Zonal Multiscale Finite-Volume framework
NASA Astrophysics Data System (ADS)
Cortinovis, Davide; Jenny, Patrick
2017-05-01
In this work, the zonal Multiscale Finite Volume (zMSFV) framework is presented. The framework generalizes previous extensions of the Multiscale Finite Volume (MSFV) method and allows to integrate additional models in a unified way. The new approach is based on splitting the domain of interest into a classical MSFV domain and additional zones. Within each zone, the solution space is spanned by so-called zonal functions. Coupling of the zonal solutions to the surrounding domain is achieved via extended zonal functions. The construction of basis, zonal and extended zonal functions can be performed such that the functions form a partition of unity. The zMSFV framework allows to include the influence of the zonal functions directly in the coarse-scale problem. Similar to previous MSFV method formulations, the zMSFV framework can ensure conservative coarse-scale solutions and allows for the construction of conservative fine-scale solutions. The main features of the zMSFV framework are used to derive robust preconditioners for iterative solutions of high-contrast problems as encountered in subsurface flow and transport simulations. It is shown that the obtained convergence rates are independent of the contrast.
Effects of finite poloidal gyroradius, shaping, and collisions on the zonal flow residual
Xiao Yong; Catto, Peter J.; Dorland, William
2007-05-15
Zonal flow helps reduce and regulate the turbulent transport level in tokamaks. Rosenbluth and Hinton have shown that zonal flow damps to a nonvanishing residual level in collisionless [M. Rosenbluth and F. Hinton, Phys. Rev. Lett. 80, 724 (1998)] and collisional [F. Hinton and M. Rosenbluth, Plasma Phys. Control. Fusion 41, A653 (1999)] banana regime plasmas. Recent zonal flow advances are summarized including the evaluation of the effects on the zonal flow residual by plasma cross-section shaping, shorter wavelengths including those less than an electron gyroradius, and arbitrary ion collisionality relative to the zonal low frequency. In addition to giving a brief summary of these new developments, the analytic results are compared with GS2 numerical simulations [M. Kotschenreuther, G. Rewoldt, and W. Tang, Comput. Phys. Commun. 88, 128 (1991)] to demonstrate their value as benchmarks for turbulence codes.
Generation of zonal flow and magnetic field by finite-amplitude waves in the ionospheric E-layer
NASA Astrophysics Data System (ADS)
Kahlon, Laila; Kaladze, Tamaz
2016-07-01
We review the generation of zonal flow and magnetic field by coupled electromagnetic (EM) ULF waves in the Earth's ionospheric E layer. It is shown that under the typical ionospheric E-layer conditions different planetary low-frequency waves can couple with each other. Propagation of coupled internal-gravity-Alfvén (CIGA), coupled Rossby-Khantadze (CRK) and coupled Rossby-Alfvén-Khantadze (CRAK) waves is revealed and studied. A set of appropriate equations describing the nonlinear interaction of such waves with sheared zonal flow is derived. The conclusion on the instability of short wavelength turbulence of such coupled waves with respect to the excitation of low-frequency and large-scale perturbation of the sheared zonal flow and sheared magnetic field is deduced. The nonlinear mechanism of the instability is based on the parametric triple interaction of finite amplitude coupled waves leading to the inverse energy cascade toward the longer wavelength. The possibility of generation of the intense mean magnetic field is shown. Obtained growth rates are discussed for each case of the considered coupled waves.
NASA Technical Reports Server (NTRS)
Sorenson, R. L.
1986-01-01
An elliptic grid-generation method for finite-difference computations about complex aerodynamic configurations is developed. A zonal approach is used, which involves first making a coarse global grid filling the entire physical domain and then subdividing regions of that grid to make the individual zone grids. The details of the grid-generation method are presented along with results of the present application, a wing-body configuration based on the F-16 fighter aircraft.
Nonlinear excitation of finite-radial-scale zonal structures by toroidal Alfvén eigenmode
NASA Astrophysics Data System (ADS)
Qiu, Zhiyong; Chen, Liu; Zonca, Fulvio
2017-05-01
The set of equations describing nonlinear evolution of a single toroidal Alfvén eigenmode are derived, including both zero frequency zonal structure (ZFZS) generation and wave-particle phase space nonlinearities. The simplified case of neglecting wave-particle phase space nonlinearity is then investigated to focus on different roles of energetic particles and bulk plasmas on ZFZS generation. It is shown that energetic particles and bulk plasma play dominant roles in ZFZS generation in different nonlinear stages, and the corresponding processes are qualitatively different. Several properties of ZFZS generation, e.g. fine- versus meso-scale, forced driven versus spontaneous excitation, are clarified by the present analysis.
Low-frequency intraseasonal variability in a zonally symmetric aquaplanet model
NASA Astrophysics Data System (ADS)
Das, Surajit; Sengupta, Debasis; Chakraborty, A.; Sukhatme, Jai; Murtugudde, Raghu
2016-12-01
We use the aquaplanet version of the community atmospheric model, with perpetual spring equinox forcing and zonally symmetric sea surface temperature (SST), to study tropical intraseasonal oscillations (ISOs). In the first two experiments, we specify zonally symmetric SST profiles that mimic observed climatological July and January SSTs as surface boundary conditions. In the January SST simulation, we find a zonal wavenumber 1 mode with dominant period of 60 days, moving east at about 6 m s-1. This mode, which resembles the Madden-Julian oscillation (MJO), is absent in the July SST case, although convectively coupled Kelvin waves are prominent in both experiments. To further investigate the influence of tropical SST on ISO and convectively coupled equatorial waves, we conduct experiments with idealised symmetric SST profiles having different widths of warm ocean centered at the equator. In the narrowest SST experiment, the variance of moist activity is predominantly in weather-scale Kelvin waves. When the latitudinal extent of warm SST is comparable to or larger than the equatorial Rossby radius, we find a dominant low frequency (50-80 days) eastward mode that resembles the MJO, as in the January SST experiment. We also find westward propagating waves with intraseasonal (30-120 days) periods and zonal wavenumber 1-3; the structure of these signals projects onto equatorially trapped Rossby waves with meridional mode numbers 1, 3 and 5, associated with convection that is symmetric about the equator. In addition, the model generates 30-80 days westward moving signals with zonal wavenumber 4-7, particularly in the narrow SST experiment. Although these waves are seen in the wavenumber-frequency spectra in the equatorial region, they have largest amplitude in the middle and high latitudes. Thus, our study shows that wider, meridionally symmetric SST profiles support a strong MJO-like eastward propagation, and even in an aquaplanet setting, westward propagating Rossby
Semianalytical calculation of the zonal-flow oscillation frequency in stellarators
NASA Astrophysics Data System (ADS)
Monreal, Pedro; Sánchez, Edilberto; Calvo, Iván; Bustos, Andrés; Parra, Félix I.; Mishchenko, Alexey; Könies, Axel; Kleiber, Ralf
2017-06-01
Due to their capability to reduce turbulent transport in magnetized plasmas, understanding the dynamics of zonal flows is an important problem in the fusion program. Since the pioneering work by Rosenbluth and Hinton in axisymmetric tokamaks, it is known that studying the linear and collisionless relaxation of zonal flow perturbations gives valuable information and physical insight. Recently, the problem has been investigated in stellarators and it has been found that in these devices the relaxation process exhibits a characteristic feature: a damped oscillation. The frequency of this oscillation might be a relevant parameter in the regulation of turbulent transport, and therefore its efficient and accurate calculation is important. Although an analytical expression can be derived for the frequency, its numerical evaluation is not simple and has not been exploited systematically so far. Here, a numerical method for its evaluation is considered, and the results are compared with those obtained by calculating the frequency from gyrokinetic simulations. This ‘semianalytical’ approach for the determination of the zonal-flow frequency is revealed to be accurate and faster than the one based on gyrokinetic simulations.
Ghizzo, A.; Palermo, F.
2015-08-15
We address the mechanisms underlying low-frequency zonal flow generation in turbulent system and the associated intermittent regime of ion-temperature-gradient (ITG) turbulence. This model is in connection with the recent observation of quasi periodic zonal flow oscillation at a frequency close to 2 kHz, at the low-high transition, observed in the ASDEX Upgrade [Conway et al., Phys. Rev. Lett. 106, 065001 (2011)] and EAST tokamak [Xu et al., Phys. Rev. Lett 107, 125001 (2011)]. Turbulent bursts caused by the coupling of Kelvin-Helmholtz (KH) driven shear flows with trapped ion modes (TIMs) were investigated by means of reduced gyrokinetic simulations. It was found that ITG turbulence can be regulated by low-frequency meso-scale zonal flows driven by resonant collisionless trapped ion modes (CTIMs), through parametric-type scattering, a process in competition with the usual KH instability.
Naidich, Thomas P; Firestone, Michael I; Blum, Jeffrey T; Abrams, Kevin J; Zimmerman, Robert D
2003-09-01
The object of the study was to test the hypotheses that analysis of the anatomic zones affected by single anterior (A), posterior (P), and middle (M) cerebral artery (CA) infarcts, and by dual- and triple-vessel infarcts, will disclose (i) sites most frequently involved by each infarct type (peak sites), (ii) sites most frequently injured by multiple different infarct types (vulnerable zones), and (iii) anatomically overlapping sites in which the relative infarct frequency becomes equal for two or more different infarct types and/or in which infarct frequency shifts greatly between single and multivessel infarcts (potential border zones). Precise definitions of each vascular territory were adopted. CT and MRI studies from 20 ACA, 20 PCA, three dual ACA-PCA, and four triple ACA-PCA-MCA infarcts were mapped onto a standard template (Part I). Relative infarct frequencies in each zone were analyzed within and across infarct types to identify the centers and peripheries of each infarct type, the zones most frequently affected by multiple different infarct types, the zones where relative infarct frequency was equal for different infarcts, and the zones where infarct frequency shifted markedly from single- to multiple-vessel infarcts. Zonal frequency analysis provided quantitative data on the relative infarct frequency in each anatomic zone for each infarct type. It displayed zones of peak infarct frequency for each infarct, zones more vulnerable to diverse types of infarct, peripheral "overlap" zones of equal infarct frequency, and zones where infarct frequency shifted markedly between single- and multiple-vessel infarcts. It is concluded that the hypotheses are correct.
The observations of Low Frequency Zonal Flow in electrode biasing experiments on J-TEXT tokamak
NASA Astrophysics Data System (ADS)
Shen, H. G.; Kong, D. F.; Zhao, H. L.; Wu, J.; Lan, T.; Liu, W. D.; Yu, C. X.; Sun, Y.; Liu, H.; Chen, Z. P.; Zhuang, G.; USTC Team; HUST Team
2013-10-01
The long-distance correlations features of potential and density fluctuations during electrode biasing (EB) have been investigated using Langmuir probe arrays in the edge of J-TEXT tokamak. During the positive edge EB, both floating potential and density fluctuations in the high frequency ambient turbulence (AT) region are suppressed and radial particle flux is decreased. But no obvious change occurs during the negative edge EB. In the positive EB cases, toroidal and poloidal long-distance correlations of floating potentials increase in the low frequency regions of f < 3 kHz and no distinct long-distance correlations is found in density fluctuations. It shows that this low frequency long-distance correlation mode is low frequency zonal flow (LFZF). In the meantime, strong Er × B shearing is observed when applying a positive EB. The results also suggests that the LFZF may be induced by AT and then regulate the AT amplitude. Supported by NNSFC (Nos. 10990210,10990211,10335060 and 10905057), CPSF (No. 20080440104), YIF (No. WK2030040019) and KIPCAS (No. kjcx-yw-n28).
Ghizzo, A.; Palermo, F.
2015-08-15
Collisionless trapped ion modes (CTIMs) turbulence exhibits a rich variety of zonal flow physics. The coupling of CTIMs with shear flow driven by the Kelvin-Helmholtz (KH) instability has been investigated. The work explores the parametric excitation of zonal flow modified by wave-particle interactions leading to a new type of resonant low-frequency zonal flow. The KH-CTIM interaction on zonal flow growth and its feedback on turbulence is investigated using semi-Lagrangian gyrokinetic Vlasov simulations based on a Hamiltonian reduction technique, where both fast scales (cyclotron plus bounce motions) are gyro-averaged.
Surface consistent finite frequency phase corrections
NASA Astrophysics Data System (ADS)
Kimman, W. P.
2016-07-01
Static time-delay corrections are frequency independent and ignore velocity variations away from the assumed vertical ray path through the subsurface. There is therefore a clear potential for improvement if the finite frequency nature of wave propagation can be properly accounted for. Such a method is presented here based on the Born approximation, the assumption of surface consistency and the misfit of instantaneous phase. The concept of instantaneous phase lends itself very well for sweep-like signals, hence these are the focus of this study. Analytical sensitivity kernels are derived that accurately predict frequency-dependent phase shifts due to P-wave anomalies in the near surface. They are quick to compute and robust near the source and receivers. An additional correction is presented that re-introduces the nonlinear relation between model perturbation and phase delay, which becomes relevant for stronger velocity anomalies. The phase shift as function of frequency is a slowly varying signal, its computation therefore does not require fine sampling even for broad-band sweeps. The kernels reveal interesting features of the sensitivity of seismic arrivals to the near surface: small anomalies can have a relative large impact resulting from the medium field term that is dominant near the source and receivers. Furthermore, even simple velocity anomalies can produce a distinct frequency-dependent phase behaviour. Unlike statics, the predicted phase corrections are smooth in space. Verification with spectral element simulations shows an excellent match for the predicted phase shifts over the entire seismic frequency band. Applying the phase shift to the reference sweep corrects for wavelet distortion, making the technique akin to surface consistent deconvolution, even though no division in the spectral domain is involved. As long as multiple scattering is mild, surface consistent finite frequency phase corrections outperform traditional statics for moderately large
Chen, R.; Xie, J. L. Yu, C. X.; Liu, A. D.; Lan, T.; Li, H.; Liu, W. D.; Zhang, S. B.; Kong, D. F.; Hu, G. H.
2015-01-15
Low-frequency zonal flow (ZF) has been observed in a linear magnetic plasma device, exhibiting significant intermittency. Using the conditional analysis method, a time-averaged fluctuation-induced particle flux was observed to consistently decrease as ZF increased in amplitude. A dominant fraction of the flux, which is driven by drift-wave harmonics, is reversely modulated by ZF in the time domain. Spectra of the flux, together with each of the related turbulence properties, are estimated subject to two conditions, i.e., when potential fluctuation series represents a strong ZF intermittency or a very weak ZF component. Comparison of frequency-domain results demonstrates that ZF reduces the cross-field particle transport primarily by suppressing the density fluctuation as well as decorrelating density and potential fluctuations.
NASA Astrophysics Data System (ADS)
Kim, Eun-Jin
2002-11-01
Zonal flows (ZF) are generated by drift wave (DW) turbulence and then regulate it near marginality by shear suppression. Since collisions damp ZF while ZF suppress DW, the amplitude of DW turbulence (i.e. turbulent transport) is, in turn, proportional to collisionality. A key question is then what happens away from marginality, namely what is the saturation mechanism of ZF in that regime? This raises the interesting physical question of how ZF interact with mne 0, poloidally non-axisymmetric modes [1], both linearly and non linearly. We investigate this issue by exploring the nonlinear excitation of GKH modes by modulational instability in the background of finite amplitude of DW turbulence, as well as the linear inflection-type instability of ZF. In a simple model with cold ions, we show that ZF can grow faster than the linear GKH for γ/ω
frequency of DW, and p and k are the characteristic wavenumbers of ZF and DW. These findings imply that the linear analysis of GKH may not always be valid and also that there may be no clear distinction between secondary (ZF) and tertiary mode (GKH). The effect of finite ion temperature fluctuations is incorporated in a simple toroidal ion temperature gradient model, within which both zonal flow and temperature are generated by modulational instability. The phase between the two is calculated self-consistently and shown to be positive. Furthermore, the correction to nonlinear generation of GKH modes appears to be small. [1] We refer to these low mne 0 modes as Generalized Kelvin-Helmholtz (GKH) modes, since they will appear as mne 0 distortions of a shear layer.
Fine structure zonal flow excitation by beta-induced Alfvén eigenmode
NASA Astrophysics Data System (ADS)
Qiu, Zhiyong; Chen, Liu; Zonca, Fulvio
2016-10-01
Nonlinear excitation of low frequency zonal structure (LFZS) by beta-induced Alfvén eigenmode (BAE) is investigated using nonlinear gyrokinetic theory. It is found that electrostatic zonal flow (ZF), rather than zonal current, is preferentially excited by finite amplitude BAE. In addition to the well-known meso-scale radial envelope structure, ZF is also found to exhibit fine radial structure due to the localization of BAE with respect to mode rational surfaces. Specifically, the zonal electric field has an even mode structure at the rational surface where radial envelope peaks.
NASA Astrophysics Data System (ADS)
Wang, L.; Lu, J.; Gerber, E. P.; Nakamura, N.
2016-12-01
Water vapor profoundly shapes our basic climate and its response to climate forcings. In mid-latitude troposphere, the radiative forcing from water vapor is roughly one third of the total solar radiation received at the ground. Idealized atmospheric dry models parameterize the radiation effects by linearly relaxing the temperature profile toward a "radiative equilibrium state" profile (Held and Surarez 1994). However, such a dry model lacks an important interactive diabatic heating that is due to the condensation of water vapor. On synoptic timescale, the diabatic heating in fact strongly interacts with the dry dynamics, shaping up a very different co-variability of atmospheric waves and mean flow compared to that in a dry model. The co-variability's intrinsic timescale is an important indicator for estimating climate sensitivity in light of the Fluctuation-Dissipation Theorem (Leith 1975), but the long-standing puzzle is that the observed decorrelation timescale of Annular Mode is substantially smaller than that in a dry atmosphere, hinting a possible negative feedback may exist in a moist atmosphere. In this presentation, we will introduce a new zonal momentum - finite-amplitude wave activity framework, in which the role of diabatic heating is explicitly incorporated and accurately quantified. We depict the mid-latitude wave-mean flow interaction through this zonal momentum-wave activity cycle. We will demonstrate a robust negative diabatic eddy feedback to the zonal index in a hierarchy of idealized GCMs and reanalysis products. This negative feedback is achieved through the changes in finite-amplitude wave activity and eddy forcing. We will discuss this negative feedback's possible role in the magnitude of the jet shift in a warming climate by extracting the interactive diabatic eddy feedback from a grey-radiation AGCM (Frierson et al. 2006). We will also discuss a further implication for the climate sensitivity that arises from the strong interactions between
Finite-frequency noise in a topological superconducting wire
NASA Astrophysics Data System (ADS)
Valentini, Stefano; Governale, Michele; Fazio, Rosario; Taddei, Fabio
2016-01-01
In this paper we study the finite-frequency current cross-correlations for a topological superconducting nanowire attached to two terminals at one of its ends. Using an analytic 1D model we show that the presence of a Majorana bound state yields vanishing cross-correlations for frequencies larger than twice the applied transport voltage, in contrast to what is found for a zero-energy ordinary Andreev bound state. Zero cross-correlations at high frequency have been confirmed using a more realistic tight-binding model for finite-width topological superconducting nanowires. Finite-temperature effects have also been investigated.
