Potential Vorticity during MJO Initiation

Structural evolution of potential vorticity during MJO initiation is examined. The characteristic features in PV that distinguish the MJO from other equatorial convectively coupled perturbations (e.g., the Rossby and Kelvin waves) can be identified in both statistical composites and case studies. They are PV generation in the lower-middle troposphere that leads to PV quadrupole straddling the equator. Associated with this PV quadrupole is a swallowtail pattern in precipitation along the equator with the tails pointing to the west. An early sign of eastward moving of PV generation with diabatic heating field is a good sign to tell the difference of the MJO from the equatorial Rossby waves. PV evolution during the initiation of MJO events covered by the DYNAMO field campaign is presented. Potential value of the PV structural evolution in MJO prediction is discussed.