The role of SST variability in modulating the periodicity of the Madden-Julian Oscillation (MJO) has been the focus of recent observational and modeling studies. Flateau et al. (1997) have suggested that SST recovery times are relevant to the modulation of the MJO periodicity while Sperber et al. (1997) have speculated that SST response to low-level wind anomalies may play an important role in the propagation of the MJO from the Indian Ocean to the western Pacific.
In this study, we examine the Reynolds and Smith (1994) optimally interpolated (OI) SSTs in the western Pacific warm pool region (120E to 160W) and TOGA TAO surface winds for evidence of coupling at MJO time scales. Empirical orthogonal function (EOF) analysis of the SST data reveals a spatial pattern with a warm-cold dipole located on the equator and centered in the warm pool region. The principal component (PC; time-varying part) of this EOF has a spectral peak at about 50 days. A cross spectrum analysis between this PC and filtered zonal wind anomalies at each TOGA TAO buoy is then performed. Cospectra indicate maximum covariance at 30-60 day periodicities within the
warm pool region (i.e., 130E ~ 170E). Farther east, maximum covariance shifts toward lower frequencies. Coherence values for these periodicities are typically >= 0.5.
A preliminary conclusion from this work is that coupling between SSTs and surface winds at MJO time scales is concentrated in the warm pool region of the western Pacific Ocean. We are currently working towards constructing composites of TOGA TAO surface variables based on the variability of the above-mentioned PC.
REFERENCES
Flatau, M., P. J. Flatau, P. Phoebus, and P. P. Niiler, 1997: The feedback between euqatorial convection and local radiative and evaporative processes: The impolications for intraseasonal oscillations. J. Atmos. Sci., 54, 2373-2386.
Reynolds, R. W., and R. M. Smith, 1994: Improved global sea surface
temperature analyses using optimum interpolation. J. Climate, 7, 929-948.
Sperber, K. R., J. M. Slingo, P. M. Inness, and W. K-M. Lau, 1997: On the maintenance and initiation of the intraseasonal oscillation in the NCEP/NCAR reanalysis and in the GLA and UKMO AMIP simulations. Climate Dynamics, 13, 769-795