Effects of wave breaking on the oceanic boundary layer in hurricane conditions

2019 ◽  
Vol 29 (3) ◽  
pp. 1167-1177
Author(s):  
Zhanhong Wan ◽  
Xiuyang Lü ◽  
Chen Jiawang ◽  
Tianyu Song ◽  
Shizhu Luo
Keyword(s):  
Boundary Layer ◽  
Wave Breaking ◽  
Exchange Process ◽  
Ocean Dynamics ◽  
Upper Ocean ◽  
Langmuir Circulation ◽  
Content Type ◽  
Wind Speeds ◽  
Penetration Ability ◽  
Oceanic Boundary Layer

Purpose Wave breaking significantly affects the exchange process between ocean and atmosphere. This paper aims to simulate the upper ocean dynamics under the influence of wave breaking, which may help to figure out the transport of energy by these breakers. Design/methodology/approach The authors use a breaker-LES model to simulate the oceanic boundary layer in hurricane conditions, in which breakers become the main source of momentum and energy instead of traditional wind stress. Findings The mean horizontal velocities and energy increase rapidly with wind speed, reflecting that input from atmosphere dominates the coherent structure in the upper ocean. The penetration ability of a breaker limits its effective depth and thus the total turbulent kinetic energy (TKE) decreases sharply near the surface. Langmuir circulation is the main source of TKE in deeper water. The authors compared the dissipation rate (e) in the simulations with two estimates and found that the model tends to the scaling of ε∼z–3.4 at extreme wind speeds. Originality/value The probability distribution of breakers is also discussed based on the balance between the input from atmosphere and output by wave breaking. The authors considered the contribution of micro-scale breakers and revaluated the probability density function. The results show stability in hurricane conditions.

scholarly journals A quasi-analytical model for the under-ice boundary layer

1991 ◽  
Vol 15 ◽  
pp. 148-154 ◽  
Author(s):  
Miles G. McPhee
Keyword(s):  
Boundary Layer ◽  
Analytical Model ◽  
Large Scale ◽  
Salt Flux ◽  
Upper Ocean ◽  
Scalar Fluxes ◽  
Pressure Ridge ◽  
Variable Surface ◽  
Oceanic Boundary Layer ◽  
Constant Heating

An implicit, analytical model for momentum, heat and salt flux within a sea-ice/upper-ocean system is developed. The model comprises three parts: (a) an equation for turbulent stress in the oceanic boundary layer and upper pycnocline, from which turbulent scalar fluxes are derived; (b) a model for heat and mass transfer in a thin sub-layer near the ice/ocean interface; and (c) a model for momentum flux lost to the internal wave-field if the ice under-surface has large-scale (pressure-ridge keel) relief. Features of the model are demonstrated by simulating response of the ice drift and upper-ocean temperature and salinity structure to constant heating and variable surface stress.

scholarly journals A quasi-analytical model for the under-ice boundary layer

1991 ◽  
Vol 15 ◽  
pp. 148-154 ◽  
Author(s):  
Miles G. McPhee
Keyword(s):  
Boundary Layer ◽  
Analytical Model ◽  
Large Scale ◽  
Salt Flux ◽  
Upper Ocean ◽  
Scalar Fluxes ◽  
Pressure Ridge ◽  
Variable Surface ◽  
Oceanic Boundary Layer ◽  
Constant Heating

An implicit, analytical model for momentum, heat and salt flux within a sea-ice/upper-ocean system is developed. The model comprises three parts: (a) an equation for turbulent stress in the oceanic boundary layer and upper pycnocline, from which turbulent scalar fluxes are derived; (b) a model for heat and mass transfer in a thin sub-layer near the ice/ocean interface; and (c) a model for momentum flux lost to the internal wave-field if the ice under-surface has large-scale (pressure-ridge keel) relief. Features of the model are demonstrated by simulating response of the ice drift and upper-ocean temperature and salinity structure to constant heating and variable surface stress.

