Numerical study of tidal front with varying sharpness in spring and neap tidal cycle |
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| Authors: | Youn-Jong Sun Atsuhiko Isobe |
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| Institution: | (1) Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga-Koen, Kasuga 816-8580, Japan |
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| Abstract: | The temporal variation of tidal-front sharpness (i.e., the maximal gradient of sea surface temperature (SST)) in Iyo-Nada,
Japan has been investigated using SST obtained by a commercial ferryboat. Tidal-front sharpness varies in time with a period
of 15 days. A numerical model approach was also adopted to investigate the temporal variation of frontal sharpness. The numerical
model, which contains a restoring term to express the tidal front reconstructed fortnightly by tides, reproduces the tidal
front accompanied by growing and/or decaying frontal waves. The amplitude of modeled frontal sharpness agrees well with the
observation. The amplitude of sharpness is much smaller than the observed value, unless frontal waves develop along the modeled
front. This therefore implies that tidal fronts are destroyed mainly due to growing frontal waves, and are restored fortnightly
at spring tides. We quantitatively evaluated the subsurface intrusion of seawater into the stratified region from the mixed
region by conducting passive-tracer experiments. We find that the cross-frontal transport with frontal waves is 4.9 times
larger than that without frontal waves. In addition, the cross-frontal transport reaches a long distance (about 25 km) because
of heton (mushroom)-type eddies developing along the front with frontal waves. |
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| Keywords: | Tidal front sharpness frontal wave cross-frontal transport heton |
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