12.8
Evaluating dissipation in NWP models using kinetic energy spectra
William C. Skamarock, NCAR, Boulder, CO; and M. E. Baldwin and W. Wang
Kinetic energy (KE) spectra derived from observations possess a k**(-3) spectral slope for large scales, characteristic of 2D turbulence, and transition to a shallower k**(-5/3) spectra at the mesoscale (i.e. for length scales of O(10-100) km). We have examined KE spectra computed using mesoscale and experimental cloudscale NWP forecasts from the WRF model, the ETA and NMM models from NCEP, and others. High resolution forecasts from the WRF model match the observational spectra well, including the transition in slope. At the highest resolved wavenumbers the WRF model shows a decaying spectra (steeper spectral slope) compared with observations, indicating energy removal by the model's implicit and explicit dissipation mechanisms. The ETA and NMM models reproduce the observed k**(-3) spectra at low wavenumbers but do not show a transition to the mesoscale k**(-5/3) spectral slope at higher wavenumbers, rather they show slopes generally steeper than k**(-3) - even well before the shorter wavelengths are reached. We will present these spectra and discuss their implications for model formulations and NWP applications. .
Session 12, WRF Model Development and Applications (ROOM 605/606)
Tuesday, 13 January 2004, 3:30 PM-5:45 PM, Room 605/606
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