Tracking the mean annual velocity and vertical mixing of bedload tracers

Abstract. With the atmosphere general circulation model ECHAM the passive transport of NOx emitted from global subsonic air traffic and the NOx concentration change due to these emissions are investigated. The source of NOx is prescribed according to an aircraft emission data base. The sink of NOx is parameterized as an exponential decay process with globally constant lifetime. Simulations in perpetual January and July modes are performed. Both the resulting mean and the standard deviation of the NOx mass mixing ratio are analysed. In January horizontal dispersion is more pronounced and vertical mixing is smaller than in July. In both cases the resulting quasi-stationary fields of the mass mixing ratio display a pronounced zonal asymmetry. The variability accounts up to 30% of the mean field.

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The Production and Dissipation of Compensated Thermohaline Variance by Mesoscale Stirring

Journal of Physical Oceanography ◽

10.1175/2009jpo4103.1 ◽

2009 ◽

Vol 39 (10) ◽

pp. 2477-2501 ◽

Cited By ~ 76

Author(s):

K. Shafer Smith ◽

Raffaele Ferrari

Keyword(s):

Large Scale ◽

Vertical Mixing ◽

Small Scale ◽

Vertical Diffusion ◽

The North ◽

Salinity Gradients ◽

Scale Temperature ◽

The Mean ◽

Geostrophic Turbulence ◽

Quasigeostrophic Model

Abstract Temperature–salinity profiles from the region studied in the North Atlantic Tracer Release Experiment (NATRE) show large isopycnal excursions at depths just below the thermocline. It is proposed here that these thermohaline filaments result from the mesoscale stirring of large-scale temperature and salinity gradients by geostrophic turbulence, resulting in a direct cascade of thermohaline variance to small scales. This hypothesis is investigated as follows: Measurements from NATRE are used to generate mean temperature, salinity, and shear profiles. The mean stratification and shear are used as the background state in a high-resolution horizontally homogeneous quasigeostrophic model. The mean state is baroclinically unstable, and the model produces a vigorous eddy field. Temperature and salinity are stirred laterally in each density layer by the geostrophic velocity and vertical advection is by the ageostrophic velocity. The simulated temperature–salinity diagram exhibits fluctuations at depths just below the thermocline of similar magnitude to those found in the NATRE data. It is shown that vertical diffusion is sufficient to absorb the laterally driven cascade of tracer variance through an amplification of filamentary slopes by small-scale shear. These results suggest that there is a strong coupling between vertical mixing and horizontal stirring in the ocean at scales below the deformation radius.

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Observations of mesoscale and boundary-layer circulations affecting dust uplift and transport in the Saharan boundary layer

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-8817-2008 ◽

2008 ◽

Vol 8 (3) ◽

pp. 8817-8846 ◽

Cited By ~ 5

Author(s):

J. H. Marsham ◽

D. J. Parker ◽

C. M. Grams ◽

W. M. F. Grey ◽

B. T. Johnson

Keyword(s):

Boundary Layer ◽

Surface Temperature ◽

Land Surface Temperature ◽

Land Surface ◽

Climate Models ◽

Vertical Mixing ◽

Large Eddy ◽

The Mean ◽

Weak Winds ◽

Along Track

Abstract. Observations of the Saharan boundary layer, made during the GERBILS field campaign, show that mesoscale land surface temperature variations (which were related to albedo variations) induced mesoscale circulations, and that mesoscale and boundary-layer circulations affected dust uplift and transport. These processes are unrepresented in many climate models, but may have significant impacts on the vertical transport and uplift of desert dust. Mesoscale effects in particular tend to be difficult to parameterise. With weak winds along the aircraft track, land surface temperature anomalies with scales of greater than 10 km are shown to significantly affect boundary-layer temperatures and winds. Such anomalies are expected to affect the vertical mixing of the dusty and weakly stratified Saharan Air Layer (SAL). Mesoscale variations in winds are also shown to affect dust loadings in the boundary-layer. In a region of local uplift, with strong along-track winds, boundary-layer rolls are shown to lead to warm moist dusty updraughts in the boundary layer. Large eddy model (LEM) simulations suggest that these rolls increased uplift by approximately 30%. The modelled effects of boundary-layer convection on uplift is shown to be larger when the boundary-layer wind is decreased, and most significant when the mean wind is below the threshold for dust uplift and the boundary-layer convection leads to uplift which would not otherwise occur.

