Frontogenesis and frontolysis of the subpolar front in the surface mixed layer of the Japan Sea

Zhao, Ning; Manda, Atsuyoshi; Han, Zhen

doi:10.1002/2013jc009419

Cited by 12 publications

(7 citation statements)

References 40 publications

(38 reference statements)

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“…Recently, Zhao et al . [] employed the Japan Coastal Ocean Predictability Experiment 2 (JCOPE2) ocean reanalysis data in a mixed‐layer model to reveal front genesis in the Japan Sea. Because the infrared SST data are easily contaminated by cloud cover [ Guan and Kawamura , ; Hosoda , ], this will impose a technical restriction on the investigation of the mechanisms of the SST front disappearance.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of the disappearance of sea surface temperature fronts in the subtropical North Pacific Ocean

et al. 2014

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The disappearance mechanisms of subtropical sea surface temperature (SST) fronts occurring from May to August were examined quantitatively using a simple mixed-layer model. Weekly 2.5 data sets were matched up between satellite and in situ observations, including cloud-free SST from Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and Global Temperature and Salinity Profile Program (GTSPP) data. A 1.5 mixed-layer model used in this study assumed that the temporal variation of the SST gradient was controlled by the resultant effect among the net heat flux, temperature advection (including Ekman and geostrophic), and the temperature entrainment at the bottom of the mixed layer. The net heat flux was found to provide a dominant contribution to the weakening of the SST front (decreasing SST gradient), while the temperature advection and the bottom entrainment were relatively weak. Decomposition of the net heat flux revealed that the meridional gradient of the latent heat flux is a direct factor in the weakening of the SST front, while the shortwave radiation could have indirect effects. The meridional gradient of the latent heat flux is induced by southerly winds, which in turn causes the weakening and disappearance of the SST front. Comparison of weekly and monthly averaged SST gradient modeling results with in situ observations demonstrated that the weekly SST gradient in the model agrees closely with AMSR-E observations, but there was a large difference between the monthly SST gradient in the model and in the observations.

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Section: Introductionmentioning

confidence: 99%

Mechanisms of the disappearance of sea surface temperature fronts in the subtropical North Pacific Ocean

et al. 2014

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“…Taking the meridional derivative of Eq. ( 1 ), we may obtain the rate of frontogenesis/frontolysis 25 , 26 , 40 : Here, the monthly mean climatology from the MIMOC data is used for the mixed layer temperature and depth, that from the J-OFURO2 data is used for the surface heat flux, and the second term on the right hand side is computed as a residual.…”

Section: Methodsmentioning

confidence: 99%

Surface frontogenesis by surface heat fluxes in the upstream Kuroshio Extension region

Tozuka

Cronin

Tomita

2017

Sci Rep

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Western boundary currents bring warm tropical water poleward and eastward and are characterized by a sharp sea surface temperature (SST) front on the poleward edge of the current as it extends into the interior basin. One of the most prominent such front is associated with the Kuroshio Extension (KE) as it extends east of Japan (“upstream KE”). Large latent and sensible heat fluxes that warm the atmosphere and cool the ocean project this front into the atmosphere, thereby affecting weather and climate both locally and remotely. While one might assume that these larger surface heat fluxes on the equatorward side would tend to damp the SST front, here we present observational evidence that the surface heat loss actually strengthens the front during October-April in monthly climatology and about 87% of months from October to January during the 2004/05–2014/15 period, although the percentage lowers to about 38% for February-April of the same period, suggesting some temporal/data dependency in the analysis. The key to understanding this counterintuitive result for frontogenesis is that the effective heat capacity of the surface water depends on mixed layer thickness. SSTs are more (less) sensitive to surface heat fluxes in regions with shallow (deep) mixed layer.

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“…In the mixed‐layer model, the time derivative of mixed‐layer temperature is expressed by the sum of heat flux, horizontal heat advection, and entrainment terms. We omitted horizontal eddy diffusion because its contribution is negligibly small in determining frontal structure in the Sea of Japan [ Zhao et al ., ]. Thus, the equation is

\frac{\partial T_{M L}^{'}}{\partial t} = \frac{{(Q_{n e t} - Q (- h))}^{'}}{c_{p} ρ h} - {boldU}_{M L}^{'} \cdot \nabla T_{M L} - \frac{w^{'} Δ T}{h},

where T and U represent temperature and current velocities, respectively, and subscript “ML” refers to the vertically averaged value in the mixed layer.…”

Section: Methodsmentioning

confidence: 99%

“…Thereafter, we decomposed the temporal variation of gradient magnitude (

Δ G_{M L}^{'}

) in the mixed‐layer model into contributions of heat flux (

Δ G_{M L_{Q}}^{'}

), horizontal heat advection (

Δ G_{M L_{A}}^{'}

), and entrainment (

Δ G_{M L_{E}}^{'}

), under the assumption of a linear relationship [e.g., Kazmin and Rienecker , ; Zhao et al ., ], as

Δ G_{M L}^{'} = Δ G_{M L_{Q}}^{'} + Δ G_{M L_{A}}^{'} + Δ G_{M L_{E}}^{'} .

…”

Section: Methodsmentioning

confidence: 99%

“…In the mixed-layer model, the time derivative of mixed-layer temperature is expressed by the sum of heat flux, horizontal heat advection, and entrainment terms. We omitted horizontal eddy diffusion because its contribution is negligibly small in determining frontal structure in the Sea of Japan [Zhao et al, 2014]. Thus, the equation is…”

Section: Mixed-layer Model Analysesmentioning

confidence: 99%

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Intensification of the subpolar front in the Sea of Japan during winter cyclones

et al. 2016

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The response of the subpolar front in the Sea of Japan (also known as the East Sea) to winter cyclones is investigated based on quantitative analyses of gridded and satellite data sets. Cyclone passages affecting the sea are detected using time series of spatially averaged surface turbulent heat fluxes. As the cyclones develop, there are strong cold‐air outbreaks that produce twice the normal heat loss over the sea. After removal of sea surface temperature (SST) seasonal trends, we found that cyclone passage (hence, cooling) mainly occurred over 3 days, with maximum SST reduction of −0.4°C. The greatest reduction was found along the subpolar front, where frontal sharpness (i.e., SST gradient) increased by 0.1°C (100 km)−1. Results of a mixed‐layer model were consistent with both temperature and frontal sharpness, and localized surface cooling along the subpolar front resulted from both horizontal heat advection and turbulent heat fluxes at the sea surface. Further analyses show that this localized cooling from horizontal heat advection is caused by the cross‐frontal Ekman flow (vertically averaged over the mixed layer) and strong northwesterly winds associated with the cold‐air outbreak during cyclone passage.

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Frontogenesis and frontolysis of the subpolar front in the surface mixed layer of the Japan Sea

Cited by 12 publications

References 40 publications

Mechanisms of the disappearance of sea surface temperature fronts in the subtropical North Pacific Ocean

Mechanisms of the disappearance of sea surface temperature fronts in the subtropical North Pacific Ocean

Surface frontogenesis by surface heat fluxes in the upstream Kuroshio Extension region

Intensification of the subpolar front in the Sea of Japan during winter cyclones

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