How Vertical Wind Shear Impacts Tropical Cyclone by Different Thermodynamic Pathways: Energetics and Lagrangian Analysis

The variation of the thermodynamic cycle and energy of tropical cyclones (TCs) under vertical wind shear (VWS) is analyzed, and its associated TC thermal and dynamical structure evolutions are explored. The thermodynamic cycles extracted using the Mean Airflow as Lagrangian Dynamics Approximation (MAFALDA) method show that the maximum energy obtained by the TC decreases with the reduction of storm intensity in VWS. The thermodynamic cycles of sheared TC experience a two-stage evolution. During the early stage, the ascending branch of the MAFALDA cycle shifts toward lower entropy, which is attributed to the reduction of the entropy in the eyewall and the increase of the upward motion and entropy outside the eyewall. In the latter stage, the entropy increases, and the downward motion weakens in the ambient and upper troposphere, allowing the descending legs shifts toward high values of entropy. A backward Lagrangian diagnostic of air parcels associated with variations in thermodynamic cycles is employed to analyze the relative importance of distinct pathways. In addition to the low-, mid-, and upper-level ventilation pathways, the enhanced inner and outer rainbands, outward advection of high entropy air in mid- and upper-troposphere eyewall, the outflow layer with reduced height, and the inflow below the outflow layer are also important for the reduction of the energy gained by TC.