Impact of air/sea interactions in simulating the transition phase of the intraseasonal oscillation

While Intraseasonal Oscillations (ISOs) are a very important element of the tropical and global climate, numerical models are not able to simulate their complete life cycle. Detailed analysis of the life cycle of ISOs over the western Pacific warm pool suggest that low-level moistening of the atmosphere during the transition phase from suppressed to active convection preconditions the atmosphere for the formation of deep convection. In order to increase our understanding of the ISOs and attempt to determine why models handle them so poorly, a numerical experiment using a coupled single column model is conducted to study the role of the atmosphere and the ocean, as well as their interaction, in triggering and sustaining the low-level moistening present during the transition periods associated to intraseasonal activity. The atmospheric component (SCCM) of the couple system corresponds to the single column model version of the NCAR Community Climate Model 3.6. The ocean component is the one-dimensional ocean mixed layer model described by Kantha and Clayson (1994, 2004). In this framework, the evolution of the transition period is studied under several different ocean-atmosphere configurations to determine the degree of local coupling associated to ISO events. For this objective, different simulations are performed using the fully coupled model and both the atmospheric and the oceanic components individually. The importance of the low-level moistening in preconditioning the atmosphere for deep convection and how the evolution of the moistening is affected by the background state of the atmospheric and oceanic mixed layer is evaluated using the model. The experiment also establishes whether or not, and how, the temporal proximity of two ISO events has an effect on the development characteristics of the second one. The model is evaluated using different data sources like TOGA COARE IOP, the Atmospheric Radiation Measurement Program (ARM), Different satellite missions and ECWMF and NCEP/NCAR reanalyses.