The Météo-France/CNRM AMIP simulation has been run in 1991 with the "EMERAUDE" T42L30 GCM. In 1992, a next GCM appeared, derived from the ARPEGE-IFS code. A T42L30 version, as close as possible to the "EMERAUDE" model, was developed. An AMIP-type simulation has been run with this version. The empirical coefficients of the physical parameterizations have been taken equal to those of EMERAUDE, and thus no "tuning" has been done. This explains why some features are not so accurate as those of EMERAUDE. The advantage of an "untuned" version is that we can change the resolution without risking to destroy a patient and brittle calibration. Three new AMIP simulations have been run with the standard horizontal resolution (T42), twice as low (T21), and twice as high (T79-in fact a T84 would have been the exact doubling).
The results of the 3 AMIP simulations are presented. Some features of the general circulation are notably improved from T21 to T42 (winter midlatitude lows, summer monsoon flow). Few improvements were found from T42 to T79. The systematic effects of increasing the resolution are: warming and drying the atmosphere, reducing the cloud cover, and increasing the precipitation.
A new version of the GCM, based on the cycle 11 of ARPEGE-IFS, has been developed in T42L30, with some improvements in the parameterization schemes, and a calibration of some empirical coefficients. An extended AMIP simulation (1979-1994) has been performed. The results will be available as a public AMIP dataset. Some results are presented. Although some degradations with respect to the EMERAUDE version have been identified, this new version provides a more realistic climate than the former AMIP dataset.