Xingru Feng

Numerical study of the ocean circulation on the East China Sea shelf and a Kuroshio bottom branch northeast of Taiwan in summer

Using the Regional Ocean Model System, the ocean circulation on the East China Sea (ECS) shelf was examined by a fine-resolution model which was nested in a coarse-resolution Pacific Ocean model. The high-resolution simulation shows an accurate volume transport of 2.70 Sv (Sv = 10(6) m(3)s(-1)) through the Tsushima Strait, which is more consistent with the previous 5.5 year observation value (2.64 Sv) than former model results. For the Taiwan Strait it also shows a close volume transport (1.03 Sv) to a recent estimate (1.20 Sv). At the same time the model results reproduced almost all of the known circulation structure on the ECS shelf. In addition, the hindcast of 2009 shows a Kuroshio Bottom Branch Current to the northeast of Taiwan (KBBCNT). The KBBCNT is confirmed by the observational bottom high-salinity water (from 15 August to 2 September 2009) whose distribution is also reproduced by the model results. Tracer and particle experiments were carried out to elucidate the formation of the high-salinity water and the pathway of the KBBCNT. In light of the field observation and numerical experiments, a new pathway of the KBBCNT is proposed: bifurcated from the subsurface water of Kuroshio northeast of Taiwan, it upwells northwestward gradually from 300 to 60 m, then turns to northeast in the region around 27.5 degrees N, 122 degrees E, and finally reaches 31 degrees N off the mouth of the Changjiang River along similar to 60 m isobaths, forming the bottom saline water off the coast of Zhejiang province, China.

Topographic Beta Spiral and Onshore Intrusion of the Kuroshio Current

This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11020104 and XDA110203052), the National Natural Science Foundation of China (NSFC) (41576023, 41376030, and 41476019), the Foundation for Innovative Research Groups of NSFC (41421005), NSFC-Shandong Joint Fund for Marine Science Research Centers (U1406401), Aoshan Sci-Tec Innovative Project of Qingdao National Laboratory for Marine Science and Technology (2016ASKJ02), the National Key Research and Development Program of China (2017YFC1404000 and 2016YFC1401601), and National Key research and development Plan Sino-Australian Center for Healthy Coasts(2016YFE0101500). It was also supported by the High Performance Computing Center at the IOCAS. We thank Fei Yus group at IOCAS for providing the CTD data. The satellites reanalyzed data (SST, SSH, heat flux, water flux, and wind stress) are publicly available, and their websites have been given where they are used. IOCAS maintains a public website (http://159.226.158.89/owncloud/index.php/s/62RnQxI6HHPjOgp) that includes the cruise data and model results. The intermediate data files and computing codes used in this study are available on request to the authors. The authors declare that they have no conflicts of interest. The altimeter products were produced by Ssalto/Duacs and distributed by Aviso, with support from CNES (http://www.aviso.altimetry.fr/(http:/www.aviso.altimetry.fr/duacs/)%22).

One possible mechanism for eddy distribution in zonal current with meridional shear

Oceanic mesoscale eddies are common, especially in areas where zonal currents with meridional shear exists. The nonlinear effects complicate the analysis of mesoscale eddy dynamics. This study proposes a solitary (eddy) solution based on an asymptotic expansion of the nonlinear potential vorticity equation with a constant meridional shear of zonal current. This solution reveals several important consequences. For example, cyclonic (anticyclonic) eddies can be generated by the negative (positive) shear of the zonal current. Furthermore, the meridional structure of an eddy is asymmetrical, and the center of a cyclonic (anticyclonic) eddy tilts poleward (equatorward). Eddy width is inversely proportional to shear intensity. Eddy phase speed is proportional to shear intensity and the wave amplitude, and their spatial distribution show band-like pattern as they propagate westward. This nonlinear solitary solution is an extension of classical linear Rossby theory. Moreover, these findings could be applied to other areas with similar zonal current shear.

Onshore warm tongue and off shore cold tongue in the western Yellow Sea in winter: the evidence

A winter onshore warm tongue extending from the Yellow Sea Warm Current to the southern Jiangsu coast, and an offshore cold tongue extending from the southern Jiangsu coast to the southwest of Jeju Island (South Korea), are newly identified based on the sea-surface temperature from satellite remote sensing, and further confirmed by the distribution of suspended sediments. In addition, there are two obvious thermal fronts associated with the onshore warm tongue and offshore cold tongue. The narrow gap between the two thermal fronts is supposed to be the pathway for the offshore transport of cold coastal water and suspended sediments. The concurrence of onshore warm and offshore cold tongues suggests the concurrence of onshore and offshore currents in the western Yellow Sea in winter, which seems to be inconsistent with the previously accepted view that, in winter, the Yellow Sea Coastal Current flows from the Old Huanghe Delta to the southwest of Jeju Island. This distinctive phenomenon helps establish an updated view of the circulation in the western Yellow Sea in winter.

Study of the Tide and Tidal Currents in the Bay of Bengal Based on Refined Simulations

ABSTRACT Wan, W.; Feng, X.; Liu, Q.; Yin, B.; Yang, D., and Gao, G., 2019. Study of the tide and tidal currents in the Bay of Bengal based on refined simulations. Journal of Coastal Research, 35(1), 33–40. Coconut Creek (Florida), ISSN 0749-0208. A high-resolution, two-dimensional, hydrodynamic tidal model of the Bay of Bengal was developed using the Advanced Circulation (ADCIRC) Model to study the tide and tidal currents in the Bay of Bengal. The simulations conformed to the observations, and because of the use of a high-resolution, triangular grid, characteristics of the tide and tidal currents were computed more accurately than in previous studies. The results indicated that tides in most of the Bay of Bengal are semidiurnal, whereas those in the seas SE of Sri Lanka are mixed and predominately semidiurnal. There are two degenerate amphidromic points, one at the NE end of the head of the bay and the other at SE Sri Lanka, whereas there is an amphidromic point at the seas SE of Sri Lanka. The form of the M2 tidal current is rotary on the continental shelf and rectilinear in coastal areas and seas distant from the continental shelf. Four major tidal currents are in a NW–SE direction, in the western part of the head of the bay, and in a NE–SW direction in river estuary areas. Results from the eastern part are the opposite. The amplitudes and major axes of four tides and tidal currents increase upon entering the head of the bay, whereas those of the M2 tide are the largest.