A Diagnosis of Boundary Layer Moistening Processes for Madden-Julian Oscillations During DYNAMO IOP

In this study, we analyze data observed during the field experiment DYNAMO (Dynamics of the MJO) from October 1 to December 31, 2011. The three Madden-Julian Oscillations (MJOs) observed over Indian Ocean are analyzed using the operational assimilation data produced by ECMWF, the soundings, and TRMM (Tropical Rainfall Measurement Mission) measurements (2A23 and 3B42).We diagnose the low level moistening of MJOs by examining moisture budgets at four different time scales: over 60 days (low frequency), 20 to 60 days (MJO scale), below 20 days (synoptic scales) and the unresolved dynamics (eddy activity). During the suppressed phase of MJO that occurred in October, convective eddy activities contribute to moistening but synoptic-scale subsidence causes drying in the boundary layer. For the MJO observed in November, vertical moisture advection by MJO scale motion is the major moisture source of lower troposphere. From TRMM 2A23, low- and mid-level cloud increases during the suppressed phase, suggesting that developing shallow convection plays an important role in the low troposphere moistening prior to the deep convective phase of MJO.