Submesoscale-enhanced filaments and frontogenetic mechanism within mesoscale eddies of the South China Sea

Ruixi Zheng Zhiyou Jing

Ruixi Zheng, Zhiyou Jing. Submesoscale-enhanced filaments and frontogenetic mechanism within mesoscale eddies of the South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-021-1971-3
Citation: Ruixi Zheng, Zhiyou Jing. Submesoscale-enhanced filaments and frontogenetic mechanism within mesoscale eddies of the South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-021-1971-3

doi: 10.1007/s13131-021-1971-3

Submesoscale-enhanced filaments and frontogenetic mechanism within mesoscale eddies of the South China Sea

Funds: The National Natural Science Foundation of China under contract Nos 92058201, 41776040, 41830538 and 41949907; the Talents Team Project of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) under contract No. GML2019ZD0303; the Chinese Academy of Sciences under contract Nos ZDBS-LY-DQC011, ZDRW-XH-2019-2, XDA15020901 and ISEE2021PY01.
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  • Figure  1.  Climatological map of eddy kinetic energy (shading) and the trajectory of mesoscale eddies (color lines) in winter (December, January, February) from 1993 to 2020 in the South China Sea (a); satellite-observed chlorophyll concentrations for the AE1 on December 4, 2014 (b) and the AE2 on November 8, 2015 (c). The data in the shelf (<500 m) have been removed. The red, green, and blue bold lines in a show the eddy case trajectory of AE1, AE2 and simulated eddy SE, respectively. Purple contours denote the sea level anomaly and vectors show the geostrophic velocity anomaly.

    Figure  2.  Snapshot of surface Rossby number ($ Ro{\text{ = }}\zeta {\text{/}}f $) in the nested South China Sea winter simulations. The boundary of the second nested domain with ∆x=500 m is delineated by a black box.

    Figure  3.  Observed sea surface temperature (SST) field at the time of Fig. 1b (a); snapshot of chlorophyll (shading) and SST (contours at an interval of 0.04°C) for the submesoscale filaments (b). Purple contours denote the sea level anomaly. Black spots show the distribution of high-productive filaments (>0.3 mg/m−3).

    Figure  4.  Simulated sea surface temperature (SST) with horizontal velocity (vectors) (a) and a cross-eddy slice of salinity along the 117.5°E section (red dashed lines) (b) on December 18; cross-eddy profiles of normalized relative vorticity and frontal sharpness averaged over the mixed layer depth (MLD) (c). The isobaths at 200 m and 1 500 m are shown by black contours. Gray contours denote the potential density at an interval of 0.1 kg/m3. The thick gray line denotes the MLD.

    Figure  5.  Frontal sharpness $ {M^4} $ (a), strain rate $ St $ (b), relative vorticity $ \zeta $ normalized by $ f $ (c), and normalized divergence $ {\delta \mathord{\left/ {\vphantom {\delta f}} \right. } f} $ (d) at the surface for the mesoscale eddy shown in Fig. 4. Black contours denote the isobaths at 200 m and 1 500 m. A segment of the strongest filament is outlined by the black box.

    Figure  6.  Surface heat flux Qnet (shading) with surface wind stress (vectors) (a); snapshot (b) and vertical section (c) of Ertel potential vorticity (PV) $ q $; filament-averaged profiles of the Ertel PV terms and Richardson number Ri (d). The cross-filament transects (shown at an interval of 30 transects) is represented by cross-filament lines in a. The filament axis is defined by the strongest frontal sharpness. Thin gray contours show the fields of frontal sharpness >1×10−13 s−4. The isopycnal surfaces are shown by black contours (kg/m3) and the mixed layer depth is denoted by the gray line in c. The segments of $0.25<Ri < 0.95$ and $Ri > 1$ are shown in dark green and green, respectively.

    Figure  7.  Submesoscale vertical velocity $ w' $ (a) and mesoscale vertical velocity $\overline w$ (b) at a depth of 40 m depth; vertical section of submesoscale along-filament velocity $ {u'_{\text{c}}} $ averaged along the filament (c); submesoscale velocity profiles averaged over the mixed layer depth (MLD) in the filamentary region (d). Vectors in a and b denote the surface submesoscale and mesoscale flow, respectively. Gray contours show the potential density at an interval of 0.1 kg/m3. Black contours show the isopycnal surfaces and the gray line denotes the MLD. Vectors at the section show the cross-filament $ {v'_{\text{c}}} $ and vertical velocities $ w' $ at submesoscale.

    Figure  8.  Vertical heat flux $ {Q_{\text{t}}} $ (a) and vertical buoyancy flux (VBF) (b) averaged over the mixed layer; vertical section of $ {Q_{\text{t}}} $ (shading), potential density (black contours; kg/m3) and the mixed layer depth (gray line) averaged along the filament (c); vertical profiles of $ {Q_{\text{t}}} $ and VBF averaged horizontally in the filamentary region (d). Contours in a denote the surface heat loss $ {Q_{{\text{net}}}} $.

    Figure  9.  Horizontal strain rate $ St $ (a) and frontogenetic tendency $ {F_{{\text{adv}}}} $ (b) at the surface; vertical distribution of frontogenetic tendency (shading) and potential density (black contours; kg/m3) along a cross-filament section (the green line in b) (c); instantaneous filament-averaged profiles for the parameters (d). Black lines in a show the direction of the principal strain axis $ {\theta _{\text{p}}} $. The gray line denotes the mixed layer depth (MLD).

    Figure  10.  Surface horizontal strain rate associated with mesoscale flows $ S{t_{\text{m}}} $ (a) and submesoscale flows $ S{t_{\text{s}}} $ (b); cross-filament slices of the $ S{t_{\text{m}}} $ (c) and $ S{t_{\text{s}}} $ (d). The horizontal mesoscale flows and submesoscale perturbations are shown by vectors. Black contours denote the isopycnal surfaces (kg/m3). The mixed layer depth is denoted by the thick gray line.

    Figure  11.  Mixed layer-averaged total frontogenetic tendency F (a) and its terms caused by geostrophic self-straining ${F_{\rm{g}}}$ (b), ageostrophic horizontal advection $ {F_u} $ (c), external straining deformation $ {F_{\alpha}}$ (d), ageostrophic vertical advection $ {F_w} $ (e), and vertical mixing ${F_{{\kappa _v}}}$ (f). Vectors in b and c show the submesoscale geostrophic and ageostrophic flows, respectively.

    Figure  12.  Schematic diagram of the phytoplankton stripe associated with the cold filament. Shading shows the observed chlorophyll (CHL) concentration at the periphery of AE1.

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  • 收稿日期:  2021-06-12
  • 录用日期:  2021-10-05
  • 网络出版日期:  2022-05-10

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