Journal of Tropical Oceanography ›› 2017, Vol. 36 ›› Issue (1): 15-24.doi: 10.11978/2016045CSTR: 32234.14.2016045

• Orginal Article • Previous Articles     Next Articles

Mixed layer depth responses to tropical cyclones Kalmaegi and Fung-Wong in the northeastern South China Sea

Yongjun SONG1,2(), Danling TANG1,2()   

  1. 1. Research Center for Remote Sensing of Marine Ecology & Environment, State Key Laboratory of Tropical Oceanography (South China Sea Institute of Oceanology, Chinese Academy of Sciences), Guangzhou 510301, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2016-05-04 Revised:2016-05-31 Online:2017-01-18 Published:2017-01-19
  • Supported by:
    Key Project of National Natural Sciences Foundation of China (41430968);Major Program of Collaborative Innovation Center for 21st-Century Maritime Silk Road Studies (2015HS05)

Abstract:

Utilizing the vertical profiles of temperature and salinity data obtained by Argo floats and multi-source satellite remote sensing data, including sea surface temperature (SST) and sea surface wind fields, combined with the National Centers for Environmental Prediction (NCEP) Ⅱ reanalysis data, we analyzed changes of mixed layer depth (MLD) in the northeastern South China Sea (SCS) in responses to tropical cyclones Kalmaegi (typhoon) and Fung-Wong (tropical storm), which passed the SCS in succession in mid and late September 2014. The results indicate that the maximum net heat flux (upward into the air) increased from 170 to 400 W·m-2 at the air-sea interface, caused the maximum SST cooling of 3℃ by the “wind pump” effect after Kalmaegi and Fung-Wong passed through. The “cold wake” induced by Kalmaegi lasted for more than 10 days thanks to the following tropical storm Fung-Wong, indicating the effect of superposition in SST cooling. MLD was deepened from 23 to 50 m in the “cold wake” one day after Kalmaegi passed by. MLD was deepened from 31 to 91 m eight hours after Fung-Wong passed by, due to the coastal upwelling induced by offshore Ekman transport driven by wind stress at the southwestern of Taiwan Island. After the tropical cyclones passed by, salinity profile in the mixed layer showed uniformity later than temperature profile, and recovered earlier than temperature profile, revealing the time lag in mixed layer responses. For the spatial variation response to the two tropical cyclones, the changes of SST and MLD were larger on the right-hand side of the tropical cyclones (along the moving directions of tropical cyclones) than on the left-hand side. The uneven deepening even shallowing in MLD in the cold wake may reveal that different depths of deep cold water uplifted by the vertical current switch between upwelling and downwelling in the Ekman layer due to the change of Ekman pumping velocity.

Key words: mixed layer, tropical cyclone, SST, wind stress, marine remote sensing