Sensitivity of MJO Eastward Propagation to Convective Parameterizations

The sensitivity of MJO east propagation to convective parameterization was studied using Nanjing University of Information Science and Technology earth system model (NESM2), which has modified Tiedtke convective scheme with the mass flux closure dependent on convective available potential energy (CAPE). Sensitivity tests using various modifications in the convective scheme were conducted. . The modified convection scheme gives an improved mean state, intraseasonal variability, space-time power spectra, and eastward propagation compared to the standard version of the model (CTL). The modifications in the convective scheme change MJO characteristics and eastward propagation speed remarkably. It is shown that proper suppression of convection improves MJO propagation speed over the Indian and western Pacific Oceans. In the CTL, the maximum precipitation (peak of deep convection) tends to response to maximum frictional low-level convection too lately. The modifications of convective scheme in this study enhance the relationship between maximum precipitation and frictional low-level convection by connecting PBL thermal with deep convection and producing shallow convection ahead of deep convection. It is shown that the ratio of the maximum low-level westerly wind speed to maximum easterly speed by Wang and Chen (2016) can be used as an index to represent MJO propagation speed.