Jianping Gan

Observed three-dimensional structure of a cold eddy in the southwestern South China Sea

National Basic Research Program of China [2009CB421208]; Natural Science Foundation of China [40821063, 40521003]; Programme of Introducing Talents of Discipline to Universities [B07034]; Research Grants Council of Hong Kong [CERG 601009]

Biological response to intensified upwelling and to a river plume in the northeastern South China Sea: A modeling study

National Key Basic Research Development Program [2009CB421208]; National Natural Science foundation of China [N_HKUST623/07, NSFC 40731160624]; Hong Kongs Research Grants Council [CERG-601008]; SCOPE project

Dynamics of the carbonate system in a large continental shelf system under the influence of both a river plume and coastal upwelling

National Basic Research Program of China (973 Program) [2009CB421201]; National Science Foundation of China (NSFC) [90711005, 40821063]; NSFC-RGC [40731160624, N_HKUST623/07]; SCOPE project

Mean seasonal cycle of isothermal depth in the South China Sea

[1] The mean seasonal cycle of isothermal depth is examined using all available temperature profiles in the South China Sea. On the annual average, the isothermal depth has two deep cores (> 45 m). One extends westward from the Luzon Strait along the continental slope south of China, and the other in the deep basin of the southern South China Sea. Harmonic analysis shows that the seasonal variation of isothermal depth is predominantly annual in the northern South China Sea, exceeding 70 m in winter and falling below 20 m in summer near the continental slope south of China. The annual variation is weaker in the southern South China Sea, where the isothermal depth approaches its seasonal maximum (> 55 m) in fall and minimum (< 35 m) in spring. The semiannual variation is most prominent in the southern South China Sea, being of comparable strength with the annual variation. Among others, local Ekman pumping appears to be an important process responsible for the semiannual variation in the southern South China Sea. A detailed description of the month-to-month variations is provided, to set a basic background for further understanding the South China Sea mixed layer dynamics and thermodynamics.

Eddy heat and salt transports in the South China Sea and their seasonal modulations

This study describes characteristics of eddy (turbulent) heat and salt transports, in the basin-scale circulation as well as in the embedded mesoscale eddy found in the South China Sea (SCS). We first showed the features of turbulent heat and salt transports in mesoscale eddies using sea level anomaly (SLA) data, in situ hydrographic data, and 375 Argo profiles. We found that the transports were horizontally variable due to asymmetric distributions of temperature and salinity anomalies and that they were vertically correlated with the thermocline and halocline depths in the eddies. An existing barrier layer caused the halocline and eddy salt transport to be relatively shallow. We then analyzed the transports in the basin-scale circulation using an eddy diffusivity method and the sea surface height data, the Argo profiles, and the climatological hydrographic data. We found that relatively large poleward eddy heat transports occurred to the east of Vietnam (EOV) in summer and to the west of the Luzon Islands (WOL) in winter, while a large equatorward heat transport was located to the west of the Luzon Strait (WLS) in winter. The eddy salt transports were mostly similar to the heat transports but in the equatorward direction due to the fact that the mean salinity in the upper layer in the SCS tended to decrease toward the equator. Using a 21/2-layer reduced-gravity model, we conducted a baroclinic instability study and showed that the baroclinic instability was critical to the seasonal variation of eddy kinetic energy (EKE) and thus the eddy transports. EOV, WLS, and WOL were regions with strong baroclinic instability, and, thus, with intensified eddy transports in the SCS. The combined effects of vertical velocity shear, latitude, and stratification determined the intensity of the baroclinic instability, which intensified the eddy transports EOV during summer and WLS and WOL during winter.

