scholarly journals Seasonal Variability of The Mixed Layer Depth in The Sulawesi Sea

2021 ◽  
Vol 6 (3) ◽  
pp. 163
Author(s):  
Mochamad Riza Iskandar ◽  
Prima Wira Kusuma Wardhani ◽  
Toshio Suga
Keyword(s):  
Wind Stress ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
World Ocean ◽  
Southwest Monsoon ◽  
Buoyancy Flux ◽  
Freshwater Flux ◽  
Layer Depth ◽  
Reanalysis Dataset ◽  
Mechanical Forcing

The Sulawesi Sea is a semi-enclosed basin located in the Indonesian Seas and considered as the one of location in the west route of Indonesian Throughflow (ITF). There is less attention on the mixed layer depth investigation in the Sulawesi Sea. Concerning that the mixed layer plays an important role in influencing the ocean in air-sea interaction and affects biological activity, the estimation of mixed layer depth (MLD) in the Sulawesi Sea is important. Seasonal variation of the mixed layer in the Sulawesi Sea between 115°-125°E and 0°-8°N is estimated by using World Ocean Atlas 2013. Forcing elements on the mixed layer in terms of surface-forced turbulent mixing from mechanical forcing of wind stress and buoyancy forcing (from heat flux as well as freshwater flux) in the Sulawesi Sea is provided by using a reanalysis dataset. The MLD is estimated directly on grid profiles with interpolated levels based on chosen density fixed criterion of 0.03 kg.m<sup>-3</sup> and temperature criterion of 0.5°C difference from the surface. The results show that mixed layer depth in the Sulawesi Sea varies both spatially and temporally. Generally, the deepest MLD was occurred during the southwest monsoon (JJA), and the lowest MLD was occurred during the first transition (MAM) and second transition monsoon (SON). Strengthening and weakening MLD are influenced by mechanical forcing from wind stress and buoyancy flux. In the Sulawesi Sea, the mixed layer deepening coincides with the occurrence of a maximum in wind stress, and low buoyancy flux at the surface. This condition is the opposite when mixed layer shallowing occurs.

scholarly journals Scaling Surface Mixing/Mixed Layer Depth under Stabilizing Buoyancy Flux

2015 ◽  
Vol 45 (1) ◽  
pp. 247-258 ◽  
Author(s):  
Yutaka Yoshikawa
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Mixing Layer ◽  
Buoyancy Flux ◽  
Earth’S Rotation ◽  
Surface Mixed Layer ◽  
Threshold Method ◽  
Layer Depth ◽  
Earth's Rotation ◽  
Surface Buoyancy

AbstractThis study concerns the combined effects of Earth’s rotation and stabilizing surface buoyancy flux upon the wind-induced turbulent mixing in the surface layer. Two different length scales, the Garwood scale and Zilitinkevich scale, have been proposed for the stabilized mixing layer depth under Earth’s rotation. Here, this study analyzes observed mixed layer depth plus surface momentum and buoyancy fluxes obtained from Argo floats and satellites, finding that the Zilitinkevich scale is more suited for observed mixed layer depths than the Garwood scale. Large-eddy simulations (LESs) reproduce this observed feature, except under a weak stabilizing flux where the mixed layer depth could not be identified with the buoyancy threshold method (because of insufficient buoyancy difference across the mixed layer base). LESs, however, show that the mixed layer depth if defined with buoyancy ratio relative to its surface value follows the Zilitinkevich scale even under such a weak stabilizing flux. LESs also show that the mixing layer depth is in good agreement with the Zilitinkevich scale. These findings will contribute to better understanding of the response of stabilized mixing/mixed layer depth to surface forcings and hence better estimation/prediction of several processes related to stabilized mixing/mixed layer depth such as air–sea interaction, subduction of surface mixed layer water, and spring blooming of phytoplankton biomass.

scholarly journals Interannual Variability of the Mixed Layer Winter Convection and Spice Injection in the Eastern Subtropical North Atlantic

2015 ◽  
Vol 45 (2) ◽  
pp. 504-525 ◽  
Author(s):  
Nicolas Kolodziejczyk ◽  
Gilles Reverdin ◽  
Alban Lazar
Keyword(s):  
Interannual Variability ◽  
Mixed Layer ◽  
North Atlantic ◽  
Mixed Layer Depth ◽  
Buoyancy Flux ◽  
Upper Ocean ◽  
Late Winter ◽  
Layer Depth ◽  
Ocean Layer ◽  
Bulk Model

