Seo, H., M. Jochum, R. Murtugudde, A. J. Miller and J. O. Roads, 2008:
Precipitation from African Easterly Waves in a coupled model of the tropical Atlantic.
Journal of Climate, 21, 1417-1431.
A regional coupled climate model is configured for the tropical Atlantic to explore the
role of synoptic-scale African Easterly Waves (AEWs) on the simulation of mean
precipitation in the marine Inter-Tropical Convergence Zone (ITCZ). Sensitivity tests
with varying atmospheric resolution in the coupled model show that these easterly waves
are well represented with comparable amplitudes on both fine and coarse grids of the
atmospheric model. Significant differences in the model simulations are found in the
precipitation fields however, where heavy rainfall events occur in the region of strong
cyclonic shear of the easterly waves only on the higher resolution grid. This is because
the low-level convergence due to the waves is much larger and more realistic in the fineresolution
simulation, which enables heavier precipitation events that skew the rainfall
distributions towards longer tails. The variability in rainfall on these time scales accounts
for more than 60-70% of the total variability. As a result, the simulation of mean rainfall
in the ITCZ and its seasonal migration improves in the higher-resolution case. This
suggests that capturing these transient waves and the resultant strong low-level
convergence is one of the key ingredients for improving the simulation of precipitation in
global coupled climate models.