Dynamics of Intensified Downwelling Circulation over a Widened Shelf in the Northeastern South China Sea

AbstractThis study reveals the dynamics behind the intensified, downslope, cross-isobath transport over a widened shelf (narrowing downwave) in the northeastern South China Sea (NSCS) during a downwelling event. Utilizing a three-dimensional numerical model over an idealized NSCS shelf, this study identified the forcing process and derived an analytical understanding of the invoked dynamics for the intensified downslope cross-isobath transport. This study found that the transport was formed by an amplified geostrophic transport because of an increased positive along-isobath pressure gradient force (PGF), PY*, and by an enhanced bottom Ekman transport due to converging flow over the widened shelf. Based on the depth-integrated vorticity dynamics, PY* was linked with net frictional stress curl in the water column and the curl was primarily associated with the shear vorticity field induced by downwelling jet. The increased positive vorticity seaside of the jet provided positive PY* for the downslope geostrop...

Excess total organic carbon in the intermediate water of the South China Sea and its export to the North Pacific

National Basic Research Program of China ; Ministry of Science and Technology [2009CB421200]; National Science Foundation of China (NSFC) [40821063, 90711005, 40490264]

Simulation of the South Atlantic Ocean circulation and its seasonal variability

The high-resolution Princeton Ocean Model is used to simulate the circulation and seasonal variability of the South Atlantic Ocean. A diagnostic calculation, using the Levitus annual mean fields and forcing consisting of the climatological annual mean wind stress, produces a realistic steady circulation pattern. In particular, the meridional overturning cell shows equatorward flow in the surface and intermediate waters and poleward flow at depth. Associated with this circulation is a northward heat transport that reaches a maximum of 1 PW near 20°S. The model results are improved when the density field near the ocean bottom is allowed to deviate from the Levitus values. Using forcing consisting of observed monthly wind stress, heat flux and a prescribed seasonally varying Antarctic Circumpolar Current (ACC), a prognostic calculation is next carried out to study the seasonal variability in the South Atlantic Ocean. With a realistic heat flux, the model output for the seasonal thermal field compares well with that in the Levitus data. An analysis suggests that the seasonal cycle of the Brazil Current separation latitude, as well as the strength of the Falkland-Malvinas Current depends more strongly on the prescribed seasonal variability in the strength of the ACC than on the seasonal variations in wind and buoyancy forcing in the South Atlantic.

Modeling Study of Variable Upwelling Circulation in the East China Sea: Response to a Coastal Promontory

AbstractA three-dimensional, high-resolution numerical model is used to investigate processes and dynamics of an intensified upwelling that is induced by a coastal promontory over the East China Sea (ECS) shelf. The center of the intensified upwelling around the promontory has been constantly observed, but, so far, it has been dynamically unexplained. Forced by an idealized southeasterly wind stress, the model results well capture the observed upwelling at the lee of the coastal promontory. The intensified upwelling is formed by a strengthened shoreward transport downstream of the promontory as the upwelling jet veers shoreward. The jet is mainly controlled by a cross-shore geostrophic balance and is largely modulated by both centrifugal acceleration associated with nonlinear advection and by bottom stress. The strengthened shoreward transport is mainly attributed to the cross-shore geostrophic current that is induced by a countercurrent (negative) pressure gradient force (PGF) and partly attributed to th...

A Three-Layer Alternating Spinning Circulation in the South China Sea

AbstractUnderstanding of the three-dimensional circulation in the South China Sea (SCS) is crucial for determining the transports of water masses, energy, and biogeochemical substances in the regional and adjacent larger oceans. The circulation’s kinematic and dynamic natures, however, are largely unclear. Results from a three-dimensional numerical ocean circulation model and geostrophic currents, derived from hydrographic data, reveal the existence of a unique, three-layer, cyclonic–anticyclonic–cyclonic (CAC) circulation in the upper ( 1500 m) layers in the SCS with differing seasonality. An inflow–outflow–inflow structure in Luzon Strait largely induces the CAC circulation, which leads to vortex stretching in the SCS basin because of a lateral planetary vorticity flux in each of the respective layers. The formation of joint effects of baroclinicity and relief (JEBAR) is an intrinsic dynamic response to the CAC circulation. The JEBAR arises from the CAC flow–topog...