Interaction between the MJO and High-Frequency Waves over the Maritime Continent in Boreal Winter

Abstract

The two-way interaction between Madden–Julian oscillation (MJO) and higher-frequency waves (HFW) over the Maritime Continent (MC) during boreal winter of 1984–2005 is investigated. It is noted from observational analysis that strengthened (weakened) HFW activity appears to the west (east) of and under MJO convection during the MJO active phase and the opposite is seen during the MJO suppressed phase. Sensitivity model experiments indicate that the control of HFW activity by MJO is through change of the background vertical wind shear and specific humidity. The upscale feedbacks from HFW to MJO through nonlinear rectification of condensational heating and eddy momentum transport are also investigated with observational data. A significantly large amount (25%–40%) of positive heating anomaly () at low levels to the east of MJO convection is contributed by nonlinear rectification of HFW. This nonlinear rectification is primarily attributed to eddy meridional moisture advection. A momentum budget diagnosis reveals that 60% of MJO zonal wind tendency at 850 hPa is attributed to the nonlinear interaction of HFW with other scale flows. Among them, the largest contribution arises from eddy zonal momentum flux divergence . Easterly (westerly) vertical shear to the west (east) of MJO convection during the MJO active phase causes the strengthening (weakening) of the HFW zonal wind anomaly. This leads to the increase (decrease) of eddy momentum flux activity to the east (west) of the MJO convection, which causes a positive (negative) eddy zonal momentum flux divergence in the zonal wind transitional region during the MJO active (suppressed) phase, favoring the eastward propagation of the MJO.

Nonlinear optimal moisture perturbations as excitation of primary MJO events in a hybrid coupled climate model

“…For example, a nonlinear view of the MJO has been offered based on resonant triad interactions of a discrete set of planetary-scale waves (Kartashova and L'vov 2007). Due to the multiscale characteristics embedded in the planetary-scale MJO envelop (Nakazawa 1988), the nonlinear upscale transports of momentum, heat, and moisture associated with subplanetary-scale convection/wave activity were demonstrated to play a key role in the MJO dynamics (e.g., Stechmann 2009, 2011;Zhou and Li 2010;Zhu et al 2019). The nonlinear dry Rossby wave dynamics was also tested to be fundamental to reproduce the eastward-propagating MJO-like structure (Wedi and Smolarkiewicz 2010).…”