Nonlinear damping of zonal flows
Koshkarov, O. Smolyakov, A. I.; Mendonca, J. T.
2016-08-15
The modulatonal instability theory for the generation of large-scale (zonal) modes by drift modes has been extended to the second order including the effects of finite amplitude zonal flows, ϕ{sub q}. The nonlinear (second-order) sidebands are included in the perturbative expansion to derive the nonlinear equation for the evolution of ϕ{sub q}. It is shown that effects of finite ϕ{sub q} reduce the growth rate of zonal flow with a possibility of oscillatory regimes at a later stage.
Finite frequency Seebeck coefficient of metals: A memory function approach
NASA Astrophysics Data System (ADS)
Bhalla, Pankaj; Kumar, Pradeep; Das, Nabyendu; Singh, Navinder
2017-10-01
We study the dynamical thermoelectric transport in metals subjected to the electron-impurity and the electron-phonon interactions using the memory function formalism. We introduce a generalized Drude form for the Seebeck coefficient in terms of thermoelectric memory function and calculate the latter in various temperature and frequency limits. In the zero frequency and high temperature limit, we find that our results are consistent with the experimental findings and with the traditional Boltzmann equation approach. In the low temperature limit, we find that the Seebeck coefficient is quadratic in temperature. In the finite frequency regime, we report new results: In the electron-phonon interaction case, we find that the Seebeck coefficient shows frequency independent behavior both in the high frequency regime (ω ≫ωD , where ωD is the Debye frequency) and in the low frequency regime (ω ≪ωD), whereas in the intermediate frequencies, it is a monotonically increasing function of frequency. In the case of the electron-impurity interaction, first it decays and then after passing through a minimum it increases with the increase in frequency and saturates at high frequencies.
NASA Astrophysics Data System (ADS)
Huang, Binke; Zhao, Chongfeng
2014-01-01
The 2-D finite-difference frequency-domain method (FDFD) combined with the surface impedance boundary condition (SIBC) was employed to analyze the propagation characteristics of hollow rectangular waveguides at Terahertz (THz) frequencies. The electromagnetic field components, in the interior of the waveguide, were discretized using central finite-difference schemes. Considering the hollow rectangular waveguide surrounded by a medium of finite conductivity, the electric and magnetic tangential field components on the metal surface were related by the SIBC. The surface impedance was calculated by the Drude dispersion model at THz frequencies, which was used to characterize the conductivity of the metal. By solving the Eigen equations, the propagation constants, including the attenuation constant and the phase constant, were obtained for a given frequency. The proposed method shows good applicability for full-wave analysis of THz waveguides with complex boundaries.
Finite difference modeling of Biot's poroelastic equations atseismic frequencies
Masson, Y.J.; Pride, S.R.; Nihei, K.T.
2006-02-24
Across the seismic band of frequencies (loosely defined as<10 kHz), a seismic wave propagating through a porous material willcreate flow in the pore space that is laminar; that is, in thislow-frequency "seismic limit," the development of viscous boundary layersin the pores need not be modeled. An explicit time steppingstaggered-grid finite difference scheme is presented for solving Biot'sequations of poroelasticity in this low-frequency limit. A key part ofthis work is the establishment of rigorous stability conditions. It isdemonstrated that over a wide range of porous material properties typicalof sedimentary rock and despite the presenceof fluid pressure diffusion(Biot slow waves), the usual Courant condition governs the stability asif the problem involved purely elastic waves. The accuracy of the methodis demonstrated by comparing to exact analytical solutions for both fastcompressional waves and slow waves. Additional numerical modelingexamples are also presented.
Finite-Frequency Tomography of USArray Receiver Functions
NASA Astrophysics Data System (ADS)
Zhou, Y.
2014-12-01
Seismic waves diffract around structure perturbations when the length scale of lateral heterogeneities is comparable to the size of the Fresnel zone. Our recent studies based on wave propagation simulations show that Born sensitivity kernels can be used in seismic tomography to account for diffractional effects in surface waves as well as body waves. In addition to direct seismic phases, teleseismic receiver functions which take advantage of secondary waves converted at seismic discontinuities can provides important constraints on discontinuity structures. In this study, we calculate finite-frequency sensitivity of receiver functions to perturbations in seismic discontinuities in the mantle transition zone. The boundary sensitivity kernels based on Born approximation are formulated in the framework of traveling-wave mode summation to account for complete wave interactions within the measurement window. The sensitivity kernels allow us to employ frequency-dependent receiver functions in tomographic inversions to map the topography of the 410-km and 660-km discontinuities. We will discuss preliminary results on the structure of mantle transition zone discontinuities beneath the continental US imaged from finite-frequency receiver-function tomography using seismograms recorded at USArray TA stations.
Good-Turing frequency estimation in a finite population.
Hwang, Wen-Han; Lin, Chih-Wei; Shen, Tsung-Jen
2015-03-01
Good-Turing frequency estimation (Good, ) is a simple, effective method for predicting detection probabilities of objects of both observed and unobserved classes based on observed frequencies of classes in a sample. The method has been used widely in several disciplines, such as information retrieval, computational linguistics, text recognition, and ecological diversity estimation. Nevertheless, existing studies assume sampling with replacement or sampling from an infinite population, which might be inappropriate for many practical applications. In light of this limitation, this article presents a modification of the Good-Turing estimation method to account for finite population sampling. We provide three practical extensions of the modified method, and we examine performance of the modified method and its extensions in simulation experiments. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Visco-hyperelastic law for finite deformations: a frequency analysis.
Charlebois, Mathieu; Motallebzadeh, Hamid; Funnell, W Robert J
2013-08-01
Some biological tissues are repeatedly stimulated under cyclic loading, and this stimulation can be combined with large pressures, thus leading to large deformations. For such applications, visco-hyperelastic models have been proposed in the literature and used in finite-element studies. An extensively used quasi-linear model (QLVH), which assumes linear evolution equations, is compared with a nonlinear model (NLVH), which assumes a multiplicative split of the deformation gradient. The comparison is made here using sets of simulations covering a large frequency range. Lost and stored energies are computed, and the additional parameter of the NLVH model is set to two values found in the literature (NLVH-2 and NLVH-30 models). The predicted behaviour is very similar for all models at small strains, with each time constant (and corresponding viscous modulus) being associated with a damping peak and a stored-energy increase. When the strain amplitude is increased, the ratio of lost to stored energy increases for the QLVH model, but decreases for the NLVH models. The NLVH-30 model also displays a shift of the peak damping towards higher frequencies. Before reaching a steady state, all models display a decay of energy independent of the frequency, and the additional parameter of the NLVH model permits the modelling of complex types of evolution of the damping. In conclusion, this study compares the behaviour of two viscous hyper-elastic laws to allow an informed choice between them.
Measuring finite-frequency body-wave amplitudes and traveltimes
NASA Astrophysics Data System (ADS)
Sigloch, Karin; Nolet, Guust
2006-10-01
We have developed a method to measure finite-frequency amplitude and traveltime anomalies of teleseismic P waves. We use a matched filtering approach that models the first 25 s of a seismogram after the P arrival, which includes the depth phases pP and sP. Given a set of broad-band seismograms from a teleseismic event, we compute synthetic Green's functions using published moment tensor solutions. We jointly deconvolve global or regional sets of seismograms with their Green's functions to obtain the broad-band source time function. The matched filter of a seismogram is the convolution of the Green's function with the source time function. Traveltimes are computed by cross-correlating each seismogram with its matched filter. Amplitude anomalies are defined as the multiplicative factors that minimize the RMS misfit between matched filters and data. The procedure is implemented in an iterative fashion, which allows for joint inversion for the source time function, amplitudes, and a correction to the moment tensor. Cluster analysis is used to identify azimuthally distinct groups of seismograms when source effects with azimuthal dependence are prominent. We then invert for one source time function per group. We implement this inversion for a range of source depths to determine the most likely depth, as indicated by the overall RMS misfit, and by the non-negativity and compactness of the source time function. Finite-frequency measurements are obtained by filtering broad-band data and matched filters through a bank of passband filters. The method is validated on a set of 15 events of magnitude 5.8 to 6.9. Our focus is on the densely instrumented Western US. Quasi-duplet events (`quplets') are used to estimate measurement uncertainty on real data. Robust results are achieved for wave periods between 24 and 2 s. Traveltime dispersion is on the order of 0.5 s. Amplitude anomalies are on the order of 1 db in the lowest bands and 3 db in the highest bands, corresponding to
Xu, M; Tynan, G R; Diamond, P H; Manz, P; Holland, C; Fedorczak, N; Thakur, S Chakraborty; Yu, J H; Zhao, K J; Dong, J Q; Cheng, J; Hong, W Y; Yan, L W; Yang, Q W; Song, X M; Huang, Y; Cai, L Z; Zhong, W L; Shi, Z B; Ding, X T; Duan, X R; Liu, Y
2012-06-15
The absolute rate of nonlinear energy transfer among broadband turbulence, low-frequency zonal flows (ZFs) and geodesic acoustic modes (GAMs) was measured for the first time in fusion-grade plasmas using two independent methods across a range of heating powers. The results show that turbulent kinetic energy from intermediate frequencies (20-80 kHz) was transferred into ZFs and GAMs, as well as into fluctuations at higher frequencies (>80 kHz). As the heating power was increased, the energy transfer from turbulence into GAMs and the GAM amplitudes increased, peaked and then decreased, while the energy transfer into the ZFs and the ZFs themselves increased monotonically with heating power. Thus there exists a competition between ZFs and GAMs for the transfer of turbulent energy, and the transfer into ZFs becomes dominant as the heating power is increased. The poloidal-radial Reynolds stress and the mean radial electric field profiles were also measured at different heating powers and found to be consistent with the energy transfer measurement. The results suggest that ZFs play an important role in the low-to-high (L-H) plasma confinement transition.
The role of plasma elongation on the linear damping of zonal flows
Angelino, P.; Garbet, X.; Ghendrih, Ph.; Grandgirard, V.; Sarazin, Y.; Dif-Pradalier, G.; Bottino, A.
2008-06-15
Drift wave turbulence is known to self-organize to form axisymmetric macroscopic flows. The basic mechanism for macroscopic flow generation is called inverse energy cascade. Essentially, it is an energy transfer from the short wavelengths to the long wavelengths in the turbulent spectrum due to nonlinear interactions. A class of macroscopic flows, the poloidally symmetric zonal flows, is widely recognized as a key constituent in nearly all cases and regimes of microturbulence, also because of the realization that zonal flows are a critical agent of self-regulation for turbulent transport. In tokamaks and other toroidal magnetic confinement systems, axisymmetric flows exist in two branches, a zero frequency branch and a finite frequency branch, named Geodesic Acoustic Modes (GAMs). The finite frequency is due to the geodesic curvature of the magnetic field. There is a growing body of evidence that suggests strong GAM activity in most devices. Theoretical investigation of the GAMs is still an open field of research. Part of the difficulty of modelling the GAMs stems from the requirement of running global codes. Another issue is that one cannot determine a simple one to one relation between turbulence stabilization and GAM activity. This paper focuses on the study of ion temperature gradient turbulence in realistic tokamak magnetohydrodynamic equilibria. Analytical and numerical analyses are applied to the study of geometrical effects on zonal flows oscillations. Results are shown on the effects of the plasma elongation on the GAM amplitude and frequency and on the zonal flow residual amplitude.
The role of plasma elongation on the linear damping of zonal flows
NASA Astrophysics Data System (ADS)
Angelino, P.; Garbet, X.; Villard, L.; Bottino, A.; Jolliet, S.; Ghendrih, Ph.; Grandgirard, V.; McMillan, B. F.; Sarazin, Y.; Dif-Pradalier, G.; Tran, T. M.
2008-06-01
Drift wave turbulence is known to self-organize to form axisymmetric macroscopic flows. The basic mechanism for macroscopic flow generation is called inverse energy cascade. Essentially, it is an energy transfer from the short wavelengths to the long wavelengths in the turbulent spectrum due to nonlinear interactions. A class of macroscopic flows, the poloidally symmetric zonal flows, is widely recognized as a key constituent in nearly all cases and regimes of microturbulence, also because of the realization that zonal flows are a critical agent of self-regulation for turbulent transport. In tokamaks and other toroidal magnetic confinement systems, axisymmetric flows exist in two branches, a zero frequency branch and a finite frequency branch, named Geodesic Acoustic Modes (GAMs). The finite frequency is due to the geodesic curvature of the magnetic field. There is a growing body of evidence that suggests strong GAM activity in most devices. Theoretical investigation of the GAMs is still an open field of research. Part of the difficulty of modelling the GAMs stems from the requirement of running global codes. Another issue is that one cannot determine a simple one to one relation between turbulence stabilization and GAM activity. This paper focuses on the study of ion temperature gradient turbulence in realistic tokamak magnetohydrodynamic equilibria. Analytical and numerical analyses are applied to the study of geometrical effects on zonal flows oscillations. Results are shown on the effects of the plasma elongation on the GAM amplitude and frequency and on the zonal flow residual amplitude.
Frequency measurements in a finite cylinder wake at a subcritical Reynolds number
NASA Technical Reports Server (NTRS)
Budair, M.; Ayoub, A.; Karamcheti, K.
1991-01-01
A spectral study of a hot-wire investigation in the near wake of a finite circular cylinder of high-aspect ratio is reported. The measurements included frequency spectra and cross correlations in spanwise and streamwise directions. The study identifies four spanwise regions, in terms of frequency, in the immediate wake of the finite cylinder.
Finite frequency tomography shows a variety of plumes
NASA Astrophysics Data System (ADS)
Nolet, G.; Montelli, R.; Masters, G.; Dahlen, F. A.; Hung, S.
2003-04-01
The new technique of finite-frequency tomography (see abstract by Montelli et al., this meeting) is very powerful in imaging objects of small dimension in the lower mantle. The first global images of P velocity anomalies obtained by using this technique to invert a small but very accurate data set of long period P arrivals bottoming in the lower mantle show 18 low velocity anomalies in excess of -0.5%, all but two of which are associated with a known hotspot at the surface, and they serve as an unprecented glimpse into the deep mechanisms that give rise to hotspots. The following synopsis is given under the caveat that we have not yet incorporated high frequency waves into the interpretation, nor completed a full resolution analysis at the time of writing of this abstract (both will be presented at the meeting). We observe six or seven hotspots fed by a plume extending to the core-mantle boundary: Cap Verde, Easter Island, Hawaii, Kerguelen, St Helena, Tahiti, and perhaps also Azores. Several hotspots, among which are Bouvet, Bowie, and Mount Erebus, seem to originate at mid-mantle depth, while others (Afar, Ascension, Galapagos, Iceland, la Reunion and others) seem to be mostly confined to the upper mantle. Many renowned hotspots (such as Eifel, Samoa and Yellowstone) have only very weak low velocity anomalies at depth and may be the result of superficial processes confined to the top of the upper mantle. We confirm the existence of the two superplumes which both have Δ V_P < -0.5% extending as high as 2000 km depth. It is clear that no one plume/hotspot model can explain the variety in deep expressions of hotspots in the mantle. If midmantle plume origins represent originally deep plumes in their end stage, while the two unidentified anomalies are either beginning new plumes (Greenland) or plumes cut off in their initial ascent (W. Pacific), the large number of plumes caught in this phase would point to lengthy rise times of the order of tens of millions of
Reprint of : Finite-frequency noise in a topological superconducting wire
NASA Astrophysics Data System (ADS)
Valentini, Stefano; Governale, Michele; Fazio, Rosario; Taddei, Fabio
2016-08-01
In this paper we study the finite-frequency current cross-correlations for a topological superconducting nanowire attached to two terminals at one of its ends. Using an analytic 1D model we show that the presence of a Majorana bound state yields vanishing cross-correlations for frequencies larger than twice the applied transport voltage, in contrast to what is found for a zero-energy ordinary Andreev bound state. Zero cross-correlations at high frequency have been confirmed using a more realistic tight-binding model for finite-width topological superconducting nanowires. Finite-temperature effects have also been investigated.
NASA Astrophysics Data System (ADS)
Tai, C.
2007-12-01
These two-dimensional spectra show the prevalence of free baroclinic Rossby waves from the equatorial region to the mid-latitudes. An innovation based on segregating the Fourier components into standing and propagating modes has helped reveal the Rossby waves more clearly where they have been obscured previously by the seal- level signatures of the seasonal heating and cooling cycle. It is found that the linear theory of Rossby waves applies well for most of the ocean (i.e., ignoring zonal and meridional density variations associated with the mean flow) with the possible exception in regions closer to the western boundary currents. That is, the Rossby wave speed is more or less uniform zonally across the North Pacific except closer to the western end in mid- latitudes. From the zonal and meridional distribution of the power of these Rossby waves, the source of these waves can be deciphered.
Bieri, Oliver
2011-02-01
Conceptually, the only flaw in the standard steady-state free precession theory is the assumption of quasi-instantaneous radio-frequency pulses, and 10-20% signal deviations from theory are observed for common balanced steady-state free precession protocols. This discrepancy in the steady-state signal can be resolved by a simple T(2) substitution taking into account reduced transverse relaxation effects during finite radio-frequency excitation. However, finite radio-frequency effects may also affect the transient phase of balanced steady-state free precession, its contrast or its spin-echo nature and thereby have an adverse effect on common steady-state free precession magnetization preparation methods. As a result, an in-depth understanding of finite radio-frequency effects is not only of fundamental theoretical interest but also has direct practical implications. In this article, an analytical solution for balanced steady-state free precession with finite radio-frequency pulses is derived for the transient phase (under ideal conditions) and in the steady state demonstrating that balanced steady-state free precession key features are preserved but revealing an unexpected dependency of finite radio-frequency effects on relaxation times for the transient decay. Finally, the mathematical framework reveals that finite radio-frequency theory can be understood as a generalization of alternating repetition time and fluctuating equilibrium steady-state free precession sequence schemes. Copyright © 2010 Wiley-Liss, Inc.
On the validation of seismic imaging methods: Finite frequency or ray theory?
Maceira, Monica; Larmat, Carene; Porritt, Robert W.; ...
2015-01-23
We investigate the merits of the more recently developed finite-frequency approach to tomography against the more traditional and approximate ray theoretical approach for state of the art seismic models developed for western North America. To this end, we employ the spectral element method to assess the agreement between observations on real data and measurements made on synthetic seismograms predicted by the models under consideration. We check for phase delay agreement as well as waveform cross-correlation values. Based on statistical analyses on S wave phase delay measurements, finite frequency shows an improvement over ray theory. Random sampling using cross-correlation values identifiesmore » regions where synthetic seismograms computed with ray theory and finite-frequency models differ the most. Our study suggests that finite-frequency approaches to seismic imaging exhibit measurable improvement for pronounced low-velocity anomalies such as mantle plumes.« less
On the validation of seismic imaging methods: Finite frequency or ray theory?
