Spatial kinetic energy spectra in the convection-permitting limited-area NWP model COSMO-DE
Bierdel, Lotte; Friederichs, Petra; Bentzien, Sabrina
Kinetic energy spectra derived from commercial aircraft observations of horizontal wind velocities exhibit a k-5/ 3 wavenumber dependence on the mesoscale that merges into a k-3 dependence on the macroscale. In this study, spectral analysis is applied to evaluate the mesoscale ensemble prediction system using the convection-permitting NWP model COSMO-DE (COSMO-DE-EPS). One-dimensional wavenumber spectra of the kinetic energy are derived from zonal and meridional wind velocities, as well as from vertical velocities. Besides a general evaluation, the model spectra reveal important information about spin-up effects and effective resolution. The COSMO-DE-EPS well reproduces the spectral k-5/3 dependence of the mesoscale horizontal kinetic energy spectrum. Due to the assimilation of high-resolution meteorological observations (mainly rain radar), there is no significant spin-up of the model simulations within the first few hours after initialization. COSMO-DE-EPS features an effective resolution of a factor of about 4 to 5 of the horizontal grid spacing. This is slightly higher in comparison to other limited area models. Kinetic energy spectra derived from vertical velocities exhibit a much flatter wavenumber dependence leading to relatively large spectral energy on smaller scales. This is in good agreement with similar models and also suggested by observations of temporal variance spectra of the vertical velocity.