Seasonal Cycle Delay of the Western North Pacific Tropical Cyclone Genesis Frequency in CMIP6 Simulations

• Published in: Geophysical research letters 2024-06, Vol.51 (12), p.n/a
• Main Authors: Peng, Yi, Guo, Yi‐Peng
• Format: Article
• Language: English
• Subjects: Autumn; Bias; Climate; Climate models; CMIP6; Cooling; Cyclones; Delay; genesis; Hurricanes; Intercomparison; Monsoon trough; Monsoons; Seasonal variation; Simulation; Summer; Surface temperature; Temperature rise; Thermal winds; tropical cyclone; Tropical cyclones; Winds
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL109150

Obvious biases in simulating tropical cyclone (TC) genesis of the current climate models hamper our understanding of TC changes. In this study, we found a delay of the seasonal cycle of TC genesis frequency over the western North Pacific (WNP) in most Coupled Model Intercomparison Project Phase 6 models. During the active TC season, the simulated south‐warming and north‐cooling surface temperature bias amplifies the meridional gradient and excites thermal winds. This weakens the western North Pacific Subtropical High and easterly monsoon trough, which further reduces TC genesis frequency over the western WNP in summer. But in autumn, positive TC genesis biases were only observed in coupled models over the eastern WNP. Both seasons contribute to the delayed seasonal cycle of TC frequency in models. Our findings highlight the importance of accurate simulation of surface temperature by climate models to TC simulations and aid in future model improvements. Plain Language Summary Tropical cyclone (TC) is a devastating weather system generated over the tropical ocean, and the climate model serves as an important tool to study the long‐term variability of TC activity. Hence, it is imperative to explore the biases of climate models in simulating TC genesis. In this investigation, we find a substantial influence of surface temperature bias in Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models on the simulation of the seasonal cycle of TC genesis frequency over the western North Pacific (WNP). The delay in the seasonal cycle of TC genesis frequency is widespread among most CMIP6 models. During boreal summer and autumn, the simulated bias of south‐warming and north‐cooling surface temperature increases its meridional gradient and triggers thermal winds. In summer, the weak western North Pacific Subtropical High and easterly monsoon trough, two crucial large‐scale circulation systems, cause a large negative TC genesis bias in models over the western WNP, substantially contributing to the delay of the seasonal cycle. Meanwhile, the relatively small positive bias of coupled models over the eastern WNP in autumn makes a secondary contribution. The combined contributions of these biases cause delays in seasonal simulation of TC genesis frequency. Key Points Coupled Model Intercomparison Project Phase 6 models produce delayed seasonal cycles of tropical cyclone genesis frequency over the western North Pacific Biases in East Asia summer monsoon and western