Tropical Indian Ocean Mjo Structure Of The Sst Intraseasonal Oscillation And Its Interannual Change

The SST intraseasonal variability is closely associated with the structure of Madden-Julian oscillation(MJO).Based on the data from remote sensing,moored buoys and air-sea fluxes reanalysis system(OAFlux),lag correlation method is used to examine the physical structure of MJO in Indian Ocean.Composite analysis based on some MJO events captured by moored buoys shows a consistent result with the above research.This part provides a good phase relations among the surface air-sea fluxes and their coherent relationships with the variability of the upper ocean.Under the center of atmospheric deep convection,the minimum of shortwave radiation coincides with the maximum of wind speed and latent heat flux.This kind of MJO structure could make the maximum amplitude of net heat flux and the most significant variation of sea surface temperature(hereafter SST)in intraseasonal timescales.It is suggested that the air-sea interaction would play an important role in the MJO progress.It is necessary to confirm whether the intraseasonal variations of SST and mixed layer depth(hereafter MLD)are induced by MJO surface forcing.A simple one-dimensional mixed layer model(PWP)is used here to examine the unification of oceanic variability and atmospheric forcing.The phase relations and amplitudes of forcing fluxes inputted into the PWP model are referred to the above research.The intraseasonal variations of SST and MLD modeled by PWP are consistent with the observational results showed in the first part.This also suggests that the PWP model is appropriate enough to the study of MJO.An interannual variability of SST intraseasonal oscillation is observed especially in southwest Indian Ocean where the MLD and thermalcline are very shallow.Data analysis based on SST from Advanced Very High Resolution Radiometer(AVHRR), thermalcline from NCEP Global Ocean Data Assimilation System(GODAS)and air-sea heat fluxes from OAFlux,reveals that surface heat fluxes and oceanic subsurface processes play important roles in the interannual variability of SST intraseasonal oscillation.The SST intraseasonal oscillation will intensify as the intraseasonal amplitude of surface heat flux improved,and the same variation appears when the thermalcline rises.The remarkable signal that subsurface process influences the SST intraseasonal oscillation is found in the area where the thermalcline has the most obvious interannual variability.PWP mixed layer model is used again to check the regulative mechanism that we proposed above about the interannual variability of SST intraseasonal oscillation.And some simply designed numerical experiments give us a validation of the regulative mechanism.