Air-Sea Keynote Presentation: Air-Sea Interaction and Coupled Boundary Layer Response during the DYNAMO program

The Dynamics of the Madden-Julian Oscillation (DYNAMO) program is the U.S. led component of the international CYNDY2011 program. The Madden-Julian Oscillation (MJO) is a quasi-period disturbance with a period between 30-90 days that propagates eastward from the Indian Ocean to the Central Pacific at an average speed of 5 m/s. The MJO is characterized by an active phase with strong deep convection and precipitation and an inactive phase with weaker deep convection and less precipitation. It has a strong impact on the timing of the Indian monsoon season and rainfall variability in the regions. The rainfall patterns and zonal wind anomalies that develop under these disturbances affect ocean waves, currents and air-sea interaction. Simply put, the eastward propagation is due to conditions that favor convection to the east of the convective center and suppress convection to the west. However, realistic simulation of the MJO remains a long-standing challenge for weather forecast and general circulation models. Therefore, DYNAMO investigator deployed a number of unique observational assets deployed in and over the Indian Ocean to investigate the MJO and improve our predictive capabilities. This talk provides examples of how these assets are being used to investigate boundary layer response to air-sea interaction. For example, the exchange of heat across the air-sea boundary layers plays an important role in the thermodynamics of the coupled ocean-atmospheric system in the tropics. Of particular interest is the relative magnitude of the net shortwave (solar) radiative flux that heat the upper ocean versus the latent heat flux that cools it and drives atmospheric convection. The net heat flux shows clear phasing with the active and inactive phases of the MJO with a release of energy during the active phase and oceanic storage of energy between events. The active phase of the MJO can also drive strong wind events and oceanic response that include rapid enhancement of the equatorial jet and deepening of the mixed layer. Observational examples of these and other processes will be provided in advance of more detailed discussions during the DYNAMO session.