On the dynamics of intraseasonal oscillations and ENSO

Abstract

For intraseasonal oscillations, results show that the slow eastward propagation in the atmosphere is due to condensation-convergence feedback leading to a reduction of the effective static stability of the troposphere. In the coupled moist atmosphere-ocean system, two unstable modes, ie an advective mode and an upwelling mode, are identified. The advective mode is due to the destabilization of atmospheric waves by air-sea interaction through east-west SST advection. In this mode, the region of maximum convection lies about 10° west of the maximum SST anomaly. The upwelling model is due to the destabilization of oceanic Kelvin waves by air-sea interaction through oceanic upwelling. This mode has no east-west displacement between atmospheric convection and SST anomaly and for low SST (typical below 26°C), corresponds to an unstable model in the "dry' atmosphere found in previous studies. Most importantly, both modes show a dramatic increase in growth rate through air-sea coupling as the mean SST increases from 27° to 28°C. -from Authors