scholarly journals Effect on Doppler Resonance From a Near-Surface Shear Layer

2017 ◽  
Author(s):  
Benjamin K. Smeltzer ◽  
Yan Li ◽  
Simen Å. Ellingsen
Keyword(s):  
Shear Layer ◽  
Finite Depth ◽  
Gravitational Acceleration ◽  
Surface Shear ◽  
Constant Frequency ◽  
Wave Source ◽  
Near Surface ◽  
Strong Shear ◽  
Uniform Current ◽  
Source Velocity

For waves generated by a wave source which is simultaneously moving and oscillating at a constant frequency ω, a resonance is well known to occur at a particular value τres of the nondimensional frequency τ = ωV/g (V: source velocity relative to the surface, g: gravitational acceleration). For quiescent, deep water, it is well known that τres = 1/4. We study the effect on τres from the presence of a shear flow in a layer near the surface, such as may be generated by wind or tidal currents. Assuming the vorticity is constant within the shear layer, we find that the effects on the resonant frequency can be significant even for sources corresponding to moderate shear and relatively long waves, while for stronger shear and shorter waves the effect is stronger. Even for a situation where the resonant waves have wavelengths about 20 times the width of the shear layer, the resonance frequency can change by ∼ 25% for even a moderately strong shear VS/g = 0.3 (S: vorticity in surface shear layer). Intuition for the problem is built by first considering two simpler geometries: uniform current with finite depth, and Couette flow of finite depth.

scholarly journals The radial gradient of the near-surface shear layer of the Sun

2014 ◽  
Vol 570 ◽  
pp. L12 ◽  
Author(s):  
A. Barekat ◽  
J. Schou ◽  
L. Gizon
Keyword(s):  
Shear Layer ◽  
The Sun ◽  
Surface Shear ◽  
Near Surface ◽  
Radial Gradient

scholarly journals GYROSCOPIC PUMPING IN THE SOLAR NEAR-SURFACE SHEAR LAYER

2011 ◽  
Vol 743 (1) ◽  
pp. 79 ◽  
Author(s):  
Mark S. Miesch ◽  
Bradley W. Hindman
Keyword(s):  
Shear Layer ◽  
Surface Shear ◽  
Near Surface

scholarly journals Modeling the Near-Surface Shear Layer: Diffusion Schemes Studied With CSS

2011 ◽  
Vol 271 ◽  
pp. 012070 ◽  
Author(s):  
Kyle Augustson ◽  
Mark Rast ◽  
Regner Trampedach ◽  
Juri Toomre
Keyword(s):  
Shear Layer ◽  
Surface Shear ◽  
Near Surface

scholarly journals Solar Meridional Flows: Recent Findings

2005 ◽  
Vol 13 ◽  
pp. 431-434
Author(s):  
Deborah A. Haber ◽  
Bradley W. Hindman
Keyword(s):  
Shear Layer ◽  
Northern Hemisphere ◽  
Meridional Circulation ◽  
Surface Shear ◽  
Near Surface ◽  
Angle Correction ◽  
New Findings ◽  
Ring Analysis ◽  
Multiple Cells ◽  
Program Data

AbstractWe report new measurements of the sun’s global meridional circulation within the near-surface shear layer for the years 1996 to 2003. The flows are obtained using the local helioseismic technique of ring analysis applied to MDI Dynamics Program data. The most recent estimates of the solar p-angle correction to this data have been incorporated. Previously published accounts that the solar meridional circulation possesses multiple cells within the northern hemisphere (Haber et al. 2002) are not contradicted by the new findings. We do find, however, that with the inclusion of the p-angle correction, cross-equator flows have been eliminated.

scholarly journals HELIOSEISMIC IMAGING OF FAST CONVECTIVE FLOWS THROUGHOUT THE NEAR-SURFACE SHEAR LAYER

2015 ◽  
Vol 803 (2) ◽  
pp. L17 ◽  
Author(s):  
Benjamin J. Greer ◽  
Bradley W. Hindman ◽  
Nicholas A. Featherstone ◽  
Juri Toomre
Keyword(s):  
Shear Layer ◽  
Surface Shear ◽  
Near Surface ◽  
Convective Flows

Diurnal Shear Instability, the Descent of the Surface Shear Layer, and the Deep Cycle of Equatorial Turbulence

2013 ◽  
Vol 43 (11) ◽  
pp. 2432-2455 ◽  
Author(s):  
W. D. Smyth ◽  
J. N. Moum ◽  
L. Li ◽  
S. A. Thorpe
Keyword(s):  
Stability Analysis ◽  
Shear Layer ◽  
Diurnal Cycle ◽  
Mixing Layer ◽  
Stable Stratification ◽  
Surface Flow ◽  
Shear Instability ◽  
Upper Ocean ◽  
Surface Shear ◽  
Near Surface

Abstract A new theory of shear instability in a turbulent environment is applied to eight days of velocity and density profiles from the upper-equatorial Pacific. This period featured a regular diurnal cycle of surface forcing, together with a clear response in upper-ocean mixing. During the day, a layer of stable stratification and shear forms at the surface. During late afternoon and evening, this stratified shear layer descends, leaving the nocturnal mixing layer above it. Using high-resolution current measurements, the detailed structure of the descending shear layer is seen for the first time. Linear stability analysis is conducted using a new method that accounts for the effects of preexisting turbulence on instability growth. Shear instability follows a diurnal cycle linked to the afternoon descent of the surface shear layer. This cycle is revealed only when the effect of turbulence is accounted for in the stability analysis. The cycle of instability leads the diurnal mixing cycle, typically by 2–3 h, consistent with the time needed for instabilities to grow and break. Late at night, the resulting turbulence suppresses further instabilities, lending an asymmetry to the mixing cycle that has not been noticed in previous measurements. Deep cycle mixing is triggered by instabilities formed as the descending shear layer merges with the marginally unstable shear of the Equatorial Undercurrent. In the morning, turbulence decays and the upper ocean restratifies. Wind accelerates the near-surface flow to form a new unstable shear layer, and the cycle begins again.

Near-field Rayleigh waves from surface explosions

1981 ◽  
Vol 71 (1) ◽  
pp. 223-248
Author(s):  
John R. Murphy
Keyword(s):  
Rayleigh Waves ◽  
Scaling Laws ◽  
Near Field ◽  
Low Frequency ◽  
Surface Shear ◽  
Low Frequencies ◽  
Wave Source ◽  
Near Surface ◽  
Frequency Components ◽  
The One

abstract The low-frequency components of the near-field ground motions produced by surface explosions are investigated and evidence is presented which suggests that much of this motion can be accounted for by the Rayleigh waves induced by the airblast loading acting on the surface exterior to the region of strong nonlinear response (i.e., the crater). Scaling laws are derived for this component of the motion which indicate that the amplitude of the Rayleigh wave source function is expected to be directly proportional to yield and independent of site geology at low frequencies and to scale as yield to the one-third power and increase with the near-surface shear wave velocity at high frequencies. Finally, an unusual arrival recorded interior to a hexagonal array of surface explosions is analyzed and shown to be consistent with Rayleigh waves converging on the center from an exterior, axisymmetric, surface-ring load which may correlate physically with the multi-burst spall closure for this event.

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