CINDY2011/DYNAMO Madden-Julian oscillation successfully reproduced in global cloud/cloud-system resolving simulations despite weak tropical wavelet power.

The role of tropical atmospheric waves in the propagation mechanism of the Madden-Julian oscillation (MJO), a huge eastward-propagating atmospheric pulse that dominates intraseasonal variation of the tropics and affects the entire globe, has been long discussed but remains unclear. An MJO event observed in a major field campaign is reproduced using a front-running global cloud/cloud-system resolving model with 3.5 km, 7 km, and 14 km meshes. The eastward-migration speed of the MJO convective envelope in the 3.5 km and 14 km simulations agree well with observation, despite weak Kelvin wave signal power calculated by applying a combined Fourier-wavelet transform method. Our results suggest that the eastward propagation of this MJO event was principally controlled by an MJO-scale energy balance, and not by dynamical interaction of embedded tropical waves. The eastward propagation is delayed in the 7 km simulation, which features the highest surface latent heat flux to the west of the convective envelope center. This latent heat flux appears to be caused by prolonged existence of westward-migrating Rossby wave-like cyclonic disturbances near the equator; the embedded waves may not be part of the essential mechanism for the MJO eastward propagation, but can affect it by altering the energy balance.

Vertical structure and physical processes of the Madden-Julian Oscillation: Biases and uncertainties at short range.

An analysis of diabatic heating and moistening processes from 12 to 36 h lead time forecasts from 12 Global Circulation Models are presented as part of the "Vertical structure and physical processes of the Madden-Julian Oscillation (MJO)" project. A lead time of 12-36 h is chosen to constrain the large-scale dynamics and thermodynamics to be close to observations while avoiding being too close to the initial spin-up of the models as they adjust to being driven from the Years of Tropical Convection (YOTC) analysis. A comparison of the vertical velocity and rainfall with the observations and YOTC analysis suggests that the phases of convection associated with the MJO are constrained in most models at this lead time although the rainfall in the suppressed phase is typically overestimated. Although the large-scale dynamics is reasonably constrained, moistening and heating profiles have large intermodel spread. In particular, there are large spreads in convective heating and moistening at midlevels during the transition to active convection. Radiative heating and cloud parameters have the largest relative spread across models at upper levels during the active phase. A detailed analysis of time step behavior shows that some models show strong intermittency in rainfall and differences in the precipitation and dynamics relationship between models. The wealth of model outputs archived during this project is a very valuable resource for model developers beyond the study of the MJO. In addition, the findings of this study can inform the design of process model experiments, and inform the priorities for field experiments and future observing systems.

Madden-Julian Oscillation prediction skill of a new-generation global model demonstrated using a supercomputer.

Global cloud/cloud system-resolving models are perceived to perform well in the prediction of the Madden-Julian Oscillation (MJO), a huge eastward -propagating atmospheric pulse that dominates intraseasonal variation of the tropics and affects the entire globe. However, owing to model complexity, detailed analysis is limited by computational power. Here we carry out a simulation series using a recently developed supercomputer, which enables the statistical evaluation of the MJO prediction skill of a costly new-generation model in a manner similar to operational forecast models. We estimate the current MJO predictability of the model as 27 days by conducting simulations including all winter MJO cases identified during 2003-2012. The simulated precipitation patterns associated with different MJO phases compare well with observations. An MJO case captured in a recent intensive observation is also well reproduced. Our results reveal that the global cloud-resolving approach is effective in understanding the MJO and in providing month-long tropical forecasts.