Simulations of the Madden – Julian Oscillation using a Tropical Channel Model

Previous studies have suggested that MJO simulations are very sensitive to the selection of cumulus parameterization schemes. Simulations with the MM5 model configured for the tropical channel (TMM5) using Betts-Miller (BM) cumulus parameterization scheme produced a realistic MJO. However, simulations with the Nested Regional Climate Model (NRCM) of the WRF (ARW) also configured for the tropical channel but using Betts-Miller-Janjic (BMJ) cumulus parameterization scheme failed to reproduce MJO events, even with time dependent lateral boundary conditions from a global reanalysis product.

This work seeks to explain if the NRCM failure to reproduce the MJO is because of the Betts-Miller-Janjic scheme. If so, which part of the revision of the original BM scheme is most responsible for it? Is it due to the control of the reference profiles of temperature and relative humidity by the new nondimensional parameter of cloud efficiency?

We implemented the original BM parameterization scheme into WRF (ARW) version 3, to replace the BMJ option of the model. We compare the results using NRCM with BM and BMJ for the 2 MJO events successfully simulated by TMM5 with BM.