Lignin-related cinnamaldehydes

International audienc

Intraseasonal oscillations in 15 atmospheric general circulation models: results from an AMIP diagnostic subproject

The ability of 15 atmospheric GCM models (AGCM) to simulate the tropical intraseasonal oscillation has been studied as part of AMIP. Time series of the daily upper tropospheric velocity potential and zonal wind, averaged over the equatorial belt, were provided from each AGCM simulation. These data were analyzed using a variety of techniques such as time filtering and space-time spectral analysis to identify eastward and westward propagating waves. The results have been compared with an identical assessment of ECMWF analyses for the period 1982-1991. The models display a wide range of skill in simulating the intraseasonal oscillation. Most models show evidence of an eastward propagating anomaly in the velocity potential field, although in some models there is a greater tendency for a standing oscillation, and in one or two the field is rather chaotic with no preferred direction of propagation. Where a model has a clear eastward propagating signal, typical periodicities seem quite reasonable although there is a tendency for the models to simulate shorter periods than in the ECMWF analyses, where it is near 50 days. The results of the space-time spectral analysis have shown that no model has captured the dominance of the intraseasonal oscillation found in the analyses. Several models have peaks at intraseasonal time scales, but nearly all have relatively more power at higher frequencies