Abstract
We investigated ocean surface and subsurface physical responses to Typhoons Kalmaegi and Sarika in the South China Sea, utilizing synergistic multiple-satellite observations, in situ measurements, and numerical simulations. We found significant typhoon-induced sea surface cooling using satellite sea surface temperature (SST) observations and numerical model simulations. This cooling was mainly caused by vertical mixing and upwelling. The maximum amplitudes were 6 °C and 4.2 °C for Typhoons Kalmaegi and Sarika, respectively. For Typhoon Sarika, Argo temperature profile measurements showed that temperature response beneath the surface showed a three-layer vertical structure (decreasing-increasing-decreasing). Satellite salinity observations showed that the maximum increase of sea surface salinity (SSS) was 2.2 psu on the right side of Typhoon Sarika’s track, and the maximum decrease of SSS was 1.4 psu on the left. This SSS seesaw response phenomenon is related to the asymmetrical rainfall on both sides of the typhoon track. Acoustic Doppler Current Profilers measurements and numerical simulations both showed that subsurface current velocities rapidly increased as the typhoon passed, with peak increases of up to 1.19 m/s and 1.49 m/s. Typhoon-generated SST cooling and current velocity increases both exhibited a rightward bias associated with a coupling between typhoon wind-stress and mixed layer velocity.
Highlights
Global warming has given rise to increased intensity of tropical cyclones in the northwest Pacific Ocean [1,2,3]
Observed TC tracks and coupled ocean-atmosphere hurricane models were used to estimate the net ocean heating induced by global tropical cyclone activity, suggesting that TCs may play an important role in driving the thermohaline circulation [9]
We focused on the upper ocean response to typhoons from 0 to 100 m, mooring-measured ddaattaasseettsswweerreennoottuusseedd..SSttaattiioonnss11aanndd44wweerreellooccaatteedd oonn tthhee rriigghhtt ooff tthhee ttrraacckk ooff TTyypphhoooonnKKaallmmaaeeggii, wwhheerreeaassSStatatitoionn22wwasasononthtehelelfet.ftA
Summary
Global warming has given rise to increased intensity of tropical cyclones in the northwest Pacific Ocean [1,2,3]. Instruments on an underwater glider observed changes in upper ocean salinity before, during, and after the passage of Hurricane Gonzalo, showing that wind-forced mixing caused a 0.6 psu salinity increase at depths above 20 m and a 0.4 psu salinity decrease between 20 m and 130 m deep [21]. Both three-dimensional numerical simulations and in situ observations have revealed that salinity anomalies generally show a three-layer vertical structure, with the surface layer becoming cooler and saltier, the subsurface layer becoming warmer and fresher, and the lower layer becoming cooler and saltier again [22].
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