NASA Astrophysics Data System (ADS)
Maceira, Monica; Larmat, Carene; Porritt, Robert W.; Higdon, David M.; Rowe, Charlotte A.; Allen, Richard M.
2015-01-01
We investigate the merits of the more recently developed finite-frequency approach to tomography against the more traditional and approximate ray theoretical approach for state of the art seismic models developed for western North America. To this end, we employ the spectral element method to assess the agreement between observations on real data and measurements made on synthetic seismograms predicted by the models under consideration. We check for phase delay agreement as well as waveform cross-correlation values. Based on statistical analyses on S wave phase delay measurements, finite frequency shows an improvement over ray theory. Random sampling using cross-correlation values identifies regions where synthetic seismograms computed with ray theory and finite-frequency models differ the most. Our study suggests that finite-frequency approaches to seismic imaging exhibit measurable improvement for pronounced low-velocity anomalies such as mantle plumes.
Zonal techniques for flowfield simulation about aircraft
NASA Technical Reports Server (NTRS)
Walters, Robert W.; Reu, Taekyu; Mcgrory, William D.; Thomas, James L.
1988-01-01
A technique for performing conservative flowfield calculations on zonal meshes is described. The underlying flow solver is an implicit, upwind finite volume scheme which can incorporate either a perfect gas or an equilibrium air equation of state. Two different approaches which yield identical results, in terms of performing a conservative flux calculation on a zonal interface, are described and compared in terms of numerical efficiency. The capability of the method to handle relatively complex geometries is demonstrated by considering the flowfield about a model SR71 aircraft.
High Frequency Ground Motion from Finite Fault Rupture Simulations
NASA Astrophysics Data System (ADS)
Crempien, Jorge G. F.
There are many tectonically active regions on earth with little or no recorded ground motions. The Eastern United States is a typical example of regions with active faults, but with low to medium seismicity that has prevented sufficient ground motion recordings. Because of this, it is necessary to use synthetic ground motion methods in order to estimate the earthquake hazard a region might have. Ground motion prediction equations for spectral acceleration typically have geometric attenuation proportional to the inverse of distance away from the fault. Earthquakes simulated with one-dimensional layered earth models have larger geometric attenuation than the observed ground motion recordings. We show that as incident angles of rays increase at welded boundaries between homogeneous flat layers, the transmitted rays decrease in amplitude dramatically. As the receiver distance increases away from the source, the angle of incidence of up-going rays increases, producing negligible transmitted ray amplitude, thus increasing the geometrical attenuation. To work around this problem we propose a model in which we separate wave propagation for low and high frequencies at a crossover frequency, typically 1Hz. The high-frequency portion of strong ground motion is computed with a homogeneous half-space and amplified with the available and more complex one- or three-dimensional crustal models using the quarter wavelength method. We also make use of seismic coda energy density observations as scattering impulse response functions. We incorporate scattering impulse response functions into our Green's functions by convolving the high-frequency homogeneous half-space Green's functions with normalized synthetic scatterograms to reproduce scattering physical effects in recorded seismograms. This method was validated against ground motion for earthquakes recorded in California and Japan, yielding results that capture the duration and spectral response of strong ground motion.
Wang, Shumin; Duyn, Jeff H
2008-05-21
A hybrid method that combines the finite-difference time-domain (FDTD) method and the finite-element time-domain (FETD) method is presented for simulating radio-frequency (RF) coils in magnetic resonance imaging. This method applies a high-fidelity FETD method to RF coils, while the human body is modeled with a low-cost FDTD method. Since the FDTD and the FETD methods are applied simultaneously, the dynamic interaction between RF coils and the human body is fully accounted for. In order to simplify the treatment of the highly irregular FDTD/FETD interface, composite elements are proposed. Two examples are provided to demonstrate the validity and effectiveness of the hybrid method in high-field receive-and-transmit coil design. This approach is also applicable to general bio-electromagnetic simulations.
A conservative treatment of zonal boundaries for Euler equation calculations
NASA Technical Reports Server (NTRS)
Rai, M. M.
1984-01-01
Finite-difference calculations require the generation of a grid for the region of interest. A zonal approach, wherein the given region is subdivided into zones and the grid for each zone is generated independently, makes the grid-generation process for complicated topologies and for regions requiring selective grid refinement a fairly simple task. This approach results in new boundaries within the given region, that is, zonal boundaries at the interfaces of the various zones. The zonal-boundary scheme (the integration scheme used to update the points on the zonal boundary) for the Euler equations must be conservative, accurate, stable, and applicable to general curvilinear coordinate systems. A zonal-boundary scheme with these desirable properties is developed in this study. The scheme is designed for explicit, first-order-accurate integration schemes but can be modified to accommodate second-order-accurate explicit and implicit integration schemes. Results for inviscid flow, including supersonic flow over a cylinder, blast-wave diffraction by a ramp, and one-dimensional shock-tube flow are obtained on zonal grids. The conservative nature of the zonal-boundary scheme permits the smooth transition of the discontinuities associated with these flows from one zone to another. The calculations also demonstrate the continuity of contour lines across zonal boundaries that can be achieved with the present zonal scheme.
Feng, Xiaobing
1996-12-31
A non-overlapping domain decomposition iterative method is proposed and analyzed for mixed finite element methods for a sequence of noncoercive elliptic systems with radiation boundary conditions. These differential systems describe the motion of a nearly elastic solid in the frequency domain. The convergence of the iterative procedure is demonstrated and the rate of convergence is derived for the case when the domain is decomposed into subdomains in which each subdomain consists of an individual element associated with the mixed finite elements. The hybridization of mixed finite element methods plays a important role in the construction of the discrete procedure.
Finite frequency effects on global S diffracted traveltimes
NASA Astrophysics Data System (ADS)
To, Akiko; Romanowicz, Barbara
2009-12-01
Many seismic observations have shown that strong heterogeneities exist in the bottom few hundreds kilometres of the mantle. Among different seismic phases, this region, that is, the D'' layer, can be most globally sampled by diffracted waves along the core mantle boundary. Here, we assess the amplitude and distribution of S-wave velocity variations in the D'' layer of an existing tomographic model. We compare observed SHdiff traveltime anomalies to synthetic ones obtained using (1) the coupled spectral element method (CSEM), which is our reference exact method, (2) non-linear asymptotic coupling theory (NACT) and (3) 1-D ray theory. Synthetic waveforms are calculated down to 0.057 Hz with a corner frequency at 0.026 Hz. In the first part of this paper, we compare the traveltime anomaly predictions from the three different methods. The anomalies from CSEM and NACT are obtained by taking cross-correlations of the 3-D and 1-D synthetic waveforms. Both NACT and standard ray theory, which are used in other recent tomographic models, suffer from biases in traveltime predictions for vertically varying structure near the core-mantle boundary: NACT suffers from saturation of traveltimes, due to the portion in the kernel calculation that is based on the reference 1-D model, while ray theory suffers from wave front healing effects in the vertical plane, exacerbated in the presence of thin low velocity layers. In the second part, we compare observed traveltime anomalies and predictions from CSEM. The data consists of 506 Sdiff traveltime anomalies from 15 events, obtained form global seismograph network records. The tomographic model does a good job at predicting traveltimes of Sdiff phases especially when the path mostly samples fast S velocity regions at the base of the mantle, such as beneath India, China, North America and Northern Pacific. The underprediction of the positive observed traveltime anomalies seems to occur in regions where the paths sample close to the border
Nonfragile filtering for discrete-time linear systems in finite-frequency domain
NASA Astrophysics Data System (ADS)
Ding, Da-Wei; Li, Xiaoli; Wang, Youyi
2013-04-01
This article investigates the problem of nonfragile filter design for discrete-time linear systems subject to noises with known frequency ranges. Additive interval uncertainty reflecting imprecision in filter implementation is considered. By the aid of generalised KYP lemma, both deterministic and randomised filtering algorithms are proposed to deal with noises in low-, middle- and high-frequency domain, respectively. The proposed nonfragile finite-frequency filters can get a better noise attenuation performance when frequency ranges of noises are known beforehand. An example about F-18 aircraft model is given to illustrate the effectiveness of the proposed algorithms.
Low-frequency scaling applied to stochastic finite-fault modeling
NASA Astrophysics Data System (ADS)
Crane, Stephen; Motazedian, Dariush
2014-01-01
Stochastic finite-fault modeling is an important tool for simulating moderate to large earthquakes. It has proven to be useful in applications that require a reliable estimation of ground motions, mostly in the spectral frequency range of 1 to 10 Hz, which is the range of most interest to engineers. However, since there can be little resemblance between the low-frequency spectra of large and small earthquakes, this portion can be difficult to simulate using stochastic finite-fault techniques. This paper introduces two different methods to scale low-frequency spectra for stochastic finite-fault modeling. One method multiplies the subfault source spectrum by an empirical function. This function has three parameters to scale the low-frequency spectra: the level of scaling and the start and end frequencies of the taper. This empirical function adjusts the earthquake spectra only between the desired frequencies, conserving seismic moment in the simulated spectra. The other method is an empirical low-frequency coefficient that is added to the subfault corner frequency. This new parameter changes the ratio between high and low frequencies. For each simulation, the entire earthquake spectra is adjusted, which may result in the seismic moment not being conserved for a simulated earthquake. These low-frequency scaling methods were used to reproduce recorded earthquake spectra from several earthquakes recorded in the Pacific Earthquake Engineering Research Center (PEER) Next Generation Attenuation Models (NGA) database. There were two methods of determining the stochastic parameters of best fit for each earthquake: a general residual analysis and an earthquake-specific residual analysis. Both methods resulted in comparable values for stress drop and the low-frequency scaling parameters; however, the earthquake-specific residual analysis obtained a more accurate distribution of the averaged residuals.
NASA Astrophysics Data System (ADS)
Wu, Shun-Der; Glytsis, Elias N.
2002-10-01
The effects of finite number of periods (FNP) and finite incident beams on the diffraction efficiencies of holographic gratings are investigated by the finite-difference frequency-domain (FDFD) method. Gratings comprising 20, 15, 10, 5, and 3 periods illuminated by TE and TM incident light with various beam sizes are analyzed with the FDFD method and compared with the rigorous coupled-wave analysis (RCWA). Both unslanted and slanted gratings are treated in transmission as well as in reflection configurations. In general, the effect of the FNP is a decrease in the diffraction efficiency with a decrease in the number of periods of the grating. Similarly, a decrease in incident-beam width causes a decrease in the diffraction efficiency. Exceptions appear in off-Bragg incidence in which a smaller beam width could result in higher diffraction efficiency. For beam widths greater than 10 grating periods and for gratings with more than 20 periods in width, the diffraction efficiencies slowly converge to the values predicted by the RCWA (infinite incident beam and infinite-number-of-periods grating) for both TE and TM polarizations. Furthermore, the effects of FNP holographic gratings on their diffraction performance are found to be comparable to their counterparts of FNP surface-relief gratings. 2002 Optical Society of America
The relationship between a Zonal index and blocking activity
Kaas, E. ); Branstator, G. )
1993-09-15
The degree to which Northern Hemisphere blocking activity is controlled by variations in zonal mean conditions is investigated. A set of Northern Hemisphere winter season 500-hPa analyzed fields is examined for blocks using an objective index defined solely from the eddy fields. With this blocking index, it is shown that in most regions enhanced blocking activity is associated with relatively strong zonally average winds around 30[degrees]N and weak winds around 50[degrees]-60[degrees]N. Also, the preferred zonal positions of blocks are related to the state of the zonal mean flow. A similar analysis is carried out using data from a perpetual January GCM (general circulation model) simulation and the sam relationship between blocking activity and zonally conditions is found to be valid to an even stronger degree for these data. To investigate whether anomalous zonal mean flows are actually controlling the associated level of blocking activity, two experiments with the GCM are performed. In one experiment the zonal mean state of the GCM is forced toward a configuration that is statistically associated with enhanced blocking activity in the control simulation. In the other, the zonal mean is forced toward a state associated with suppressed blocking activity. Blocking frequency is enhanced in the first experiment and weakened in the second. Futhermore, the preferred locations for blocking in the experiments match the locations found to be associated with zonal mean anomalies in the control. This suggests the zonal mean state is influencing blocking activity. Results from a steady barotropic linear model indicate that adjustments made by the planetary waves in reaction to anomalies in the zonal mean flow are partly responsible for the relationship between blocking and the zonal mean state. 30 refs., 14 figs.
Witteveen, Jeroen A.S. Bijl, Hester
2009-10-01
The Unsteady Adaptive Stochastic Finite Elements (UASFE) method resolves the effect of randomness in numerical simulations of single-mode aeroelastic responses with a constant accuracy in time for a constant number of samples. In this paper, the UASFE framework is extended to multi-frequency responses and continuous structures by employing a wavelet decomposition pre-processing step to decompose the sampled multi-frequency signals into single-frequency components. The effect of the randomness on the multi-frequency response is then obtained by summing the results of the UASFE interpolation at constant phase for the different frequency components. Results for multi-frequency responses and continuous structures show a three orders of magnitude reduction of computational costs compared to crude Monte Carlo simulations in a harmonically forced oscillator, a flutter panel problem, and the three-dimensional transonic AGARD 445.6 wing aeroelastic benchmark subject to random fields and random parameters with various probability distributions.
Finite element modeling of truss structures with frequency-dependent material damping
NASA Technical Reports Server (NTRS)
Lesieutre, George A.
1991-01-01
A physically motivated modelling technique for structural dynamic analysis that accommodates frequency dependent material damping was developed. Key features of the technique are the introduction of augmenting thermodynamic fields (AFT) to interact with the usual mechanical displacement field, and the treatment of the resulting coupled governing equations using finite element analysis methods. The AFT method is fully compatible with current structural finite element analysis techniques. The method is demonstrated in the dynamic analysis of a 10-bay planar truss structure, a structure representative of those contemplated for use in future space systems.
NASA Technical Reports Server (NTRS)
Lee, L. C.
1976-01-01
The cross correlation of the intensity fluctuations between different frequencies and finite bandwidth effects on the intensity correlations based on the Markov approximation were calculated. Results may be applied to quite general turbulence spectra for an extended turbulent medium. Calculations of the cross-correlation function and of finite bandwidth effects are explicitly carried out for both Gaussian and Kolmogorov turbulence spectra. The increases of the correlation scale of intensity fluctuations are different for these two spectra and the difference can be used to determine whether the interstellar turbulent medium has a Gaussian or a Kolmogorov spectrum.
Generation of zonal flow and magnetic field in the ionospheric E-layer
NASA Astrophysics Data System (ADS)
Kahlon, L. Z.; Kaladze, T. D.
2015-10-01
> We review the generation of zonal flow and magnetic field by coupled electromagnetic ultra-low-frequency waves in the Earth's ionospheric E-layer. It is shown that, under typical ionospheric E-layer conditions, different planetary low-frequency waves can couple with each other. Propagation of coupled internal-gravity-Alfvén, coupled Rossby-Khantadze and coupled Rossby-Alfvén-Khantadze waves is revealed and studied. A set of appropriate equations describing the nonlinear interaction of such waves with sheared zonal flow is derived. The conclusion on the instability of short-wavelength turbulence of such coupled waves with respect to the excitation of low-frequency and large-scale perturbation of the sheared zonal flow and sheared magnetic field is deduced. The nonlinear mechanism of the instability is based on the parametric triple interaction of finite-amplitude coupled waves leading to the inverse energy cascade towards longer wavelength. The possibility of generation of an intense mean magnetic field is shown. Obtained growth rates are discussed for each case of the considered coupled waves.
NASA Astrophysics Data System (ADS)
Kumar, Ramesh; Kore, Sachin D.
2016-10-01
Electromagnetic compression of the tube is a high strain rate forming process, in this process formability of the material can be increased by reducing the spring back effect developed in the process. High electrical conductivity materials like copper, aluminum are generally used for electromagnetic compression. In electromagnetic compression, frequency of the current pulse is an important parameter to be analyzed. In this work the effect of current pulse frequency on the electromagnetic compression of the tube has been studied. The tube and coil were modelled and analyzed using finite element software LS-DYNA. It has been found that the deformation obtained during tube compression were increases first with the increase in frequency, obtained a maximum value and then decreases with the further increase in the frequency. The change in frequency greatly influences the deformation obtained during the electromagnetic compression of tubes.
NASA Astrophysics Data System (ADS)
Chen, M.; Wei, S.
2016-12-01
The serious damage of Mexico City caused by the 1985 Michoacan earthquake 400 km away indicates that urban areas may be affected by remote earthquakes. To asses earthquake risk of urban areas imposed by distant earthquakes, we developed a hybrid Frequency Wavenumber (FK) and Finite Difference (FD) code implemented with MPI, since the computation of seismic wave propagation from a distant earthquake using a single numerical method (e.g. Finite Difference, Finite Element or Spectral Element) is very expensive. In our approach, we compute the incident wave field (ud) at the boundaries of the excitation box, which surrounding the local structure, using a paralleled FK method (Zhu and Rivera, 2002), and compute the total wave field (u) within the excitation box using a parallelled 2D FD method. We apply perfectly matched layer (PML) absorbing condition to the diffracted wave field (u-ud). Compared to previous Generalized Ray Theory and Finite Difference (Wen and Helmberger, 1998), Frequency Wavenumber and Spectral Element (Tong et al., 2014), and Direct Solution Method and Spectral Element hybrid method (Monteiller et al., 2013), our absorbing boundary condition dramatically suppress the numerical noise. The MPI implementation of our method can greatly speed up the calculation. Besides, our hybrid method also has a potential use in high resolution array imaging similar to Tong et al. (2014).
Robust fault-tolerant H∞ control of active suspension systems with finite-frequency constraint
NASA Astrophysics Data System (ADS)
Wang, Rongrong; Jing, Hui; Karimi, Hamid Reza; Chen, Nan
2015-10-01
In this paper, the robust fault-tolerant (FT) H∞ control problem of active suspension systems with finite-frequency constraint is investigated. A full-car model is employed in the controller design such that the heave, pitch and roll motions can be simultaneously controlled. Both the actuator faults and external disturbances are considered in the controller synthesis. As the human body is more sensitive to the vertical vibration in 4-8 Hz, robust H∞ control with this finite-frequency constraint is designed. Other performances such as suspension deflection and actuator saturation are also considered. As some of the states such as the sprung mass pitch and roll angles are hard to measure, a robust H∞ dynamic output-feedback controller with fault tolerant ability is proposed. Simulation results show the performance of the proposed controller.
Reliable finite frequency filter design for networked control systems with sensor faults.
Ju, He-Hua; Long, Yue; Wang, Heng
2012-01-01
This paper is concerned with the reliable finite frequency filter design for networked control systems (NCSs) subject to quantization and data missing. Taking into account quantization, possible data missing and sensor stuck faults, NCSs are modeled in the framework of discrete time-delay switched systems, and the finite frequency l(2) gain is adopted for the filter design of discrete time-delay switched systems, which is converted into a set of linear matrix inequality (LMI) conditions. By the virtues of the derived conditions, a procedure of reliable filter synthesis is presented. Further, the filter gains are characterized in terms of solutions to a convex optimization problem which can be solved by using the semi-definite programme method. Finally, an example is given to illustrate the effectiveness of the proposed method.
