On the mechanism of the cyclonic circulation in the Gulf of Tonkin in the summer

Abstract

[1] The circulation in the Gulf of Tonkin had been traditionally considered to be anticyclonic in the summer. This view was challenged recently by results from reanalyzing observational data, which clearly revealed that the circulation is cyclonic in all seasons. The surface wind stress is monsoonal, southwesterly in the summer and reversed in the winter. It remains unexplained why the circulation is always cyclonic, while the surface forcing reverses seasonally. In this study, we hypothesize that the inflow through Qiongzhou Strait, a shallow and narrow channel between Hainan Island and the Chinese mainland, is responsible for maintaining the cyclonic circulation in the summer. Besides the requirements of mass conservation and bathymetry constraint, this flow, even with a rather small transport, carries a considerable amount of potential vorticity (PV) into the gulf, and the integral constraint of PV requires the presence of a frictional torque to be associated with a cyclonic circulation. Several numerical experiments with a three-dimensional model have been conducted to test this hypothesis. When the westward flow through Qiongzhou Strait is blocked, the model simulates an anticyclonic circulation in the summer. When the westward flow through Qiongzhou Strait is allowed, the circulation changes to a cyclonic one, consistent with our hypothesis.

Particulate organic matter dynamics in coastal systems of the northern Beibu Gulf

“…The traditional concept of long shore currents in the northern Beibu Gulf, with seasonally alternating transport directions, has been contested in a recent modeling study indicating year round westward currents (Wu et al, 2008). Nevertheless, freshwater from polluted rivers, including the Nanliu, disperses along the entire northern Beibu Gulf coast .…”

“…1). This subtropical coast is influenced by the East Asian monsoon with dry boreal winter-spring and wet boreal summer-autumn seasons (Wu et al, 2008). Long term average annual precipitation is 179 cm yr À 1 but was considerably lower at 152 cm yr À 1 during the study period (Climate.usurf.usu.edu, Beihai meteorological station, 1954.…”

Climate Change on the Urban Scale – Effects and Counter-Measures in Central Europe

“…1) Benjamin & Winer 1998;Chameides et al, 1988;Dawson et al, 2007;Demuzere & van Lipzig, 2010;Emeis et al, 1997;Forkel & Knoche, 2006;Held et al, 2004;Klemm et al, 2000;Mayer & Schmidt, 1998;Meleux et al, 2007;Meng et al, 1997;Narumi et al, 2009;Pöschl, 2005;Sillmann, 1999;Solberg et al, 2005;Solmon et al, 2004;Straßburger, 2004;Wu et al, 2008;Yashuda et al, 2009 Figure 13. Four groups of factors leading to ozone formation during calm and clear summer weather, compiled according to several authors 1)…”

Tidal and residual currents in the Qiongzhou Strait estimated from shipboard ADCP data using a modified tidal harmonic analysis method

“…The deepest location in the strait lies below 100 m. The QS is a key passage for water exchange between the northern SCS and the Beibu Gulf. Quantifying the tidal current and volume transport through the QS is vital to understanding the continental shelf circulation in the northern SCS [Wang et al, 2010] and the cyclonic circulation in the Beibu Gulf [Wu et al, 2008].…”