Saji, N. H., B. N. Goswami, 1997: Intercomparison of the seasonal
cycle of tropical surface stress in 17 AMIP atmospheric general circulation
models. Climate Dynamics, 13, 561-585
The mean state of the tropical atmosphere is important as the nature
of the coupling between the ocean and the atmosphere depends non linearly
on the basic state of the coupled system. The simulation of the annual
cycle of the tropical surface wind stress by 17 atmospheric general circulation
models (AGCMs) is examined and intercompared. The models considered were
part of the Atmospheric Model Intercomparison Project (AMIP) and were integrated
with observed sea surface temperature (SST) for the decade 1979-1988. Several
measures have been devised to intercompare the performance of the 17 models
on global tropical as well as regional scales. Within the limits of observational
uncertainties, the models under examination simulate realistic tropical
area averaged zonal and meridional annual mean stresses. This is a noteworthy
improvement over older generation low resolution models which were noted
for their simulation of surface stresses considerably weaker than the observations.
The models also simulate realistic magnitudes of the spatial distribution
of the annual mean surface stress field and are seen to reproduce realistically
its observed spatial pattern. Similar features are observed in the simulations
of the annual variance field. The models perform well over almost all the
tropical regions apart from a few. Of these. the simulations over Somali
are interesting. Over this region, the models are seen to underestimate
the annual mean zonal and meridional stresses. There is also wide variance
between the different models in simulating these quantities. Large model-to-model
variations were also seen in the simulations of the annual mean meridional
stress field over equatorial Indian Ocean, south central Pacific, north
east Pacific and equatorial eastern Pacific oceans. It is shown that the
systematic errors in simulating the surface winds are related to the systematic
errors in simulating the Inter-Tropical Convergence Zone (ITCZ) in its
location and intensity. Weaker than observed annual mean southwesterlies
simulated by most models over Somali is due to weaker than observed southwesterlies