Intraseasonal Extratropical Precursors to the Indian Ocean Madden-Julian Oscillation (MJO) Proximate to Africa

Suny At Albany, Albany NY

Investigators

Abstract

The Madden-Julian Oscillation (MJO) is a large envelope of clouds and precipitation that forms over the Indian Ocean and slowly propagates eastward to the middle of the equatorial Pacific. It affects weather conditions worldwide including atmospheric rivers and flooding in California and hurricane formation in the Gulf of Mexico. Some MJO events appear to form independently and are designated as "primary" events. Other "secondary" events appear to be triggered by wave disturbances in the upper troposphere which propagate into the Indian Ocean from regions to the west, in the subtropical belts of the Northern and Southern Hemispheres. The triggering of MJO events by upstream wave disturbances has been well documented, but the processes through which the waves induce MJO events are not well known, and this project seeks to better understand them. Preliminary work by the PI suggests that the precursor waves are not fast moving triggers that impulsively kick-start the MJO, but slowly propagating Rossby waves with intraseasonal timescales. One possibility is that a secondary MJO events can be promoted by an earlier MJO event, which generates Rossby waves in the central equatorial Pacific which propagate eastward and toward higher latitudes, later recurving back into the tropics where they arrive over the equatorial Indian Ocean to induce the subsequent MJO. The project has a focus on Africa because the precursor waves enter the Indian Ocean from the African subtropics. A variety of statistical methods are used to detect and characterize the precursor waves, which are identified in observational data from satellites as well as reanalysis products. Moisture and momentum budgets are then used to understand how the waves contribute to the formation of secondary MJO events. The work has societal broader impacts due to the variety of weather impacts associated with the MJO. There is some skill in forecasts of the propagation of MJO events, but predictions of the initiation of MJO events would allow greater lead times for prediction of MJO impacts. As the project focuses on precursor meteorology over Africa, the project may also have benefit for understanding and predicting African weather. In addition, the project provides support and training to two graduate students, thereby building the future workforce in this research area.