The radiosondes were launched at two islands, Gan (0.7S, 73.2E) and Hulhule (4.2N, 73.5E) at 2 or 4 times per day. Including the R/V Mirai at (Eq., 80.5E), the three points of radiosonde sounding consist an array to enable budget analyses for 25 days from Oct.31 to Nov.25. The days correspond to the transition period from the inactive to active period of MJO convection.
The active convections were frequently observed after Nov.15. Toward the active period, three significant convectively active events were observed over the array with the period of about 6 days. The hovmellor diagram shows these events were eastward-propagating convective features with the speed of about 8 m/s. Each event accompanies westerly anomaly below 700 hPa height, large positive Q1 and Q2, updraft, positive vapor anomaly. The layer with high humidity, large Q1 and negative omega in each feature were getting taller toward the MJO active period. In other words, the humid layer was deepen when the eastward-propagating convective features passed, with the deepening of the convective features.
On the other hand, the depth of large Q2 layer and low-level convergence layer unchanged for all features. The vertical profile of the radar echo area extends toward the MJO active period below 8-km height, while almost same above. These suggest that the precipitating systems within the convective features developed horizontally and organized towards the MJO active period.
These observed results imply that the eastward-propagating convective features play an important role to precondition toward the MJO active phase.
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