Vertical structure and physical processes of the Madden‐Julian oscillation: Linking hindcast fidelity to simulated diabatic heating and moistening

Abstract

Many theories for the Madden‐Julian oscillation (MJO) focus on diabatic processes, particularly the evolution of vertical heating and moistening. Poor MJO performance in weather and climate models is often blamed on biases in these processes and their interactions with the large‐scale circulation. We introduce one of the three components of a model evaluation project, which aims to connect MJO fidelity in models to their representations of several physical processes, focusing on diabatic heating and moistening. This component consists of 20 day hindcasts, initialized daily during two MJO events in winter 2009–2010. The 13 models exhibit a range of skill: several have accurate forecasts to 20 days lead, while others perform similarly to statistical models (8–11 days). Models that maintain the observed MJO amplitude accurately predict propagation, but not vice versa. We find no link between hindcast fidelity and the precipitation‐moisture relationship, in contrast to other recent studies. There is also no relationship between models' performance and the evolution of their diabatic heating profiles with rain rate. A more robust association emerges between models' fidelity and net moistening: the highest‐skill models show a clear transition from low‐level moistening for light rainfall to midlevel moistening at moderate rainfall and upper level moistening for heavy rainfall. The midlevel moistening, arising from both dynamics and physics, may be most important. Accurately representing many processes may be necessary but not sufficient for capturing the MJO, which suggests that models fail to predict the MJO for a broad range of reasons and limits the possibility of finding a panacea.

Validity of parameter optimization in improving MJO simulation and prediction using the sub-seasonal to seasonal forecast model of Beijing Climate Center

“…For the model used in this study, higher fidelity of MJO is accompanied by a better mean state in the model, and is also associated with overall better performance in MJO forecast. However, our results also indicate that improvement of MJO simulation does not necessarily translate into enhancement of MJO forecast skill at any time, which agrees with the finding that there are weak relationships between MJO fidelity in 2-day hindcasts and 20-day hindcasts (Klingaman et al 2015b). The irregular correspondence between simulation and forecast may be attributed to the complex and modeldependent interaction between model error and initial condition error; thus, improvement of forecast should rely more on describing the uncertainty of these two errors, rather than on only decreasing the magnitude of the errors.…”

Resolution dependence of precipitation statistical fidelity in hindcast simulations

“…This design choice makes the framework ideal for rapid testing of new parameterizations using a variety of metrics. The CAPT‐like use of hindcasts allows the myriad evaluation techniques employed in the CAPT and transpose‐AMIP communities for diagnosing rapid‐onset biases due to errors in fast physical processes [ Phillips et al ., ; Williamson and Olson , ; Waliser et al ., ; Williams et al ., ; Wan et al ., ; Klingaman et al ., ; Ma et al ., ]. The multiresolution experimental protocol allows for direct assessment of the degree to which new parameterizations are scale‐aware: e.g., using the scale‐aware cloud metric described by O'Brien et al [] and the precipitation fidelity and statistics metrics described here.…”

A Systematic Relationship between the Representations of Convectively Coupled Equatorial Wave Activity and the Madden–Julian Oscillation in Climate Model Simulations

“…This MJO model intercomparison project consists of three experimental components, including (i) a 20-yr climate simulation, (ii) a 20-day hindcast, and (iii) a 2-day hindcast component. Comprehensive results based on each component are being first reported in three research papers, respectively (Jiang et al 2015;Xavier et al 2015;Klingaman et al 2015).…”