J. Atmos. Sci., 71, 4276-4291.
Adam H. Sobel
Department of Applied Physics and Applied Mathematics, Department of Earth and Environmental Sciences, and Lamont-Doherty Earth Observatory, Columbia University, New York, NY.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY.
Department of Atmospheric Sciences, University of Washington, Seattle WA.
The authors analyze the column-integrated moist static energy budget over the region of the tropical Indian ocean
covered by the sounding array during the CINDY/DYNAMO field experiment in late 2011. The analysis is
performed using data from the the sounding array complemented by additional observational
data sets for surface turbulent fluxes and atmospheric
radiative heating. The entire analysis is repeated using the ERA Interim Reanalysis. The roles of
surface turbulent fluxes, radiative heating, and advection are quantified
for the two Madden-Julian oscillation (MJO) events that occurred in October and November using the sounding data; a third event in
December is also studied in the ERA Interim data.
These results are consistent with the view that the MJO's moist static energy anomalies grow and are sustained to a significant extent by the radiative feedbacks associated with MJO water vapor and cloud anomalies, and that propagation of the MJO is associated with advection of moist static energy. Both horizontal and vertical advection appear to play significant roles in the events studied here. Horizontal advection strongly moistens the atmosphere during the buildup to the active phase of the October event when the low-level winds switch from westerly to easterly. Horizontal advection strongly dries the atmosphere in the wake of the active phases of the November and December events as the westerlies associated with off-equatorial cyclonic gyres bring subtropical dry air into the convective region from the west and north. Vertical advection provides relative moistening ahead of the active phase and drying behind it, associated with an increase of the normalized gross moist stability.