This project examines the Boreal Summer Intraseasonal Oscillation (BSISO), a tropical mode of variation in precipitation, cloudiness, and winds of large spatial extent. The work examines the impact of the BSISO on the Asian summer monsoon and the extent to which this impact is predictable. The research also considers the relationship between the BSISO and the Quasi-Biweekly (QBW) Oscillation, which is of interest because the combined activity of the BSISO and QBW oscillation is associated with droughts and floods over northern India. The BSISO can be regarded as a large and slow moving envelope of cloud systems and precipitation, and a specific focus of the work is the extent to which upscale transports of heat and momentum from the cloud systems within the BSISO are responsible for its development and propagation. The research will be conducted using a combination of statistical diagnostic analysis, experiments with a global cloud resolving model, and a coupled ocean-atmosphere general circulation model.
The BSISO is thought to be important for determining the active and break periods of the Asian monsoon and may thus be of great agricultural importance for a large and densely populated region of the earth. A better understanding of the BSISO may lead to improvements in forecasts of precipitation, floods, and droughts for South and Southeast Asia. in addition, the project provides support and training for a postdoctoral researcher, thereby providing for the development of the scientific work force in this area.
Our weather forecast does not go beyond two weeks. However, there is an urgent societal demand to predict anomalous weather conditions beyond two weeks and within 6 weeks. Is this "extended range" (2-6 week) prediction possible? It has been observed that in the tropics monsoon exhibits active and calm phases that occur alternatively with an irregular 2-6 week period, which is called boreal summer intraseasonal oscillation (BSISO). The BSISO regulates summer monsoon rainfall intensity, tropical storm activities and flood/drought disasters that affect billions’ people’s daily life. We are interested in the mechanisms that determine the variability of BSISO; in particular how the multiscale interaction involved in the BSISO or its winter counterpart, the Madden-Julian Oscillation (MJO), contributes to its variability. The research supported by this award was designed to study what roles the multiscale interaction plays in the dynamics of MJO and BSISO. The results of our experiments gave us a number of new insights into what drives BSISO, especially how the weather-scale or sub-weather scale disturbance contributes to the BSISO and MJO evolution. In particular, we learned how these smaller-scale systems transport momentum, heat, and moisture upscale to affect MJO dynamics. We also learned how important the planetary boundary layer moisture convergence and atmosphere-ocean interaction affect the 2-6 week variability, how to monitor in real time the evolution of BSISO, and how the MJO and BSISO influence midlatitude extreme event such as the 2009-2010 winter eastern US snow storm.
