Composite Madden-Julian Oscillation Cloud Structures from Satellite Observations and a Multiscale Modeling Framework Simulation

The temporal variation characteristics of various cloud regimes associated with the Madden-Julian oscillation (MJO) are still lacking although its dynamics are well understood. In this study, we analyze the temporal characteristics of cloud object data from the Aqua satellite observations between July 2006 and June 2010 for ten cloud regime types based upon the real-time multivariate MJO (RMM) index, which assigns the tropics to one of the eight MJO phases each day. The cloud object is a contiguous region of the Earth with a single dominant cloud-system type. Aqua satellite observations reveals that the prevailing description of MJO cloud regime types and their temporal evolution is qualitatively correct. But the contrasts between the suppressed and active phases are exaggerated; in particular, deep convection is more active than previously thought during the depressed phases. The change from minimum to maximum cloud areas is only 11% for deep convective (DC) regime, but ~27% for stratocumulus/overcast (SC/OC) cloud regimes. Compared to climatology, more large-size cloud objects are present at the expense of small-size cloud objects, particularly during the active phases. Exceptions are cumulus (Cu) cloud object during the depressed phases and OC cloud objects at the phases preceding and succeeding the active phases. There are phase lags between DC and SC/OC cloud objects. Eastward propagation is only pronounced for DC cloud objects. The frequencies of occurrence for Cu/SC/OC are modulated by the deep convective activities even though the physical locations of these cloud object types are far away from the convective centers. Changes in the properties within each cloud type from one phase to another are relatively small with a few exceptions. Phase 7 seems to be very different for Cu/SC/DC cloud object properties.

In the second part of this study, a multiscale modeling framework (MMF) global simulation will be analyzed to examine the horizontal and vertical distributions of clouds in the tropics, following the same compositing procedure with the RMM index. In an MMF, a two-dimensional cloud-resolving model replaces conventional cloud parameterizations used in each grid column of a general circulation model. The embedded CRM incorporates an advanced third-order turbulence closure so that the low clouds are realistically simulated (Xu and Cheng 2013a, b; Cheng and Xu 2013a, b), in addition to the realistic deep convective clouds. The analysis will provide an insight into the relative role of deep and shallow clouds in the evolution of a composite MJO and their remote connections.

Cheng, A., and K.-M. Xu, 2013a: Diurnal variability of low clouds in the Southeast Pacific simulated by a multiscale modeling framework model. J. Geophys. Res., 118, 9191-9208, DOI: 10.1002/jgrd.50683. Cheng, A., and K.-M. Xu, 2013b: Evaluating low cloud simulation from an upgraded multiscale modeling framework. Part III: Tropical and subtropical cloud transitions over the northern Pacific. J. Climate, 26, 5761-5781. doi: 10.1175/JCLI-D-12-00650.1. Xu, K.-M., and A. Cheng, 2013a: Evaluating low cloud simulation from an upgraded multiscale modeling framework. Part I: Sensitivity to spatial resolution and climatology. J. Climate, 26, 5717-5740. doi:10.1175/JCLI-D-12-00200.1. Xu, K.-M., and A. Cheng, 2013b: Evaluating low cloud simulation from an upgraded multiscale modeling framework. Part II: Seasonal variations over the Eastern Pacific, J. Climate, 26, 5741-5760. doi:10.1175/JCLI-D-12-00276.1.