Western Pacific tropical cyclones over the past 500 years: when a deep-learning climate emulator meets a Chinese handwritten historical record

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Digitized handwritten Chinese historical records REACHES show that tropical cyclone (TC) landfall frequency peaked in 1650-1680 AD over the past 500 years. However, the environmental conditions that lead to this peak remain unknown. This study uses a novel deep-learning climate emulator, ACE2, and a dynamical model, HiRAM, both forced with the last-millennium reconstructed sea surface temperatures and sea ice to uncover the large-scale climate states that drive the long-term variability in Western Pacific TC frequency and track. We find that simulated TC landfall frequency in East Asia also peaks in ACE2 during the 1650-1680 AD period, consistent with REACHES data. Furthermore, the seasonal cycle of Western Pacific TC activity has two peaks during this period, different from a single peak in the current climate, possibly associated with the shift from the East Asian monsoon to the South Asian monsoon. We investigate the large-scale circulation and environmental conditions that drive changes in TC genesis, track, and seasonal cycle over the past 500 years. Our lessons learned have implications for future changes in TC activities in the Western Pacific. Meanwhile, our work proposes a framework to investigate paleoclimate TCs by combining an AI global climate emulator with proxy data.