Investigating the Role of Tropospheric Water Vapor on Tropical Cyclone Development: Water Vapor and Angular Momentum Budgets

Previous studies have demonstrated the importance of tropospheric moisture on tropical cyclone (TC) development, but a quantitative measure of this importance has yet to be completed. To gain quantitative insight, this study employs the axisymmetric version of the Cloud Model 1 (CM1) to conduct experiments with various relative humidity profiles. Area-averaged and volume-integrated moisture and relative angular momentum budgets are utilized to quantitatively compare and assess the impact of these profiles on TC development. Furthermore, the volume-integrated budgets are separated into two layers to assess the contributions of the inflow and outflow layers on TC development. Results suggest that a preconditioning stage exists, in which low-level moisture is transported radially inward into the TC inner-core region. Low-level moisture is then fluxed upwards by the secondary circulation to reduce the moist static energy minimum at mid-levels, promoting deep convection and demonstrating the bottom-up process of TC development. This moistening process seems to be a necessary, but not entirely sufficient, condition that controls the rate of intensification of the simulated TCs. Additionally, the changes in the internal structure of the simulated TCs are similar for all cases, albeit exhibiting a slower evolution for the drier cases. The quantitative results of this modeling study suggest that the moistening of low and mid-levels is needed in order to spin-up the TC low-level vortex.