Why Tropical Cyclones Over Oceanic Cyclonic Eddies Can Be Intensified in Global Basins

ABSTRACT This study investigates the intensification of tropical cyclones (TCs) that encounter oceanic cyclonic eddies (CEs) across global ocean basins from 1993 to 2021. TCs of all intensity levels are likely to intensify when passing over CEs, with more than 33% of them having experienced intensification. These intensification events mainly occur in regions where sea surface temperatures (SSTs) exceed 26°C. This spatial distribution of TC intensity change aligns well with that of SST anomalies (SSTAs) and sea surface height anomalies (SSHAs) observed at the centres of encountered CEs, with the SSTAs and SSHAs gradually decreasing as latitude increases. Composite analyses reveal that the intensification of TCs associated with CEs can be mainly attributed to three favourable oceanic and atmospheric conditions. First, warm SST prevails within CEs. Second, high upper ocean heat content (UOHC) exists within CEs, which can be inferred from the thick upper ocean layer and the uniform upper ocean thermal structure. Third, the environmental vertical wind shear (VWS) surrounding TC centres is weak, while the mid‐troposphere relative humidity (RH) around TC centres is high. Additionally, the small scale of TCs is also conducive to their intensification when encountering CEs. Furthermore, weak TCs are more prone to intensification compared to strong TCs, even when the CEs they encounter exhibit similar central SSTA and SSHA values. Our work provides, for the first time, valuable insights into the relationship between TC intensification and CEs, thereby enhancing our understanding of the role CEs play in influencing TC intensity.