On the response of the horizontal mean vertical density distribution in a fjord to low-frequency density fluctuations in the coastal water

1990 ◽  
Vol 42 (5) ◽  
pp. 605-614 ◽  
Author(s):  
Anders Stigebrandt
Keyword(s):  
Density Distribution ◽  
Coastal Water ◽  
Low Frequency ◽  
Density Fluctuations ◽  
Vertical Density

Frontogenesis in a fluid with horizontal density gradients

1989 ◽  
Vol 202 ◽  
pp. 1-16 ◽  
Author(s):  
J. E. Simpson ◽  
P. F. Linden
Keyword(s):  
Density Distribution ◽  
Density Gradient ◽  
Initial Density ◽  
Vertical Shear ◽  
Horizontal Gradient ◽  
Constant Density ◽  
Piecewise Constant ◽  
Vertical Density ◽  
Step Density ◽  
Horizontal Density Gradient

The adjustment under gravity of a fluid containing a horizontal density gradient is described.’ The fluid is initially at rest and the resulting motion is calculated as the flow accelerates, driven by the baroclinic density field. Two forms of the initial density distribution are considered. In the first the initial horizontal gradient is constant. A purely horizontal motion develops as the isopycnals rotate towards the horizontal. The vertical density gradient increases continually with time but the horizontal density gradient remains unchanged. The horizontal velocity has a uniform vertical shear, and the gradient Richardson number is constant in space and decreases monotonically with time to ½. The second density distribution consists of a piecewise constant gradient with a jump in the gradient along a vertical isopycnal. The density is continuous. In this case frontogenesis is predicted to occur on the isopycnal between the two constant-density-gradient regions, and the timescale for the formation of a front is determined. Laboratory experiments are reported which confirm the results of these calculations. In addition, lock exchange experiments have been carried out in which the horizontal mean gradient is represented by a series of step density differences separated by vertical gates.

Experimental investigation of turbulent density fluctuations and noise generation from heated jets

2007 ◽  
Vol 591 ◽  
pp. 73-96 ◽  
Author(s):  
J. PANDA
Keyword(s):  
Rayleigh Scattering ◽  
Pressure Fluctuations ◽  
Low Frequency ◽  
Correlation Coefficients ◽  
Density Fluctuations ◽  
Frequency Noise ◽  
Noise Sources ◽  
Plume Temperature ◽  
Jet Velocity ◽  
Temperature Constant

Low-frequency noise sources in heated single-stream jets were identified by cross-correlating turbulent density fluctuations ρ′ with the far-field sound pressure fluctuations p′. The turbulent density fluctuations were measured by a molecular Rayleigh-scattering technique. For a fixed jet velocity Uj, the normalized correlation coefficient 〈ρ′; p′〉/(ρ′rmsp′rms is found to increase progressively with an increase in the plume temperature (subscript rms stands for root-mean-square). The result indicates an improvement of the noise radiation efficiency with heating. Directly measured noise spectra from fixed velocity jets with increasing temperature ratio show confusing trends. However, if such spectra are normalized by theplume density, then a consistent trend of increasing noise level with increased plume temperature emerges. The increased noise is the most prominent at the low-frequency end, consistent with the correlation data. The effect of increasing jet velocity keeping the plume temperature constant was also studied. The correlation coefficients were found to improve significantly with velocity; a result consistent with prior observation from unheated jets. Additional findings on the time-averaged density variations and the changes in the air density fluctuations with increasing plume temperature are also discussed.

The finite probe size effect in fluctuation measurements; application to dusty plasmas

2016 ◽  
Vol 82 (2) ◽  
Author(s):  
P. Tolias ◽  
S. Ratynskaia ◽  
U. de Angelis ◽  
E. Lazzaro
Keyword(s):  
Size Effect ◽  
Low Frequency ◽  
Form Factors ◽  
Diagnostic Technique ◽  
Dusty Plasmas ◽  
Acoustic Mode ◽  
Density Fluctuations ◽  
Plasma Parameters ◽  
Volume Average ◽  
Probe Size

The effect of the finite probe size in plasma fluctuation measurements is revisited for dusty plasmas, where it has been argued that dust leads to a significant low-frequency enhancement in the spectral densities of ion density fluctuations, which can constitute the physical basis of a dust diagnostic technique. Theoretical predictions for the spectral modifications are presented and the dust acoustic mode contribution is analysed. The finite probe size effect is treated within the volume average approach, which introduces geometry dependent form factors that are calculated for spherical and cylindrical probes. The volume average approach is compared with the typically employed cutoff wavenumber approximation for various dust and plasma parameters. The contribution of temperature fluctuations to the spectral density of current fluctuations is also evaluated.