Reliable Finite Frequency Filter Design for Networked Control Systems with Sensor Faults
Ju, He-Hua; Long, Yue; Wang, Heng
2012-01-01
This paper is concerned with the reliable finite frequency filter design for networked control systems (NCSs) subject to quantization and data missing. Taking into account quantization, possible data missing and sensor stuck faults, NCSs are modeled in the framework of discrete time-delay switched systems, and the finite frequency l2 gain is adopted for the filter design of discrete time-delay switched systems, which is converted into a set of linear matrix inequality (LMI) conditions. By the virtues of the derived conditions, a procedure of reliable filter synthesis is presented. Further, the filter gains are characterized in terms of solutions to a convex optimization problem which can be solved by using the semi-definite programme method. Finally, an example is given to illustrate the effectiveness of the proposed method. PMID:22969382
Global tomography using finite-frequency kernels in the wavelet domain
NASA Astrophysics Data System (ADS)
Douma, H.; Loris, I.; Fornasier, M.; Vetter, P.; Judd, S.; Nolet, G.; Daubechies, I.
2007-12-01
Finite-frequency tomographic methods find their origin in the recognition that seismic waves are sensitive to the earth's structure not only on but also in a neighborhood of the ray connecting source and receiver. The sensitivity kernels are therefore nonzero within some positive distance from this ray. Real-life tomographic applications often need to employ a coarse model parameterization to reduce the number of model parameters and make the inversion practical from a computational point of view. This coarse parameterization, however, substantially reduces the benefit in resolution of finite-frequency tomography when compared to classical tomographic methods; standard coarse parameterization effectively turns the finite-frequency sensitivity kernels into 'fat' rays. To overcome this we are developing global-scale finite-frequency tomography in the wavelet domain, where the sparseness of both the sensitivity kernel and the model can be exploited in carrying out the inversion. We work on the cubed sphere to allow us to use wavelet transforms in Cartesian coordinates. This cubed sphere is built through a one-to-one mapping of Cartesian coordinates on each face of the cube to the corresponding "faces of the sphere". At the edges of each of the faces of the cube, the mapping is singular; this induces artifical singularities in the model and kernel, which in the wavelet domain would show up as large coefficients. We avoid these artificially large wavelet coefficients by using domain-adapted wavelets based on the construction of wavelets on the interval. The inversion is based on an l1-norm minimization procedure. We will present some preliminary examples.
A double expansion method for the frequency response of finite-length beams with periodic parameters
NASA Astrophysics Data System (ADS)
Ying, Z. G.; Ni, Y. Q.
2017-03-01
A double expansion method for the frequency response of finite-length beams with periodic distribution parameters is proposed. The vibration response of the beam with spatial periodic parameters under harmonic excitations is studied. The frequency response of the periodic beam is the function of parametric period and then can be expressed by the series with the product of periodic and non-periodic functions. The procedure of the double expansion method includes the following two main steps: first, the frequency response function and periodic parameters are expanded by using identical periodic functions based on the extension of the Floquet-Bloch theorem, and the period-parametric differential equation for the frequency response is converted into a series of linear differential equations with constant coefficients; second, the solutions to the linear differential equations are expanded by using modal functions which satisfy the boundary conditions, and the linear differential equations are converted into algebraic equations according to the Galerkin method. The expansion coefficients are obtained by solving the algebraic equations and then the frequency response function is finally determined. The proposed double expansion method can uncouple the effects of the periodic expansion and modal expansion so that the expansion terms are determined respectively. The modal number considered in the second expansion can be reduced remarkably in comparison with the direct expansion method. The proposed double expansion method can be extended and applied to the other structures with periodic distribution parameters for dynamics analysis. Numerical results on the frequency response of the finite-length periodic beam with various parametric wave numbers and wave amplitude ratios are given to illustrate the effective application of the proposed method and the new frequency response characteristics, including the parameter-excited modal resonance, doubling-peak frequency response
Ahmed, B.; Ahmad, J.; Guy, G.
1994-09-01
A finite elements method coupled with the Preisach model of hysteresis is used to compute-the ferrite losses in medium power transformers (10--60 kVA) working at relatively high frequencies (20--60 kHz) and with an excitation level of about 0.3 Tesla. The dynamic evolution of the permeability is taken into account. The simple and doubly cubic spline functions are used to account for temperature effects respectively on electric and on magnetic parameters of the ferrite cores. The results are compared with test data obtained with 3C8 and B50 ferrites at different frequencies.
Algorithms for Zonal Methods and Development of Three Dimensional Mesh Generation Procedures.
1984-02-01
zonal methods and 4D-grid generation procedures for application of finite difference methods to solve complex aircraft con- figurations. For the task...this research has been to further develop grid generation procedures and zonal methods so as to extend the applications of nonlinear finite difference ...C - - A CHIMERA GRID SCHEME .................... 51 APPENDIX D - - A CONSERVATIVE FINITE DIFFERENCE ALGORITHM FOR THE UNSTEADY TRANSONIC POTENTIAL
Zonal matrix iterative method for wavefront reconstruction from gradient measurements.
Panagopoulou, Sophia I; Neal, Daniel R
2005-01-01
To present an alternate method to Zemike decomposition (modal) of wavefront reconstruction using iterative implicit solution to the finite difference equations (zonal). Different reconstruction methods, modal and zonal, were compared and the advantages of each method were analyzed. Although the modal or Zemike method allows for quantitative interpretation of some of the aberrations, it is cumbersome for use with fine details and may lead to errors for eyes with keratoconus or other rapidly varying aberration. The zonal method produces a very high-resolution map that can be used for identifying irregular structures. The distinction between the two methods is useful to maintain, and the solution methods are generally different. In practice, both methods are useful and, with modern computers, both zonal and lower-order modal may be calculated rapidly. The difference between the wavefronts derived from the two methods may provide useful insight or interpretation of the infornation.
Stochastically forced zonal flows
NASA Astrophysics Data System (ADS)
Srinivasan, Kaushik
This thesis investigates the dynamics of multiple zonal jets, that spontaneously emerge on the barotropic beta-plane, driven by a homogenous and rapidly decorrelating forcing and damped by bottom drag. Decomposing the barotropic vorticity equation into the zonal-mean and eddy equations, and neglecting the eddy-eddy interactions, defines the quasi-linear (QL) system. Numerical solution of the QL system shows zonal jets with length scales comparable to jets obtained by solving the nonlinear (NL) system. Starting with the QL system, one can construct a deterministic equation for the evolution of the two-point single-time correlation function of the vorticity, from which one can obtain the Reynolds stress that drives the zonal mean flow. This deterministic system has an exact nonlinear solution, which is a homogenous eddy field with no jets. When the forcing is also isotropic in space, we characterize the linear stability of this jetless solution by calculating the critical stability curve in the parameter space and successfully comparing this analytic result with numerical solutions of the QL system. But the critical drag required for the onset of NL zonostrophic instability is up to a factor of six smaller than that for QL zonostrophic instability. The constraint of isotropic forcing is then relaxed and spatially anisotropic forcing is used to drive the jets. Meridionally drifting jets are observed whenever the forcing breaks an additional symmetry that we refer to as mirror, or reflexional symmetry. The magnitude of drift speed in our results shows a strong variation with both mu and beta: while the drift speed decreases almost linearly with decreasing mu, it actually increases as beta decreases. Similar drifting jets are also observed in QL, with the same direction (i.e. northward or southward) and similar magnitude as NL jet-drift. Starting from the laminar solution, and assuming a mean-flow that varies slowly with reference to the scale of the eddies, we obtain
NASA Technical Reports Server (NTRS)
Baumeister, Kenneth J.; Kreider, Kevin L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in aircraft engine nacelles. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
NASA Technical Reports Server (NTRS)
Baumeister, K. J.; Kreider, K. L.
1996-01-01
An explicit finite difference iteration scheme is developed to study harmonic sound propagation in ducts. To reduce storage requirements for large 3D problems, the time dependent potential form of the acoustic wave equation is used. To insure that the finite difference scheme is both explicit and stable, time is introduced into the Fourier transformed (steady-state) acoustic potential field as a parameter. Under a suitable transformation, the time dependent governing equation in frequency space is simplified to yield a parabolic partial differential equation, which is then marched through time to attain the steady-state solution. The input to the system is the amplitude of an incident harmonic sound source entering a quiescent duct at the input boundary, with standard impedance boundary conditions on the duct walls and duct exit. The introduction of the time parameter eliminates the large matrix storage requirements normally associated with frequency domain solutions, and time marching attains the steady-state quickly enough to make the method favorable when compared to frequency domain methods. For validation, this transient-frequency domain method is applied to sound propagation in a 2D hard wall duct with plug flow.
Finite-frequency-dependent noise of a quantum dot in a magnetic field
NASA Astrophysics Data System (ADS)
Moca, C. P.; Simon, P.; Chung, Chung-Hou; Zaránd, G.
2014-04-01
We present a detailed study for the finite-frequency current noise of a Kondo quantum dot in the presence of a magnetic field by using a recently developed real-time functional renormalization group approach [C. P. Moca, P. Simon, C. H. Chung, and G. Zaránd, Phys. Rev. B 83, 201303(R) (2011), 10.1103/PhysRevB.83.201303]. The scaling equations are modified in an external magnetic field; the couplings and nonlocal current vertices become strongly anisotropic, and develop new singularities. Consequently, in addition to the natural emission threshold frequency, ℏω =|eV|, a corresponding singular behavior is found to emerge in the noise spectrum at frequencies ℏω ≈|eV±B|. The predicted singularities are measurable with present-day experimental techniques.
A wide-range programmable frequency synthesizer based on a finite state machine filter
NASA Astrophysics Data System (ADS)
Alser, Mohammed H.; Assaad, Maher M.; Hussin, Fawnizu A.
2013-11-01
In this article, an FPGA-based design and implementation of a fully digital wide-range programmable frequency synthesizer based on a finite state machine filter is presented. The advantages of the proposed architecture are that, it simultaneously generates a high frequency signal from a low frequency reference signal (i.e. synthesising), and synchronising the two signals (signals have the same phase, or a constant difference) without jitter accumulation issue. The architecture is portable and can be easily implemented for various platforms, such as FPGAs and integrated circuits. The frequency synthesizer circuit can be used as a part of SERDES devices in intra/inter chip communication in system-on-chip (SoC). The proposed circuit is designed using Verilog language and synthesized for the Altera DE2-70 development board, with the Cyclone II (EP2C35F672C6) device on board. Simulation and experimental results are included; they prove the synthesizing and tracking features of the proposed architecture. The generated clock signal frequency of a range from 19.8 MHz to 440 MHz is synchronized to the input reference clock with a frequency step of 0.12 MHz.
Bora, B. Soto, L.
2014-08-15
Capacitively coupled radio frequency (CCRF) plasmas are widely studied in last decades due to the versatile applicability of energetic ions, chemically active species, radicals, and also energetic neutral species in many material processing fields including microelectronics, aerospace, and biology. A dc self-bias is known to generate naturally in geometrically asymmetric CCRF plasma because of the difference in electrode sizes known as geometrical asymmetry of the electrodes in order to compensate electron and ion flux to each electrode within one rf period. The plasma series resonance effect is also come into play due to the geometrical asymmetry and excited several harmonics of the fundamental in low pressure CCRF plasma. In this work, a 13.56 MHz CCRF plasma is studied on the based on the nonlinear global model of asymmetric CCRF discharge to understand the influences of finite geometrical asymmetry of the electrodes in terms of generation of dc self-bias and plasma heating. The nonlinear global model on asymmetric discharge has been modified by considering the sheath at the grounded electrode to taking account the finite geometrical asymmetry of the electrodes. The ion density inside both the sheaths has been taken into account by incorporating the steady-state fluid equations for ions considering that the applied rf frequency is higher than the typical ion plasma frequency. Details results on the influences of geometrical asymmetry on the generation of dc self-bias and plasma heating are discussed.
2.5-D frequency-domain viscoelastic wave modelling using finite-element method
NASA Astrophysics Data System (ADS)
Zhao, Jian-guo; Huang, Xing-xing; Liu, Wei-fang; Zhao, Wei-jun; Song, Jian-yong; Xiong, Bin; Wang, Shang-xu
2017-10-01
2-D seismic modelling has notable dynamic information discrepancies with field data because of the implicit line-source assumption, whereas 3-D modelling suffers from a huge computational burden. The 2.5-D approach is able to overcome both of the aforementioned limitations. In general, the earth model is treated as an elastic material, but the real media is viscous. In this study, we develop an accurate and efficient frequency-domain finite-element method (FEM) for modelling 2.5-D viscoelastic wave propagation. To perform the 2.5-D approach, we assume that the 2-D viscoelastic media are based on the Kelvin-Voigt rheological model and a 3-D point source. The viscoelastic wave equation is temporally and spatially Fourier transformed into the frequency-wavenumber domain. Then, we systematically derive the weak form and its spatial discretization of 2.5-D viscoelastic wave equations in the frequency-wavenumber domain through the Galerkin weighted residual method for FEM. Fixing a frequency, the 2-D problem for each wavenumber is solved by FEM. Subsequently, a composite Simpson formula is adopted to estimate the inverse Fourier integration to obtain the 3-D wavefield. We implement the stiffness reduction method (SRM) to suppress artificial boundary reflections. The results show that this absorbing boundary condition is valid and efficient in the frequency-wavenumber domain. Finally, three numerical models, an unbounded homogeneous medium, a half-space layered medium and an undulating topography medium, are established. Numerical results validate the accuracy and stability of 2.5-D solutions and present the adaptability of finite-element method to complicated geographic conditions. The proposed 2.5-D modelling strategy has the potential to address modelling studies on wave propagation in real earth media in an accurate and efficient way.
NASA Astrophysics Data System (ADS)
Bora, B.
2015-10-01
In recent years, dual capacitively coupled radio frequency (CCRF) glow discharge plasma has been widely studied in the laboratory because of its simpler design and high efficiency for different material processing applications such as thin-film deposition, plasma etching, sputtering of insulating materials etc. The main objective of studies on dual frequency CCRF plasma has been the independent control of ion energy and ion flux using an electrical asymmetry effect (EAE). Most studies have been reported in electrode configurations that are either geometrically symmetric (both electrodes are equal) or completely asymmetric (one electrode is infinitely bigger than the other). However, it seems that most of the laboratory CCRF plasmas have finite electrode geometry. In addition, plasma series resonance (PSR) and electron bounce resonance (EBR) heating also come into play as a result of geometrical asymmetry as well as EAE. In this study, a dual frequency CCRF plasma has been studied in which the dual frequency CCRF has been coupled to the lumped circuit model of the plasma and the time-independent fluid model of the plasma sheath, in order to study the effect of finite geometrical asymmetry on the generation of dc-self bias and plasma heating. The dc self-bias is found to strongly depend on the ratio of the area between the electrodes. The dc self-bias is found to depend on the phase angle between the two applied voltage waveforms. The EAE and geometrical asymmetry are found to work differently in controlling the dc self-bias. It can be concluded that the phase angle between the two voltage waveforms in dual CCRF plasmas has an important role in determining the dc self-bias and may be used for controlling the plasma properties in the dual frequency CCRF plasma.
Brigham, John C.; Aquino, Wilkins; Aguilo, Miguel A.; Diamessis, Peter J.
2010-01-01
An approach for efficient and accurate finite element analysis of harmonically excited soft solids using high-order spectral finite elements is presented and evaluated. The Helmholtz-type equations used to model such systems suffer from additional numerical error known as pollution when excitation frequency becomes high relative to stiffness (i.e. high wave number), which is the case, for example, for soft tissues subject to ultrasound excitations. The use of high-order polynomial elements allows for a reduction in this pollution error, but requires additional consideration to counteract Runge's phenomenon and/or poor linear system conditioning, which has led to the use of spectral element approaches. This work examines in detail the computational benefits and practical applicability of high-order spectral elements for such problems. The spectral elements examined are tensor product elements (i.e. quad or brick elements) of high-order Lagrangian polynomials with non-uniformly distributed Gauss-Lobatto-Legendre nodal points. A shear plane wave example is presented to show the dependence of the accuracy and computational expense of high-order elements on wave number. Then, a convergence study for a viscoelastic acoustic-structure interaction finite element model of an actual ultrasound driven vibroacoustic experiment is shown. The number of degrees of freedom required for a given accuracy level was found to consistently decrease with increasing element order. However, the computationally optimal element order was found to strongly depend on the wave number. PMID:21461402
Bouayed, Kaïss; Hamdi, Mohamed-Ali
2012-08-01
This paper presents numerical and experimental validation of results obtained by a shell finite element, which has been developed for modeling of the dynamic behavior of sandwich multilayered structures with a viscoelastic core. The proposed shell finite element is very easy to implement in existing finite element solvers, since it uses only the displacements as degrees of freedom at external faces and at inter-layer interfaces. The displacement field is linearly interpolated in the thickness direction of each layer, and analytical integration is made in the thickness direction in order to avoid meshing of each sandwich layer by solid elements. Only the two dimensional mid-surface of reference is meshed, facilitating the mesh generation task. A simplified modal approach using a real modal basis is also proposed to efficiently calculate the dynamic response of the sandwich structure. The proposed method reduces the memory size and computing time and takes into account the frequency-dependence of the polymer core mechanical properties. Results obtained by the proposed element in conjunction with the simplified modal method have been numerically and experimentally validated by comparison to results obtained by commercial software codes (MSC/NASTRAN and ESI/RAYON-VTM), and to measurements done on automobile windscreens.
Brigham, John C; Aquino, Wilkins; Aguilo, Miguel A; Diamessis, Peter J
2011-01-15
An approach for efficient and accurate finite element analysis of harmonically excited soft solids using high-order spectral finite elements is presented and evaluated. The Helmholtz-type equations used to model such systems suffer from additional numerical error known as pollution when excitation frequency becomes high relative to stiffness (i.e. high wave number), which is the case, for example, for soft tissues subject to ultrasound excitations. The use of high-order polynomial elements allows for a reduction in this pollution error, but requires additional consideration to counteract Runge's phenomenon and/or poor linear system conditioning, which has led to the use of spectral element approaches. This work examines in detail the computational benefits and practical applicability of high-order spectral elements for such problems. The spectral elements examined are tensor product elements (i.e. quad or brick elements) of high-order Lagrangian polynomials with non-uniformly distributed Gauss-Lobatto-Legendre nodal points. A shear plane wave example is presented to show the dependence of the accuracy and computational expense of high-order elements on wave number. Then, a convergence study for a viscoelastic acoustic-structure interaction finite element model of an actual ultrasound driven vibroacoustic experiment is shown. The number of degrees of freedom required for a given accuracy level was found to consistently decrease with increasing element order. However, the computationally optimal element order was found to strongly depend on the wave number.
