What was done
This study, quoting the authors, "evaluates the simulation of the Madden-Julian oscillation (MJO) and convectively coupled equatorial waves (CCEWs) in 20 models from the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) and compares the results with the simulation of CMIP phase 3 (CMIP3) models in the IPCC Fourth Assessment Report (AR4)."

What was learned
Although Hung et al. report that their results show that "the CMIP5 models exhibit an overall improvement over the CMIP3 models in the simulation of tropical intra-seasonal variability, especially the MJO and several CCEWs," they concede that (1) "the phase speeds of the model MJO tend to be too slow and the period is longer than observations as part of an over-reddened spectrum, which in turn is associated with too strong persistence of equatorial precipitation," that (2) "the persistence of precipitation in many CMIP5 models is still larger than observations, which is also reflected by the too red precipitation and space-time spectra," and that (3) "only one of the 20 models is able to simulate a realistic eastward propagation of the MJO."

What it means
The only thing one can probably say for sure in respect to the implications of these results is that there will likely be more government money made available to climate modelers to complete the unfinished task of accomplishing what yet remains to be done in order to be able to do what they were not able to successfully do this time around. So there will likely be a CMIP6 or 7 sometime in the not-too-distant future. Be prepared!