scholarly journals Destratification and Restratification of the Spring Surface Boundary Layer in a Subtropical Front

2021 ◽  
Author(s):  
Eric Kunze ◽  
John B. Mickett ◽  
James B. Girton
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Surface Fluxes ◽  
Minor Role ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
Subtropical Front ◽  
The North ◽  
A Minor ◽  
The North Pacific

AbstractDestratification and restratification of a ~50-m thick surface boundary layer in the North Pacific Subtropical Front are examined during 24-31 March 2017 in the wake of a storm using a ~ 5-km array of 23 chi-augmented EM profiling floats (u, v, T, S, χT), as well as towyo and ADCP ship surveys, shipboard air-sea surface fluxes and parameterized shortwave penetrative radiation. During the first four days, nocturnal destabilizing buoyancy-fluxes mixed the surface layer over almost its full depth every night followed by restratification to N ~ 2 × 10–3 rad s–1 during daylight. Starting on 28 March, nocturnal destabilizing buoyancy-fluxes weakened because weakening winds reduced the latent heat-flux. Shallow mixing and stratified transition layers formed above ~20-m depth. The remnant layer in the lower part of the surface layer was insulated from destabilizing surface forcing. Penetrative radiation, turbulent buoyancy-fluxes and horizontal buoyancy advection all contribute to restratification of this remnant layer, closing the budget to within measurement uncertainties. Buoyancy advective restratification (slumping) plays a minor role. Before 28 March, measured advective restratification ∫(uzbx + vzby)dt is confined to daytime, is often destratifying and is much stronger than predictions of geostrophic adjustment, mixed-layer eddy instability and Ekman buoyancy-flux predictions because of storm-forced inertial shear. Starting on 28 March, the subinertial envelope of measured buoyancy advective restratification in the remnant layer resembles MLE parameterization predictions.

Interaction of Langmuir Turbulence and Inertial Currents in the Ocean Surface Boundary Layer under Tropical Cyclones

2018 ◽  
Vol 48 (9) ◽  
pp. 1921-1940 ◽  
Author(s):  
Dong Wang ◽  
Tobias Kukulka ◽  
Brandon G. Reichl ◽  
Tetsu Hara ◽  
Isaac Ginis ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Tropical Cyclones ◽  
Ocean Surface ◽  
Stokes Drift ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer ◽  
Wave Forcing ◽  
Inertial Currents

AbstractBased on a large-eddy simulation approach, this study investigates the response of the ocean surface boundary layer (OSBL) and Langmuir turbulence (LT) to extreme wind and complex wave forcing under tropical cyclones (TCs). The Stokes drift vector that drives LT is determined from spectral wave simulations. During maximum TC winds, LT substantially enhances the entrainment of cool water, causing rapid OSBL deepening. This coincides with relatively strong wave forcing, weak inertial currents, and shallow OSBL depth , measured by smaller ratios of , where denotes a Stokes drift decay length scale. LT directly affects a near-surface layer whose depth is estimated from enhanced anisotropy ratios of velocity variances. During rapid OSBL deepening, is proportional to , and LT efficiently transports momentum in coherent structures, locally enhancing shear instabilities in a deeper shear-driven layer, which is controlled by LT. After the TC passes, inertial currents are stronger and is greater while is shallower and proportional to . During this time, the LT-affected surface layer is too shallow to directly influence the deeper shear-driven layer, so that both layers are weakly coupled. At the same time, LT reduces surface currents that play a key role in the surface energy input at a later stage. These two factors contribute to relatively small TKE levels and entrainment rates after TC passage. Therefore, our study illustrates that inertial currents need to be taken into account for a complete understanding of LT and its effects on OSBL dynamics in TC conditions.

scholarly journals North Pacific Upper-Ocean Cold Temperature Biases in CMIP6 Simulations and the Role of Regional Vertical Mixing

