The mean flow systematic error in the extended AMIP integration (14 years) of the COLA GCM takes the form of wave-train like features emanating from the western tropical Pacific in all seasons. The response of the GCM to warm ENSO SSTs is of the correct form but tends to be weak. A large set of experiments with a wavy-basic state linear model implicates the structure of the GCM diabatic heating patterns in the tropics in both these problems. The variability of seasonal means in the integration and ECMWF analyses is compared, with reasons for the somewhat lower level in the GCM being explored.
The structure of the transients in the GCM integration are examined,
including the energetics, time and space-scale dependence, and geographical
relationships of the transients to the mean flow gradients. Comparison
with ECMWF analyses will emphasize the seasonal dependence of these statistics,
and the variability of single season statistics within the run. The role
of rapidly growing optimal modes in the analyses and the GCM will be touched
upon.