The Role of Diabatic Heating, Torques and Stabilities in Forcing the Radial-Vertical Circulation within Cyclones Part III: Case Study of Lee-side Cyclones

Abstract: Two phases of extratropical cyclone development identified in previous mass and angular momentum budget studies have been confirmed through the numerical simulations of the azimuthally-averaged mass-weighted radial motion within two leeside cyclones: a Mediterranean and an Alberta cyclone. In the Mediterranean cyclone, a moist baroclinic phase is identified with inward (outward) mass and storm angular momentum transport in the lower (higher) value isentropic layers. The mass and storm angular momentum are then transported diabatically from lower to higher value isentropic layers through latent heat release. In addition, storm angular mo-mentum is transferred horizontally across the inclined isentropic surfaces by pressure stresses due to the paired negative and positive pressure torque in lower and higher value isentropic layers respectively. A dry-leeside baroclinic phase is identified in the early stage of the Alberta cyclone with inward (outward) transport of mass and angular momentum in the higher (lower) value isentropic layers. The redistribution of angular momentum is associated with the virtual transfer by torques. A transition from dry to moist phase is identified in the life cycle of the Alberta cyclone. The present numerical results show that the dominant internal physical processes responsible for forcing the inflow and outflow within the Mediterranean cyclone are associated with pressure torque and horizontal eddy angular momentum transport, while within the Alberta cyclone the dominant internal processes are associated with inertial torque and pressure torque. The transfer of angular momentum from the higher value isentropic layer to the lower value isentropic layer is due to the virtual transfer by inertial torque in the dry phase of the Alberta cyclone. The transition from dry to moist phase within the Alberta cyclone results from the decrease of positive inertial torque and the intensification of negative pressure torque in the lower value isentropic layers.

Keywords:
• Lee-side cyclone,
• Radial-vertical circulation