scholarly journals Small-Scale Potential Vorticity in the Upper-Ocean Thermocline

2019 ◽  
Vol 49 (7) ◽  
pp. 1845-1872 ◽  
Author(s):  
Ren-Chieh Lien ◽  
Thomas B. Sanford
Keyword(s):  
Internal Wave ◽  
Frequency Spectrum ◽  
Frequency Band ◽  
Potential Vorticity ◽  
Wave Frequency ◽  
Energy Ratio ◽  
Upper Ocean ◽  
Vertical Vorticity ◽  
Vertical Scales ◽  
Mode Energy

AbstractTwenty Electromagnetic Autonomous Profiling Explorer (EM-APEX) floats in the upper-ocean thermocline of the summer Sargasso Sea observed the temporal and vertical variations of Ertel potential vorticity (PV) at 7–70-m vertical scale, averaged over O(4–8)-km horizontal scale. PV is dominated by its linear components—vertical vorticity and vortex stretching, each with an rms value of ~0.15f. In the internal wave frequency band, they are coherent and in phase, as expected for linear internal waves. Packets of strong, >0.2f, vertical vorticity and vortex stretching balance closely with a small net rms PV. The PV spectrum peaks at the highest resolvable vertical wavenumber, ~0.1 cpm. The PV frequency spectrum has a red spectral shape, a −1 spectral slope in the internal wave frequency band, and a small peak at the inertial frequency. PV measured at near-inertial frequencies is partially attributed to the non-Lagrangian nature of float measurements. Measurement errors and the vortical mode also contribute to PV in the internal wave frequency band. The vortical mode Burger number, computed using time rates of change of vertical vorticity and vortex stretching, is 0.2–0.4, implying a horizontal kinetic energy to available potential energy ratio of ~0.1. The vortical mode energy frequency spectrum is 1–2 decades less than the observed energy spectrum. Vortical mode energy is likely underestimated because its energy at vertical scales > 70 m was not measured. The vortical mode to total energy ratio increases with vertical wavenumber, implying its importance at small vertical scales.

scholarly journals Full-field broadband invisibility through reversible wave frequency-spectrum control

Optica ◽  
2018 ◽  
Vol 5 (7) ◽  
pp. 779 ◽  
Author(s):  
Luis Romero Cortés ◽  
Mohamed Seghilani ◽  
Reza Maram ◽  
José Azaña
Keyword(s):  
Frequency Spectrum ◽  
Wave Frequency ◽  
Full Field ◽  
Spectrum Control

scholarly journals Surface signature of Mediterranean water eddies in the Northeastern Atlantic: effect of the upper ocean stratification

Ocean Science ◽  
2012 ◽  
Vol 8 (6) ◽  
pp. 931-943 ◽  
Author(s):  
I. Bashmachnikov ◽  
X. Carton
Keyword(s):  
Potential Vorticity ◽  
Initial Period ◽  
Relative Vorticity ◽  
Sea Surface ◽  
Upper Ocean ◽  
Buoyancy Frequency ◽  
Coriolis Parameter ◽  
Ocean Stratification ◽  
Surface Signature ◽  
Mediterranean Water

Abstract. Meddies, intra-thermocline eddies of Mediterranean water, can often be detected at the sea surface as positive sea-level anomalies. Here we study the surface signature of several meddies tracked with RAFOS floats and AVISO altimetry. While pushing its way through the water column, a meddy raises isopycnals above. As a consequence of potential vorticity conservation, negative relative vorticity is generated in the upper layer. During the initial period of meddy acceleration after meddy formation or after a stagnation stage, a cyclonic signal is also generated at the sea-surface, but mostly the anticyclonic surface signal follows the meddy. Based on geostrophy and potential vorticity balance, we present theoretical estimates of the intensity of the surface signature. It appears to be proportional to the meddy core radius and to the Coriolis parameter, and inversely proportional to the core depth and buoyancy frequency. This indicates that surface signature of a meddy may be strongly reduced by the upper ocean stratification. Using climatic distribution of the stratification intensity, we claim that the southernmost limit for detection in altimetry of small meddies (with radii on the order of 10–15 km) should lie in the subtropics (35–45° N), while large meddies (with radii of 25–30 km) could be detected as far south as the northern tropics (25–35° N). Those results agree with observations.

scholarly journals Marginal Sea Overflows and the Upper Ocean Interaction

2009 ◽  
Vol 39 (2) ◽  
pp. 387-403 ◽  
Author(s):  
Shinichiro Kida ◽  
Jiayan Yang ◽  
James F. Price
Keyword(s):  
Ocean Circulation ◽  
Potential Vorticity ◽  
Baroclinic Instability ◽  
Upper Ocean ◽  
Marginal Sea ◽  
The Mediterranean ◽  
The Difference ◽  
Set Up ◽  
Numerical Model Experiments ◽  
Gyre Circulation

Abstract Marginal sea overflows and the overlying upper ocean are coupled in the vertical by two distinct mechanisms—by an interfacial mass flux from the upper ocean to the overflow layer that accompanies entrainment and by a divergent eddy flux associated with baroclinic instability. Because both mechanisms tend to be localized in space, the resulting upper ocean circulation can be characterized as a β plume for which the relevant background potential vorticity is set by the slope of the topography, that is, a topographic β plume. The entrainment-driven topographic β plume consists of a single gyre that is aligned along isobaths. The circulation is cyclonic within the upper ocean (water columns are stretched). The transport within one branch of the topographic β plume may exceed the entrainment flux by a factor of 2 or more. Overflows are likely to be baroclinically unstable, especially near the strait. This creates eddy variability in both the upper ocean and overflow layers and a flux of momentum and energy in the vertical. In the time mean, the eddies accompanying baroclinic instability set up a double-gyre circulation in the upper ocean, an eddy-driven topographic β plume. In regions where baroclinic instability is growing, the momentum flux from the overflow into the upper ocean acts as a drag on the overflow and causes the overflow to descend the slope at a steeper angle than what would arise from bottom friction alone. Numerical model experiments suggest that the Faroe Bank Channel overflow should be the most prominent example of an eddy-driven topographic β plume and that the resulting upper-layer transport should be comparable to that of the overflow. The overflow-layer eddies that accompany baroclinic instability are analogous to those observed in moored array data. In contrast, the upper layer of the Mediterranean overflow is likely to be dominated more by an entrainment-driven topographic β plume. The difference arises because entrainment occurs at a much shallower location for the Mediterranean case and the background potential vorticity gradient of the upper ocean is much larger.

Computer Restoration of 2D Medical Diagnostic Signals with Noise Frequency Spectrum

1970 ◽  
Vol 111 (5) ◽  
pp. 133-136
Author(s):  
M. Nikolova ◽  
Tz. Dimitrova
Keyword(s):  
Mathematical Method ◽  
Frequency Spectrum ◽  
Frequency Band ◽  
Low Frequency ◽  
Experimental Results ◽  
Medical Diagnostic ◽  
Noise Frequency ◽  
Influence Of Noise

An application of mathematical method of Aisenberg for restoration of low frequency medical diagnostic signals after influence of noise is described in the paper. The restoration of frequency spectrum of medical diagnostic signals has been done after preliminary analyses of frequency spectrum of signals with noise and disposition of frequency band of noise in the frequency band of information signals. Some experimental results obtained on the base of application of Aisenberg's method for restoration of medical diagnostic signals are described in the paper. Ill. 9, bibl. 8 (in English; abstracts in English and Lithuanian).http://dx.doi.org/10.5755/j01.eee.111.5.374

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