AbstractThe Argo dataset is used to study the winter upper-ocean conditions in the northeastern subtropical (NEA) Atlantic during 2006–12. During late winter 2010, the mixed layer depth is abnormally shallow and a negative anomaly of density-compensated salinity, the so-called spiciness, is generated in the permanent pycnocline. This is primarily explained by unusual weak air–sea buoyancy flux during the late winter 2010, in contrast with the five other studied winters. Particularly deep mixed layers and strong spiciness anomalies are observed during late winter 2012. The 2010 winter conditions appear to be related to historically low North Atlantic Oscillation (NAO) and high tropical North Atlantic index (TNA). Interannual variability of the eastern subtropical mixed layer is further investigated using a simple 1D bulk model of mean temperature and salinity linear profiles, based on turbulent kinetic energy conservation in the upper-ocean layer, and forced only with seasonal air–sea buoyancy forcing corresponding to fall–winter 2006–12. It suggests that year-to-year variability of the winter convective mixing driven by atmospheric buoyancy flux is able to generate interannual variability of both late winter mixed layer depth and spiciness in a strongly compensated layer at the base of the mixed layer and in the permanent pycnocline.

scholarly journals Control of salinity on the mixed layer depth in the world ocean: 1. General description

2007 ◽  
Vol 112 (C6) ◽  
Author(s):  
Clément de Boyer Montégut ◽  
Juliette Mignot ◽  
Alban Lazar ◽  
Sophie Cravatte
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
World Ocean ◽  
General Description ◽  
Layer Depth ◽  
The World

scholarly journals Control of salinity on the mixed layer depth in the world ocean: 2. Tropical areas

2007 ◽  
Vol 112 (C10) ◽  
Author(s):  
Juliette Mignot ◽  
Clement de Boyer Montégut ◽  
Alban Lazar ◽  
Sophie Cravatte
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
World Ocean ◽  
Layer Depth ◽  
The World ◽  
Tropical Areas

scholarly journals Using dissolved oxygen concentrations to determine mixed layer depths in the Bellingshausen Sea

2011 ◽  
Vol 8 (3) ◽  
pp. 1505-1533
Author(s):  
K. Castro-Morales ◽  
J. Kaiser
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Potential Temperature ◽  
World Ocean ◽  
Reference Value ◽  
Relative Difference ◽  
Layer Depth ◽  
Biological Production ◽  
World Ocean Atlas

Abstract. Concentrations of oxygen (O2) and other dissolved gases in the oceanic mixed layer are often used to calculate air-sea gas exchange fluxes; for example, in the context of net and gross biological production estimates. The mixed layer depth (zmix) may be defined using criteria based on temperature or density differences to a reference depth near the ocean surface. However, temperature criteria fail in regions with strong haloclines such as the Southern Ocean where heat, freshwater and momentum fluxes interact to establish mixed layers. Moreover, the time scales of air-sea exchange differ for gases and heat, so that zmix defined using O2 may be different to zmix defined using temperature or density. Here, we propose to define an O2-based mixed layer depth, zmix(O2), as the depth where the relative difference between the O2 concentration and a reference value at a depth equivalent to 10 dbar equals 0.5 %. This definition was established by numerical analysis of O2 profiles in coastal areas of the Southern Ocean and corroborated by visual inspection. Comparisons of zmix(O2) with zmix based on potential temperature differences, i.e. zmix(Δθ = 0.2 °C) and zmix(Δθ = 0.5 °C), and potential density differences, i.e. zmix(Δσθ = 0.03 kg m−3) and zmix(Δσθ = 0.125 kg m−3), showed that zmix(O2) closely follows zmix(Δσθ = 0.03 kg m−3). Further comparisons with published zmix climatologies and zmix derived from World Ocean Atlas 2005 data were also performed. To establish zmix for use with biological production estimates in the absence of O2 profiles, we suggest using zmix(Δσθ = 0.03 kg m−3), which is also the basis for the climatology by de Boyer Montégut et al. (2004).

scholarly journals Note on the Rate of Restratification in the Baroclinic Spindown of Fronts

2018 ◽  
Vol 48 (7) ◽  
pp. 1543-1553 ◽  
Author(s):  
Jörn Callies ◽  
Raffaele Ferrari
Keyword(s):  
Mixed Layer ◽  
Environmental Conditions ◽  
Initial Phase ◽  
Nonlinear Evolution ◽  
Mixed Layer Depth ◽  
Buoyancy Flux ◽  
Layer Depth ◽  
Coriolis Parameter ◽  
Coarse Resolution ◽  
Geostrophic Shear

AbstractThis paper revisits how the restratifying buoyancy flux generated by baroclinic mixed layer instabilities depends on environmental conditions. The frontal spindown is shown to produce buoyancy fluxes that increase significantly beyond the previously proposed and widely used scaling (f is the Coriolis parameter, Λ is the geostrophic shear, and H is the mixed layer depth), irrespective of whether the initial front is broad or narrow. This increase occurs after the initial phase of the nonlinear evolution, when the baroclinic eddies grow in size and develop velocities significantly in excess of the scaling assumption V ~ ΛH. Implications for parameterizing the restratification caused by baroclinic mixed layer instabilities in coarse-resolution models are discussed.

scholarly journals Ekman layers in the Southern Ocean: spectral models and observations, vertical viscosity and boundary layer depth

2009 ◽  
Vol 6 (1) ◽  
pp. 277-341 ◽  
Author(s):  
S. Elipot ◽  
S. T. Gille
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Transfer Function ◽  
Southern Ocean ◽  
Wind Stress ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Surface Velocity ◽  
Layer Depth ◽  
Second Best

