Zhenxin Ruan ¹ Bo Li ^1* Chengcheng Yu ¹ Ruibin Ding ² Peng Bai ¹ Qiong Wu ¹

• ¹ Zhejiang Ocean University, Zhoushan, China
• ² Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, Zhejiang Province, China

We use daily sea surface temperature (SST) data and hourly drifter data to investigate ocean responses to tropical cyclone (TC) intensity and outer size (wind radius of 34 kt, or R34) in the Northwest Pacific. Results show that SST cooling is more sensitive to TC R34 than to TC intensity, namely TCs with larger R34 cause stronger SST cooling regardless of their intensity. TCs with R34 ≥125 nmi can cool SST 0.9℃ more than TCs with R34 <125 nmi. Drifter data indicate that TC generate large current with near-inertial periods. The filtered near-inertial currents were used to calculate the time series of nearinertial kinetic energy 𝐸 ! , and found that TCs with larger R34 will trigger stronger 𝐸 ! . Further analysis reveals that the nondimensional storm speed 𝑆, which is defined as the ratio of the local near-inertial period to the residence time of TC, is correlated closely with the amplitude of SST cooling when R34 is used to quantify the scale of TC. Most TCs have residence time smaller than the local near-inertial period, and therefore TCs with large R34 have longer residence times and closer to the local nearinertial period, which is favorable for stronger SST and current responses. This impact of TC outer size on surface ocean response implies the critical role of TC outer size in ocean processes under TC background.