scholarly journals Hopf bifurcations and transitions of two-dimensional Quasi-Geostrophic flows

2021 ◽  
Vol 0 (0) ◽  
pp. 0
Author(s):  
Zhigang Pan ◽  
Chanh Kieu ◽  
Quan Wang
Keyword(s):  
Hopf Bifurcations ◽  
Two Dimensional ◽  
Geostrophic Flows

scholarly journals The stability of a two-dimensional vorticity filament under uniform strain

1991 ◽  
Vol 230 ◽  
pp. 647-665 ◽  
Author(s):  
D. G. Dritschel ◽  
P. H. Haynes ◽  
M. N. Juckes ◽  
T. G. Shepherd
Keyword(s):  
Three Dimensional ◽  
Threshold Value ◽  
Shear Instability ◽  
Uniform Strain ◽  
Two Dimensional ◽  
Constant Vorticity ◽  
Coherent Vortices ◽  
Geostrophic Flows ◽  
Stabilization Effect ◽  
The Stability

The quantitative effects of uniform strain and background rotation on the stability of a strip of constant vorticity (a simple shear layer) are examined. The thickness of the strip decreases in time under the strain, so it is necessary to formulate the linear stability analysis for a time-dependent basic flow. The results show that even a strain rate γ (scaled with the vorticity of the strip) as small as 0.25 suppresses the conventional Rayleigh shear instability mechanism, in the sense that the r.m.s. wave steepness cannot amplify by more than a certain factor, and must eventually decay. For γ < 0.25 the amplification factor increases as γ decreases; however, it is only 3 when γ ė 0.065. Numerical simulations confirm the predictions of linear theory at small steepness and predict a threshold value necessary for the formation of coherent vortices. The results help to explain the impression from numerous simulations of two-dimensional turbulence reported in the literature that filaments of vorticity infrequently roll up into vortices. The stabilization effect may be expected to extend to two- and three-dimensional quasi-geostrophic flows.

Eulerian and Lagrangian velocity correlations in two-dimensional random geostrophic flows

1997 ◽  
Vol 338 ◽  
pp. 249-276 ◽  
Author(s):  
H. L. PÉCSELI ◽  
J. TRULSEN
Keyword(s):  
Two Dimensional ◽  
Velocity Correlation ◽  
Flow Parameters ◽  
Velocity Correlation Function ◽  
Fluid Layers ◽  
Lagrangian Velocity ◽  
Spatial Dimensions ◽  
Geostrophic Flows ◽  
Two Dimensional Flow ◽  
Analytical Expressions

Random flows in rotating fluid layers are studied in two spatial dimensions. The Eulerian and Lagrangian correlation functions for such flows are analysed by approximating the actual two-dimensional flow by an autonomous system consisting of many overlapping and mutually convecting vortices. Analytical expressions for the full space–time-varying Eulerian velocity correlation are derived solely in terms of flow parameters. An extension of the arguments giving these results also allows the derivation of analytical expressions for the Lagrangian velocity correlation function. The analytical results are supported by a numerical simulation.

Spectrophotometric measurements of objective-prism spectra

1966 ◽  
Vol 24 ◽  
pp. 118-119
Author(s):  
Th. Schmidt-Kaler
Keyword(s):  
Progress Report ◽  
Two Dimensional ◽  
Objective Prism ◽  
Made In

I should like to give you a very condensed progress report on some spectrophotometric measurements of objective-prism spectra made in collaboration with H. Leicher at Bonn. The procedure used is almost completely automatic. The measurements are made with the help of a semi-automatic fully digitized registering microphotometer constructed by Hög-Hamburg. The reductions are carried out with the aid of a number of interconnected programmes written for the computer IBM 7090, beginning with the output of the photometer in the form of punched cards and ending with the printing-out of the final two-dimensional classifications.

Introductory paper

1966 ◽  
Vol 24 ◽  
pp. 3-5
Author(s):  
W. W. Morgan
Keyword(s):  
Line Intensity ◽  
Classification Scheme ◽  
Two Dimensional ◽  
Spectral Classification ◽  
Dimensional Array ◽  
Rr Lyrae ◽  
Metallic Line ◽  
Introductory Paper ◽  
Parameter Varying ◽  
Definition Of

1. The definition of “normal” stars in spectral classification changes with time; at the time of the publication of theYerkes Spectral Atlasthe term “normal” was applied to stars whose spectra could be fitted smoothly into a two-dimensional array. Thus, at that time, weak-lined spectra (RR Lyrae and HD 140283) would have been considered peculiar. At the present time we would tend to classify such spectra as “normal”—in a more complicated classification scheme which would have a parameter varying with metallic-line intensity within a specific spectral subdivision.

A one-dimensional self-gravitating stellar gas

1966 ◽  
Vol 25 ◽  
pp. 46-48 ◽  
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.

Analysis of the 9th November 1990 flare

2000 ◽  
Vol 179 ◽  
pp. 229-232
Author(s):  
Anita Joshi ◽  
Wahab Uddin
Keyword(s):  
Image Processing ◽  
Two Dimensional ◽  
Temporal Behaviour ◽  
Contour Maps ◽  
Dimensional Measurements ◽  
Processing Software ◽  
Image Processing Software

AbstractIn this paper we present complete two-dimensional measurements of the observed brightness of the 9th November 1990Hαflare, using a PDS microdensitometer scanner and image processing software MIDAS. The resulting isophotal contour maps, were used to describe morphological-cum-temporal behaviour of the flare and also the kernels of the flare. Correlation of theHαflare with SXR and MW radiations were also studied.

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