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Observed upper ocean response to typhoon Megi (2010) in the Northern South China Sea

Guan, Shoude; Zhao, Wei; Huthnance, John; Tian, Jiwei; Wang, Jinhu. 2014 Observed upper ocean response to typhoon Megi (2010) in the Northern South China Sea. Journal of Geophysical Research: Oceans, 119 (5). 3134-3157. 10.1002/2013JC009661

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Abstract/Summary

Typhoon Megi passed between two subsurface moorings in the northern South China Sea in October 2010 and the upper ocean thermal and dynamical response with strong internal tides present was examined in detail. The entire observed water column (60–360 m) was cooled due to strong Ekman-pumped upwelling (up to 50 m in the thermocline) by Megi, with maximum cooling of 4.2°C occurring in thermocline. A relatively weak (maximum amplitude of 0.4 m s−1) and quickly damped (e-folding time scale of 2 inertial periods) near-inertial oscillation (NIO) was observed in the mixed layer. Power spectrum and wavelet analyses both indicated an energy peak appearing at exactly the sum frequency fD1 (with maximum amplitude up to 0.2 m s−1) of NIO (f) and diurnal tide (D1), indicating enhanced nonlinear wave-wave interaction between f and D1 during and after typhoon. Numerical experiments suggested that energy transfer from NIO to fD1 via nonlinear interaction between f and D1 may have limited the growth and accelerated the damping of mixed layer NIO generated by Megi. The occurrence of fD1 had a high correlation with NIO; the vertical nonlinear momentum term, associated with the vertical shear of NIO and vertical velocity of D1 or vertical shear of D1 and vertical velocity of NIO, was more than 10 times larger than the horizontal terms and was responsible for forcing fD1. After Megi, surface-layer diurnal energy was enhanced by up to 100%, attributed to the combined effect of the increased surface-layer stratification and additional Megi-forced diurnal current.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1002/2013JC009661
ISSN: 21699275
Additional Keywords: typhoon; near-inertial oscillation; nonlinear wave-wave interaction; diurnal internal tides; stratification
Date made live: 02 Jun 2014 10:43 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/507340

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