The tropical intraseasonal oscillation in SAMIL coupled and uncoupled general circulation models

Simulations of tropical intraseasonal oscillation (TISO) in SAMIL, theSpectral Atmospheric Model from the Institute of Atmospheric Physics (IAP)State Key Laboratory of Numerical Modeling for Atmospheric Sciences andGeophysical Fluid Dynamics (LASG) coupled and uncoupled general circulationmodels were comprehensively evaluated in this study. Compared to theuncoupled model, the atmosphere--ocean coupled model improved the TISOsimulation in the following aspects: (1) the spectral intensity for the30--80-day peak eastward periods was more realistic; (2) the eastwardpropagation signals over western Pacific were stronger; and (3) the variancedistribution and stronger signals of Kelvin waves and mixed Rossby gravitywaves were more realistic. Better performance in the coupled run was assumedto be associated with a better mean state and a more realistic relationshipbetween precipitation and SST. In both the coupled and uncoupled runs, theunrealistic simulation of the eastward propagation over the equatorialIndian Ocean might have been associated with the biases of the precipitationmean state over the Indian Ocean, and the unrealistic split of maximum TISOprecipitation variance over the Pacific might have corresponded to theexaggeration of the double Intertropical Convergence Zone (ITCZ) structurein precipitation mean state. However, whether a better mean state leads tobetter TISO activity remains questionable. Notably, the northwardpropagation over the Indian Ocean during summer was not improved in the meanlead--lag correlation analysis, but case studies have shown some strongcases to yield remarkably realistic northward propagation in coupled runs.