Do the stability indices indicate the formation of deep convection?

The present study investigates the relation between the stability indices and different types of precipitating clouds during the active and the suppressed periods of deep convection of the Madden-Julian oscillation. This is achieved by utilizing three-hourly radiosonde (RS92) data and merged cloud radar data over the Gan Island (0.69 degrees S, 73.15 degrees E) from October 2011 to January, 2012. The active and the suppressed periods are defined based on the rainfall. Three periods of active (15-27 October, 15-28 November and 15-27 December) and suppressed periods (01-14 November, 0-14 December and 01-14 January) are identified. During the above periods, the stability indices are calculated to distinguish the background meteorological conditions. The analysis shows that during both the active and the suppressed periods, the magnitude of the stability indices are not much different. During both the periods, the indices attain their respective threshold corresponding to the occurrence of deep convection. However, the third suppressed period shows a dry condition compared to the other two suppressed periods. The relation between the stability indices and the precipitating cloud categories (shallow, congestus and deep) indicate that even though the threshold in the stability indices were attained, deep convective clouds were not observed during the suppressed periods. The active period correlates well with the stability indices. Therefore, the stability indices do not clearly and directly determine the state of the atmosphere during deep convection. The result shows stability indices need to be substantially improved in the context of deep convection prediction.