Effect of shallow cumulus convection on the eastern Pacific climate in a coupled model

Shallow cumulus convection evaporates stratocumulus clouds in the atmospheric boundary layer. The effect of shallow convection on the large-scale climate of the eastern tropical Pacific is investigated with a coupled ocean-atmosphere model by disabling the shallow convection parameterization (noSC). Without shallow convection, the stratiform cloud fraction increases and surface solar radiation decreases. The sea surface temperature (SST) cools on average by 2 degrees C. The cooling in noSC is larger under the low cloud deck south of the equator than north of the equator, resulting in an increase in the climatic meridional asymmetry. In the control run an ITCZ forms south of the equator in March-April. In noSC the SST is at most 24 degrees C south of the equator and an ITCZ does not form. The perennial northern-hemisphere ITCZ in noSC is accompanied by year-round southerlies of at least similar to 3 m s(-1) on the equator, considerably reducing the seasonal cycle of equatorial SST.