25 km High-resolution Climate System Model Reproduces Tropical Cyclone Activities Better


Tropical cyclones (TC) have a serious impact on economy and social life and thus has drawn considerable public concern. According to The Atlas of Mortality and Economic Losses from Weather, Climate and Water Extremes (1970–2019) published by the World Meteorological Organization (WMO) September 2021, in the past 50 years, three of the top ten global disasters were caused by TC, and seven of the top ten disasters with most economic losses were also caused by TC.

TC has become more intense and frequent under the background of global warming, the simulation and prediction of TC has become particularly important and is an international frontier hotspot. However, due to the huge biases of simulated TC in the global climate model, there are still huge challenges in accurately simulating and predicting TC activities.
The modeling team at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) of the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS) developed a new generation global climate system model of LASG named CAS FGOALS-f3-H. Their recent study published in Geoscientific Model Development shows that this 25 km high-resolution climate system model can simulate the global TC activities in finer ways as compared to that at low resolution, capturing and reproducing more realistic features of TC activities.
Researchers assessed the TC performance simulated by CAS FGOALS-f3-H. Based on the FGOALS-f3 simulation in the medium resolution (CAS FGOALS-f3-L, the horizontal resolution is about 100 km) and the high resolution (CAS FGOALS-f3-H, the average horizontal resolution is about 25 km), they quantitatively evaluated the impact of the horizontal resolution of the FGOALS-f3 on the TC simulation capabilities and analyzed the possible causes of the horizontal resolution on the TC simulation capabilities. 
"We found that FGOALS-f3 can resolve TC activities in both high- and low-resolution conditions, and has outstanding performance in terms of the number, generating positions, tracks, and life cycles of global TCs." Introduced Dr. LI Jinxiao, the first author of the paper. As the horizontal resolution of the FGOALS-f3 increases, the negative biases of the simulation TC are significantly reduced. Besides, the TC horizontal structure becomes clear when the horizontal resolution was increased from 100 km to 25 km. Furthermore, the multi-model analysis in the High Resolution Model Intercomparison Project (HighResMIP) of WCRP Coupled Model Intercomparison Project phase 6 (CMIP6) finds the fidelity of TC genesis potential index (GPI) significantly improves when the models’ horizontal resolution increases. Further analyses revealed the possible physical linkage between the performance of the tropical cyclone simulation and the horizontal resolution.
Besides, the study also investigated the possible reasons for the improvement of TC simulation performance resulting from the refinement of model resolution from multiple angles, referring to the El Nino–Southern Oscillation and large-scale circulation. "By comparison, the FGOALS-f3-H shows excellent performance in depicting the global tropical cyclone activities. "We intend to establish a high-resolution coupled dynamic prediction system based on FGOALS-f3-H to improve the prediction skill of tropical cyclones on subseasonal to seasonal (S2S) scales." added Prof. BAO Qing, the corresponding author of the paper.
The research was funded by the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB40030205) and the National Natural Science Foundation of China (grant no. 42005117). 
Li, J., Bao, Q*., Liu, Y., Wang, L., Yang, J., Wu, G., Wu, X., He, B., Wang, X., Zhang, X., Yang, Y., and Shen, Z.: Effect of horizontal resolution on the simulation of tropical cyclones in the Chinese Academy of Sciences FGOALS-f3 climate system model, Geosci. Model Dev., 14, 6113–6133, https://doi.org/10.5194/gmd-14-6113-2021, 2021.
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