Cloud-Resolving Model Sensitivity Studies of MJO Events during DYNAMO

The Goddard Cumulus Ensemble (GCE) model is used to simulate two MJO events in October and November 2011, during the DYNAMO field campaign in central Indian Ocean. The cloud-resolving model is forced by observed large-scale forcing over the northern sounding array where the MJO signals are strong. Each simulation runs for 40 days, covering the entire initiation to mature phase of the MJO events. The simulated surface rainfall and cloud structure compare well with radar observations.

In order to gain understanding of how model configurations affect simulated MJOs, we have conducted systematic sensitivity tests using the two established MJO events simulations. A reference simulation is carried out using ultra-high resolution (~250m horizontal and vertical), large-domain (~1000 km) and three-dimensional configuration. Comparisons between the reference simulations and field campaign observations show good agreements. Sensitivity tests with the same GCE model are then compared with the reference simulations in order to understand how these factors affect MJO simulations. The sensitivity factors include two-dimensional vs. three-dimensional simulations, changes of domain size and model resolutions, as well as different microphysical schemes. These sensitivity tests are compared with the reference simulation to understand how domain size, resolution and microphysics affect simulated MJO events. Our emphases are on how these factors affect surface rainfall pattern, cloud top height distributions, the vertical velocities, as well as simulated diurnal variations during DYNAMO field campaign.