Application of generalized Snoek's law over a finite frequency range: A case study
NASA Astrophysics Data System (ADS)
Rozanov, Konstantin N.; Koledintseva, Marina Y.
2016-02-01
Generalized Snoek's law proposed in an integral form by Acher and coauthors is a useful tool for investigation of high-frequency properties of magnetic materials. This integral law referred to as Acher's law allows for evaluating the ultimate performance of RF and microwave devices which employ magnetic materials. It may also be helpful in obtaining useful information on the structure and morphology of the materials. The key factor in practical application of Acher's law is an opportunity to employ either measured or calculated data available over a finite frequency range. The paper uses simple calculations to check the applicability of Acher's law in cases when the frequency range is limited and the magnetic loss peak is comparatively wide and has a distorted shape. The cases of large magnetic damping, pronounced skin effect, and inhomogeneity of the material are considered. It is shown that in most cases calculation of the integral through fitting of actual magnetic frequency dispersion by the Lorentzian dispersion law results in accurate estimations of the ultimate high-frequency performance of magnetic materials.
Dependence of exponents on text length versus finite-size scaling for word-frequency distributions
NASA Astrophysics Data System (ADS)
Corral, Álvaro; Font-Clos, Francesc
2017-08-01
Some authors have recently argued that a finite-size scaling law for the text-length dependence of word-frequency distributions cannot be conceptually valid. Here we give solid quantitative evidence for the validity of this scaling law, using both careful statistical tests and analytical arguments based on the generalized central-limit theorem applied to the moments of the distribution (and obtaining a novel derivation of Heaps' law as a by-product). We also find that the picture of word-frequency distributions with power-law exponents that decrease with text length [X. Yan and P. Minnhagen, Physica A 444, 828 (2016), 10.1016/j.physa.2015.10.082] does not stand with rigorous statistical analysis. Instead, we show that the distributions are perfectly described by power-law tails with stable exponents, whose values are close to 2, in agreement with the classical Zipf's law. Some misconceptions about scaling are also clarified.
Electromagnetic zonal flow residual responses
NASA Astrophysics Data System (ADS)
Catto, Peter J.; Parra, Felix I.; Pusztai, István
2017-08-01
The collisionless axisymmetric zonal flow residual calculation for a tokamak plasma is generalized to include electromagnetic perturbations. We formulate and solve the complete initial value zonal flow problem by retaining the fully self-consistent axisymmetric spatial perturbations in the electric and magnetic fields. Simple expressions for the electrostatic, shear and compressional magnetic residual responses are derived that provide a fully electromagnetic test of the zonal flow residual in gyrokinetic codes. Unlike the electrostatic potential, the parallel vector potential and the parallel magnetic field perturbations need not relax to flux functions for all possible initial conditions.
Determination of cutoff frequencies of simple waveguides using finite difference method
NASA Astrophysics Data System (ADS)
Kolagani, Sridhar
Waveguides are used to transfer electromagnetic energy from one location to another. Within many electronic circles, waveguides are commonly used for microwave RF signals; the same principle can be used for many forms of waves from sound to light. They have been used in many technologies like acoustic waveguide speaker technology, high-performance passive waveguide technologies for remote sensing and communication, optical computing, robotic-vision, biochemical sensing and many more. Modern waveguide technology employs a variety of waveguides with different cross sections and perturbations, the cutoff frequencies and mode shapes of many of these waveguides are ill-suited for determination by an analytical method. In this thesis, we solve this type of waveguides by employing the numerical procedure of finite difference method. By adopting finite difference approach with an application of eigenvalue method, we discuss about few different types of these waveguides in determining the cutoff frequencies of supported modes, and extracting the possible degenerate modes and their field distributions. To validate the method and its accuracy, it is applied to the two well known rectangular waveguides, viz. PEC Rectangular Waveguide and Artificial Rectangular Waveguide (consists of PEC and PMC walls) and compared with the analytical solutions.
Finite-frequency sensitivity of surface waves to anisotropy based upon adjoint methods
NASA Astrophysics Data System (ADS)
Sieminski, Anne; Liu, Qinya; Trampert, Jeannot; Tromp, Jeroen
2007-03-01
We calculate finite-frequency anisotropic traveltime sensitivity kernels for Rayleigh and Love waves using the recently developed combination of the adjoint method with spectral-element modelling of seismic wave propagation. We describe anisotropy following the `natural' 13 elastic parameters for surface waves (A, C, F, L, N, Bc,s, Hc,s, Gc,s and Ec,s) complemented by eight `body-wave parameters' (Jc,s, Kc,s, Mc,s and Dc,s). Along the ray path, the adjoint spectral-element computations agree well with asymptotic theory, but also expose the limitations of the asymptotic description. The adjoint spectral-element method is an efficient and flexible numerical tool, but it does not allow one to identify the various wave propagation phenomena contributing to the observed sensitivity. To decipher the numerical results, we apply Born scattering theory together with a surface-wave mode-coupling formulation. We identify a strong effect due to mode coupling. The sensitivity of Rayleigh waves for some of the anisotropic parameters is affected by Love-Rayleigh coupling, while Love-wave sensitivity is affected by cross-branch coupling. In addition, and very specific to anisotropy, the directional dependence of the sensitivity to azimuthal anisotropy may strongly distort the kernels, rendering them highly path-dependent. Because of these combined effects, the anisotropic sensitivity kernels can deviate substantially from the simple elliptical kernels used in recent isotropic finite-frequency tomography.
Finite-frequency global mantle tomography in the Cubed Earth from Rayleigh wave dispersion
NASA Astrophysics Data System (ADS)
Mikesell, T. D.; Nolet, G.; Charlety, J.; Ritsema, J. E.; van Heijst, H. J.
2012-12-01
Recently, shear wave velocity models of the mantle have been created using combinations of long period surface wave dispersion data, teleseismic body waveforms and travel times, and normal modes (e.g., S40RTS, S362ANI, TX2008). These models use different measurement techniques, and furthermore, such models are usually derived from ray theoretical methods if only to render the very large combined data sets solvable with present day computational resources. We present the first finite frequency interpretation of the updated van Heijst and Woodhouse (1999) Rayleigh wave phase velocity dispersion data set. Taking PREM as the background Earth model, we compute finite frequency kernels in the isotropic Cubed Earth for global Rayleigh wave phases (fundamental mode up to the fourth overtone). The Cubed Earth parametrization allows us to easily project the solution on different bases. In particular, wavelet bases allow for localization in both the spatial and spectral domains and are suitable to study the large variability of scales in the tomographic solutions and their resolvability geographically. In addition, we allow for Love-Rayleigh interaction. This is particularly important for the higher modes and allows us to study the effects of mode conversion due to scattering. Finally, we compare our preferred model with existing models of shear wave velocity for the upper mantle.
Finite Element Prediction of Loss Factors for Structures with Frequency-dependent Damping Treatments
NASA Technical Reports Server (NTRS)
Everstine, G. C.; Marcus, M. S.
1985-01-01
A finite element procedure is described for calculating the loss factors for elastic structures to which frequency-dependent viscoelastic damping treatments were applied. The frequency dependence of the viscoelastic damping material is treated by approximating its shear modulus with a second-order polynomial so that the stiffnesses associated with the constant, linear, and quadratic terms can be combined, respectively, with the stiffness, damping, and mass matrices assembled for the rest of the structure. A single complex eigenvalue analysis is then performed in which the eigenvalues are purely imaginary. The loss factor is computed by the modal strain energy (MSE) approach. In the the MSE approach, the loss factor of a composite structure vibrating in one of its natural modes may be visualized as a weighted average of the loss factors of the component parts, with the relative stored energies as weighting constants. The finite element procedure, which can treat very general geometries, is illustrated for the case of a vibrating constrained-layer damped plate.
Hsu, Hung-Yao
2016-01-01
Bone cells are deformed according to mechanical stimulation they receive and their mechanical characteristics. However, how osteoblasts are affected by mechanical vibration frequency and acceleration amplitude remains unclear. By developing 3D osteoblast finite element (FE) models, this study investigated the effect of cell shapes on vibration characteristics and effect of acceleration (vibration intensity) on vibrational responses of cultured osteoblasts. Firstly, the developed FE models predicted natural frequencies of osteoblasts within 6.85–48.69 Hz. Then, three different levels of acceleration of base excitation were selected (0.5, 1, and 2 g) to simulate vibrational responses, and acceleration of base excitation was found to have no influence on natural frequencies of osteoblasts. However, vibration response values of displacement, stress, and strain increased with the increase of acceleration. Finally, stress and stress distributions of osteoblast models under 0.5 g acceleration in Z-direction were investigated further. It was revealed that resonance frequencies can be a monotonic function of cell height or bottom area when cell volumes and material properties were assumed as constants. These findings will be useful in understanding how forces are transferred and influence osteoblast mechanical responses during vibrations and in providing guidance for cell culture and external vibration loading in experimental and clinical osteogenesis studies. PMID:28074178
Zonal flows in tokamaks with anisotropic pressure
Ren, Haijun
2014-04-15
Zonal flows (ZFs) in a tokamak plasma with anisotropic pressure are investigated. The dynamics of perpendicular and parallel pressures are determined by the Chew-Goldberger-Low double equations and low-β condition is adopted, where β is the ratio of plasma pressure to the magnetic field pressure. The dispersion relation is analytically derived and illustrates two branches of ZFs. The low frequency zonal flow (LFZF) branch becomes unstable when χ, the ratio of the perpendicular pressure to the parallel one, is greater than a threshold value χ{sub c}, which is about 3.8. In the stable region, its frequency increases first and then decreases with increasing χ. For χ = 1, the frequency of LFZF agrees well with the experimental observation. For the instability, the growth rate of LFZF increases with χ. The geodesic acoustic mode branch is shown to be always stable with a frequency increasing with χ. The safety factor is shown to diminish the frequencies of both branches or the growth rate of LFZF.
Zonal flows in tokamaks with anisotropic pressure
NASA Astrophysics Data System (ADS)
Ren, Haijun
2014-04-01
Zonal flows (ZFs) in a tokamak plasma with anisotropic pressure are investigated. The dynamics of perpendicular and parallel pressures are determined by the Chew-Goldberger-Low double equations and low-β condition is adopted, where β is the ratio of plasma pressure to the magnetic field pressure. The dispersion relation is analytically derived and illustrates two branches of ZFs. The low frequency zonal flow (LFZF) branch becomes unstable when χ, the ratio of the perpendicular pressure to the parallel one, is greater than a threshold value χc, which is about 3.8. In the stable region, its frequency increases first and then decreases with increasing χ. For χ = 1, the frequency of LFZF agrees well with the experimental observation. For the instability, the growth rate of LFZF increases with χ. The geodesic acoustic mode branch is shown to be always stable with a frequency increasing with χ. The safety factor is shown to diminish the frequencies of both branches or the growth rate of LFZF.
Stochastic finite element model calibration based on frequency responses and bootstrap sampling
NASA Astrophysics Data System (ADS)
Vakilzadeh, Majid K.; Yaghoubi, Vahid; Johansson, Anders T.; Abrahamsson, Thomas J. S.
2017-05-01
A new stochastic finite element model calibration framework for estimation of the uncertainty in model parameters and predictions from the measured frequency responses is proposed in this paper. It combines the principles of bootstrapping with the technique of FE model calibration with damping equalization. The challenge for the calibration problem is to find an initial estimate of the parameters that is reasonably close to the global minimum of the deviation between model predictions and measurement data. The idea of model calibration with damping equalization is to formulate the calibration metric as the deviation between the logarithm of the frequency responses of FE model and a test data model found from measurement where the same level of modal damping is imposed on all modes. This formulation gives a smooth metric with a large radius of convergence to the global minimum. In this study, practical suggestions are made to improve the performance of this calibration procedure in dealing with noisy measurements. A dedicated frequency sampling strategy is suggested for measurement of frequency responses in order to improve the estimate of a test data model. The deviation metric at each frequency line is weighted using the signal-to-noise ratio of the measured frequency responses. The solution to the improved calibration procedure with damping equalization is viewed as a starting value for the optimization procedure used for uncertainty quantification. The experimental data is then resampled using the bootstrapping approach and the FE model calibration problem, initiating from the estimated starting value, is solved on each individual resampled dataset to produce uncertainty bounds on the model parameters and predictions. The proposed stochastic model calibration framework is demonstrated on a six degree-of-freedom spring-mass system prior to being applied to a general purpose satellite structure.
Zhang, Ke; Jiang, Bin; Shi, Peng; Xu, Jinfa
2015-07-01
This paper addresses the problem of fault estimation observer design with finite-frequency specifications for discrete-time Takagi-Sugeno (T-S) fuzzy systems. First, for such T-S fuzzy models, an H∞ fault estimation observer with pole-placement constraint is proposed to achieve fault estimation. Based on the generalized Kalman-Yakubovich-Popov lemma, the given finite-frequency observer possesses less conservatism compared with the design of the entire-frequency domain. Furthermore, the performance of the presented fault estimation observer is further enhanced by adding the degree of freedom. Finally, two examples are presented to illustrate the effectiveness of the proposed strategy.
NASA Technical Reports Server (NTRS)
Bland, S. R.
1982-01-01
Finite difference methods for unsteady transonic flow frequency use simplified equations in which certain of the time dependent terms are omitted from the governing equations. Kernel functions are derived for two dimensional subsonic flow, and provide accurate solutions of the linearized potential equation with the same time dependent terms omitted. These solutions make possible a direct evaluation of the finite difference codes for the linear problem. Calculations with two of these low frequency kernel functions verify the accuracy of the LTRAN2 and HYTRAN2 finite difference codes. Comparisons of the low frequency kernel function results with the Possio kernel function solution of the complete linear equations indicate the adequacy of the HYTRAN approximation for frequencies in the range of interest for flutter calculations.
3D frequency-domain finite-difference modeling of acoustic wave propagation
NASA Astrophysics Data System (ADS)
Operto, S.; Virieux, J.
2006-12-01
We present a 3D frequency-domain finite-difference method for acoustic wave propagation modeling. This method is developed as a tool to perform 3D frequency-domain full-waveform inversion of wide-angle seismic data. For wide-angle data, frequency-domain full-waveform inversion can be applied only to few discrete frequencies to develop reliable velocity model. Frequency-domain finite-difference (FD) modeling of wave propagation requires resolution of a huge sparse system of linear equations. If this system can be solved with a direct method, solutions for multiple sources can be computed efficiently once the underlying matrix has been factorized. The drawback of the direct method is the memory requirement resulting from the fill-in of the matrix during factorization. We assess in this study whether representative problems can be addressed in 3D geometry with such approach. We start from the velocity-stress formulation of the 3D acoustic wave equation. The spatial derivatives are discretized with second-order accurate staggered-grid stencil on different coordinate systems such that the axis span over as many directions as possible. Once the discrete equations were developed on each coordinate system, the particle velocity fields are eliminated from the first-order hyperbolic system (following the so-called parsimonious staggered-grid method) leading to second-order elliptic wave equations in pressure. The second-order wave equations discretized on each coordinate system are combined linearly to mitigate the numerical anisotropy. Secondly, grid dispersion is minimized by replacing the mass term at the collocation point by its weighted averaging over all the grid points of the stencil. Use of second-order accurate staggered- grid stencil allows to reduce the bandwidth of the matrix to be factorized. The final stencil incorporates 27 points. Absorbing conditions are PML. The system is solved using the parallel direct solver MUMPS developed for distributed
Finite-difference modeling of Biot's poroelastic equations across all frequencies
Masson, Y.J.; Pride, S.R.
2009-10-22
An explicit time-stepping finite-difference scheme is presented for solving Biot's equations of poroelasticity across the entire band of frequencies. In the general case for which viscous boundary layers in the pores must be accounted for, the time-domain version of Darcy's law contains a convolution integral. It is shown how to efficiently and directly perform the convolution so that the Darcy velocity can be properly updated at each time step. At frequencies that are low enough compared to the onset of viscous boundary layers, no memory terms are required. At higher frequencies, the number of memory terms required is the same as the number of time points it takes to sample accurately the wavelet being used. In practice, we never use more than 20 memory terms and often considerably fewer. Allowing for the convolution makes the scheme even more stable (even larger time steps might be used) than it is when the convolution is entirely neglected. The accuracy of the scheme is confirmed by comparing numerical examples to exact analytic results.
Finite element based contact analysis of radio frequency MEMs switch membrane surfaces
NASA Astrophysics Data System (ADS)
Liu, Jin-Ya; Chalivendra, Vijaya; Huang, Wenzhen
2017-10-01
Finite element simulations were performed to determine the contact behavior of radio frequency (RF) micro-electro-mechanical (MEM) switch contact surfaces under monotonic and cyclic loading conditions. Atomic force microscopy (AFM) was used to capture the topography of RF-MEM switch membranes and later they were analyzed for multi-scale regular as well as fractal structures. Frictionless, non-adhesive contact 3D finite element analysis was carried out at different length scales to investigate the contact behavior of the regular-fractal surface using an elasto-plastic material model. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly cluster around the regular pattern. The contribution from the fractal structure is not significant. Under cyclic loading conditions, plastic deformation in the 1st loading/unloading cycle smooth the surface. The subsequent repetitive loading/unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of the switch surface contact as well as the optimum design of RF MEM switch surfaces.
NASA Astrophysics Data System (ADS)
Cunningham, Ian A.; Westmore, Michael S.; Fenster, Aaron
1995-05-01
Image blur in digital imaging systems results from both the spatial spreading of quanta representing the image in the detector system and from the integration of quanta over the finite detector element width. Linear-systems theory has often been used to describe these blurring mechanisms as a convolution, implying the existence of a corresponding modulation transfer function (MTF) in the spatial-frequency domain. This also implies that the resulting noise- power spectrum (NPS) is modified by the square of the blurring MTF. This deterministic approach correctly describes the effect of each blurring mechanism on the overall system MTF, but does not correctly describe image noise characteristics. This is because the convolution is a deterministic calculation, and neglects the statistical properties of the image quanta. Rabbani et al. developed an expression for the NPS following a stochastic spreading mechanism that correctly accounts for these statistical properties. Use of their results requires a modification in how we should interpret the convolution theorem. We suggest the use of a `stochastic' convolution operator, that uses the Rabbani equation for the NPS rather than the deterministic result. This approach unifies the description of both image blur and image noise into a single linear-systems framework. This method is then used to develop expressions for the signal, NPS, DQE, and pixel SNR for a hypothetical digital detector design that includes the effects of conversion to secondary quanta, stochastic spreading of the secondary quanta, and a finite detector-element width.
Zonal Flows: Comparisons of Basic Experiments and Theories
NASA Astrophysics Data System (ADS)
Sen, A. K.; Sokolov, V.; Wei, X.; Avinash, K.
