The modulation of Madden–Julian oscillation(MJO)pattern evolution over the Maritime Continent(MC)by El Nino–Southern Oscillation(ENSO)was investigated through a combined observational and modeling study.MJO convecti...The modulation of Madden–Julian oscillation(MJO)pattern evolution over the Maritime Continent(MC)by El Nino–Southern Oscillation(ENSO)was investigated through a combined observational and modeling study.MJO convective branches shifted south of the equator over the MC during eastern Pacific(EP)El Nino winters,while it became relatively symmetric about the equator during La Ni?a winters.The impact of central Pacific(CP)El Ninos to MJO pattern,on the other hand,is not statistically significant.The cause of the distinctive MJO pattern evolutions is likely attributed to the ENSO-induced changes of the background moisture and vertical shear over the MC.Idealized numerical experiments with a 2.5-layer model were carried out,and the result revealed that the background moisture change played a dominant role.An observational diagnosis of column-integrated moist static energy(MSE)budgets was further conducted.The result indicated that the MJO pattern difference was attributed to the MSE tendency asymmetry in front of MJO convection between EP El Nino and La Ni?a,caused by the advection of the mean MSE by anomalous meridional wind.The difference in the MJO-scale anomalous meridional wind was ultimately controlled by the change of the background meridional moisture gradient associated with EP El Nino and La Ni?a.展开更多
An operational weather forecast model,coupled to an oceanic model,was used to predict the initiation and propagation of two major Madden–Julian Oscillation(MJO)events during the dynamics of the MJO(DYNAMO)campaign pe...An operational weather forecast model,coupled to an oceanic model,was used to predict the initiation and propagation of two major Madden–Julian Oscillation(MJO)events during the dynamics of the MJO(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-and45-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 is attributed to the model capability to reproduce the observed intraseasonal outgoing longwave radiation–sea surface temperature(OLR–SST)relationship.On one hand,the SST anomaly(SSTA)over the WEIO was induced by surface heat flux anomalies associated with the preceding suppressed-phase MJO.The change of 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.展开更多
基金Supported by the National Natural Science Foundation of China(42088101 and 41875069)US National Science Foundation(AGS-2006553)+2 种基金US NOAA Grant(NA18OAR4310298)SOEST contribution number 11206IPRC contribution number 1494。
文摘The modulation of Madden–Julian oscillation(MJO)pattern evolution over the Maritime Continent(MC)by El Nino–Southern Oscillation(ENSO)was investigated through a combined observational and modeling study.MJO convective branches shifted south of the equator over the MC during eastern Pacific(EP)El Nino winters,while it became relatively symmetric about the equator during La Ni?a winters.The impact of central Pacific(CP)El Ninos to MJO pattern,on the other hand,is not statistically significant.The cause of the distinctive MJO pattern evolutions is likely attributed to the ENSO-induced changes of the background moisture and vertical shear over the MC.Idealized numerical experiments with a 2.5-layer model were carried out,and the result revealed that the background moisture change played a dominant role.An observational diagnosis of column-integrated moist static energy(MSE)budgets was further conducted.The result indicated that the MJO pattern difference was attributed to the MSE tendency asymmetry in front of MJO convection between EP El Nino and La Ni?a,caused by the advection of the mean MSE by anomalous meridional wind.The difference in the MJO-scale anomalous meridional wind was ultimately controlled by the change of the background meridional moisture gradient associated with EP El Nino and La Ni?a.
基金Supported by the NOAA of U.S.(NA18OAR4310298)National Natural Science Foundation of U.S.(AGS-1643297)National Natural Science Foundation of China(41875069).
文摘An operational weather forecast model,coupled to an oceanic model,was used to predict the initiation and propagation of two major Madden–Julian Oscillation(MJO)events during the dynamics of the MJO(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-and45-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 is attributed to the model capability to reproduce the observed intraseasonal outgoing longwave radiation–sea surface temperature(OLR–SST)relationship.On one hand,the SST anomaly(SSTA)over the WEIO was induced by surface heat flux anomalies associated with the preceding suppressed-phase MJO.The change of 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.
