Convective activity over the Indonesian maritime continent during CPEA-I as evaluated by lightning activity and Q1 and Q2 profiles

Abstract

Lightning activity observed by the Tropical Rainfall Measuring Mission-Lightning Image Sensor (TRMM-LIS) and aerological data from the first campaign of the Coupled Process in the Equatorial Atmosphere (CPEA-I) were used to diagnose convective activity over the western part of the Indonesian maritime continent (MC) for the period between 10 April and 9 May 2004. Lightning and many deep but small convective clouds associated with low outgoing longwave radiation (OLR) dominated over large islands of the MC before the onset of a Madden Julian Oscillation (MJO) active period. During the MJO active period, a MJO cloud system composed of three super-cloud clusters (SCCs) passed eastwardly over the study area. The first SCC (SCC1) was accompanied by active lightning. After SCC1 passed, lower OLR extended over a wide area including both islands and ocean, and lightning was suppressed over the large islands. Lightning activity was weaker in subsequent SCCs. Atmospheric stratification, vertical winds, the apparent heat source (Q1), and apparent moisture sink (Q2) were studied using rawinsonde observations for two areas: one over Sumatera and the other over the ocean between Sumatera and Kalimantan. Differences in vertical wind profiles between land and ocean suggest stronger onshore land-sea circulations in the break period than in the active period. Convective instability was greatest before the onset of the MJO active period over land and then weakened after onset. Over land, height of the positive peak was much higher in Q1 than in Q2 before onset. The height of the peak was comparable after onset; this change suggests that subarea-scale deep convective rain (stratiform rain) dominated before (after) the onset. These observations are consistent with variations in lightning activity. Previous observations showed that MJO cloud systems over the western Pacific have enhanced convection in their eastern portions and stratiform rain in western parts. A similar large-scale structure was maintained in the MJO cloud system over the western part of the MC, despite blocking effects by the MC on the MJO cloud system, especially in mesoscale and synoptic-scale structures. © 2006, Meteorological Society of Japan.