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Ocean eddies, fronts, and air-sea exchanges: Observations and high resolution simulations
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High-resolution cross-frontal observations in the Taiwan Strait
P-P4-06-S
Zhu Wenjun* , Xiamen University, China
Lin Hongyang, Xiamen University, China
Liu Zhiyu, Xiamen University, China
Hu Jianyu, Xiamen University, China
Presenter Email: wjzhu@stu.xmu.edu.cn |
| Fronts are a prominent feature in the Taiwan Strait. In cold seasons (winter and spring), a sea surface temperature (SST) front is formed as the southward-flowing, cold and fresh China Coastal Current interfaces with the northward-flowing, warm and saline South China Sea Warm Current extension. The hydrography and dynamic processes in this frontal region are explored based on high-resolution in situ measurements (with horizontal resolution of 1~4 km) from two spring cruises (May 2017 and April 2018) and the MODIS satellite SST data. The main results are summarized as follows. Both the satellite SST and in situ salinity data indicate that the China Coastal Current reaches around 25°N in late spring where it sets the southern boundary for this along-strait front. Comparisons of the satellite and in situ data suggest that the MODIS SST data, although sometimes underestimate the observed frontal intensity, are generally able to capture the location of the front. Temperature and salinity gradients appear to have compensating effects on density gradients at both sides of the frontal region, whereas density gradients in the frontal region are strengthened by both temperature and salinity variations. The observed turbulent kinetic energy dissipation rate indicates enhanced turbulence in the surface and bottom boundary layers, but the calculated Richardson number (Ri) tends to suggest that flows were prone to shear instability (Ri < 0.25) east of the front. A comparison of the observed horizontal density gradient and the vertical shear of the horizontal velocity suggests that the thermal wind relation does not hold for the observed flow. Ekman dynamics seemed to be the dominant process in this shallow coastal region, where the surface and the bottom Ekman layers were likely overlapped. |
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