PNNL

The Science

Proper infrastructure planning requires accurately predicting how tropical cyclones respond to environmental changes. Making those predictions is challenging because Earth system models are generally run at low resolution and poorly simulate storm behavior. Analysis of tropical cyclones simulated by the Department of Energy’s Energy Exascale Earth System Model (E3SM) at low and high resolutions was performed to gain an understanding of how well they simulate storm characteristics such as frequency and intensity. The high-resolution configuration was found to be significantly better at simulating tropical cyclones and their interactions with the ocean below, underscoring the value of increasing model resolution. Further, at all resolutions, systematic coupled model biases introduced errors in simulating storm activity, notably in the subtropics, motivating the need for future improvements. 

The Impact

This study demonstrates that the high-resolution version of E3SM is a valuable tool for tropical cyclone-related research as it well represents characteristics relevant to predicting hurricane impacts such as storm surge and flooding. The model is particularly useful for studies focusing on global tropical cyclone climatology and the role of air-sea coupling in these storms. In addition, the results suggest that reducing coupled model sea surface temperature biases could improve tropical cyclone simulation by reducing the spurious and unrealistic tropical cyclone activity produced in the model. 

Summary

Researchers analyzed of version 1 of the E3SM model at both low/standard (1o atmosphere) and high resolution (0.25o atmosphere). Compared to the low-resolution simulation, the salient tropical cyclone features, such as the seasonal cycle, global frequency, lifetime maximum intensity, and distribution among different basins, are improved noticeably in the high-resolution model. However, the model produces spurious activity in the subtropical southeast Pacific and the south Atlantic at both resolutions. An investigation of the large-scale tropical cyclone environment reveals that this spurious activity is likely the result of errors in the thermodynamic potential intensity caused by inaccuracies in sea surface temperature modeling. An examination of tropical cyclone-ocean interactions suggests that the model can resolve both the upper-ocean response to these storms and the ocean’s feedback to the storms realistically. Finally, the researchers found that the influence of the El Niño-Southern Oscillation on tropical cyclones in the model has the correct sign but is weak relative to observations. 

PNNL Contact

L. Ruby Leung, Pacific Northwest National Laboratory, Ruby.Leung@pnnl.gov

Funding

This work was sponsored by the Energy Exascale Earth System Model project, funded by the U.S. Department of Energy, Office of Science, Biological and Environmental Research (BER) program. This work was also supported by BER’s Regional and Global Modeling and Analysis Program.