Regional Simulation of the October and November MJO Events Observed during the CINDY/DYNAMO Field Campaign at Gray Zone Resolution

Abstract

This study investigates the October and November MJO events observed during the Cooperative Indian Ocean Experiment on Intraseasonal Variability in the Year 2011 (CINDY)/Dynamics of the MJO (DYNAMO) field campaign through cloud-permitting numerical simulations. The simulations are compared to multiple observational datasets. The control simulation at 9-km horizontal grid spacing captures the slow eastward progression of both the October and November MJO events in surface precipitation, outgoing longwave radiation, zonal wind, humidity, and large-scale vertical motion. The vertical motion shows weak ascent in the leading edge of the MJO envelope, followed by deep ascent during the peak precipitation stage and trailed by a broad second baroclinic mode structure with ascent in the upper troposphere and descent in the lower troposphere. Both the simulation and the observations also show slow northward propagation components and tropical cyclone-like vortices after the passage of the MJO active phase. Comparison with synthesized observations from the northern sounding array shows that the model simulates the passage of the two MJO events over the sounding array region well. Sensitivity experiments to SST indicate that daily SST plays an important role for the November MJO event, but much less so for the October event.Analysis of the moist static energy (MSE) budget shows that both advection and diabatic processes (i.e., surface fluxes and radiation) contribute to the development of the positive MSE anomaly in the active phase, but their contributions differ by how much they lead the precipitation peak. In comparison to the observational datasets used here, the model simulation may have a stronger surface flux feedback and a weaker radiative feedback. The normalized gross moist stability in the simulations shows an increase from near-zero values to ;0.8 during the active phase, similar to what is found in the observational datasets.

Intraseasonal Variability and Seasonal March of the Moist Static Energy Budget over the Eastern Maritime Continent during CINDY2011/DYNAMO

“…Their definition of NGMS is the ratio between the anomaly of column-integrated vertical advection of MSE to that of DSE. Testing this assumption is complicated by the difficulty of precisely estimating NGMS from observations; however, several modeling and observational studies indicate that NGMS significantly varies with the MJO phase (Benedict et al 2014;SWK;Wang et al 2015;Inoue and Back 2015). SWK found that NGMS increases as the MJO convective active phase passes.…”

“…Because these processes are sources of column-integrated moist static energy (MSE) or moist entropy, it may be useful to focus attention on the budget of that quantity as it varies in association with MJO events. The column-integrated MSE and moist entropy budgets have been studied using numerical simulation outputs (Maloney 2009;Andersen and Kuang 2012;Hannah and Maloney 2014;Benedict et al 2014;Wang et al 2015) and reanalysis datasets (Kiranmayi and Maloney 2011;Kim et al 2014).…”

An Ensemble Hindcast of the Madden-Julian Oscillation during the CINDY2011/DYNAMO Field Campaign and Influence of Seasonal Variation of Sea Surface Temperature

“…3 of Fu et al (2015), although they did not point these explicitly. In contrast, the 76 day simulation of Wang et al (2015) appears to successfully reproduce the strong convection approximately on 6 November. However, the eastern boundary of their regional model was at 120°E and the evolution of the atmosphere in the MC was strongly constrained by the realistic evolution of the atmosphere that is provided to the computational domain as boundary conditions.…”

“…Their successful simulation indicates that a proper simulation of a westward moving signal in the western Pacific may be a key to reproduce the enhancement of convection in the MC in early November. Initiation of MJO2 delays by several days in Wang et al (2015). The reason for these earlier or later initiations of MJO2 has not been clarified.…”

“…Fu et al (2015) and Wang et al (2015) have already reported successful simulations of MJO2 by coupled/ atmosphere-only global models and a regional atmospheric model, respectively. They showed that MJO2 representation was improved significantly by using daily SST values instead of a constant SST value throughout the simulation as the bottom boundary condition.…”