Simulation of the κ−5/3 mesoscale spectral regime in the GFDL SKYHI General Circulation Model

Abstract

Data from very high horizontal resolution simulations with the Geophysical Fluid Dynamics Laboratory SKYHI general circulation model are used to calculate the kinetic energy spectrum as a function of horizontal wavenumber, κ, in the upper troposphere. The spectrum shows the familiar ∼ −3 slope at scales longer than ∼ 1000 km, in agreement with previous general circulation model and observational studies. At shorter scales, the spectrum becomes shallower with a slope ∼ −5/3, also in agreement with available observations. The −5/3 slope spans about a decade of the resolved scales and this result represents the first successful simulation of such a broad range of the mesoscale regime by a global model. Partitioning of the flow between rotational and divergent components shows that the rotational part dominates at large scales and that there is approximate equipartition between rotational and divergent parts at mesoscales. Analysis of the parameterized kinetic energy dissipation shows that vertical diffusion dominates horizontal diffusion for a wide range of wavenumbers extending well into the κ−5/3 regime.