Tracking Surface Cyclones with Moist Potential Vorticity

Surface cyclone tracks are investigated in the context of moist potential vorticity (MPV). A prognostic equation of surface absolute vorticity is derived which provides a basis for using negative MPV (NMPV) in the troposphere as an alternative approach to track surface cyclones. An observed case study of explosive lee cyclogenesis is performed to test the effectiveness of the MPV approach. It is shown that when a surface cyclone signal is absent due to the blocking of the Rocky Mountains, the surface cyclone can be well identified by tracing the peak NMPV.