American monsoon season (SAM) is associated with the El Nino and the
Southern Oscillation (ENSO). Although this teleconnection provides a
basis for the seasonal predictability of SAM, it is shown that
conventional tier-2 modeling approach of prescribing observed sea
surface temperature (SST) is inappropriate to capture this teleconnection.
Furthermore, such a forced atmospheric general circulation model (AGCM)
simulation leads to degradation of the SAM precipitation variability.
However, when the same AGCM is coupled to an ocean general circulation
model to allow for coupled air-sea interactions, then this ENSO-SAM
teleconnection is reasonably well simulated. This is attributed to the
role of air-sea coupling in modulating the large-scale east-west
circulation especially associated with Nino3 SST anomalies. It is also shown that the land-atmosphere feedback over the SAM region as a result of air-sea coupling is more robust that results in augmenting the decorrelation time of the daily SAM precipitation.
A subtle difference in the austral summer seasonal precipitation
anomalies between that over the Amazon River Basin (ARB) and the SAM
core region is also drawn from this study in reference to the influence
of the air-sea interaction. It is shown that the dominant interannual
precipitation variability over the ARB is simulated both by the
uncoupled and coupled (to OGCM) AGCM in contrast to that over the
SAM core region in Southeastern Brazil.