Madden-Julian Oscillation, Tropical Cyclones, and Precipitation Extremes in E3SM
Despite recent improvements, many earth system models (ESMs) still show strong biases in the representation of the Madden-Julian oscillation (MJO), tropical cyclones (TC), and mid-latitude precipitation extreme events. These biases limit the reliability of model predictions and projections for informing societally-relevant decisions.
We propose a project focused on the diagnosis of process-level errors in the model representation of the MJO, TCs, and precipitation extremes, especially in our primary ESM: DOE’s Energy Exascale Earth System Model (E3SM). Strong connections among the MJO, TCs, and precipitation extremes motivate the needs to understand these processes and errors in their representations synergistically. Our proposed work involves analyzing ESM simulations together with observations and using E3SM v1 as a tool to understand model biases and the Earth system, which will be made possible by combining our expertise in process-based diagnosis and in Earth system modeling.
First, we will analyze key processes associated with MJO propagation and maintenance, TC genesis and intensification, and frequency and location of mid-latitude precipitation extremes in the ESMs. We will also examine the multiscale connections among our target phenomena, including the modulation of TC genesis by the MJO, and the association of precipitation events in the US with the MJO and TCs. Our evaluation of E3SM and the other CMIP6 models against observations using the process-based diagnostics will identify process-level biases in the model simulations.
Second, we will carry out a focused parameter sensitivity study with the E3SM Atmosphere Model (EAM) to quantify uncertainties in the model representing the MJO, TCs and precipitation extremes. Perturbed parameter ensemble simulations will be performed with both low- and high-resolution versions of EAM by varying key parameters in the model physics and the simulations will be thoroughly analyzed using our diagnostics to reveal the connections between the key parameters and model performance at the process level.
Lastly, we will use E3SM v1 to perform a series of numerical experiments to address unresolved science questions about the MJO’s propagation and Atlantic TC activity. The diurnal cycle of convection in the Maritime Continent islands will be perturbed in multiple ways to investigate its role on the propagation of the MJO. The role of air-sea coupling and the African easterly waves on the Atlantic TC activity (e.g., number, tracks, and intensity) will be examined by disabling air-sea coupling and weakening the activity of African easterly waves, respectively.
Our proposed work will provide a deeper process-level understanding of the phenomena and identify the source of ESM biases in the MJO, TCs, and extreme precipitation simulations and provide paths toward the model improvement at the same time. This advancement in our understanding of MJO, TC, and extreme precipitation simulations will be extremely valuable for improving the next generation of ESMs, which is vital for making robust projections of future activity of the phenomena and their impacts.