Exploring the Synoptic Differences Between MJO Initiation Events Identified by Multiple Algorithms

Abstract:

The Madden-Julian Oscillation (MJO) is a tropical phenomenon that develops over the Indian Ocean. This intraseasonal oscillation consists of an extensive area of convection, about 1000 km across, that releases latent heat in the mid-troposphere, and this heating forces planetary-scale waves to travel through the upper troposphere. These waves can affect weather and climate in the extratropical regions. Since our computational models do not simulate the MJO correctly, international efforts are underway to improve our understanding of the processes involved, especially during the MJO’s early stages. This study examines and compares MJO initiation events and types (primary, intensifying, non-MJO) identified by researchers using four methods during 1998–2009 boreal winters. Two methods focused on the precipitation aspect of the oscillation, and the others focused on circulation. Five variables were selected for analysis: temperature at 400 hPa, outgoing long-wave radiation (OLR), sea level pressure (SLP), and zonal winds at 200 and 850 hPa. Twelve MJO events were selected, and four were analyzed. The five variables’ contributions to each event were mapped using the MJO-like mode recently identified by other scientists from unfiltered five-day mean gridded data. These visualizations show consistent behaviors in OLR, temperature, and SLP. Positive OLR anomalies occurred in the Indian Ocean before MJO convection began, supporting another research group’s idea of an MJO “dry dynamic mode.” The MJO-like mode also depicts some previously observed behavior in MJO precursor variables. The results also serve to validate the MJO-like mode and demonstrate that it identifies both MJO and non-MJO convection.