Upwelling induced by the frictional stress curl and vertical squeezing of the vortex tube over a submerged valley in the East China Sea

Abstract

We conducted a process‐oriented modeling study to investigate the characteristics and dynamics of the prominent upwelling over a vast submerged valley in the East China Sea (ECS). The valley is inversely funnel‐shaped with the west bank and the east bank oriented in the north‐south direction. A cross‐bank upward transport occurred along the west bank. It intensified northward and peaked around the head of the valley. An along‐bank southward pressure gradient force ( PGF) formed the cross‐bank geostrophic transport for the upwelling over the valley. The PGF reached its maxima at the head of the valley. Our momentum and vorticity dynamic analyses revealed that a bottom stress curl mainly contributed the PGF along the west bank. At the same time, both the bottom stress curl and the nonlinear vorticity advection contributed to the PGF around the head. The bottom stress curl was due to the bottom shear vorticity of the coastal current and the curvature vorticity around the head. The nonlinear vorticity advection formed because of the vertical squeezing of vortex tube as the current flowed over the valley. The nonlinearity mainly affected the PGF around the head, whereas the bottom stress curl contributed to the PGF over the entire valley. The ratio of the nonlinear to frictional contributions to the PGF increased as the coastal current intensified. Our study demonstrates that the PGF that drives the upwelling over the valley is the combined result of the nonlinearity due to vertical squeezing of vortex tube and bottom frictional effects.

Coupled Summer Circulation and Dynamics Between a Bay and the Adjacent Shelf Around Hong Kong: Observational and Modeling Studies

“… SSC in equation occasionally contributed to the formation of this PGF y * when there was a positive wind stress curl, for example, on 14–24 July 2011. Different from what Liu and Gan (; ) reported, BSC was not critical in determining the formation of the negative PGF y * in the study area. The positive BSC offsets the negative PGF y * and was mainly formed by the positive ξ s on the shore side of the coastal jet.…”

Environmental controls on marine productivity near Cape St. Francis, South Africa

“…Vertical motion is generated by vorticity within the longshore wind stress ζ τ and current ζ U 10 (Hsueh and O'Brien, 1971;Gill and Schumann, 1979;Blanton et al, 1981;Brink, 1998) according to ζ τ/ρf = W = ζ U 10 (C D Z/f dt). Using the above vorticity values, water density (ρ) is 10 3 kg m −3 , coriolis parameter (f ) is 7.7×10 −5 s −1 , bottom drag (C D ) is 10 −2 (Liu and Gan, 2015), and depth of current shear (Z) is 2×10 2 m, over a multiday time (dt) of 10 5 s. The wind stress curl and the current shear each generate vertical motion of ∼ 10 −5 m s −1 . In the 2014 case study, the easterly winds and currents combined to lift water off Cape Padrone.…”

Numerical modeling of intrinsically and extrinsically forced seasonal circulation in the China Seas: A kinematic study

“…In summer , the shear vorticity, which arises from the shoreward decrease in the northward wind‐driven alongshore velocity, contributes to the positive vorticity (Figure d). The northward shelf current has a multicore structure, which is induced by the variable slope of shelf topography [ Liu and Gan , ]. The multicore shelf current leads to variable, but mainly positive vorticities between the no‐slip coast and jet, and between the jets themselves.…”