How does tropical cyclone genesis frequency respond to a changing climate?

Global tropical cyclone (TC) genesis frequency (TCGF) has been documented to decrease or increase linearly in a changing climate. However, our numerical experiments show that the global TCGF exhibits a parabolic relation withspatio-uniform climate changes in sea surface temperature (SST) from -15K to 5K relative to the present climate, with the peak in the 5K-cooler climate. The parabolic relation is found in all TC basins except the eastern North Pacific where TCGF keeps increasing with the changing climate. TCGF can be expressed as the product of the frequency of TC seeds and the TC survival rate. Further analysis shows that this parabolic structure in the global TCGF depends on TC seeds rather than the TC survival rate. The TC survival rate exhibits an increasing trend with the SST increase, while TC seeds show a consistent change with TCGF, which might be linked to the changes in low-level relative humidity.已有研究表明，在气候变化背景下，全球热带气旋（TC）生成频数（TCGF）呈现线性增加或线性减少的变化态势。然而本研究的数值试验结果显示，在相对于当前气候的海表温度（SST）变化范围为-15K至5K的空间均匀气候变化情境下，全球TCGF呈现抛物线型变化关系，且其峰值出现在较当前气候偏冷5K的情境中。该抛物线型变化关系在所有热带气旋活动洋盆中均成立，但东北太平洋洋盆除外——该区域的TCGF随气候变化持续呈增加趋势。TCGF可表示为热带气旋种子频数与热带气旋存活率的乘积。进一步分析表明，全球TCGF的抛物线型变化特征主要由热带气旋种子的变化主导，而非热带气旋存活率。热带气旋存活率随SST升高呈持续增加趋势，而热带气旋种子的变化则与TCGF的变化保持一致，这一现象可能与低层相对湿度的变化有关。