Impacts of Cumulus Schemes on the Initiation and Propagation of MJO

• Main Authors: Mei-Yu Chang, 張美玉
• Other Authors: Pay-Liam Lin
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/x2ud38

博士 === 國立中央大學 === 大氣科學學系 === 107 === An operational weather forecast model, coupled to an oceanic model, was used to predict the initiation and propagation of two major MJO events during the DYNAMO campaign period. Two convective parameterization schemes were used to understand the sensitivity of the forecast to the model cumulus scheme. The first is the Tiedtke (TDK) scheme, and the second is the Simplified Arakawa-Schubert (SAS) scheme. The TDK scheme was able to forecast the MJO-1 and MJO-2 initiation at 15-day and 45-day lead, respectively, while the SAS scheme failed to predict the convection onset in the western equatorial Indian Ocean (WEIO). The diagnosis of the forecast results indicates that the successful prediction with the TDK scheme was attributed to the model capability to reproduce the observed intraseasonal OLR-SST relationship. On one hand, the SSTA over the WEIO was induced by surface heat flux anomalies associated with the preceding suppressed-phase MJO. The change of the SSTA, in turn, caused boundary layer convergence and ascending motion, which further induced a positive column-integrated moist static energy (MSE) tendency, setting up a convectively unstable stratification for MJO initiation. The forecast with the SAS scheme failed to reproduce the observed OLR-SST-MSE relation. The propagation characteristics differed markedly between the two forecasts. Pronounced eastward phase propagation in the TDK scheme is attributed to a positive zonal gradient of the MSE tendency relative to the MJO center, similar to the observed, whereas a reversed gradient appeared in the forecast with the SAS scheme with dominant westward propagation. The difference is primarily attributed to anomalous vertical and horizontal MSE advection.