroid over these three
islands to estimate vertical profiles of MSE. By analyzing the composite of MSE vertical profiles
for different MJO phases, seasons, propagation modes, and climate regimes, we find that the
MSE anomalies are largely modulated by moisture tendencies in the lower to mid-troposphere,
which is consistent with moisture-mode theory. Analysis of diurnal variations in column MSE
suggests that the patterns vary depending on the MJO phase. Results also indicate that the
diurnal variation of MSE is better correlated with temperature during the suppressed phases
and moisture during the convective/active phases of the MJO. Although the diurnal MSE peaks
during the afternoon as expected, a distinct sub-diurnal signal is visible during the days of MJO
passage over the island.