Intraseasonal Oscillations as triggers for warm events in a three-dimensional ocean model: sensitivity at various time scales

It is widely believed that intraseasonal westerly wind bursts can be an important triggering mechanism for the onset of El Niño events. This behavior is readily seen in a three-dimensional primitive equation ocean model for the equatorial Pacific Ocean. Using ECMWF operational analyses of surface winds as the primary top boundary condition, the model is able to reproduce many of the characteristics of a typical El Niño. In this paper, the impact of westerly wind bursts occurring on different time scales on the model ocean circulation is examined. The control run utilizes ECMWF analyses that are known to trigger a warm event in the model ocean. In the experimental runs, the analyses are processed through a bandstop filter to remove intraseasonal forcings such as westerly wind bursts while maintaining stochastic forcings at higher and lower frequencies. The impact of both high frequency and low frequency (6-25 day or 25-70 day, respectively) intraseasonal oscillations will be examined.