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Using Depth-Normalized Coordinates to Examine Mass Transport Residual Circulation in Estuaries with Large Tidal Amplitude Relative to the Mean Depth

Journal of Physical Oceanography ◽

10.1175/jpo-d-12-0201.1 ◽

2014 ◽

Vol 44 (1) ◽

pp. 128-148 ◽

Cited By ~ 14

Author(s):

Sarah N. Giddings ◽

Stephen G. Monismith ◽

Derek A. Fong ◽

Mark T. Stacey

Keyword(s):

Mass Transport ◽

Coordinate System ◽

Vertical Mixing ◽

Eof Analysis ◽

Residual Circulation ◽

Tidal Amplitude ◽

Transport Velocity ◽

The Mean ◽

Σ Coordinate ◽

Normalized Coordinates

Abstract Residual (subtidal) circulation profiles in estuaries with a large tidal amplitude-to-depth ratio often are quite complex and do not resemble the traditional estuarine gravitational circulation profile. This paper describes how a depth-normalized σ-coordinate system allows for a more physical interpretation of residual circulation profiles than does a fixed vertical coordinate system in an estuary with a tidal amplitude comparable to the mean depth. Depth-normalized coordinates permit the approximation of Lagrangian residuals, performance of empirical orthogonal function (EOF) analysis, estimation of terms in the along-stream momentum equations throughout depth, and computation of a tidally averaged momentum balance. The residual mass transport velocity has an enhanced two-layer exchange flow relative to an Eulerian mean because of the Stokes wave transport velocity directed upstream at all depths. While the observed σ-coordinate profiles resemble gravitational circulation, and pressure and friction are the dominant terms in the tidally varying and tidally averaged momentum equations, the two-layer shear velocity from an EOF analysis does not correlate with the along-stream density gradient. To directly compare to theoretical profiles, an extension of a pressure–friction balance in σ coordinates is solved. While the barotropic riverine residual matches theory, the mean longitudinal density gradient and mean vertical mixing cannot explain the magnitude of the observed two-layer shear residual. In addition, residual shear circulation in this system is strongly driven by asymmetries during the tidal cycle, particularly straining and advection of the salinity field, creating intratidal variation in stratification, vertical mixing, and shear.

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Effects of Wave–Current Interactions on Bay–Shelf Exchange

Journal of Physical Oceanography ◽

10.1175/jpo-d-20-0222.1 ◽

2021 ◽

Vol 51 (5) ◽

pp. 1637-1654

Author(s):

Dehai Song ◽

Wen Wu ◽

Qiang Li

Keyword(s):

Southern China ◽

Vertical Mixing ◽

Momentum Equation ◽

Wave Radiation ◽

Wave Dissipation ◽

Form Drag ◽

Northerly Wind ◽

The Mean ◽

Wave Induced ◽

Wave Radiation Stress

AbstractBay–shelf exchange is critical to coastal systems because it promotes self-purification or pollution dilution of the systems. In this study, the effects of wave–current interactions on bay–shelf exchange are explored in a micromesotidal system—Daya Bay in southern China. Waves can enlarge the shear-induced seaward transport and reduce the residual-current-induced landward transport, which benefits the bay–shelf exchange; however, tides work oppositely and slow the wave-induced bay–shelf exchange through vertical mixing and reduced shear-induced exchange. Five wave–current interactions are compared, and it is found that the depth-dependent wave radiation stress (WRS) contributes most to the bay–shelf exchange, followed by the wave dissipation as a source term in the turbulence kinetic energy equation, and the mean current advection and refraction of wave energy (CARWE). The vertical transfer of wave-generated pressure to the mean momentum equation (also known as the form drag) and the combined wave–current bottom stress (CWCBS) play minor roles in the bay–shelf exchange. The bay–shelf exchange is faster under southerly wind than under northerly wind because the bay is facing southeast; synoptic events such as storms enhance the bay–shelf exchange. The CARWE terms are dominant in both seasonal and synoptic variations of the bay–shelf exchange because they can considerably change the distribution of significant wave height. The WRS changes the bay–shelf exchange mainly through altering the flow velocity, whereas the wave dissipation on turbulence alters the vertical mixing. The form drag and the CWCBS have little impact on the bay–shelf exchange or its seasonal and synoptic variations.

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The hydrography of Irvine Bay and its relation to the Clyde Sea Area

Proceedings of the Royal Society of Edinburgh Section B Biological Sciences ◽

10.1017/s0269727000004917 ◽

1986 ◽

Vol 90 ◽

pp. 117-126

Author(s):

R. E. Lewis

Keyword(s):

Vertical Mixing ◽

Density Structure ◽

Water Density ◽

Meteorological Forcing ◽

Longshore Drift ◽

Inshore Waters ◽

The Mean ◽

Clyde Sea ◽

Sea Area ◽

Mean Current

SynopsisOver the period 1973–75, detailed studies were made of the water density structure and circulation of Irvine Bay. Observations showed that offshore waters were influenced by water originating in the Clyde Estuary and the inshore waters were affected by brackish outflow from the Irvine-Garnock Estuary. Long period current records indicated that the movement of water in Irvine Bay and the eastern Clyde Sea Area was particularly responsive to meteorological forcing. Based on data for 1974, the estimated annual mean longshore drift was about 5·0cm/s and directed towards the northwest. Studies of a tracer dye patch over a 1·5 day period showed that horizontal dispersion was influenced by vertical shears in the mean current and that vertical mixing was inhibited by a density interface at less than 4 m depth. The average longitudinal and transverse dispersion coefficients were 2·17m2/s and 0·25 m2/s respectively.

