This study analyzes radiosonde observations and other datasets to examine variability in the moist static energy (MSE) budget over the eastern Maritime Continent during the CINDY2011/DYNAMO field campaign of October 2011-March 2012. During this period, five events bearing key characteristics of the Madden-Julian oscillation (MJO) are identified. Our analysis focuses on both these events and longer-term seasonal evolution.
On the seasonal time scale, the characteristics of column-integrated MSE budget are different between periods before and after the Australasian summer monsoon onset in early December. Both the net source term (the sum of surface turbulent fluxes and radiative heating) and the net advection term (the sum of horizontal and vertical advection of MSE) have small magnitudes before the onset. After the onset, the source term becomes large and positive, while the advection term becomes large and negative.
On the intraseasonal scale, both the source and advection terms fluctuate as the MJO events come and go. The surface fluxes and radiative heating contribute to the maintenance of the amplitude of column-integrated MSE anomaly and thus to the intensity of MJO. The vertical advection term, along with horizontal advection term, seems to contribute to the phase progression and eastward propagation of MJO, mainly because of lower-tropospheric descent after the precipitation and MSE maxima, presumably associated with rain re-evaporation.
This study also examines how the MSE budget would be different if key components of the budget were parameterized by two assumptions used in recent idealized models of MJO: (1) the column-integrated radiative heating anomaly is considered proportional to the column water vapor anomaly and (2) the normalized gross moist stability is considered constant. We find that the former tends to speed up the phase progression of MJO, while the latter tends to slow it down.
2015 by Meteorological Society of Japan