Madden-Julian Oscillation Simulation in E3SM and the Roles of Convective Cloud Microphysics
As a primary source of the global Earth system predictability on subseasonal time scale, Madden-Julian Oscillation (MJO) plays crucial roles in the global water cycle and has profound impacts on global climate and weather extremes. In spite of the progress made in the past, state-of-the-art global climate models (GCMs), including DOE E3SM, still have great difficulty in realistically simulating MJOs. The MJO improvement in GCMs often results in degradations of the mean state and other climate aspects. Most theories for MJO consider moisture-convection feedback to be crucial for the growth and propagation of the MJO. Microphysical processes in convective clouds can greatly affect cloud precipitation efficiency, latent heating, cloud water detrainment, and cloud radiative properties. Therefore, it may play important roles in the MJO occurrence, development, and evolution. However, due to the extreme complexity of microphysics in convective clouds and computational limitations, the representation of microphysical processes in convection is a critical component missing or poorly treated in convection parameterization schemes in GCMs. As a result, the impacts of convective microphysics parameterization (CMP) on the MJO simulation have not been studied. A recent model development effort for E3SM shows that a CMP scheme we developed not only significantly improves simulations of the MJO and convectively coupled Kelvin waves but also moderately improves the climatological mean states, which was not often seen in previous MJO improvement efforts. In this project, we will thoroughly analyze and quantify the impacts of the CMP on all important characteristics of the MJO simulated in E3SM. We will apply a diagnostic tool under the weak temperature gradient (WTG) framework and other state-of-the-art diagnostic tools to the MJO analysis to understand the mechanisms through which the CMP improves the MJO simulation. We will also conduct process-level sensitivity experiments to understand how the CMP influences the MJO simulation at microphysical process level. The process-level metrics for evaluating MJO simulation will be developed. The MJO characteristics and teleconnection are expected to change in future warmer climate. Since E3SM with the CMP can realistically simulate the MJO in the current climate, it can be used to investigate the MJO changes in warming climate with high confidence. We will conduct coupled simulations for the 21 century under the highest shared socioeconomic pathway (SSP) emission scenarios (SSP5-8.5) using E3SM with and without the CMP. The simulated MJO characteristics and teleconnection will be compared to the corresponding AMIP simulations of the current climate to identify the MJO changes in warming climate. The impacts of the CMP on the MJO changes in future climate will be investigated. Diagnostic analysis will be conducted to understand the key processes that modulate the MJO in warming climate.
This project will improve the scientific understanding of the impacts and mechanism of CMP influencing the MJO in E3SM. The in-depth understanding of influencing mechanisms will provide tangible guidance for improving the MJO simulation and reducing the uncertainty in the projection of the MJO changes in warming climate. The knowledge gained from this work will also be of benefit to the boarder set of GCMs in which the convective microphysics is represented very crudely. In addition, the project will provide training for a postdoctoral researcher, thus promoting the development of next generation climate science researchers.