Intensity oscillations of tropical cyclones: surface versus mid and
upper tropospheric processes
Abstract
Some of the classical models of tropical cyclone intensification predict
tropical cyclones to intensify up to a steady intensity, which depends
on surface fluxes only, without any relevant role played by convective
motions in the troposphere, typically assumed to have a moist adiabatic
lapse rate. Simulations performed using the non-hydrostatic,
high-resolution model SAM in idealized settings (rotating
radiative-convective equilibrium on a doubly-periodic domain) show early
intensification consistent with these theoretical expectations, but
different intensity evolution, with the cyclone undergoing an
oscillation in wind speed. This oscillation can be linked to feedbacks
between the cyclone intensity and air buoyancy: convective heating,
radiative heating, and mixing with warm low stratospheric air warm the
mid and upper troposphere of the cyclone stabilizing the air column and
thus reducing its intensity. After the intensity decay phase, mid and
upper tropospheric cooling, mostly through cold advection from the
surroundings, cooled by radiation, rebuilds CAPE and triggers a new
intensification.
These idealized simulations thus highlight the potentially important
interactions between a tropical cyclone, its environment and radiation.