A Comparison of Initial Developments Between Explosive and Ordinary Mid-latitude Cyclones Off the East Asian Coast in Winter

Abstract Explosive cyclones (ECs) off the East Asian coast post challenges in forecasting and significant threats to human life and property. In searching for the key features that distinguish explosive cyclones (ECs) from ordinary extratropical cyclones (OCs), this study presents detailed comparison of winter ECs versus OCs in the perspective of potential vorticity (PV) using 10 years of reanalysis data with high temporal and spatial resolutions. ECs feature greater low-level baroclinity and stronger PV than OCs. The decomposition of local PV tendency shows the important contribution of cold advection (with correlation coefficient of 0.8) in the initial development of ECs. A stronger cold advection for ECs increases upstream static stability, leading to intrusion of higher PV along the steeper isentropic surfaces. The importance of cold advection is further proved by numerical experiments with the Weather Research and Forecast (WRF) model on a typical winter EC. The weakening of cold advection within low-troposphere in sensitivity experiment can significantly decrease PV and stop the cyclone from explosive deepening. In addition to the consensus that diabatic processes play important roles in the intensification of explosive cyclogenesis, this study emphasizes the importance of horizontal cold advection (which is also associated with baroclinic instability) in the preconditioning PV for explosive cyclogenesis.