Shallow-to-Deep Transition of Madden-Julian Oscillation Convection as Observed by TRMM and GPM

Abstract:

This study uses TRMM and GPM data to study the evolution of Madden-Julian Oscillation (MJO) convection over the Indian Ocean (IO). Radar observations from the 2011-2012 DYNAMO field campaign in the central IO have provided rich information on the 3D structure of MJO convection, including the transition from shallow to deep convection during the MJO onset. However, DYNAMO radar measurements are limited to only three MJO events and three radar sites. In this study, the shallow to deep transition (SDT) problem and lifecycle evolution of MJO events over the IO is revisited using longer term, larger-scale TRMM and GPM data. Our analysis indicates that the TRMM and GPM satellite is able to capture the evolution of individual MJO events (e.g., precipitation) on the daily and regional (e.g., 2000 km x 2000 km) scale. We have investigated the evolution and properties of ~40 prominent MJO events in terms of precipitation amounts, three-dimensional radar reflectivity, microwave ice scattering signatures, cloud top brightness temperature, and lightning flash rates. We track the SDT time scale and lifecycle evolution of each MJO using these multiple parameters, instead of composites in previous TRMM studies. MJO events have also been examined as a function of the MJO type (e.g., duration of MJO lifecycles and MJO strength). Preliminary results show that the SDT is on the scale of 7-10 days with small variations among different MJO types. SDT trends are less well-defined by the 20 dBZ (TRMM PR) echo top height compared to lower thresholds. In contrast, the satellite IR brightness temperature (TRMM VIRS), the 12 dBZ (GPM DPR Ka-band) echo top heights, and lightning flash rate (TRMM LIS) depict the STD rather well.