Outflow layer influences on tropical cyclone structure and intensity

Compared to boundary layer processes, tropical cyclone outflow layer processes have drawn considerably less attention. It is suggested that tropical cyclone outflow is the link between environmental systems and the inner core. The outflow is not a passive consequence of inner core convection, but rather mediates the interaction between tropical cyclone convection and environmental asymmetries. Enhanced outflow toward weaknesses in environmental rotation act to strengthen the secondary circulation and minimize the work done against static and inertial stabilities. There is no clear link between evolving conditions in the outflow layer and a source of thermodynamic instability in the core that can organize the convective structure in the tropical cyclone eyewall. However, low-level inflow may develop so that convection develops which allows outflow layer ventilation direct access to regions of weak environmental inertial stability. The strong winds of the inflow develop enhanced (diminished) paths of CAPE (CIN) which promotes deep convection in regions of frictional convergence that can modify intensity and low-level wind structure. In addition to the enhanced outflow aloft, intense tropical cyclones which exhibit multiple outflow channels may promote more symmetric inflow and convection in the core. Both idealized and real data simulations are conducted to determine the influence of an evolving environmental outflow layer on tropical cyclone structure and intensity. Idealized simulations provide a setting where the vertical shear associated with environmental asymmetries can be minimized so the focus is on the evolving outflow and inflow. Potential vorticity inversion is performed to modify the outflow layer environmental flow field in real data simulations in order to provide a more complex system to gauge the influence of outflow on structure and intensity.