One of possible mechanisms is that dir air intrusions into the near-equatorial Indian Ocean may affect the convection in the ITCZ, which contribute to the shift of convection toward the equator during the onset of MJO. The NOAA P3 aircraft dropsonde data from DYNAMO show a sharp moisture gradient near 5oS on 22 November 2011, which is confirmed by satellite retrievals over a large region. Soundings taken at Diego Garcia showed an abrupt transition between moist and dry conditions in 3-6 hours when the dry air moved in from the south. Similar equator-ward push of dry air seems to exist a few days prior to the initiation of the MJO convection in the October and November MJO initiation events in DYNAMO. This synoptic evolution forced convection to preferentially develop on the Equator. Equatorial convection associated with a third MJO event in late February 2012 was also preceded by a push of dry air, this time from the northern Hemisphere.
This study examines the global model predictions of the moist convection and associated synoptic systems during DYNAMO. The initiation of convection in the Indian Ocean and eastward propagation of the MJO active convection envelope depend critically on stochastic, synoptic/mesoscale events, which the models often predict poorly. We use the satellite IR-based hourly cloud clusters tracking over the entire tropical Indian, the NOAA aircraft dropsonde and sounding data from the DYNAMO sites, and satellite TPW and AIRS data to evaluate the ECMWF and GFS model forecasts. At this initial phase, the verification is based on feature identification for these cases. The question is whether the GFS and ECMWF forecasts could predict these observed features for the MJO events observed during DYNAMO (October 2011 March 2012). Also, the model forecast statistics of convective activity and vertical moisture profile are compared with cloud cluster tracks and DYNAMO radiosonde data.