Intensity oscillations of tropical cyclones: surface versus mid and upper tropospheric processes

Classical models of tropical cyclone intensification often predict that cyclones will intensify to a steady-state intensity determined primarily by surface fluxes, while convection maintains the atmosphere close to a neutrally stable state (Emanuel et al. (2003); Emanuel (1995)). However, simulations using the non-hydrostatic, high-resolution SAM model under idealized conditions (rotating radiative-convective equilibrium in a doubly-periodic domain) reveal a more complex intensity evolution.
While the early intensification aligns with theoretical predictions, later in its evolution, the cyclone exhibits oscillations in wind speed. This oscillation can be linked to feedbacks between the cyclone intensity and air buoyancy: convective 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, due to both local longwave radiation emission and cold advection from the surroundings, rebuilds CAPE, that peaks just before a new intensification phase. These idealized simulations highlight the potentially important interactions between a tropical cyclone, its environment and radiation.

 

 

References

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