A Space-Time Spectral Comparison of the NCAR and GFDL General Circulation Models to the Atmosphere

Robert W. Pratt National Center for Atmospheric Research, Boulder, CO 80307

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Abstract

Spectra computed for the midlatitude troposphere indicate that both the NCAR and GFDL models have less variance than the atmosphere in most space and time scales. The deficiency is most serious for low-frequency planetary waves near 50°N. The low-frequency planetary-scale fluctuations also show less tendency for westward movement than is observed. In both models, especially NCAR's, the 4–5 day wavenumber 1 variance is relatively too large.

The GFDL spectra are generally closer to observed values than the NCAR spectra, probably because of the GFDL model's higher horizontal and vertical resolution. The NCAR spectra show an abnormal level of variance at a period of 5 days in zonal wavenumbers 8–12.

Abstract

Spectra computed for the midlatitude troposphere indicate that both the NCAR and GFDL models have less variance than the atmosphere in most space and time scales. The deficiency is most serious for low-frequency planetary waves near 50°N. The low-frequency planetary-scale fluctuations also show less tendency for westward movement than is observed. In both models, especially NCAR's, the 4–5 day wavenumber 1 variance is relatively too large.

The GFDL spectra are generally closer to observed values than the NCAR spectra, probably because of the GFDL model's higher horizontal and vertical resolution. The NCAR spectra show an abnormal level of variance at a period of 5 days in zonal wavenumbers 8–12.

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