Investigation on thermal comfort of the uniform for workers in tropical monsoon climates

2020 ◽  
Vol 32 (6) ◽  
pp. 849-868
Author(s):  
Jingxian Xu ◽  
Huijuan Liu ◽  
Yunyi Wang ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Thermal Comfort ◽  
Dynamic Condition ◽  
Thermal Manikin ◽  
Content Type ◽  
Wind Speeds ◽  
Subjective Perceptions ◽  
Tropical Monsoon ◽  
Four Levels ◽  
Thermal Insulations

PurposeThis study aims to investigate the heat transfer mechanism of the uniforms used by people working in hot, humid and windy environments. Furthermore, the effectiveness of an opening structure added to the armpit of the uniforms in improving thermal comfort was comparatively examined.Design/methodology/approachA set of uniforms was tested with the opening at the armpit alternatively zipped or unzipped. Thermal manikin and human tests were performed in a climatic chamber simulating the specific environmental conditions, including wind speeds at four levels (0.15, 0.5, 2, 4 m/s) and relative humidities at two levels (50 and 85%). Static and dynamic thermal insulations of clothing (IT) were examined by the thermal manikin tests. The human bodies' thermal responses, including heart rates (HR), eardrum temperatures (Te), skin temperatures (Tsk) and subjective perceptions, were given by the human tests.FindingsSpecial mechanisms of heat transfer in the specific uniforms used in tropical monsoon climates were revealed. Reductions on IT were caused by the movement of the human body and the environmental wind, and the empirical equations would underestimate this reduction. The opening at the armpit was able to prompt more heat transfer under dynamic condition, with reducing the IT by 11.8%, lowering the mean Tsk by 0.92°C, and significantly improving the subjective perceptions (p < 0.05). The heat exhaustion was alleviated with lowering the Te by 0.32°C.Originality/valueThis study managed to improve the thermal performance of uniforms for workers under unforgiving conditions. The evaluation and design methods introduced by this study provided practical guidance for similar products with strict dress codes and cost control requirements based on the findings from thorough product tests and analysis.

Frontogenesis and frontal arrest of a dense filament in the oceanic surface boundary layer

2017 ◽  
Vol 837 ◽  
pp. 341-380 ◽  
Author(s):  
Peter P. Sullivan ◽  
James C. McWilliams
Keyword(s):  
Boundary Layer ◽  
Turbulent Mixing ◽  
Shear Instability ◽  
Upper Ocean ◽  
Surface Boundary ◽  
Horizontal Shear ◽  
Boundary Layer Turbulence ◽  
Filament Axis ◽  
Small Width ◽  
The Cross

The evolution of upper ocean currents involves a set of complex, poorly understood interactions between submesoscale turbulence (e.g. density fronts and filaments and coherent vortices) and smaller-scale boundary-layer turbulence. Here we simulate the lifecycle of a cold (dense) filament undergoing frontogenesis in the presence of turbulence generated by surface stress and/or buoyancy loss. This phenomenon is examined in large-eddy simulations with resolved turbulent motions in large horizontal domains using${\sim}10^{10}$grid points. Steady winds are oriented in directions perpendicular or parallel to the filament axis. Due to turbulent vertical momentum mixing, cold filaments generate a potent two-celled secondary circulation in the cross-filament plane that is frontogenetic, sharpens the cross-filament buoyancy and horizontal velocity gradients and blocks Ekman buoyancy flux across the cold filament core towards the warm filament edge. Within less than a day, the frontogenesis is arrested at a small width,${\approx}100~\text{m}$, primarily by an enhancement of the turbulence through a small submesoscale, horizontal shear instability of the sharpened filament, followed by a subsequent slow decay of the filament by further turbulent mixing. The boundary-layer turbulence is inhomogeneous and non-stationary in relation to the evolving submesoscale currents and density stratification. The occurrence of frontogenesis and arrest are qualitatively similar with varying stress direction or with convective cooling, but the detailed evolution and flow structure differ among the cases. Thus submesoscale filament frontogenesis caused by boundary-layer turbulence, frontal arrest by frontal instability and frontal decay by forward energy cascade, and turbulent mixing are generic processes in the upper ocean.

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