Spatial kinetic energy spectra in the convection-permitting limited-area NWP model COSMO-DE

Abstract

1 Kinetic energy spectra derived from commercial aircraft observations of horizontal wind 2 velocities exhibit a k−5/3 wavenumber dependence on the mesoscale that merges into a 3 k−3 dependence on the macroscale. In this study, spectral analysis is applied to evalu4 ate the mesoscale ensemble prediction system using the convection-permitting NWP model 5 COSMO-DE (COSMO-DE-EPS). One-dimensional wavenumber spectra of the kinetic en6 ergy are derived from zonal and meridional wind velocities, as well as from vertical velocities. 7 Besides a general evaluation, the model spectra reveal important information about spin-up 8 effects and effective resolution. 9 The COSMO-DE-EPS well reproduces the spectral k−5/3 dependence of the mesoscale 10 horizontal kinetic energy spectrum. Due to the assimilation of high-resolution meteorologi11 cal observations (mainly rain radar), there is no significant spin-up of the model simulations 12 within the first few hours after initialization. COSMO-DE-EPS features an effective reso13 lution of a factor of about 4 to 5 of the horizontal grid spacing. This is slightly higher in 14 comparison to other limited area models. Kinetic energy spectra derived from vertical ve15 locities exhibit a much flatter wavenumber dependence leading to relatively large spectral 16 energy on smaller scales. This is in good agreement with similar models and also suggested 17 by observations of temporal variance spectra of the vertical velocity. 18