Sensitivity of the MJO Simulations to the Mixing Length Formulations

Abstract:

Three physically based and non-local turbulent mixing length scale formulations implemented in COAMPS® are used for the MJO simulations to compare with conventional formulation as a function of boundary layer depth. The MJO simulations performed during the DYNAMO MJO2 suppressed and active phases. The objective is to examine the initiation of the MJO. The results are evaluated using the observations from the DYNAMO NOAA-P3 Dropsondes. The three formulations show general agreement during the suppressed phase of the MJO, which is important for the initiation of the MJO. During the active phase of the MJO, the modified Bougeault mixing length formulation shows improvement in the lower layer. This modified formulation enhances the convection by applying the Bougeault up-down-ward parcel approach to the levels above 2000 m and the approach of Mellor-Yamada below 2000 m. The other modified formulation that removes the discontinuities in the parameterized eddy viscosity and diffusivity terms is able to reduce the mean bias of temperature in the upper layer. This study suggests the importance of vertical mixing in modulating convective activities during the active phase of the MJO.