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Nitrates in eastern Australian coastal waters

Marine and Freshwater Research ◽

10.1071/mf9840385 ◽

1984 ◽

Vol 35 (4) ◽

pp. 385 ◽

Cited By ~ 23

Author(s):

DJ Rochford

Keyword(s):

Coastal Waters ◽

Nitrate Concentration ◽

Vertical Mixing ◽

Early Summer ◽

Nitrate Content ◽

Surface Salinity ◽

Transient Time ◽

The North ◽

Eastern Australia ◽

The Mean

Mean monthly temperature, salinity and nitrate concentration of eastern Australian coastal waters, at 0 and 50 m depth, for periods of up to 36 years have been determined. Using the seasonal changes in the mean properties it has been shown that the prime source of nitrates in coastal waters of eastern Australia between Evans Head and Eden is the intrusion, at various times in the spring-summer seasons, of subsurface slope waters, which are relatively rich in nitrates. Once present in the bottom layers of these coastal waters, these nitrates form a reservoir from which local processes of mixing in the autumn-winter seasons create a surface nitrate maximum, which persists for several months into the following spring. Off Evans Head and particularly off Laurieton, upwelling later in the spring creates a secondary nitrate maximum but these are of a transient time scale and little residual surface nitrate remains after the upwelling ceases. In summer, thermal capping, aided, particularly in the north, by surface salinity dilution, greatly limits the vertical mixing of nitrates to the surface, resulting in very low surface nitrate concentrations in summer. Off Eden, the spring introduction of nitrates by slope-water intrusions is impeded by a northward flow of Bass Strait waters which, because of their low nitrate content, act as a nutrient diluent. It is only when this northward flow ceases in early summer that these slope-water intrusions occur off Eden and provide the nitrate reservoir for the winter turnover. Off Maria I., slope-water intrusions are not an important contribution to the nitrate economy. The winter maximum in nitrate concentration at the Maria I. site is attributed to an onshore drift of nitrate-richer offshore waters, containing Sub-Antarctic elements. In spring, snow-melt waters mix with these winter waters off Maria I. and decrease both the salinity and nitrate content of these waters. In summer, subtropical waters of low nitrate content occur off Maria I.

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Photo-electric Hβ and uvby photometry

Symposium - International Astronomical Union ◽

10.1017/s0074180900053407 ◽

1966 ◽

Vol 24 ◽

pp. 170-180

Author(s):

D. L. Crawford

Keyword(s):

Narrow Band ◽

Line Strength ◽

Interference Filter ◽

B Stars ◽

Relative Line ◽

The Mean ◽

F Stars ◽

Two Parameters ◽

Filter Photometry ◽

The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

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A one-dimensional self-gravitating stellar gas

Symposium - International Astronomical Union ◽

10.1017/s0074180900105261 ◽

1966 ◽

Vol 25 ◽

pp. 46-48 ◽

Cited By ~ 2

Author(s):

M. Lecar

Keyword(s):

Gravitational Field ◽

Phase Space ◽

Motion Picture ◽

Space Distribution ◽

Two Dimensional ◽

One Dimensional ◽

Phase Space Distribution ◽

Dimensional Phase Space ◽

The Mean

“Dynamical mixing”, i.e. relaxation of a stellar phase space distribution through interaction with the mean gravitational field, is numerically investigated for a one-dimensional self-gravitating stellar gas. Qualitative results are presented in the form of a motion picture of the flow of phase points (representing homogeneous slabs of stars) in two-dimensional phase space.

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The motion of a lunar orbiter

Symposium - International Astronomical Union ◽

10.1017/s0074180900105686 ◽

1966 ◽

Vol 25 ◽

pp. 373

Author(s):

Y. Kozai

Keyword(s):

Degrees Of Freedom ◽

Dimensional Space ◽

Artificial Satellite ◽

Equations Of Motion ◽

Triaxial Ellipsoid ◽

The Moon ◽

Secular Motion ◽

The Earth ◽

Close Satellite ◽

The Mean

The motion of an artificial satellite around the Moon is much more complicated than that around the Earth, since the shape of the Moon is a triaxial ellipsoid and the effect of the Earth on the motion is very important even for a very close satellite.The differential equations of motion of the satellite are written in canonical form of three degrees of freedom with time depending Hamiltonian. By eliminating short-periodic terms depending on the mean longitude of the satellite and by assuming that the Earth is moving on the lunar equator, however, the equations are reduced to those of two degrees of freedom with an energy integral.Since the mean motion of the Earth around the Moon is more rapid than the secular motion of the argument of pericentre of the satellite by a factor of one order, the terms depending on the longitude of the Earth can be eliminated, and the degree of freedom is reduced to one.Then the motion can be discussed by drawing equi-energy curves in two-dimensional space. According to these figures satellites with high inclination have large possibilities of falling down to the lunar surface even if the initial eccentricities are very small.The principal properties of the motion are not changed even if plausible values ofJ3andJ4of the Moon are included.This paper has been published in Publ. astr. Soc.Japan15, 301, 1963.

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