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Ocean Science An interactive open-access journal of the European Geosciences Union

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Ocean Sci., 12, 733-742, 2016
http://www.ocean-sci.net/12/733/2016/
doi:10.5194/os-12-733-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
27 May 2016
Current temporal asymmetry and the role of tides: Nan-Wan Bay vs. the Gulf of Elat
Yosef Ashkenazy1, Erick Fredj2, Hezi Gildor3, Gwo-Ching Gong4, and Hung-Jen Lee5 1Department of Solar Energy and Environmental Physics, BIDR, Ben-Gurion University, Midreshet Ben-Gurion, 84990, Israel
2The Jerusalem College of Technology, Jerusalem, Israel
3Institute of Earth Sciences, The Hebrew University, Edmond J. Safra Campus, Givat Ram, Jerusalem, 91904, Israel
4Institute of Marine Environment and Ecology, National Taiwan Ocean University, Keelung, Taiwan
5Department of Marine Environmental Informatics, National Taiwan Ocean University, Keelung, Taiwan
Abstract. Nan-Wan Bay in Taiwan and the Gulf of Elat in Israel are two different coastal environments, and as such, their currents are expected to have different statistical properties. While Nan-Wan Bay is shallow, has three open boundaries, and is directly connected to the open ocean, the Gulf of Elat is deep, semi-enclosed, and connected to the Red Sea via the Straits of Tiran. Surface currents have been continuously measured with fine temporal (less than or equal to 1 h) and spatial resolution (less than or equal to 1 km) for more than a year in both environments using coastal radars (CODARs) that cover a domain of roughly 10  ×  10 km. These measurements show that the currents in Nan-Wan Bay are much stronger than those in the Gulf of Elat and that the mean current field in Nan-Wan Bay exhibits cyclonic circulation, which is stronger in the summer; in the Gulf of Elat, the mean current field is directed southward and is also stronger during the summer. We have compared the statistical properties of the current speeds in both environments and found that both exhibit large spatial and seasonal variations in the shape parameter of the Weibull distribution. However, we have found fundamental and significant differences when comparing the temporal asymmetry of the current speed (i.e., the ratio between the time during which the current speed increases and the total time). While the Nan-Wan Bay currents are significantly asymmetric, those of the Gulf of Elat are not. We then extracted the tidal component of the Nan-Wan Bay currents and found that it is strongly asymmetric, while the asymmetry of tidally filtered currents is much weaker. We thus conclude that the temporal asymmetry of the Nan-Wan Bay currents reported here is due to the strong tides in the region. We show that the asymmetry ratio in Nan-Wan Bay varies spatially and seasonally: (i) the currents increase rapidly and decay slowly in the northern part of the domain and vice versa in the southern part, and (ii) the asymmetry is stronger during summer.

Citation: Ashkenazy, Y., Fredj, E., Gildor, H., Gong, G.-C., and Lee, H.-J.: Current temporal asymmetry and the role of tides: Nan-Wan Bay vs. the Gulf of Elat, Ocean Sci., 12, 733-742, doi:10.5194/os-12-733-2016, 2016.
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Short summary
Nan-Wan Bay in Taiwan and the Gulf of Elat in Israel are two different coastal environments, and as such, their currents are expected to have different statistical properties. We find that in spite of these differences, the statistical properties of the surface currents are similar in both basins. Still, surface currents are temporally asymmetric in Nan-Wan but not in Elat; we attribute this difference to the strong tides that exist in Nan-Wan but not in Elat.
Nan-Wan Bay in Taiwan and the Gulf of Elat in Israel are two different coastal environments, and...
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