Intraseasonal Eastern Pacific Precipitation and SST Variations in a GCM Coupled to a Slab Ocean Model

Abstract

Coupling the NCAR Community Climate Model version 3.6 (CCM3.6) with relaxed Arakawa?Schubert convection to a slab ocean model (SOM) improves the simulation of eastern Pacific convection during a composite June?November intraseasonal oscillation (ISO) life cycle. Intraseasonal oscillations in the SOM simulation produce convective variability over the tropical northeastern Pacific that is similar to that produced by the observed Madden?Julian oscillation (MJO). A composite ISO life cycle in the SOM simulation exhibits stronger, more coherent, and more widespread eastern Pacific warm pool convective anomalies than in a control simulation using climatological SSTs. Competing convective forcings over land and ocean make eastern Pacific low-level circulation anomalies more complex in the SOM simulation than in the observed MJO. Off-equatorial eastern Pacific SST variations of more than 0.6°C are associated with the June?November SOM simulation ISO. These variations are similar to those observed with the MJO. No significant equatorial east Pacific SST anomalies occur in the model, supporting the contention that observed MJO SST anomalies on the equator are caused by ocean dynamics. Positive off-equatorial SOM simulation SST anomalies are nearly in phase with enhanced precipitation during significant MJO events, whereas observed SST anomalies lead enhanced precipitation by just under 10 days. Latent heat flux and surface shortwave radiation anomalies are the dominant terms in controlling east Pacific intraseasonal SST in the SOM simulation, as in observations. Positive latent heat flux and shortwave radiation anomalies (positive defined as downward into the ocean) lead enhanced SST by about 10 days during significant ISO events in the SOM simulation.