Symmetric and antisymmetric convection signals in the 1 Madden - Julian oscillation . Part I : Basic modes in infrared

6 This work studies the significance of north-south asymmetry in convection associated with 7 the 20–90-day Madden-Julian oscillation (MJO) propagating across the equatorial Indo8 Pacific warm-pool region. Satellite infrared brightness temperature data in the tropical belt 9 for the period 1983–2006 were decomposed into components symmetric and antisymmetric 10 about the equator. Using a recent nonlinear objective method called nonlinear Laplacian 11 spectral analysis, modes of variability were extracted representing symmetric and antisym12 metric features of MJO convection signals, along with a plethora of other modes of tropical 13 convective variability spanning diurnal to interannual time scales. The space-time recon14 struction of these modes during the 1992–1993 TOGA COARE period is described in detail. 15 In particular, the boreal winter MJO emerges as a single pair of modes in both symmetric 16 and antisymmetric convection signals. Both signals originate in the Indian Ocean around 17 60◦ E. They coexist for all significant MJO events with a varying degree of relative impor18 tance which is affected by ENSO. The symmetric signals tend to be suppressed when crossing 19 the Maritime Continent, while the antisymmetric signals are not as inhibited. Their differ20 ences in peak phase and propagation speed suggest fundamental differences in the underlying 21 mechanisms. The multiscale interactions between the diurnal, MJO, and ENSO modes of 22 convection were studied. It was found that the symmetric component of MJO convection is 23 out of phase with the symmetric component of the diurnal cycle, while the antisymmetric 24 component of MJO convection is in phase with the antisymmetric diurnal cycle. The former 25 relationship breaks down during strong El Niño events, and both relationships break down 26 during prolonged La Niñas. 27