2006-11-01
Zonal flows driven by the ITG (ion temperature gradient) drift modes has been performed in the Columbia Linear Machine [R. Scarmozzino, A.K. Sen, and G.A. Navratil, Phys.Rev.Lett. 57, 1729 (1986)]. The difficult problem of detection of zonal flows has been solved via a novel diagnostic using the paradigm of FM (frequency modulation) in radio transmission. Using this and Discrete Short Time Fourier Transform, we find a power spectrum peak at ITG (`carrier') frequency of ˜120kHz and FM sidebands at frequency of ˜2kHz, which has all the signatures of a zonal flow. The results have only partial agreement with most theoretical estimates including the one proposed here.
Space-Frequency Sampling Criteria for Electromagnetic Scattering of a Finite Object.
1985-08-01
3 *W2**2 -0 PUNCTMN FUNC2 (R, W2) I r C2ud1./ 3 .)*(sIntRIW2))**2. ED 161 C C FUNCrIOt4: FUNC3 C THIS FUNCION WILL PROCC THE LINEAR ITERKLATION )RITDN...8217N’) GO M 50 IF ( OMEGA . NE. ’Y’) GO) MI 3 0 CALL TRAN2D (DATA, MSIZE,-1) CALL rLUT(DATA,MSIZ EARAY1 .ARRAY2 .ARRAYP) GO MD25 C C INVERSE FOURE...AO-A162 553 SPACE-FREQUENCY SAMPLING CRITERIA FOR ELECTROINNINETIC 1/ 3 SCATTERING OF A FINITE UBJECT(U) OHI10 STATE UNIV COLUMBUS ELECTROSCIENCE LAB
Effect of Finite Pulse Length and Laser Frequency Chirp on HGHG and EEHG Seeding
Stupakov, G.; /SLAC
2011-11-18
Theoretical studies of high-gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) often start from a simplified model in which the beam is assumed infinitely long and longitudinally uniform and the laser induced energy modulation is perfectly sinusoidal and of infinite duration. In such a model the resulting seed has a spectrum consisting of a collection of delta-functions (of zero width) located at the harmonics of the laser frequency. Being a useful tool for study of the seed bunching amplitudes, such a model cannot be used for realistic analysis the spectral properties of the seed. In this paper we take into account the finite duration of the laser pulse as well as some possible laser phase errors to study their effect on the spectrum of the seed.
Real-time simulation of finite-frequency noise from a single-electron emitter
NASA Astrophysics Data System (ADS)
Jonckheere, T.; Stoll, T.; Rech, J.; Martin, T.
2012-01-01
We study the real-time emission of single electrons from a quantum dot coupled to a one dimensional conductor, using exact diagonalization on a discrete tight-binding chain. We show that, from the calculation of the time evolution of the one-electron states, we have simple access to all the relevant physical quantities in the system. In particular, we are able to compute accurately the finite-frequency current autocorrelation noise. The method that we use is general and versatile, allowing us to study the impact of many different parameters, such as the dot transparency or level position. Our results can be directly compared with existing experiments, and can also serve as a basis for future calculations including electronic interactions using the time-dependent density-matrix renormalization group and other techniques based on tight-binding models.
Discrete- and finite-bandwidth-frequency distributions in nonlinear stability applications
NASA Astrophysics Data System (ADS)
Kuehl, Joseph J.
2017-02-01
A new "wave packet" formulation of the parabolized stability equations method is presented. This method accounts for the influence of finite-bandwidth-frequency distributions on nonlinear stability calculations. The methodology is motivated by convolution integrals and is found to appropriately represent nonlinear energy transfer between primary modes and harmonics, in particular nonlinear feedback, via a "nonlinear coupling coefficient." It is found that traditional discrete mode formulations overestimate nonlinear feedback by approximately 70%. This results in smaller maximum disturbance amplitudes than those observed experimentally. The new formulation corrects this overestimation, accounts for the generation of side lobes responsible for spectral broadening, and results in disturbance representation more consistent with the experiment than traditional formulations. A Mach 6 flared-cone example is presented.
NASA Astrophysics Data System (ADS)
Nolet, G.; Mercerat, D.; Zaroli, C.
2012-12-01
We present the first complete test of finite frequency tomography with banana-doughnut kernels, from the generation of seismograms in a 3D model to the final inversion, and are able to lay to rest all of the so-called `controversies' that have slowed down its adoption. Cross-correlation delay times are influenced by energy arriving in a time window that includes later arrivals, either scattered from, or diffracted around lateral heterogeneities. We present here the results of a 3D test in which we generate 1716 seismograms using the spectral element method in a cross-borehole experiment conducted in a checkerboard box. Delays are determined for the broadband signals as well as for five frequency bands (each one octave apart) by cross-correlating seismograms for a homogeneous pattern with those for a checkerboard. The large (10 per cent) velocity contrast and the regularity of the checkerboard pattern causes severe reverberations that arrive late in the cross-correlation window. Data errors are estimated by comparing linearity between delays measured for a model with 10 per cent velocity contrast with those with a 4 per cent contrast. Sensitivity kernels are efficiently computed with ray theory using the `banana-doughnut' kernels from Dahlen et al. (GJI 141:157, 2000). The model resulting from the inversion with a data fit with reduced χ2red=1 shows an excellent correspondence with the input model and allows for a complete validation of the theory. Amplitudes in the (well resolved) top part of the model are close to the input amplitudes. Comparing a model derived from one band only shows the power of using multiple frequency bands in resolving detail - essentially the observed dispersion captures some of the waveform information. Finite frequency theory also allows us to image the checkerboard at some distance from the borehole plane. Most disconcertingly for advocates of ray theory are the results obtained when we interpret cross-correlation delays with ray theory
Fast time- and frequency-domain finite-element methods for electromagnetic analysis
NASA Astrophysics Data System (ADS)
Lee, Woochan
Fast electromagnetic analysis in time and frequency domain is of critical importance to the design of integrated circuits (IC) and other advanced engineering products and systems. Many IC structures constitute a very large scale problem in modeling and simulation, the size of which also continuously grows with the advancement of the processing technology. This results in numerical problems beyond the reach of existing most powerful computational resources. Different from many other engineering problems, the structure of most ICs is special in the sense that its geometry is of Manhattan type and its dielectrics are layered. Hence, it is important to develop structure-aware algorithms that take advantage of the structure specialties to speed up the computation. In addition, among existing time-domain methods, explicit methods can avoid solving a matrix equation. However, their time step is traditionally restricted by the space step for ensuring the stability of a time-domain simulation. Therefore, making explicit time-domain methods unconditionally stable is important to accelerate the computation. In addition to time-domain methods, frequency-domain methods have suffered from an indefinite system that makes an iterative solution difficult to converge fast. The first contribution of this work is a fast time-domain finite-element algorithm for the analysis and design of very large-scale on-chip circuits. The structure specialty of on-chip circuits such as Manhattan geometry and layered permittivity is preserved in the proposed algorithm. As a result, the large-scale matrix solution encountered in the 3-D circuit analysis is turned into a simple scaling of the solution of a small 1-D matrix, which can be obtained in linear (optimal) complexity with negligible cost. Furthermore, the time step size is not sacrificed, and the total number of time steps to be simulated is also significantly reduced, thus achieving a total cost reduction in CPU time. The second contribution
Finite-frequency Sensitivity Kernels in Spherical Geometry for Time-Distance Helioseismology
NASA Astrophysics Data System (ADS)
Mandal, Krishnendu; Bhattacharya, Jishnu; Halder, Samrat; Hanasoge, Shravan M.
2017-06-01
The inference of internal properties of the Sun from surface measurements of wave travel times is the goal of time-distance helioseismology. A critical step toward the accurate interpretation of shifts in travel time is the computation of sensitivity functions linking seismic measurements to internal structure. Here we calculate finite-frequency sensitivity kernels in spherical geometry for two-point measurements of travel time. We numerically build Green’s function by solving for it at each frequency and each degree of spherical harmonic and summing over all these pieces. These computations are performed in parallel (“embarrassingly”), thereby achieving significant speedup in wall-clock time. Kernels are calculated by invoking the first-order Born approximation connecting deviations in the wave field to perturbations in the operator. Validated flow kernels are shown to produce travel times within 0.47% of the true value for uniform flows up to 750 {{m}} {{{s}}}-1. We find that travel time can be obtained with errors of 1 ms or less for flows having magnitudes similar to meridional circulation. Alongside flows, we also compute and validate a sensitivity kernel for perturbations in sound speed. These accurate sensitivity kernels might improve the current inferences of subsurface flows significantly.
Finite-frequency traveltime tomography of San Francisco Bay region crustal velocity structure
Pollitz, F.F.
2007-01-01
Seismic velocity structure of the San Francisco Bay region crust is derived using measurements of finite-frequency traveltimes. A total of 57 801 relative traveltimes are measured by cross-correlation over the frequency range 0.5-1.5 Hz. From these are derived 4862 'summary' traveltimes, which are used to derive 3-D P-wave velocity structure over a 341 ?? 140 km2 area from the surface to 25 km depth. The seismic tomography is based on sensitivity kernels calculated on a spherically symmetric reference model. Robust elements of the derived P-wave velocity structure are: a pronounced velocity contrast across the San Andreas fault in the south Bay region (west side faster); a moderate velocity contrast across the Hayward fault (west side faster); moderately low velocity crust around the Quien Sabe volcanic field and the Sacramento River delta; very low velocity crust around Lake Berryessa. These features are generally explicable with surface rock types being extrapolated to depth ???10 km in the upper crust. Generally high mid-lower crust velocity and high inferred Poisson's ratio suggest a mafic lower crust. ?? Journal compilation ?? 2007 RAS.
Finite-frequency sensitivity kernels of seismic waves to fault zone structures
NASA Astrophysics Data System (ADS)
Allam, A. A.; Tape, C.; Ben-Zion, Y.
2015-12-01
We analyse the volumetric sensitivity of fault zone seismic head and trapped waves by constructing finite-frequency sensitivity (Fréchet) kernels for these phases using a suite of idealized and tomographically derived velocity models of fault zones. We first validate numerical calculations by waveform comparisons with analytical results for two simple fault zone models: a vertical bimaterial interface separating two solids of differing elastic properties, and a `vertical sandwich' with a vertical low velocity zone surrounded on both sides by higher velocity media. Establishing numerical accuracy up to 12 Hz, we compute sensitivity kernels for various phases that arise in these and more realistic models. In contrast to direct P body waves, which have little or no sensitivity to the internal fault zone structure, the sensitivity kernels for head waves have sharp peaks with high values near the fault in the faster medium. Surface wave kernels show the broadest spatial distribution of sensitivity, while trapped wave kernels are extremely narrow with sensitivity focused entirely inside the low-velocity fault zone layer. Trapped waves are shown to exhibit sensitivity patterns similar to Love waves, with decreasing width as a function of frequency and multiple Fresnel zones of alternating polarity. In models that include smoothing of the boundaries of the low velocity zone, there is little effect on the trapped wave kernels, which are focused in the central core of the low velocity zone. When the source is located outside a shallow fault zone layer, trapped waves propagate through the surrounding medium with body wave sensitivity before becoming confined. The results provide building blocks for full waveform tomography of fault zone regions combining high-frequency head, trapped, body, and surface waves. Such an imaging approach can constrain fault zone structure across a larger range of scales than has previously been possible.
Liquid-metal flow in a finite-length cylinder with a high-frequency rotating magnetic field
NASA Astrophysics Data System (ADS)
Witkowski, L. Martin; Marty, P.; Walker, J. S.
2001-06-01
A liquid-metal flow driven by a rotating magnetic field in a finite-length cylinder is studied numerically as a function of the field frequency. In the high-frequency case, the magnetic field is expelled from the liquid-metal except in a skin-depth layer along the side and top walls of the cylinder. In the corner region, where the skin-depth layers intersect, the body force exhibits a large positive and negative azimuthal component as well as inward radial and axial components which are rotational. The flows for various frequencies are compared to the low-frequency flow.
NASA Technical Reports Server (NTRS)
Smith, Wayne Farrior
1973-01-01
The effect of finite source size on the power statistics in a reverberant room for pure tone excitation was investigated. Theoretical results indicate that the standard deviation of low frequency, pure tone finite sources is always less than that predicted by point source theory and considerably less when the source dimension approaches one-half an acoustic wavelength or greater. A supporting experimental study was conducted utilizing an eight inch loudspeaker and a 30 inch loudspeaker at eleven source positions. The resulting standard deviation of sound power output of the smaller speaker is in excellent agreement with both the derived finite source theory and existing point source theory, if the theoretical data is adjusted to account for experimental incomplete spatial averaging. However, the standard deviation of sound power output of the larger speaker is measurably lower than point source theory indicates, but is in good agreement with the finite source theory.
Finite-frequency sensitivity kernels for global seismic wave propagation based upon adjoint methods
NASA Astrophysics Data System (ADS)
Liu, Qinya; Tromp, Jeroen
2008-07-01
We determine adjoint equations and Fréchet kernels for global seismic wave propagation based upon a Lagrange multiplier method. We start from the equations of motion for a rotating, self-gravitating earth model initially in hydrostatic equilibrium, and derive the corresponding adjoint equations that involve motions on an earth model that rotates in the opposite direction. Variations in the misfit function χ then may be expressed as , where δlnm = δm/m denotes relative model perturbations in the volume V, δlnd denotes relative topographic variations on solid-solid or fluid-solid boundaries Σ, and ∇Σδlnd denotes surface gradients in relative topographic variations on fluid-solid boundaries ΣFS. The 3-D Fréchet kernel Km determines the sensitivity to model perturbations δlnm, and the 2-D kernels Kd and Kd determine the sensitivity to topographic variations δlnd. We demonstrate also how anelasticity may be incorporated within the framework of adjoint methods. Finite-frequency sensitivity kernels are calculated by simultaneously computing the adjoint wavefield forward in time and reconstructing the regular wavefield backward in time. Both the forward and adjoint simulations are based upon a spectral-element method. We apply the adjoint technique to generate finite-frequency traveltime kernels for global seismic phases (P, Pdiff, PKP, S, SKS, depth phases, surface-reflected phases, surface waves, etc.) in both 1-D and 3-D earth models. For 1-D models these adjoint-generated kernels generally agree well with results obtained from ray-based methods. However, adjoint methods do not have the same theoretical limitations as ray-based methods, and can produce sensitivity kernels for any given phase in any 3-D earth model. The Fréchet kernels presented in this paper illustrate the sensitivity of seismic observations to structural parameters and topography on internal discontinuities. These kernels form the basis of future 3-D tomographic inversions.
Global Upper Mantle Structure from Finite-Frequency Surface-Wave Tomography
NASA Astrophysics Data System (ADS)
Zhou, Y.; Nolet, G.; Dahlen, F.; Laske, G.
2004-12-01
We report global shear-wave velocity structure and radial anisotropy in the upper mantle obtained by finite-frequency surface-wave tomography, based on complete three-dimensional Born sensitivity kernels developed by Zhou et al (2004). Because wavefront healing effects are properly taken into account, finite-frequency surface-wave tomography improves the resolution of small-scale mantle heterogeneities using long-period surface waves. The resulting S-wave velocity models fit the dispersion data better, and show stronger small-scale mantle anomalies compare to traditional ray-theory-based tomographic models. Separate inversions of Love wave (SH-type) and Rayleigh wave (SV-type) dispersion provide insight into the radial anisotropy in the upper mantle. In our model, the globally averaged radial anisotropy is positive (V SH > V SV) (horizontal flow) in the top 220 km, and becomes negative (V SV > V SH) (vertical flow) below 220 km depth. In cratons, both SH and SV velocities show strong fast anomalies down to 250 km depth, and the fast anomalies gradually diminish below 250 km. Radial anisotropy beneath cratons is positive, which largely agrees with a recent global model by Gung et.~al (2003). The old Pacific plate is characterized by strong positive anisotropy with its maximum centered west of Hawaii; this supports an earlier observation on Pacific radial anisotropy by Ekstrom & Dziewonski (1998). The depth extent of mid-ocean ridges and the primary force that drives plate tectonics has been a long-standing question. In our model, ridge anomalies are characterized by strong negative radial anisotropy (vertical flow). Ridge anomalies at fast-spreading centers are stronger than those at slow-spreading centers at shallow depth, but the amount of velocity reduction rapidly decreases below 250 km. However, at slow-spreading centers such as the north Mid-Atlantic ridge (MAR) and East Africa (Red Sea), ridge anomalies extend down at least to the top of the transition zones
Finite beta effects on low- and high-frequency magnetosonic waves in a two-ion-species plasma
Toida, Mieko; Aota, Yukio
2013-08-15
A magnetosonic wave propagating perpendicular to a magnetic field in a two-ion-species plasma has two branches, high-frequency and low-frequency modes. The finite beta effects on these modes are analyzed theoretically on the basis of the three-fluid model with finite ion and electron pressures. First, it is shown that the Korteweg-de Vries (KdV) equation for the low-frequency mode is valid for amplitudes ε<ε{sub max}, where the upper limit of the amplitude ε{sub max} is given as a function of β (β is the ratio of the kinetic and magnetic energy densities), the density ratio, and the cyclotron frequency ratio of two ion species. Next, the linear dispersion relation and KdV equation for the high-frequency mode are derived, including β as a factor. In addition, the theory for heavy ion acceleration by the high-frequency mode pulse and the pulse damping due to this energy transfer in a finite beta plasma are presented.
NASA Astrophysics Data System (ADS)
Ashbach, Jason A.
Periodic metallodielectric frequency selective surface (FSS) designs have historically seen widespread use in the microwave and radio frequency spectra. By scaling the dimensions of an FSS unit cell for use in a nano-fabrication process, these concepts have recently been adapted for use in optical applications as well. While early optical designs have been limited to wellunderstood geometries or optimized pixelated screens, nano-fabrication, lithographic and interconnect technology has progressed to a point where it is possible to fabricate metallic screens of arbitrary geometries featuring curvilinear or even three-dimensional characteristics that are only tens of nanometers wide. In order to design an FSS featuring such characteristics, it is important to have a robust numerical solver that features triangular elements in purely two-dimensional geometries and prismatic or tetrahedral elements in three-dimensional geometries. In this dissertation, a periodic finite element method code has been developed which features prismatic elements whose top and bottom boundaries are truncated by numerical integration of the boundary integral as opposed to an approximate representation found in a perfectly matched layer. However, since no exact solution exists for the calculation of triangular elements in a boundary integral, this process can be time consuming. To address this, these calculations were optimized for parallelization such that they may be done on a graphics processor, which provides a large increase in computational speed. Additionally, a simple geometrical representation using a Bezier surface is presented which provides generality with few variables. With a fast numerical solver coupled with a lowvariable geometric representation, a heuristic optimization algorithm has been used to develop several optical designs such as an absorber, a circular polarization filter, a transparent conductive surface and an enhanced, optical modulator.
Multiscale finite-frequency Rayleigh wave tomography of the Kaapvaal craton
NASA Astrophysics Data System (ADS)
Chevrot, S.; Zhao, L.
