Sensitivity of the Simulated Tropical Intraseasonal Oscillation to Cumulus Parameterizations

The sensitivity of the simulated tropical intraseasonal oscillation or MJO (Madden and Julian oscillation) to different cumulus parameterizations is studied by using an atmospheric general circulation model(GCM)-SAMIL (Spectral Atmospheric Model of IAP LASG). Results show that performance of the modelin simulating the MJO alters widely when using two di erent cumulus parameterization schemes-the moistconvective adjustment scheme (MCA) and the Zhang-McFarlane (ZM) scheme. MJO simulated by the MCAscheme was found to be more realistic than that simulated by the ZM scheme. MJO produced by the ZM scheme is too weak and shows little propagation characteristics. Weak moisture convergence at low levels simulated by the ZM scheme is not enough to maintain the structure and the eastward propagation of the oscillation. These two cumulus schemes produced di erent vertical structures of the heating pro le. The heating profile produced by the ZM scheme is nearly uniform with height and the heating is too weak compared to that produced by the MCA, which maybe contributes greatly to the failure of simulating a reasonable MJO. Comparing the simulated MJO by these two schemes indicate that the MJO simulated by the GCM is highly sensitive to cumulus parameterizations implanted in. The diabatic heating profile plays an important role in the performance of the GCM. Three sensitivity experiments with di erent heating pro les are designed in which modified heating pro les peak respectively in the upper troposphere (UH), middle troposphere (MH), and lower troposphere (LH). Both the LH run and the MH run produce eastward propagating signals on the intraseasonal timescale, while it is interesting that the intraseasonal timescale signals produced by the UH run propagate westward. It indicates that a realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low levels, especially in the middle levels, while westward propagating disturbances are more prone to be produced when the maximum heating appears very high.