Modulation Effect of Mesoscale Eddies on Sequential Typhoon-Induced Oceanic Responses in the South China Sea

Abstract

The impacts of mesoscale eddies on the modulation of typhoon-induced oceanic responses are important for understanding ocean dynamics. Satellite observations identified prominent ocean surface temperature and chlorophyll changes over the regions with mesoscale eddies after two sequential typhoons, e.g., Linfa and Nangka, in the South China Sea. The impacts of typhoons on the ocean surface were more prominent within cyclonic eddies than within anticyclonic eddies. The wind speed (translation speed) of Linfa was much larger (slower) than that of Nangka; thus, the changes induced by Linfa were stronger. However, the second typhoon easily generated mixing through the weak stratification induced by the first typhoon and impacted the upper ocean. The strong chlorophyll enhancement induced by Nangka was identified at a cyclonic eddy. Using a combination of reanalysis data, the depth of water origin (DWO) was applied to quantify the depth to which a typhoon’s impact could be exerted. Prominent changes were identified when the DWO reached the depth at which the temperature and nutrients differed from those within the mixed layer. This method can overcome the impacts of cloud coverage when examining a typhoon’s influence with remotely sensed data and offers a quantitative approach to determine the mechanisms responsible for typhoon-induced ocean surface changes.

Upper ocean response to tropical cyclones: a review

“…The latent and sensible heat transfer coefficients are constant at low wind speeds and increase sharply when wind speed at the height of 10 m is greater than 35 m/s (Komori et al 2018). The air-sea gas transfer also increased significantly due to the surface wave breaking (Iwano et al 2013;Krall and Jähne 2014;Liang et al 2020).…”

“…For example, weak and slowmoving TCs induce phytoplankton blooms with higher chlorophyll-a concentrations, while strong and fastmoving TCs induce blooms over a larger area . A pre-existing cold core eddy plays an important role in the increase in chlorophyll-a concentration by TCs (Chen and Tang 2012;Shang et al 2015;Xu et al 2017a;Jin et al 2020), and the concentration of pre-existing chlorophyll-a in cold core eddies is approximately 25-45% (8-25%) of that of the post-existing chlorophylla in cold core eddies for relatively high (low) TC transition speeds (Shang et al 2015). The biological response in coastal regions is more complicated than that in the open ocean (Pan et al 2017).…”

The Response and Feedback of Ocean Mesoscale Eddies to Four Sequential Typhoons in 2014 Based on Multiple Satellite Observations and Argo Floats

“…If sequential typhoons occurred, even the intensity of the subsequent typhoon was weak, and the moving speed was high; the weak stratification caused by the first typhoon could be mixed, thus causing the ocean responses. However, we noted that the subsequent typhoon Nangka in the study of Jin et al [68] was a category 3 typhoon. If the subsequent typhoon was a weaker typhoon (or even a tropical cyclone) or a super typhoon, what would the differences and relationships between the ocean response and ocean feedback in the CE and AE be?…”

“…We focused on the comparison of interactions between the FTC ocean environment and different subsequent typhoons. Compared with the subsequent typhoons in previous studies, e.g., the category 5 typhoon, Nangka (2015), in Wu et al [26]; the category 5 typhoon, Haima (2016), in Zhang et al [27]; and the category 3 typhoon, Nangka (2009), in Jin et al [68], the category 2 typhoons, Matmo (2014) and TC Nakri (2014), in our study were much weaker and also caused a secondary SST cooling of approximately −2 • C in the FTC ocean. Furthermore, the category 5 subsequent typhoon Halong caused a maximum SST cooling of over −8 • C in the FTC ocean, which was more severe than that caused by the category 5 typhoons Nangka (2015) and Haima (2016) in Wu et al [26] and Zhang et al [27], respectively.…”

“…Yang et al [25] and Wu et al [26] mainly showed the responses in the CEs, and the research results of Zhang et al [27] were mainly based on observations of Station 2 located in an AE. Jin et al [68] studied the modulation effect of mesoscale eddies on the oceanic responses to sequential typhoons Linfa and Nangka in 2009. The results showed that cyclonic eddies enhanced SST cooling and chlorophyll enhancement, while anti-cyclonic eddies prevented the ocean response.…”