2007-04-01
We have measured phase delays of fundamental-mode Rayleigh waves for 12 events recorded by the Southern Africa Seismic Experiment at frequencies between 0.005 and 0.035 Hz. A novel multiscale finite-frequency tomographic method based on wavelet decomposition of 3-D sensitivity kernels for the phase of Rayleigh waves is used to map the shear velocities in the upper mantle beneath southern Africa. The kernels are computed by summing coupled normal modes over a very fine grid surrounding the seismic array. To estimate and minimize the biases in the model resulting from structures outside the tomographic grid, a jackknife inversion method is implemented. The contribution of heterogeneities outside the target volume is significant, but produces artefacts in the tomographic model that are easily identified and discarded before interpretation. With structures on length scales as short as 100 km retrieved beneath the array, the deep structure of the Kaapvaal craton is revealed with unprecedented detail. Outside the array, the corresponding resolution is 200 km. High velocity cratonic roots are confined to the Archean craton, and extend to depths of at least 250 km. Confirming earlier surface structural studies, we recognize two distinct units in the Kaapvaal craton. The eastern Witwatersrand block and the western Kimberley block are separated by a major near-vertical translithospheric boundary which coincides with the Colesberg Lineament. Lower than average velocities south and east of the Kaapvaal craton reveal extensive metasomatism and heating of the lithosphere, probably related to the Karoo magmatic event and to the opening of the South Atlantic Ocean.
NASA Astrophysics Data System (ADS)
Liang, Xiaofeng; Chen, Yun; Tian, Xiaobo; Wang, Minling; Xu, Tao; Sun, Changqing; Si, Shaokun; Lan, Haiqiang; Teng, Jiwen
2015-04-01
Combining the new collected teleseismic body waves recorded by TIBET-31N passive seismic array with waveforms from several previous temporary seismic arrays, we carried out finite-frequency tomographic inversions to image three-dimensional velocity structures beneath southern-central Tibet to examine the roles of the upper mantle in the formation of the Tibetan plateau. Strong low P- and S-wave velocity anomalies that extend from the lower crust to about 200 km depth beneath the Comei rift, Yadong-Gulu rift, Tangra Yum Co rift, suggesting that rifting in southern Tibet is probably a process that involves the entire lithosphere. At the same time there is only the low velocity close to Yadong-Gulu rift extending further north and connecting with the massive upper mantle low velocity beneath central Tibet, and moreover, the other two are limited in southern Tibet. This observation implies that the previous proposed fragmentation of underthrusting Indian lithosphere might not happen underneath all the north-south trending rifts. Instead, it only happens close to Yadong-Gulu rift, then hot temperature upwelling materials fill up this lithospheric crack and might stuff the other weak zones in shallow depths beneath southern Tibet. Continuous high velocities are observed beneath Himalayas and Lhasa Terrance with a moderate northward inclination angle. We interpret this anomaly as the subducting/underthrusting Indian continental lithosphere.
Robust non-fragile finite-frequency H∞ static output-feedback control for active suspension systems
NASA Astrophysics Data System (ADS)
Wang, Gang; Chen, Changzheng; Yu, Shenbo
2017-07-01
This paper deals with the problem of non-fragile H∞ static output-feedback control of vehicle active suspension systems with finite-frequency constraint. The control objective is to improve ride comfort within the given frequency range and ensure the hard constraints in the time-domain. Moreover, in order to enhance the robustness of the controller, the control gain perturbation is also considered in controller synthesis. Firstly, a new non-fragile H∞ finite-frequency control condition is established by using generalized Kalman-Yakubovich-Popov (GKYP) lemma. Secondly, the static output-feedback control gain is directly derived by using a non-iteration algorithm. Different from the existing iteration LMI results, the static output-feedback design is simple and less conservative. Finally, the proposed control algorithm is applied to a quarter-car active suspension model with actuator dynamics, numerical results are made to show the effectiveness and merits of the proposed method.
A finite-difference frequency-domain code for electromagnetic induction tomography
Sharpe, R M; Berryman, J G; Buettner, H M; Champagne, N J.,II; Grant, J B
1998-12-17
We are developing a new 3D code for application to electromagnetic induction tomography and applications to environmental imaging problems. We have used the finite-difference frequency- domain formulation of Beilenhoff et al. (1992) and the anisotropic PML (perfectly matched layer) approach (Berenger, 1994) to specify boundary conditions following Wu et al. (1997). PML deals with the fact that the computations must be done in a finite domain even though the real problem is effectively of infinite extent. The resulting formulas for the forward solver reduce to a problem of the form Ax = y, where A is a non-Hermitian matrix with real values off the diagonal and complex values along its diagonal. The matrix A may be either symmetric or nonsymmetric depending on details of the boundary conditions chosen (i.e., the particular PML used in the application). The basic equation must be solved for the vector x (which represents field quantities such as electric and magnetic fields) with the vector y determined by the boundary conditions and transmitter location. Of the many forward solvers that could be used for this system, relatively few have been thoroughly tested for the type of matrix encountered in our problem. Our studies of the stability characteristics of the Bi-CG algorithm raised questions about its reliability and uniform accuracy for this application. We have found the stability characteristics of Bi-CGSTAB [an alternative developed by van der Vorst (1992) for such problems] to be entirely adequate for our application, whereas the standard Bi-CG was quite inadequate. We have also done extensive validation of our code using semianalytical results as well as other codes. The new code is written in Fortran and is designed to be easily parallelized, but we have not yet tested this feature of the code. An adjoint method is being developed for solving the inverse problem for conductivity imaging (for mapping underground plumes), and this approach, when ready, will
Zonal flow dynamics in the double tearing mode with antisymmetric shear flows
Mao, Aohua; Li, Jiquan; Liu, Jinyuan; Kishimoto, Yasuaki
2014-05-15
The generation dynamics and the structural characteristics of zonal flows are investigated in the double tearing mode (DTM) with antisymmetric shear flows. Two kinds of zonal flow oscillations are revealed based on reduced resistive magnetohydrodynamics simulations, which depend on the shear flow amplitudes corresponding to different DTM eigen mode states, elaborated by Mao et al. [Phys. Plasmas 20, 022114 (2013)]. For the weak shear flows below an amplitude threshold, v{sub c}, at which two DTM eigen states with antisymmetric or symmetric magnetic island structure are degenerated, the zonal flows grow oscillatorily in the Rutherford regime during the nonlinear evolution of the DTMs. It is identified that the oscillation mechanism results from the nonlinear interaction between the distorted islands and the zonal flows through the modification of shear flows. However, for the medium shear flows above v{sub c} but below the critical threshold of the Kelvin-Helmholtz instability, an oscillatory growing zonal flow occurs in the linear phase of the DTM evolution. It is demonstrated that the zonal flow oscillation originates from the three-wave mode coupling or a modulation instability pumped by two DTM eigen modes with the same frequency but opposite propagating direction. With the shear flows increasing, the amplitude of zonal flow oscillation increases first and then decreases, whilst the oscillation frequency as twice of the Doppler frequency shift increases. Furthermore, impacts of the oscillatory zonal flows on the nonlinear evolution of DTM islands and the global reconnection are also discussed briefly.
Investigation of equinoctial asymmetry in the latitudinal variation of zonal scintillation drift
NASA Astrophysics Data System (ADS)
Abadi, P.; Otsuka, Y.; Shiokawa, K.; Shinagawa, H.; Liu, H.
2016-12-01
We investigate latitudinal variation of zonal scintillation drift for Mar and Sep equinox by using three single-frequency GPS receivers spaced closely with mutual distances 100 m, in Kototabang (0.2°S, 100.3°E; Mag. Lat.: 9.9°S), Indonesia. The zonal drift is estimated from cross-correlation analysis of time series of GPS signal intensity among the three receivers. We have collected the zonal drift data for Mar and Sep during 20-24 LT in 2003-2015. Fig. 1 shows the latitudinal profile of zonal drift velocity both for Mar and Sep which are classified also into high and moderate solar activity levels (F10.7). As shown in Fig. 1, the latitudinal gradient of zonal shear is negative for both Mar and Sept and at both moderate and high F107. The negative gradient indicates that the zonal drift velocity is larger at magnetic equator and that it decreases as increasing the latitude. Our interesting finding is that the latitudinal gradient of the zonal drift velocity in Mar equinox is more negative than that in Sep equinox at both moderate and high F10.7. Because the zonal scintillation drift velocity can be assumed to represent the zonal background plasma drift in the nighttime F-region, we can consider that latitudinal shear of zonal background plasma drift in Mar equinox is more negative than that in Sep equinox. Furthermore, the zonal background plasma drift is caused by zonal neutral wind through the F-region dynamo. We then investigate the latitudinal shear of zonal neutral wind velocity for Mar and Sep equinoxes, obtained by in-situ measurement from CHAMP satellite (altitude of 400 km). Fig. 2 shows the latitudinal variation of the zonal wind velocity. Interestingly, we also find that the latitudinal gradient of the zonal wind is more negative in Mar equinox than that in Sep equinox at both moderate and high F10.7. We find also the equinoctial asymmetry in the latitudinal variation of the zonal wind. We, thus, conclude that the equinoctial asymmetry of zonal drift
NASA Astrophysics Data System (ADS)
Hongsresawat, Sutatcha
micro terranes with both continental and oceanic origins throughout its accretion history making it a very complex geological setting including the presence of the north-striking western Idaho shear zone (WISZ) in the middle. We deployed 85 temporary seismic stations with station-spacing of ˜30 km during 2011--2013 and passively recorded seismic data for an average duration of 1.5 years. The SKS phase of the seismogram is used to obtain splitting intensity, which we use to model realistic 3-D upper-mantle anisotropy. There are two parts in this study, first SKS splitting intensity measurements were made from seismograms recorded at 83 IDOR seismic stations and 45 USArray-TA stations, which consist of analyzing more than 75,000 individual traces. As a result, we obtain high-resolution and spatially coherent shear-wave splitting dataset of the IDOR region. Second, we use back-azimuthal variations of splitting intensity at all stations to model for 3-D anisotropy using the finite-frequency approach. Preliminary models show depth-dependent behaviors of both fast polarization direction and strength of anisotropy down to ˜150 km where the model starts to show poor resolution due to the size of the SKS fresnel zone. Last, we show preliminary inverted models for 3-D upper-mantle anisotropy of North America as well as our progress of spherical coordinate inversion of the USArray-TA splitting measurements. This will set up a starting point for performing a joint-inversion with surface wave dataset that will be measured at exact seismic stations. This last task will be exercised by the help of 3-D finite-frequency Frechet sensitivity kernels for surface waveforms based on the Born approximation with a model parametrized for hexagonal symmetry. Their formulation will provide a complementary approach to invert surface wave data in combination with our SI data for upper mantle anisotropy model of North America with highest resolution for the first time.
NASA Astrophysics Data System (ADS)
Biryol, C. B.; Wagner, L. S.; Fischer, K. M.; Hawman, R. B.
2014-12-01
Our new results from teleseismic, finite-frequency, body-wave tomography analysis reveal a relatively steep east-dipping fast velocity anomaly beneath the Southeastern US. The resolving power of our dataset is good enough to retrieve major mantle anomalies, such as this fast velocity body, owing to the dense receiver coverage provided by US Transportable Array (TA) and the SouthEastern Suture of the Appalachian Margin Experiment (SESAME). Various resolution and recovery tests demonstrate the robustness of this anomaly in our tomographic model between the depths of 60 and 660 km. Our images reveal that the dip of this structure decreases significantly in the mantle transition zone where it terminates. We also observe major gaps in the lateral continuity of this structure. Based on the amplitude, location and geometry of the velocity perturbation, we interpret this anomaly as remnant subducted lithosphere, suspended in the upper mantle after a subduction phase as young as 100-110 Ma or as old as 1Ga. Basic calculations and evaluations on the geometry and location of this anomaly help us to narrow down the origin of this slab to the Farallon flat-slab subduction in the west and Grenville Subduction during assembly of supercontinent Rodinia. Our images reveal possible mechanisms that would allow this slab to remain in the upper mantle without sinking into deeper mantle for such extended periods of time. We believe the flat geometry of the slab near the transition zone and the fragmented nature provide important clues about processes that could delay/resist the sinking while providing necessary time for it to transform into a more neutrally buoyant state. In this respect, we believe our results have broad implications for subduction processes and piece-meal slab failure, as well as tectonic implications for characteristics of former subduction zones that help shape North American Plate.
NASA Astrophysics Data System (ADS)
Tape, Carl; Liu, Qinya; Tromp, Jeroen
2007-03-01
We employ adjoint methods in a series of synthetic seismic tomography experiments to recover surface wave phase-speed models of southern California. Our approach involves computing the Fréchet derivative for tomographic inversions via the interaction between a forward wavefield, propagating from the source to the receivers, and an `adjoint' wavefield, propagating from the receivers back to the source. The forward wavefield is computed using a 2-D spectral-element method (SEM) and a phase-speed model for southern California. A `target' phase-speed model is used to generate the `data' at the receivers. We specify an objective or misfit function that defines a measure of misfit between data and synthetics. For a given receiver, the remaining differences between data and synthetics are time-reversed and used as the source of the adjoint wavefield. For each earthquake, the interaction between the regular and adjoint wavefields is used to construct finite-frequency sensitivity kernels, which we call event kernels. An event kernel may be thought of as a weighted sum of phase-specific (e.g. P) banana-doughnut kernels, with weights determined by the measurements. The overall sensitivity is simply the sum of event kernels, which defines the misfit kernel. The misfit kernel is multiplied by convenient orthonormal basis functions that are embedded in the SEM code, resulting in the gradient of the misfit function, that is, the Fréchet derivative. A non-linear conjugate gradient algorithm is used to iteratively improve the model while reducing the misfit function. We illustrate the construction of the gradient and the minimization algorithm, and consider various tomographic experiments, including source inversions, structural inversions and joint source-structure inversions. Finally, we draw connections between classical Hessian-based tomography and gradient-based adjoint tomography.
Seismic structure beneath the Rivera subduction zone from finite-frequency seismic tomography
NASA Astrophysics Data System (ADS)
Yang, Ting; Grand, Stephen P.; Wilson, David; Guzman-Speziale, Marco; Gomez-Gonzalez, Juan Martin; Dominguez-Reyes, Tonatiuh; Ni, James
2009-01-01
The subduction zone of western Mexico is a unique region on Earth where microplate capture and overriding plate disruption are occurring today. The young, small Rivera plate and the adjacent Cocos plate are subducting beneath the Jalisco block of Mexico. Here, we present a P wave tomographic model of the upper mantle to 400 km depth beneath the Jalisco block and surrounding regions using teleseismic P waves recorded by the Mapping the Rivera Subduction Zone (MARS) and Colima Volcano Deep Seismic Experiment (CODEX) seismic arrays. The inversion used 12,188 P wave residuals and finite-frequency theory to backproject the 3-D traveltime sensitivity kernels through the model. Below a depth of 150 km, the tomography model shows a clear gap between the Rivera and Cocos slabs that increases in size with depth. The gap between the plates lies beneath the northern part of the Colima graben and may be responsible for the location of Colima volcano. The images indicate that the deep Rivera plate is subducting more steeply than does the adjacent Cocos plate and also has a more northerly trajection. At a depth of about 100 km, both the Rivera and Cocos slabs have increased dips such that the slabs are deeper than 200 km beneath the Trans-Mexican Volcanic Belt (TMVB). It is also found that the Rivera plate is at roughly 140-km depth beneath the young central Jalisco Volcanic lineament. Our images suggest that the Rivera plate and westernmost Cocos plate have recently rolled back toward the trench. This scenario may explain the unusual magmatic activity seen in the TMVB.
NASA Astrophysics Data System (ADS)
Hung, S. H.; Liao, T. Y.; Sales de Andrade, E.; Liu, Q.
2014-12-01
The existence of seismic anisotropy in D" has been diagnosed by the evident arrival-time shifts between SVdiff and SHdiff phases and discrepancies in SKS and SKKS splitting. Previous numerical modeling of seismic wave propagation demonstrates that the SVdiff and SHdiff arrivals are not synchronized in time even in an isotropic Earth model due to intrinsically different finite-frequency sensitivity of non-geometrical diffracted S waves between radial and transverse components. Therefore, prior to using diffracted shear wave phases to constrain seismic anisotropy in the lowermost mantle, we need to first clarify the finite-frequency effects of diffracted shear waves propagating through D" velocity heterogeneity. In this study, we collect broadband waveforms from intermediate and deep-focus earthquakes (> 150 km) with epicentral distances of 90-145o and magnitudes greater than 5.8 during 1997-2012. The splitting between the vertically (SV) and transversely (SH) polarized arrivals of S(diff) phases after correcting for upper mantle anisotropy are analyzed to investigate seismic anisotropy in D" induced by anisotropic material elasticity and finite-frequency wave propagation effects. Both positive and negative SVdiff-SHdiff split times are observed in seismically slow regions; however, the proposed viable scenario in which partial melts produced at the base of the hot mantle plumes have been aligned laterally in D" by the basal boundary flow can only explain relatively earlier SHdiff arrivals. Positive SV-SH times (i.e., SH traveling faster) found in high-velocity regions are consistent with the consequences caused by intrinsic LPO of pPv-MgSiO3 in horizontally-lying slabs and different finite-frequency sensitivity between SVdiff and SHdiff in the heterogeneous lowermost mantle. We will differentiate and quantify these two effects on the observed Sdiff splitting through simulating ground-truth finite-frequency shear wave diffraction in the 3-D tomography Earth model and
Zonal Acoustic Velocimetry in 30-cm, 60-cm, and 3-m Laboratory Models of the Outer Core
NASA Astrophysics Data System (ADS)
Rojas, R.; Doan, M. N.; Adams, M. M.; Mautino, A. R.; Stone, D.; Lekic, V.; Lathrop, D. P.
2016-12-01
A knowledge of zonal flows and shear is key in understanding magnetic field dynamics in the Earth and laboratory experiments with Earth-like geometries. Traditional techniques for measuring fluid flow using visualization and particle tracking are not well-suited to liquid metal flows. This has led us to develop a flow measurement technique based on acoustic mode velocimetry adapted from helioseismology. As a first step prior to measurements in the liquid sodium experiments, we implement this technique in our 60-cm diameter spherical Couette experiment in air. To account for a more realistic experimental geometry, including deviations from spherical symmetry, we compute predicted frequencies of acoustic normal modes using the finite element method. The higher accuracy of the predicted frequencies allows the identification of over a dozen acoustic modes, and mode identification is further aided by the use of multiple microphones and by analyzing spectra together with those obtained at a variety of nearby Rossby numbers. Differences between the predicted and observed mode frequencies are caused by differences in flow patterns present in the experiment. We compare acoustic mode frequency splittings with theoretical predictions for stationary fluid and solid body flow condition with excellent agreement. We also use this technique to estimate the zonal shear in those experiments across a range of Rossby numbers. Finally, we report on initial attempts to use this in liquid sodium in the 3-meter diameter experiment and parallel experiments performed in water in the 30-cm diameter experiment.
