Impacts of a GCM’s resolution on MJO simulation

Abstract

Long-term integrations are conducted using the Spectral Atmospheric Model (referred to as SAMIL), which was developed in the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) in the Institute of Atmospheric Physics (IAP), with different resolutions to investigate sensitivity of the Madden-Julian Oscillation (MJO) simulations to the model’s resolution (horizontal and vertical). Three resolutions of the model, R15L9, R42L9 and R42L26, with identical physical processes, all produced the basic observed features of the MJO, including the spatiotemporal space-time spectra and eastward propagation. No fundamental differences among these simulations were found. This indicates that the model resolution is not a determining factor for simulating the MJO. Detailed differences among these modeling results suggest, however, that model resolution can substantially affect the simulated MJO in certain aspects. For instance, at a lower horizontal resolution, high frequency disturbances were weaker and the structures of the simulated MJO were better defined to a certain extent. A higher vertical resolution led to a more realistic spatiotemporal spectrum and spatial distribution of MJO precipitation. Meanwhile, increasing the model’s resolution improved simulation of the climatology. However, increasing the resolution should be based on improving the cumulus parameterization scheme.