Abstract. Spectral characteristics of the oceanic boundary-layer response to wind stress forcing are assessed by comparing surface drifter observations from the Southern Ocean to a suite of idealized models that parameterize the vertical flux of horizontal momentum using a first-order turbulence closure scheme. The models vary in their representation of vertical viscosity and boundary conditions. Each is used to derive a theoretical transfer function for the spectral linear response of the ocean to wind stress. The transfer functions are evaluated using observational data. The ageostrophic component of near-surface velocity is computed by subtracting altimeter-derived geostrophic velocities from observed drifter velocities (nominally drogued to represent motions at 15-m depth.) Then the transfer function is computed to link these ageostrophic velocities to observed wind stresses. The traditional Ekman model, with infinite depth and constant vertical viscosity is among the worst of the models considered in this study. The model that most successfully describes the variability in the drifter data has a shallow layer of depth O(30–50 m), in which the viscosity is constant and O(100–1000 m2 s−1), with a no-slip bottom boundary condition. The second best model has a vertical viscosity with a surface value O(200 m2 s−1), which increases linearly with depth at a rate O(0.1–1 cm s−1) and a no-slip boundary condition at the base of the boundary layer of depth O(103m). The best model shows little latitudinal or seasonal variability, and there is no obvious link to wind stress or climatological mixed-layer depth. In contrast, in the second best model, the linear coefficient and the boundary layer depth seem to covary with wind stress. The depth of the boundary layer for this model is found to be unphysically large at some latitudes and seasons, possibly a consequence of the inability of Ekman models to remove energy from the system by other means than shear-induced dissipation. However, the Ekman depth scale appears to scale like the climatological mixed-layer depth.

scholarly journals Using dissolved oxygen concentrations to determine mixed layer depths in the Bellingshausen Sea

Ocean Science ◽  
2012 ◽  
Vol 8 (1) ◽  
pp. 1-10 ◽  
Author(s):  
K. Castro-Morales ◽  
J. Kaiser
Keyword(s):  
Mixed Layer ◽  
Mixed Layer Depth ◽  
Potential Temperature ◽  
World Ocean ◽  
Reference Value ◽  
Relative Difference ◽  
Layer Depth ◽  
Bellingshausen Sea ◽  
World Ocean Atlas ◽  
Mixed Layers

Abstract. Concentrations of oxygen (O2) and other dissolved gases in the oceanic mixed layer are often used to calculate air-sea gas exchange fluxes. The mixed layer depth (zmix) may be defined using criteria based on temperature or density differences to a reference depth near the ocean surface. However, temperature criteria fail in regions with strong haloclines such as the Southern Ocean where heat, freshwater and momentum fluxes interact to establish mixed layers. Moreover, the time scales of air-sea exchange differ for gases and heat, so that zmix defined using oxygen may be different than zmix defined using temperature or density. Here, we propose to define an O2-based mixed layer depth, zmix(O2), as the depth where the relative difference between the O2 concentration and a reference value at a depth equivalent to 10 dbar equals 0.5 %. This definition was established by analysis of O2 profiles from the Bellingshausen Sea (west of the Antarctic Peninsula) and corroborated by visual inspection. Comparisons of zmix(O2) with zmix based on potential temperature differences, i.e., zmix(0.2 °C) and zmix(0.5 °C), and potential density differences, i.e., zmix(0.03 kg m−3) and zmix(0.125 kg m−3), showed that zmix(O2) closely follows zmix(0.03 kg m−3). Further comparisons with published zmix climatologies and zmix derived from World Ocean Atlas 2005 data were also performed. To establish zmix for use with biological production estimates in the absence of O2 profiles, we suggest using zmix(0.03 kg m−3), which is also the basis for the climatology by de Boyer Montégut et al. (2004).

scholarly journals Surface buoyancy flux in Bay of Bengal and Arabian Sea

2008 ◽  
Vol 26 (3) ◽  
pp. 395-400 ◽  
Author(s):  
G. Anitha ◽  
M. Ravichandran ◽  
R. Sayanna
Keyword(s):  
Mixed Layer ◽  
Bay Of Bengal ◽  
Arabian Sea ◽  
Mixed Layer Depth ◽  
Buoyancy Flux ◽  
Layer Depth ◽  
Obukhov Length ◽  
Surface Buoyancy ◽  
Quantitative Influence ◽  
Surface Buoyancy Flux

Abstract. The seasonal variation of thermal, haline, net surface buoyancy flux, the Monin-Obukhov length (M-O length, L) and stability parameter, i.e. the ratio of M-O length to mixed layer depth (h) were studied in the Bay of Bengal (BoB) and the Arabian Sea (AS) for the years 2003 and 2004 using Argo temperature and salinity profiles. The relative quantitative influence of winds to surface buoyancy and the applicability of scaling mixed layer using M-O length in BoB and AS was brought out. Rotation and light penetration modify the mixed layer depth from M-O length during shoaling in spring giving L/h<1.

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