Role Of Moisture Feedback And Moisture Adjustment Time In The Propagation Of MJO

MJO is an important mode in troposphere. In simulating these features of MJO,there are three main theory models :The Frictional Convergence (FC) model, The Moisture Feedback (MF) model and The Frictional Convergence-Moisture Feedback(FC-MF) model. For the effect of the westward-propagating Rossby waves and moisture feedback, the phase speed of MJO would be slowly. To discuss the effect of moisture feedback, we separate the Kelvin waves in MJO to remove the effect of Rossby waves. We compared the Kelvin waves in three models and the result shows that moisture feedback can slow down the frequency of Kelvin waves into 10-30 days.We present a theoretical model that a delay process for triggering the deep convection from the additional planetary boundary layer (PBL) pumped moisture is implemented. This model has a moist Kelvin wave-like dispersion relation,and short waves grow fast when all moisture pumped by the PBL excites the deep convection instantly. When the moisture pumped by the PBL is delayed to stay in the lower troposphere for a time scale on the order of a day before triggering the deep convection, this model simulates a MJO-like mode, for which three features of the MJO, the peculiar dispersion relation, the horizontal quadrupole-vortex structure, and longest waves having maximum growth rate, have been simulated. Both moist Kelvin wave-like mode and MJO-like mode are simulated simultaneously when part of the deep convection is delayed, where the strong instability occurs at low-frequency long wavelength for the MJO-like mode and at high-frequency short wavelength for the moist Kelvin wave-like mode.In the delay process, the adjustment time means the lag time between the moisture collected by advection in troposphere and it transforms into precipitation. It is interesting that the adjustment times in long wave and short wave are different in the phase relationship.so we make the adjustment time changed with the scale of waves, which means the long waves have long adjustment times and short waves have short adjustment times. The result shows that it can simulate the unstable low frequency Kelvin wave part of MJO and unstable high frequency Kelvin waves at the same time, which is hopeful to improve the ability of GCMs in simulating the MJO.