This study reveals the inadequacy of the Center for Ocean-Land-Atmosphere Studies (COLA) Atmospheric General Circulation Model (AGCM) and National Center for Environmental Prediction (NCEP) reanalysis to resolve the variance of the intraseasonal anomalies of outgoing longwave radiation (OLR) over the South American summer monsoon (SASM) domain and the equatorial eastern Pacific Ocean (EEPO) owing to their coarse horizontal resolution. However, when the NCEP reanalysis is downscaled by roughly a factor of 2.5 using the regional spectral model (RSM, Control-A experiment) the simulation of the seasonal mean variance of intra-seasonal anomalies of OLR improve significantly. But downscaling the results of the COLA AGCM (control-B experiment) by roughly a factor of 4 led to no further improvement.

Using the novel technique of anomaly nesting which replaces the climatology of the COLA AGCM of the nested variables at the lateral boundaries of the RSM with the NCEP reanalysis climatology (AN experiment), the simulation of the intraseasonal variance of OLR improves significantly over control-B runs. This improvement is shown to coincide with a distinct diurnal variation of the intraseasonal scales displayed in the AN integrations which compare reasonably well with control-A integrations. A disappointing result of this study is that the generated variance of intraseasonal anomalies of OLR in the AN integrations arises from the internal variability of the model. However, it is concluded that the systematic errors of the COLA AGCM imposed on RSM from the lateral boundary conditions suppresses the generation of intraseasonal variability.