Does the Inertial Wave in an Axisymmetric Tropical Cyclone Rectify its Thermodynamic Behavior?

Abstract:

This study investigates whether the presence of an inertial wave in the outflow region of an axisymmetric tropical cyclone’s secondary circulation affects its thermodynamic behavior. Recent work has demonstrated the existence of an inertial wave in the subsiding branch of axisymmetric tropical cyclones (TCs) using the Bryan Cloud Model 1 (CM1). This inertial wave implies a periodic venting of the TC core with low-entropy environmental air. The existence of the inertial wave was demonstrated from an isentropic averaging perspective. However, the technique of isentropic averaging involves an artificial closure of the overturning mass flux of the TC in order to resolve motions near the eye. Hence, a different approach that allows us to both conserve mass and focus on the closed, near-eye circulation is employed here. Using CM1, we analyze Lagrangian parcels that recirculate through an axisymmetric TC after being exhausted in the outflow and determine whether the inertial wave can still be observed from this perspective.

The periodic ventilation of the TC core with low-entropy air and exhausting of high-entropy air out of the TC core that is implied by the inertial wave suggests that the thermodynamic behavior of the TC might be rectified by the inertial wave. Rectification means that the time-mean response of a system to forcing differs from the time-mean response of the system to the time-mean of the same forcing. We investigate whether the inertial wave rectifies the thermodynamic cycle of an axisymmetric TC, including in T-s space. Such a rectification would imply that the inertial wave incurs an energetic cost, limiting the amount of work available for the TC to do. The Lagrangian parcel analysis together with the isentropic averaging approach uniquely permits a quantification of the impact of the inertial wave on the mean behavior of a TC.