scholarly journals A vertical-mode decomposition to investigate low-frequency internal motion across the Atlantic at 26° N

Ocean Science ◽  
2012 ◽  
Vol 8 (3) ◽  
pp. 345-367 ◽  
Author(s):  
Z. B. Szuts ◽  
J. R. Blundell ◽  
M. P. Chidichimo ◽  
J. Marotzke
Keyword(s):  
Low Frequency ◽  
Western Boundary ◽  
Original Signal ◽  
Baroclinic Mode ◽  
Eastern Boundary ◽  
Mode Decomposition ◽  
Oceanic Response ◽  
Vertical Density ◽  
Baroclinic Modes ◽  
Pressure Perturbations

Abstract. Hydrographic data from full-depth moorings maintained by the Rapid/\\-MOCHA project and spanning the Atlantic at 26° N are decomposed into vertical modes in order to give a dynamical framework for interpreting the observed fluctuations. Vertical modes at each mooring are fit to pressure perturbations using a Gauss-Markov inversion. Away from boundaries, the vertical structure is almost entirely described by the first baroclinic mode, as confirmed by high correlation between the original signal and reconstructions using only the first baroclinic mode. These first baroclinic motions are also highly coherent with altimetric sea surface height (SSH). Within a Rossby radius (45 km) of the western and eastern boundaries, however, the decomposition contains significant variance at higher modes, and there is a corresponding decrease in the agreement between SSH and either the original signal or the first baroclinic mode reconstruction. Compared to the full transport signal, transport fluctuations described by the first baroclinic mode represent <25 km of the variance within 10 km of the western boundary, in contrast to 60 km at other locations. This decrease occurs within a Rossby radius of the western boundary. At the eastern boundary, a linear combination of many baroclinic modes is required to explain the observed vertical density profile of the seasonal cycle, a result that is consistent with an oceanic response to wind-forcing being trapped to the eastern boundary.

scholarly journals Is there a Depolarization Horizon?

2018 ◽  
Author(s):  
A. S. Hill
Keyword(s):  
Interstellar Medium ◽  
Density Distribution ◽  
Electron Density ◽  
High Frequency ◽  
Electron Density Distribution ◽  
Low Frequency ◽  
Line Of Sight ◽  
Low Frequencies ◽  
Ionic Medium ◽  
Spiral Arm

Modern radio spectrometers make measurement of polarized intensity as a function of Faraday depth possible. I investigate the effect of depolarization along a model line of sight. I model sightlines with two components informed by observations: a diffuse interstellar medium with a lognormal electron density distribution and a narrow, denser component simulating a spiral arm or H~{\sc ii} region, all with synchrotron-emitting gas mixed in. I then calculate the polarized intensity from 300-1800 MHz and calculate the resulting Faraday depth spectrum. The idealized synthetic observations show far more Faraday complexity than is observed in Global Magneto-Ionic Medium Survey observations. In a model with a very nearby H~{\sc ii} region observed at low frequencies, most of the effects of a ``depolarization wall'' are evident: the H~{\sc ii} region depolarizes background emission and less (but not zero) information from beyond the H~{\sc ii} region reaches the observer. In other cases, the effects are not so clear, as significant amounts of information reach the observer even through significant depolarization, and it is not clear that low-frequency observations sample largely different volumes of the interstellar medium than high-frequency observations. The observed Faraday depth can be randomized such that it does not always have any correlation with the true Faraday depth.

Horizontal And Vertical Dencity Distribution of Platfarm and Cirripede Larvae Over an Inshore Rock Platform Off Northumberland

1982 ◽  
Vol 62 (4) ◽  
pp. 907-917
Author(s):  
Stephen R. Wilson
Keyword(s):  
Density Distribution ◽  
Larval Dispersal ◽  
Bottom Water ◽  
Density Distributions ◽  
Vertical Density ◽  
Slow Moving ◽  
The Relationship

A fixed bottom net was used to study the relationship between the horizontal and vertical density distribution of polychaete and cirripede larvae over an inshore rock platform.Strong horizontal density distributions were obtained close to the bottom in many species from both groups, while the vertical samples showed larvae to be distributed towards the bottom both during the day and at night. It is suggested that the concentration of larvae within the slow-moving bottom water was responsible for the observed limited lateral larval dispersal.The results are discussed in relation to their bearing upon a number of problems within the field of meroplanktonic ecology.

Sign in / Sign up

Export Citation Format

Share Document