Idealized numerical experiments associated with the intensity and rapid intensification of stationary tropical-cyclone-like vortex and its relation to initial sea-surface temperature and vortex-induced sea-surface cooling

Abstract

Idealized numerical experiments were performed using a nonhydrostatic atmospheric model coupled with a slab mixed-layer ocean model with a horizontal grid spacing of 2 km in order to investigate the roles of initial sea-surface temperature (SST) and vortex-induced sea-surface cooling (SSC) in the intensity and intensification of a stationary idealized tropical-cyclone-like vortex. Numerical experiment results indicate that the coupled model reproduces rapid intensification, transition, and mature phases in the SST-central pressure (CP) relation. CP is better approximated by a power function of mixed-layer heat potential (MLHP) accumulated every 3 hours. The evolution of the vortex and the impacts of initial SST and SSC on the vortex's structural evolution were investigated using potential vorticity (PV) and filamentation time (FT). Mesovortices are rapidly intensified wherein both a steep PV gradient and a positive FT exist. Mesovortices yield the acceleration of inward angular momentum transports, resulting in enhanced inertial forcing. SSC decelerates inward angular momentum transports by reducing PV around the mesovortices. This deceleration suppresses periodic variations of the average atmospheric boundary layer heights, reduces warm-core temperature anomalies, and lowers their existing heights during the rapid intensification phase. The role of the initial SST in the vortex's evolution is that a high initial SST accelerates the rapid intensification process. Even if accumulated MLHP increases during the mature phase, the vortex Rossby number is reduced, indicating that enhanced vortex Rossby waves increase the radius of maximum wind speed due to high SST. Copyright 2009 by the American Geophysical Union.