Impact of explicit atmosphere–ocean coupling on tropical intraseasonal ocillations

Tropical intraseasonal oscillations concern variability of the tropical climate on time scales between several days and a few months and are the strongest mode of atmospheric variability in the tropics. Their best known example is the Madden-Julian Oscillation (MJO), which is a coherent pattern of deep convection, large-scale circulation, and sea-surface temperature that propagates toward the east across the tropical warm pool (eastern Indian and western Pacific Oceans) with a typical speed of 5 m/s. Typically, MJO is poorly represented in climate models and it has been suggested that MJO is a coupled atmosphere-ocean phenomenon, where the atmosphere and the ocean work had-in-hand to create the observed variability. This conjecture is supported by simulations using traditional climate models where typically, enhanced intraseasonal variability is observed when the atmospheric model is coupled to the interactive ocean model. This talk will show that this conclusion does not hold when the same problem is investigated in idealized aquaplanet simulations using the super-parameterization coupled to a simple mixed-layer ocean model. In these simulations, the ocean appears to be merely responding to the atmospheric forcing with, if anything, the negative feedback from the ocean on the atmosphere. An explanation of these conflicting views, involving the positive moisture-convection feedback in the atmosphere and the negative convection-SST feedback in the ocean, will be discussed.