2020 ◽  
Vol 33 (17) ◽  
pp. 7523-7538 ◽  
Author(s):  
Yuchao Zhu ◽  
Rong-Hua Zhang ◽  
Jichang Sun
Keyword(s):  
North Pacific ◽  
Vertical Mixing ◽  
Cold Temperature ◽  
Cold Bias ◽  
Surface Boundary ◽  
Surface Boundary Layer ◽  
The North ◽  
Vertical Diffusivity ◽  
The North Pacific

AbstractSubstantial model biases are still prominent even in the latest CMIP6 simulations; attributing their causes is defined as one of the three main scientific questions addressed in CMIP6. In this paper, cold temperature biases in the North Pacific subtropics are investigated using simulations from the newly released CMIP6 models, together with other related modeling products. In addition, ocean-only sensitivity experiments are performed to characterize the biases, with a focus on the role of oceanic vertical mixing schemes. Based on the Argo-derived diffusivity, idealized vertical diffusivity fields are designed to mimic the seasonality of vertical mixing in this region, and are employed in ocean-only simulations to test the sensitivity of this cold bias to oceanic vertical mixing. It is demonstrated that the cold temperature biases can be reduced when the mixing strength is enhanced within and beneath the surface boundary layer. Additionally, the temperature simulations are rather sensitive to the parameterization of static instability, and the cold biases can be reduced when the vertical diffusivity for convection is increased. These indicate that the cold temperature biases in the North Pacific can be largely attributed to biases in oceanic vertical mixing within ocean-only simulations, which likely contribute to the even larger biases seen in coupled simulations. This study therefore highlights the need for improved oceanic vertical mixing in order to reduce these persistent cold temperature biases seen across several CMIP models.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

scholarly journals Diet among oil-workers on off-shore oil installations in the Norwegian sector of the North Sea

1992 ◽  
Vol 68 (1) ◽  
pp. 11-19 ◽  
Author(s):  
A. Oshaug ◽  
L. I. Østgård ◽  
K. U. Trygg
Keyword(s):  
North Sea ◽  
Heart Diseases ◽  
Daily Intake ◽  
Minor Role ◽  
Coronary Heart Diseases ◽  
Average Daily Intake ◽  
The North ◽  
The North Sea ◽  
Oil Workers ◽  
A Minor

Dietary studies based on 24 h recalls were carried out on four oil installations in the Norwegian sector of the North Sea. Two hundred and three persons were interviewed about what they had eaten the previous 24 h. Food purchased for the installations in the previous 5 months was recorded. Results based on 24 h recalls showed that average daily intake of energy was 12.2 MJ of which 17% came from protein, 44% from fat and 39% from carbohydrate, including 8% from sugar. Meat, vegetables, fresh fruits, seafood (shellfish), french fries, eggs, cream and ice-cream were important components of the diet, while bread, fish and cereals played a minor role. Average daily intake (mg) of nutrients were: calcium 1244, iron 15, vitamin A 1049 μg, vitamin D 4.1 μg, thiamin 1.6, riboflavin 2.2, nicotinic acid 22, ascorbic acid 143. Dietary fibre intake, estimated as unavailable carbohydrate, was on average 19 g, and the average daily intake of cholesterol was 755 mg. Intakes were compared with the Norwegian recommended dietary allowance. Most of the employees chose a diet which when eaten over a longer period of time may contribute to the development of coronary heart diseases (CHD) and thereby increase the morbidity and mortality from CHD in the oil industry.

scholarly journals A global perspective on Langmuir turbulence in the ocean surface boundary layer

2012 ◽  
Vol 39 (18) ◽  
Author(s):  
Stephen E. Belcher ◽  
Alan L. M. Grant ◽  
Kirsty E. Hanley ◽  
Baylor Fox-Kemper ◽  
Luke Van Roekel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Ocean Surface ◽  
Global Perspective ◽  
Surface Boundary ◽  
Langmuir Turbulence ◽  
Surface Boundary Layer
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