Characteristics of the kinetic energy spectrum of NICAM model atmosphere

Abstract

In this study, characteristics of the energy spectrum in the zonal wavenumber domain are examined for the cloud resolving global model NICAM. A series of numerical experiments are conducted for NICAM with various horizontal resolutions from 224 km (glevel-5) to 7.0 km (glevel-10) using the T2K-Tsukuba System and 3.5 km (glevel-11) using the Earth Simulator (ES). The energy spectra of most of horizontal resolutions obey k-3 power law in synoptic and sub-synoptic scales (wavenumbers k = 5 to 30). However, the energy slope for glevel-5 becomes much steeper around zonal wavenumber k = 10. Nastrom et al. (1985) explained that the energy spectrum near the tropopause at wavelengths below 400 km appears to follow the k-5/3 power. This scale corresponds to about k = 70 near 45°N. It is found that the energy spectra for k > 30 for glevel-10 and 11 follow the k-5/3 power law. These results agree quite well with the observational studies. It is also found that the kinetic energy of the vertical wind is white noise spectrum.