Maintenance and initiation of the intraseasonal oscillation in the NCEP/NCAR and ECMWF reanalyses and in the GLA and UKMO AMIP simulations

摘要

Julian Intraseasonal (Madden-Julian) oscillations are a dominant model of tropical variability. Satellite derived outgoing longwave radiation (OLR) and reanalyses from NCEP/NCAR and ECMWF are used as verification data in a study of intraseasonal variability in the Goddard Laboratory for Atmospheres (GLA) and the United Kingdom Meteorological Office (UKMO) atmospheric general circulation models. We examine the November-May period during which these models exhibited their strongest and most coherent IO's. 1987/88 from observations and the reanalyses are compared with 1986/87 from GLA and 1980/81 from UKMO. During the active phase of the IO, convection migrates from the Indian Ocean to the western/central Pacific Ocean, and into the SPCZ. To demonstrate this, we have calculated an IO index to be used for lagged correlation analysis. Both models fail to simulate IO related convection over the Indian Ocean and the propagation eastward into the west Pacific. The maintenance and initiation of the intraseasonal oscillation has also been investigated. We have correlated the IO index with 20-100 day bandpass filtered latent heat flux from NCEP/NCAR reanalysis and ECWMF reanalysis. This result indicates that evaporative wind feedback is not the dominant process by which the eastward propagation of the intraseasonal oscillation is maintained.