Recovery of Tropical Cyclone Induced SST Cooling Observed by Satellite in the Northwestern Pacific Ocean

Abstract

Based on the satellite observed sea surface temperature (SST), the recovery of SST cooling induced by the tropical cyclones (TCs) over the northwestern Pacific Ocean is investigated. The results show that the passage of a TC induces a mean maximum cooling in the SST of roughly −1.25 °C. It was also found that most of this cooling (~87%) is typically erased within 30 days of TC passage. This recovery time depends upon the degree of cooling, with stronger (weaker) SST cooling corresponding to longer (shorter) recovery time. Further analyses show that the mixed layer depth (MLD) and the upper layer thermocline temperature gradient (UTTG) also play an important role in the SST response to TCs. The maximum cooling increases ~0.1 °C for every 7 m decrease in the MLD or every 0.04 °C/m increase in the UTTG. The combined effects of MLD and TC intensity and translation speed on the SST response are also discussed.

Seasonal differences in tropical cyclone—induced sea surface cooling in the western North Pacific

“…MLD plays a crucial role in TC‐induced SST cooling (Ling et al, 2021). Large TC‐induced SST cooling is observed in the regions with shallower MLD than in regions with deeper MLD (Mei et al, 2015).…”

“…On average, the SST felt by a TC when it encounters a previously induced cold wake is 0.25°C lower than the SST when there is no previously TC‐induced cold wake (Balaguru et al, 2014). Additionally, Ling et al (2021) demonstrated that weaker cold wakes result in a faster recovery of the SST to its pre‐TC state. Our analysis shows that TC‐induced SST cooling is less in autumn than in summer; therefore, during autumn, this reduced SST cooling will result in a reduced negative feedback of cold wakes by the previous TC on the next TC.…”

“…Days on which TCs made landfall and their centers are above land are excluded. To determine a TC's impact on SST, the initial SST anomalies averaged from Day −5 to Day −3 are subtracted from the SST anomalies from Day −2 to Day +20 (Ling et al, 2021; Sriver & Huber, 2007).…”

“…The western North Pacific (WNP) is the most active TC basin, accounting for 30% of global annual TC genesis (Singh & Roxy, 2022). Over the past few decades, numerous studies have been conducted to understand TC‐induced SST cooling in the WNP basin, including the South China Sea (Chu et al, 2000; Guan et al, 2021; Kuo et al, 2011; Lin, 2012; Lin et al, 2003; Ling et al, 2021; Shang et al, 2008). Price (1981) was among the first to study TC‐induced SST cooling and found that SST cooling has a rightward bias along the TC track due to the asymmetrical response of the ocean's inertial currents.…”