Propagating and Standing Components of the Intraseasonal Oscillationin Tropical Convection

Two questions related to the intraseasonal variability of tropical convection and circulation remain controversial. 1) To what degree is the convective component of the Madden–Julian oscillation (MJO) a standing oscillation? 2) Is the eastward propagating circulation anomaly of the MJO coherent with a standing oscillation in convection? In an attempt to settle these issues, the authors undertake a series of statistical analyses of gridded outgoing longwave radiation and winds to quantify the magnitudes of the propagating and standing components of convection and their coherence with the propagating component of the circulation. They demonstrate that no dominant standing oscillation in convection can be identified. Instead, intraseasonal variability of convection is dominated by an eastward propagating mode, which the authors interpret as the convective signal of the MJO. This propagating component accounts for almost all of the convective variance that is coherent with the eastward propagating disturbance in the zonal wind, which is a traditional measure of the MJO. Analysis of synthetic time series illustrates that an impression of a standing oscillation in convection may come forth because of the modulation of the eastward propagating convective disturbance by an amplitude envelope with maxima in the eastern Indian and western Pacific Oceans and a minimum over the maritime continents.