Planetary Scale Intraseasonal Disturbances

There are two planetary disturbances that by definition prefer long wavelengths. One moves eastward and is associated with the Madden-Julian oscillation, while another moves westward and is called the Rossby wave.
Using the simple linear analytical model on an equatorial beta plane we model two unstable modes, eastward at meridional number n=-1 and westward propagating mode at meridional number n=1. Both of those modes are moisture modes, but the instability mechanism is not necessarily associated with the moisture mode instability, i.e. the negative gross-moist instability and cloud-radiation interactions. Instead the primary cause for the instability is mean easterlies. This makes sense when modeling the planetary disturbances as mean easterlies are present in the real atmosphere on a planetary scale due to the Hadley cell (GMS and CRI do not scale as planetary mechanisms).
We speculate that our modeled eastward and westward propagating WISHE-moisture modes incorporate the basics of physics for the MJO and Rossby waves. Other effects as well as the nonlinearity play an important role, but the essence of the MJO and Rossby waves, according to our model, only requires mean easterlies and moisture mode physics.