773 / 2024-09-19 12:11:39

Storm Size Modulates Tropical Cyclone Intensification Through an Oceanic Pathway in Global Oceans

storm size; sea surface cooling; tropical cyclone intensification; negative feedback; TC-active oceans

Session 6 - Tropical Cyclone-Ocean Interactions: From Weather to Climate Scales

Typical tropical cyclone (TC) attributes, including translation speed and intensity, have been demonstrated to affect TC intensification via modulating sea surface temperature (SST) cooling effect underneath TCs, while the effect of storm size is relatively less explored. Using satellite-observed SST during 2004–2021, we examine the effect of storm size on TC-induced SST anomalies (SSTA) and TC intensification in global TC-active oceans (including the western north Pacific, eastern north Pacific, north Atlantic, southern Indian Ocean, and southern Pacific), and compare their inter-basin differences. In all basins, SSTA has the strongest correlation with 34-kt wind radius (R34), which is thus utilized as the representative storm size among various TC wind radii. Generally, large TCs generate stronger and more widespread SSTA than small TCs. Despite the same effect on prolonging residence time of TC winds, the effect of doubling R34 on SSTA is more profound than halving translation speed, due to more wind energy input into the upper ocean. This study further demonstrates that storm size regulates TC intensification through an oceanic pathway: large TCs induce stronger and more widespread SSTA, which reduces ocean’s enthalpy flux supply and thus suppresses TC intensification, as compared to small TCs (e.g., for Category 1-2 TCs in the western north Pacific, R34: 322 vs. 133 km; SSTA: -1.9 vs. -0.7 ℃; enthalpy flux: 686 vs. 420 W m^-2; TC intensification rate: 8.6 vs. -3.0 m s^-1 per 24-h). This modulating effect emerges in each basin, suggesting a globally consistent effect of storm size on TC intensification through an oceanic pathway. Small TCs, occupying weaker SST cooling and larger enthalpy flux, are more likely to undergo rapid intensification, with the probability of 1.1–1.8 times larger than large TCs in global TC-active oceans. Storm size varies greatly across global basins, and thus its effect on TC intensification through this oceanic pathway exhibits considerable inter-basin differences. The inter-basin difference in storm size partly contributes to the inter-basin difference in SSTA under same TC intensity. Our results suggest that accurately representing storm size in TC coupled models, can potentially improve cooling estimation and TC intensity prediction.