Intraseasonal surface cooling in the equatorial western Pacific

Three idealized models for the surface structure of the Madden-Julian oscil lation (MJO) were summarized from observations, numerical simulations, and theories, which demonstrate contrasting phase relationships of surface vari ables. To explore which model represents the most commonly observed feature s of the MJO in the western Pacific, in situ observations from moored buoys and satellite data were used to construct composite time series for compon ents of surface fluxes of heat, momentum, and buoyancy during intraseasonal cooling episodes, defined as periods when the ocean loses heat through the surface. The composites show a near in-phase relationship among maxima in net surface cooling, latent heat Bur, precipitation rate, wind stress, west erly wind, and minima in solar radiation flux and net buoyancy flux. The ph ase of net buoyancy flux is determined by the net heat flux, whereas its ma gnitude is substantially compensated by freshwater flux. During the composi te cooling episode, both the oceanic isothermal layer and mixed layer becom e deeper, the barrier layer becomes thinner, and the sea surface becomes co oler. The strength of atmospheric forcing and the oceanic response increase s with the length of the cooling episodes. The phase relationships found in the composites are consistent with one of the three MJO models and with so me previous studies based on observations and global model analyses but are inconsistent with others. Possible reasons for the disagreement among diff erent studies and the implications of the disagreement are discussed.