J. Meteor. Soc. Japan, submitted 2/15.
Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan, and
Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY
Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences, Columbia University, New York, NY.
This study analyzes radiosonde observations and other datasets to examine variability in the moist static energy (MSE) budget over eastern part of the Maritime Continent during the CINDY2011/DYNAMO field campaign project from October 2011 through March 2012. During this period, five events bearing key characteristics of the Madden-Julian oscillation (MJO) are identified. Our analysis focuses both on these events, and on the longer-term seasonal evolution of the MSE budget terms.
On the seasonal time scale, the characteristics of the column-integrated MSE budget are different between periods before and after the Australasian summer monsoon onset, whose timing coincides with that of the second MJO event's active phase in early December. Both the net diabatic source term (the sum of surface turbulent uxes 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 after the onset.
On the intraseasonal scale, both the source and advection terms uctuate as the MJO events come and go. It is shown that the surface fluxes and radiative heating contribute to the maintenance of the amplitude of column-integrated MSE anomaly and thus to the intensity of the MJO. The vertical advection term, along with horizontal advection term, seems to contribute to the phase progression and eastward propagation of MJO, mainly due to lower-tropospheric descent after the precipitation and MSE maxima, presumably associated with rain re-evaporation. On the other hand, the source term tends to hinder eastward propagation.
This study also examines how the MSE budget would be different if key components of the budget were parameterized by two assumptions that have been used in recent idealized models of the MJO: (1) the column-integrated radiative heating anomaly is taken proportional to the column water vapor anomaly, and (2) the normalized gross moist stability is taken constant. We find that the former tends to speed up the phase progression of MJO, while the latter tends to slow it down.