Investigation of Mesoscale Available Potential Energy Spectra in a Simulated Tropical Cyclone

Abstract

We investigated the moist mesoscale available potential energy (APE) spectra and corresponding spectral budgets of an idealized tropical cyclone (TC). The APE is defined with respect to a dry air mass using a modified potential temperature. For wavelengths below 500 km, the mesoscale APE spectra show a consistent quasi-linear shape and a -5/3 spectral slope in the troposphere and lower stratosphere during the mature period of the TC. The spectral APE budget in the troposphere is dominated by diabatic and energy conversion processes. The mesoscale APE is forcefully injected by the diabatic effect and immediately partially converted to other forms of energy by the buoyancy effect. The diabatic effect contains a positive contribution from the heating effect and a negative contribution from the dehumidifying effect, which weakens the heating effect by about 16%. The energy conversion tends toward the horizontal kinetic energy at larger scales and toward the gravitational potential energy of the total moist species at smaller scales. In the lower stratosphere, the mesoscale APE is primarily deposited by the three-dimensional divergent effect and removed by nonlinear interactions; however, the effect of the energy conversion is noisy. The lower troposphere and lower stratosphere are governed by clear downscale and upscale APE cascades, respectively, whereas the mid- and upper tropospheric mesoscale APE spectra undergo more complex cascade processes.