Sodar investigations of gravity waves by cross spectral analysis

1997 ◽  
pp. 275-292
Author(s):  
Günther Bull
Keyword(s):  
Spectral Analysis ◽  
Gravity Waves

scholarly journals The Atmospheric Limitation on the Precision of Ground-Based Astrometry

1995 ◽  
Vol 166 ◽  
pp. 371-371
Author(s):  
I.S. Guseva
Keyword(s):  
Spectral Analysis ◽  
Gravity Waves ◽  
Systematic Errors ◽  
Upper Atmosphere ◽  
Random Errors ◽  
Critical Problem ◽  
Pulkovo Observatory ◽  
Long Period ◽  
Wide Range ◽  
Period Variations

Anomalous refraction remains to be the most critical problem in the meridian astrometry measuring large angles on the sky. I study slow quasi-periodical variations of refraction caused by the processes in the middle and upper atmosphere, such as gravity waves, etc., which can not be detected and calibrated out by use of any on-ground meteorological measurements. For this study, very old observations at large zenith distances of 80 to 90 degrees made by V. Fuss at Pulkovo Observatory in 1867-1869 [1] were used. The Deeming's method [2] of spectral analysis of data was applied to examine the characteristic variations of refraction in a wide range of periods. Very powerful quasi-periodical processes with periods of 7-8, 11-14, 18-22, 36-44 minutes and with amplitudes of 0.3 to 0.5 arcsec in the zenith were found when short sets of observations (1-5 days) were considered. They increase random errors of astrometric observations with meridian circles, transit instruments, astrolabes, etc. The periods of very slow variations — 152, 122, 93, 82.5, 73, 61 and 50 days, – are close to the well known periods discovered in other astronomical phenomena, for instance, in solar activity and in Earth rotation. I note also, that some of the long-period variations of refraction may cause quasi-systematic errors in astrometric measurements and catalogues.

scholarly journals Internal gravity waves: Analysis using the periodic, inverse scattering transform

1999 ◽  
Vol 6 (1) ◽  
pp. 11-26 ◽  
Author(s):  
W. B. Zimmerman ◽  
G. W. Haarlemmer
Keyword(s):  
Spectral Analysis ◽  
Inverse Scattering ◽  
Gravity Waves ◽  
Water Waves ◽  
Nonlinear Filtering ◽  
Kdv Equation ◽  
Internal Gravity Waves ◽  
Inverse Scattering Transform ◽  
Linear Superposition ◽  
Scattering Transform

Abstract. The discrete periodic inverse scattering transform (DPIST) has been shown to provide the salient features of nonlinear Fourier analysis for surface shallow water waves whose dynamics are governed by the Korteweg-de Vries (KdV) equation - (1) linear superposition of components with power spectra that are invariants of the motion of nonlinear dispersive waves and (2) nonlinear filtering. As it is well known that internal gravity waves also approximately satisfy the KdV equation in shallow stratified layers, this paper investigates the degree to which DPIST provides a useful nonlinear spectral analysis of internal waves by application to simulations and wave tank experiments of internal wave propagation from localized dense disturbances. It is found that DPIST analysis is sensitive to the quantity λ = (r/6s) * (ε/μ2), where the first factor depends parametrically on the Richardson number and the background shear and density profiles and the second factor is the Ursell number-the ratio of the dimensionless wave amplitude to the dimensionless squared wavenumber. Each separate wave component of the decomposition of the initial disturbance can have a different value, and thus there is usually just one component which is an invariant of the motion found by DPIST analysis. However, as the physical applications, e.g. accidental toxic gas releases, are usually concerned with the propagation of the longest wavenumber disturbance, this is still useful information. In cases where only long, monochromatic solitary waves are triggered or selected by the waveguide, the entire DPIST spectral analysis is useful.

scholarly journals The Relationship between Equatorial Mixed Rossby–Gravity and Eastward Inertio-Gravity Waves. Part I

2016 ◽  
Vol 73 (5) ◽  
pp. 2123-2145 ◽  
Author(s):  
George N. Kiladis ◽  
Juliana Dias ◽  
Maria Gehne
Keyword(s):  
Spectral Analysis ◽  
Gravity Waves ◽  
Empirical Orthogonal Function ◽  
Equatorial Waves ◽  
Synoptic Scale ◽  
Shallow Water Theory ◽  
Orthogonal Function ◽  
Convectively Coupled Equatorial Waves ◽  
Beta Plane ◽  
The Relationship

Abstract The relationship between n = 0 mixed Rossby–gravity waves (MRGs) and eastward inertio-gravity waves (EIGs) from Matsuno’s shallow-water theory on an equatorial beta plane is studied using statistics of satellite brightness temperature Tb and dynamical fields from ERA-Interim data. Unlike other observed convectively coupled equatorial waves, which have spectral signals well separated into eastward and westward modes, there is a continuum of MRG–EIG power standing above the background that peaks near wavenumber 0. This continuum is also present in the signals of dry stratospheric MRGs. While hundreds of papers have been written on MRGs, very little work on EIGs has appeared in the literature to date. The authors attribute this to the fact that EIG circulations are much weaker than those of MRGs for a given amount of divergence, making them more difficult to observe even though they strongly modulate convection. Empirical orthogonal function (EOF) and cross-spectral analysis of 2–6-day-filtered Tb isolate zonally standing modes of synoptic-scale convection originally identified by Wallace in 1971. These display antisymmetric Tb signals about the equator that propagate poleward with a period of around 4 days, along with westward-propagating MRG-like circulations that move through the Tb patterns. Further analysis here and in Part II shows that these signatures are not artifacts of the EOF approach but result from a mixture of MRG or EIG modes occurring either in isolation or at the same time.

scholarly journals Fractal trajectories in a numerical model of the upper Indian Ocean

1994 ◽  
Vol 1 (1) ◽  
pp. 45-50 ◽  
Author(s):  
S. D. Meyers ◽  
J. F. Magnan ◽  
J. J. O'Brien
Keyword(s):  
Spectral Analysis ◽  
Numerical Model ◽  
Indian Ocean ◽  
Gravity Waves ◽  
Equatorial Zone ◽  
Geographic Locations ◽  
Model Domain ◽  
The Indian Ocean ◽  
Passive Tracers ◽  
Scaling Dimension

Abstract. A wind-driven numerical model of the Indian Ocean is used to examine the horizontal statistics of hundreds of passive tracers spread evenly over the model domain. The distribution covers several dynamically distinct regions, revealing a variety of Lagrangian behaviours associated with different geographic locations. In particular, a cluster of trajectories with scaling dimension as large as 1.3 exists throughout the equatorial zone. Spectral analysis of trajectory displacements indicates mixed Rossby-gravity waves are involved in the production of some fractal trajectories.

scholarly journals Higher-order spectral analysis of nonlinear ocean surface gravity waves

1995 ◽  
Vol 100 (C3) ◽  
pp. 4977 ◽  
Author(s):  
Steve Elgar ◽  
T. H. C. Herbers ◽  
Vinod Chandran ◽  
R. T. Guza
Keyword(s):  
Spectral Analysis ◽  
Gravity Waves ◽  
Ocean Surface ◽  
Higher Order ◽  
Surface Gravity ◽  
Surface Gravity Waves
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