Convective Systems in and around the ITCZ over the Indian Ocean during CINDY2011 Observed by the Shipboard C-band Doppler Radar

Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 (CINDY 2011) was conducted to capture atmospheric and oceanic characteristics of the Madden-Julian Oscillation (MJO) in the central Indian Ocean. During the field campaign, we deployed the research vessel MIRAI for two months at (8S, 80.5E) to occupy the southeastern corner of the CINDY/DYNAMO observation array. The C-band Doppler radar onboard R/V MIRAI successfully captured convective systems in and around the intertropical convergence zone (ITCZ) and its variation during periods toward the two active MJO events.

The active convections were well-captured in the inactive stage of the MJO. The convection over Mirai (at 8S) had the characteristics of ITCZ in which the clouds were elongated zonally at off-equatorial latitude. The active convection appeared with about 3- to 5-day cycle. Each event were well characterized by the leading convective-dominant periods and trailing stratiform-dominant period. However the VAD-derived divergence profile was characterized by the two prominent convergent layers peaked at 850 hPa and 450 hPa, with distinguishing non-convergent or even divergent layer at 600 hPa. This mid-level divergent layer may be related to the observed plenty of shallow convections in and around the ITCZ convections, and/or “melting reverberation” in the stratiform precipitating region.