Showing papers by "Quanan Zheng published in 2012"

Penetration of nonlinear Rossby eddies into South China Sea evidenced by cruise data

Abstract: National Basic Research Program of China [2009CB421208, 2007CB411803]; Natural Science Foundation of China [40976013, 41121091]; United States of America National Oceanic; Atmospheric Administration National Environmental Satellite, Data, and Information Service Ocean Remote Sensing [3000-11-03241]

Modulation of El Niño-Southern Oscillation by freshwater flux and salinity variability in the tropical Pacific

Abstract: The El Nino-Southern Oscillation (ENSO) is modulated by many factors; most previous studies have emphasized the roles of wind stress and heat flux in the tropical Pacific. Freshwater flux (FWF) is another environmental forcing to the ocean; its effect and the related ocean salinity variability in the ENSO region have been of increased interest recently. Currently, accurate quantifications of the FWF roles in the climate remain challenging; the related observations and coupled ocean-atmosphere modeling involve large elements of uncertainty. In this study, we utilized satellite-based data to represent FWF-induced feedback in the tropical Pacific climate system; we then incorporated these data into a hybrid coupled ocean-atmosphere model (HCM) to quantify its effects on ENSO. A new mechanism was revealed by which interannual FWF forcing modulates ENSO in a significant way. As a direct forcing, FWF exerts a significant influence on the ocean through sea surface salinity (SSS) and buoyancy flux (Q B) in the western-central tropical Pacific. The SSS perturbations directly induced by ENSO-related interannual FWF variability affect the stability and mixing in the upper ocean. At the same time, the ENSO-induced FWF has a compensating effect on heat flux, acting to reduce interannual Q B variability during ENSO cycles. These FWF-induced processes in the ocean tend to modulate the vertical mixing and entrainment in the upper ocean, enhancing cooling during La Nina and enhancing warming during El Nino, respectively. The interannual FWF forcing-induced positive feedback acts to enhance ENSO amplitude and lengthen its time scales in the tropical Pacific coupled climate system.

Deep‐water seamount wakes on SEASAT SAR image in the Gulf Stream region

Abstract: [1] A SEASAT synthetic aperture radar (SAR) image taken over the Gulf Stream region shows streak-like patterns. The physics of their generation and interaction with the Gulf Stream are disputed. This study seeks a convincing interpretation for the SAR imagery patterns. Bathymetric maps show that the sea floor area beneath the streaks is the northeast Hoyt Hills, where isolated seamounts with the heights of 20 to 140 m above the background sea floor are distributed. All the SAR imagery streaks originate from these seamounts and extend downstream. Thus the SAR imagery streaks are interpreted as surface roughness imprints of the seamount wakes. Hydrostatic flow dynamics of the generation of wakes on the lee side of a solid obstacle is used to explain the generation mechanism and internal structure of the seamount wakes. The analysis indicates that boundary conditions and hydrodynamic conditions are favorable for the generation and vertical propagation of the seamount wakes to the upper layer.

Upper ocean near-inertial response to 1998 Typhoon Faith in the South China Sea

Abstract: During the South China Sea monsoon experiment (SCSMEX), three autonomous temperature line acquisition system (ATLAS) buoys with acoustic Doppler current profiler (ADCP) were moored in the South China Sea to measure temperature, salinity and current velocity. Typhoon Faith passed through about 250 km south to one of the mooring buoys located at 12°58.5′N, 114°24.5′E from December 11 to 14, 1998. The data analysis indicates that the typhoon winds induce a great increase in the kinetic energy at near-inertial frequencies with two maxima in the mixed layer and thermocline. The near-inertial oscillations were observed at the upper 270 m in the wake of Typhoon Faith. The oscillations were originally excited in the sea surface layer and propagated downward. The amplitudes of the oscillations decrease with depth except in the thermocline. The near-inertial oscillation signals are also remarkable in temperature and salinity fields.

Shear-flow induced secondary circulation in parallel underwater topographic corrugation and its application to satellite image interpretation

Abstract: This study aims to figure out satellite imaging mechanisms for submerged sand ridges in the shallow water region in the case of the flow parallel to the topography corrugation. Solving the disturbance governing equations of the shear-flow yields the analytical solutions of the secondary circulation. The solutions indicate that a flow with a parabolic horizontal velocity shear and a sinusoidal vertical velocity shear will induce a pair of vortexes with opposite signs distributed symmetrically on the two sides of central line of a rectangular canal. In the case of the presence of surface Ekman layer with the direction of Ekman current opposite to (coincident with) the mean flow, the two vortexes converge (diverge) at the central line of canal in the upper layer and form a surface current convergent (divergent) zone along the central line of the canal. In the case of the absence of surface Ekman layer, there is no convergent (divergent) zone formed over the sea surface. The theoretical results are applied to interpretations of three convergent cases, one divergent case and statistics of 27 cases of satellite observations in the submerged sand ridge region of the Liaodong Shoal in the Bohai Sea. We found that the long, finger-like, bright patterns on SAR images are corresponding to the locations of the canals (or tidal channels) formed by two adjacent sand ridges rather than the sand ridges themselves.