Finite Frequency Measurements of Conventional and Core-diffracted P-waves (P and Pdiff)
NASA Astrophysics Data System (ADS)
Hosseini, K.; Sigloch, K.; Stähler, S. C.
2014-12-01
Core-diffracted waves are body waves that dive deep enough to sense the core, and by interaction with this wave guide become dispersive. They sample the core-mantle boundary and the lower third of the mantle extensively. In ray theoretical modeling, the deepest part of the ray starts to graze the core at around 97 degrees distance, but ray theory is a very poor approximation to propagation of core-diffracted waves. In reality, finite-frequency waves with their spatially extend sensitivity regions start to sense the core at significantly smaller distances already. The actual, non-ray-like sensitivities have been difficult to model, as have been the associated synthetic seismograms. Core-diffracted waves have therefore not been used in tomography, despite abundant observations of these phases on modern broadband seismograms. Hence current global body-wave tomographies illuminate the lower third of the mantle much less well than the upper and especially the middle third. This study aims for broadband, global waveform tomography that seamlessly incorporates core-diffracted phases alongside conventional, teleseismic waves as well as regional body-waves. Here, we investigate the properties of P-diffracted waves in terms of waveform characteristics and travel-time measurements as compared to teleseismic P-wave measured by the same methods. Travel time anomalies, the primary data for tomography, are measured by waveform cross-correlation of data with synthetics, where the synthetics are calculated from fully numerical wave propagation in a spherically symmetric background model. These same numerical tools will be used to calculate the associated sensitivity kernels for tomography (figure, top). Demonstrating the extent to which waveform modeling can fit real data, we assemble and discuss a global data set of 851,905 Pdiff and 2,368,452 P-wave multi-frequency cross-correlation travel times. Findings are summarized in the Pdiff travel time map (figure, bottom) in which most
Factors Controlling the Evolution of Anatolia: Clues from Teleseismic Finite-Frequency Tomography
NASA Astrophysics Data System (ADS)
Biryol, C. B.; Beck, S. L.; Zandt, G.; Ozacar, A. A.
2010-12-01
The complex and sinusoidal pattern of subduction zones of the Mediterranenan region plays an important role in controlling the current tectonic framework of the Alpine-Himalayan orogenic belt. The Anatolian region is part of this belt and it displays the complex characteristics of the interplay between continent collision in the east and subduction-rollback related backarc extension in the west. The ongoing northward subduction of the African Plate beneath the Anatolian Plate contributes significantly to the emergence of the current tectonic setting of this region. Despite its crucial effect on the tectonics of Anatolia, there are only a few studies that focus on the deeper extent of this zone. In this study we provide higher resolution tomographic images of the subducting African lithosphere beneath Anatolia. Our approach is based on analysis of teleseismic body-wave travel-time data using a finite-frequency seismic tomography algorithm. The data for our analysis comes from multiple permanent and temporary networks deployed in the region. A major part of our dataset is formed by the multiple frequency-band picks of P-wave arrival times recorded at more than 100 broadband and short-period seismic stations of the National Earthquake Monitoring Center and 39 broadband seismic stations of the North Anatolian Passive Seismic Experiment network. The results of our analysis indicates the presence of large and smaller scale gaps in the subducting African Lithosphere, that are interpreted as slab tears. The most significant tear is located beneath western Anatolia with a maximum width of ~250 km. This tear is marked by lack of intermediate to deep seismicity and is associated with slow seismic speed perturbations that we interpret as ascending hot, buoyant asthenosphere. The configuration of the edges of this gap at depths between 50 to 200 km provides clues about how the impediments on the subducting seafloor could have an influence on rates of roll-back on both sides
NASA Technical Reports Server (NTRS)
Dinyavari, M. A. H.; Friedmann, P. P.
1984-01-01
Several incompressible finite-time arbitrary-motion airfoil theories suitable for coupled flap-lag-torsional aeroelastic analysis of helicopter rotors in hover and forward flight are derived. These theories include generalized Greenberg's theory, generalized Loewy's theory, and a staggered cascade theory. The generalized Greenberg's and staggered cascade theories were derived directly in Laplace domain considering the finite length of the wake and using operational methods. The load expressions are presented in Laplace, frequency, and time domains. Approximate time domain loads for the various generalized theories, discussed in the paper, are obtained by developing finite state models using the Pade approximant of the appropriate lift deficiency functions. Three different methods for constructing Pade approximants of the lift deficiency functions were considered and the more flexible one was used. Pade approximants of Loewy's lift deficiency function, for various wake spacing and radial location parameters of a helicopter typical rotor blade section, are presented.
Global Time Tomography of Finite Frequency Waves with Optimized Tetrahedral Grids.
NASA Astrophysics Data System (ADS)
Montelli, R.; Montelli, R.; Nolet, G.; Dahlen, F. A.; Masters, G.; Hung, S.
2001-12-01
Besides true velocity heterogeneities, tomographic images reflect the effect of data errors, model parametrization, linearization, uncertainties involved with the solution of the forward problem and the greatly inadequate sampling of the earth by seismic rays. These influences cannot be easily separated and often produce artefacts in the final image with amplitudes comparable to those of the velocity heterogeneities. In practice, the tomographer uses some form of damping of the ill-resolved aspects of the model to get a unique solution and reduce the influence of the errors. However damping is not fully adequate, and may reveal a strong influence of the ray path coverage in tomographic images. If some cells are ill determinated regularization techniques may lead to heterogeneity because these cells are damped towards zero. Thus we want a uniform resolution of the parameters in our model. This can be obtained by using an irregular grid with variable length scales. We have introduced an irregular parametrization of the velocity structure by using a Delaunay triangulation. Extensively work on error analysis of tomographic images together with mesh optimization has shown that both resolution and ray density can provide the critical informations needed to re-design grids. However, criteria based on resolution are preferred in the presence of narrow ray beams coming from the same direction. This can be understood if we realise that resolution is not only determined by the number of rays crossing a region, but also by their azimutal coverage. We shall discuss various strategies for grid optimization. In general the computation of the travel times is restricted to ray theory, the infinite frequency approximation of the elastodynamic equation of motion. This simplifies the mathematic and is therefore widely applied in seismic tomography. But ray theory does not account for scattering, wavefront healing and other diffraction effects that render the traveltime of a finite
Nonlinear excitation of zonal flows and streamers in plasmas
Benkadda, S.; Klochkov, D. N.; Popel, S. I.; Izvekova, Yu. N.
2011-05-15
Nonlinear excitation of zonal flows and streamers in plasmas is considered. The emphasis is given to the nonlinear interaction of low- and high-frequency drift waves which can result in the excitation of zonal flows and streamers in a plasma of fusion devices. For this purpose, an inhomogeneous nonisothermal plasma in a strong external magnetic field whose characteristic frequencies are lower than the ion Langmuir frequency but higher than the collision frequency is studied. The excitation of a long-wavelength low-frequency drift wave during the development of the nonlinear modulational interaction of a high-frequency drift pump wave is investigated. The growth rates of the modulational instability are obtained, and the conditions for its development are determined. Self-organized structures described by solutions of evolutionary equations for the modulational interaction are associated with zonal flows and streamers. A possible relation of the modulational interaction in Earth's ionospheric plasma to the formation of dust flows and transport of dust particles in the ionosphere is also discussed. It is shown that one of the ways of transport of dust particles in the ionosphere is vertical flows (streamers), which are generated by dust vortices as a result of development of the modulational instability.
Two dimensional non-local transport across zonal shear flows
NASA Astrophysics Data System (ADS)
Kullberg, A.; Del-Castillo-Negrete, D.; Morales, G. J.; Maggs, J. E.
2011-10-01
The standard diffusive model assumes that the fluxes are entirely determined by the local value of the gradient. Although this paradigm has had considerable success, there are situations in which this prescription (i.e. Fick's law) does not hold; instead, the flux at a point may depend on the gradients throughout the entire spatial domain. Examples of this type of transport include perturbative experiments in tokamaks, numerical simulations of turbulent plasmas, and generalized random walk theoretical models. This presentation describes recent results on non-local transport in the presence of zonal shear flows. The study is based on a 2-dimensional equation that has a poloidal zonal flow coupled to a radial non-local transport channel. This work extends upon previous research by incorporating a cylindrical, 2-dimensional (albeit azimuthally averaged), non-local radial transport operator. Numerical results relating to several aspects of transport across the zonal shear flow are presented, including a numerical study of the creation of resonant traveling thermal waves inside the flow by an oscillating heat source, and the propagation of cold pulses across the zonal flow. In the case of thermal waves, resonance occurs when the source frequency matches the rotational angular frequency of the flow.
Finite frequency tomography of D″ shear velocity heterogeneity beneath the Caribbean
NASA Astrophysics Data System (ADS)
Hung, Shu-Huei; Garnero, Edward J.; Chiao, Ling-Yun; Kuo, Ban-Yuan; Lay, Thorne
2005-07-01
The shear velocity structure in the lowermost 500 km of the mantle beneath the Caribbean and surrounding areas is determined by seismic tomography applied to a suite of Sd-SKS, ScS-S, (Scd + Sbc)-S, and ScS-(Scd + Sbc) differential times, where (Scd + Sbc) is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the D″ region. The inclusion of the triplication arrivals in the inversion, a first for a deep mantle tomographic model, is possible because of the widespread presence of a D″ velocity discontinuity in the region. The improved ray path sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the D″ region. The reference velocity model, taken from a prior study of waveforms in the region, has a 2.9% shear velocity discontinuity 250 km above the core-mantle boundary (CMB). Effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long-wavelength shear velocity tomography models. Born-Fréchet kernels are used to characterize how the finite frequency data sample the structure for all of the differential arrival time combinations; inversions are performed with and without the kernels. The use of three-dimensional kernels stabilizes the tomographic inversion relative to a ray theory parameterization, and a final model with 60- and 50-km correlation lengths in the lateral and radial dimensions, respectively, is retrieved. The resolution of the model is higher than that of prior inversions, with 3-4% velocity fluctuations being resolved within what is commonly described as a circum-Pacific ring of high velocities. A broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the Gulf of Mexico, with several percent lower shear velocities being found beneath northern South America
Finite-Frequency Tomography of D'' Shear Velocity Heterogeneity beneath the Caribbean
NASA Astrophysics Data System (ADS)
Hung, S.; Garnero, E. J.; Chiao, L.; Kuo, B.; Lay, T.
2004-12-01
The shear velocity structure in the lowermost 500 km of the mantle beneath the Caribbean and surrounding areas is determined by seismic tomography applied to a suite of Sdiff-SKS, ScS-S, (Scd+Sbc)-S, and ScS-(Scd+Sbc) differential times, where (Scd+Sbc) is a pair of overlapping triplication arrivals produced by shear wave interaction with an abrupt velocity increase at the top of the D'' region. The inclusion of the triplication arrivals in the inversion, a first for a deep mantle tomographic model, is possible because of the widespread presence of a D'' velocity discontinuity in the region. The additional raypath sampling provided by the triplication arrivals yields improved vertical resolution of velocity heterogeneity within and above the D'' region. The reference velocity model, taken from a prior study of waveforms in the region, has a 2.9% shear velocity discontinuity 250 km above the CMB. Effects of aspherical structure in the mantle at shallower depths than the inversion volume are suppressed by applying corrections for several different long-wavelength shear velocity tomography models. Born-Fréchet kernels are used to characterize how the finite-frequency data sample the structure for all of the differential arrival time combinations; inversions are performed with and without the kernels. The use of 3-D kernels stabilizes the tomographic inversion relative to a ray theory parameterization, and a final model with 60 and 50 km correlation lengths in the the lateral and radial dimensions, respectively, is retrieved. The resolution of the model is higher than that of prior inversions, with 3 to 4% velocity fluctuations being resolved within what is commonly described as a circum-Pacific ring of high velocities. A broad zone of relatively high shear velocity material extends throughout the lower mantle volume beneath the Gulf of Mexico, with several percent lower shear velocities being found beneath northern South America. Concentrated low velocity regions
Seismic imaging beneath southwest Africa based on finite-frequency body wave tomography
NASA Astrophysics Data System (ADS)
Youssof, Mohammad; Yuan, Xiaohui; Tilmann, Frederik; Heit, Benjamin; Weber, Michael; Jokat, Wilfried; Geissler, Wolfram; Laske, Gabi
2016-04-01
We present a seismic model of southwest Africa from teleseismic tomographic inversion of the P- and S- wave data recorded by an amphibious temporary seismic network. The area of study is located at the intersection of the Walvis Ridge with the continental margin of northern Namibia, and extends into the Congo craton. Utilizing 3D finite-frequency sensitivity kernels, we invert traveltime residuals of the teleseismic body waves to image seismic structures in the upper mantle. To test the robustness of our tomographic imaging, we employed various resolution assessments that allow us to inspect the extent of smearing effects and to evaluate the optimum regularization weights (i.e., damping and smoothness). These tests include applying different (ir)regular parameterizations, classical checkerboard and anomaly tests and squeezing modeling. Furthermore, we performed different kinds of weighing schemes for the traveltime dataset. These schemes account for balancing between the picks data amount with their corresponding events directions. Our assessment procedure involves also a detailed investigation of the effect of the crustal correction on the final velocity image, which strongly influenced the image resolution for the mantle structures. Our model can resolve horizontal structures of 1° x 1° below the array down to 300-350 km depth. The resulting model is mainly dominated by the difference in the oceanic and continental mantle lithosphere beneath the study area, with second-order features related to their respective internal structures. The fast lithospheric keel of the Congo Craton reaches a depth of ~250 km. The orogenic Damara Belt and continental flood basalt areas are characterized by low velocity perturbations down to a depth of ~150 km, indicating a normal fertile mantle. High velocities in the oceanic lithosphere beneath the Walvis Ridge appear to show signatures of chemical depletion. A pronounced anomaly of fast velocity is imaged underneath continental NW
NASA Astrophysics Data System (ADS)
Geddes, Earl Russell
The details of the low frequency sound field for a rectangular room can be studied by the use of an established analytic technique--separation of variables. The solution is straightforward and the results are well-known. A non -rectangular room has boundary conditions which are not separable and therefore other solution techniques must be used. This study shows that the finite element method can be adapted for use in the study of sound fields in arbitrary shaped enclosures. The finite element acoustics problem is formulated and the modification of a standard program, which is necessary for solving acoustic field problems, is examined. The solution of the semi-non-rectangular room problem (one where the floor and ceiling remain parallel) is carried out by a combined finite element/separation of variables approach. The solution results are used to construct the Green's function for the low frequency sound field in five rooms (or data cases): (1) a rectangular (Louden) room; (2) The smallest wall of the Louden room canted 20 degrees from normal; (3) The largest wall of the Louden room canted 20 degrees from normal; (4) both the largest and the smallest walls are canted 20 degrees; and (5) a five-sided room variation of Case 4. Case 1, the rectangular room was calculated using both the finite element method and the separation of variables technique. The results for the two methods are compared in order to access the accuracy of the finite element method models. The modal damping coefficient are calculated and the results examined. The statistics of the source and receiver average normalized RMS P('2) responses in the 80 Hz, 100 Hz, and 125 Hz one-third octave bands are developed. The receiver averaged pressure response is developed to determine the effect of the source locations on the response. Twelve source locations are examined and the results tabulated for comparison. The effect of a finite sized source is looked at briefly. Finally, the standard deviation of the
NASA Astrophysics Data System (ADS)
Zhao, L.; Chevrot, S.
2007-12-01
Numerical modeling experiments of wave propagation have shown that the traveltime and amplitude anomalies of a finite-frequency seismic wave are influenced by the heterogeneities in the first Fresnel zone of the wave, a region surrounding its ray path. This leads to the so-called 'banana-doughnut' sensitivity (Fr{é}chet) kernels for finite-frequency waves whose values vary in the first Fresnel zone, rather than concentrate only on the ray path. Therefore, if finite-frequency effect is not taken into account in seismic tomography, the unrealistic sensitivity kernels will limit the resolution to roughly the widths of the first Fresnel zones of the seismic waves, even if all the other aspects are perfect. For the same reason, to realize the full potential of finite-frequency approach in seismic tomography, the spatial sampling in computing the Fr{é}chet kernels and in discretizing the structural model must be sufficiently small so that there are enough sampling points within the width of the first Fresnel zone. This introduces a high demand in computational resources including memory, CPU time, disk storage and the input/output (I/O) operations. To facilitate the practice of finite-frequency high-resolution tomography, we develop an efficient algorithm for computing the Fr{é}chet kernels based on the normal-mode theory in spherically symmetric earth models. The strain Green tensors (SGTs) for a spherically symmetric reference model are computed by normal-mode summation on a dense depth-distance grid by normal-mode summation. This normal-mode SGT database can then be used to calculate all the wavefield quantities needed in seismic studies including synthetic seismograms, partial derivatives with respect to source parameters for the inversion of CMT solutions, and the Fr{é}chet kernels for various kinds of model parameters for the inversions of anelastic and anisotropic structures. The SGT database approach provides the necessary efficiency for calculating the Fr
Zonal flow formation in the Earth's core.
Miyagoshi, Takehiro; Kageyama, Akira; Sato, Tetsuya
2010-02-11
Zonal jets are very common in nature. Well-known examples are those in the atmospheres of giant planets and the alternating jet streams found in the Earth's world ocean. Zonal flow formation in nuclear fusion devices is also well studied. A common feature of these zonal flows is that they are spontaneously generated in turbulent systems. Because the Earth's outer core is believed to be in a turbulent state, it is possible that there is zonal flow in the liquid iron of the outer core. Here we report an investigation at the current low-viscosity limit of numerical simulations of the geodynamo. We find a previously unknown convection regime of the outer core that has a dual structure comprising inner, sheet-like radial plumes and an outer, westward cylindrical zonal flow. We numerically confirm that the dual-convection structure with such a zonal flow is stable under a strong, self-generated dipole magnetic field.
Ozdemir, Nilufer A; Craeye, Christophe
2013-12-01
The optical response of dense finite arrays of nanoparticles can be efficiently analyzed with the help of macro basis functions obtained by employing the array scanning method. This is demonstrated by analyzing optical collimation in arrays of silver nanorods. The accuracy of the solution obtained with the proposed method has been validated by comparison with solutions obtained employing the Krylov subspace iterative method. The relative error in the electric field distribution on an observation plane above the finite array is of the order of -25 dB, while the number of unknowns is reduced by a factor of 32.
Localized Single Frequency Lasing States in a Finite Parity-Time Symmetric Resonator Chain
Phang, Sendy; Vukovic, Ana; Creagh, Stephen C.; Sewell, Phillip D.; Gradoni, Gabriele; Benson, Trevor M.
2016-01-01
In this paper a practical case of a finite periodic Parity Time chain made of resonant dielectric cylinders is considered. The paper analyzes a more general case where PT symmetry is achieved by modulating both the real and imaginary part of the material refractive index along the resonator chain. The band-structure of the finite periodic PT resonator chains is compared to infinite chains in order to understand the complex interdependence of the Bloch phase and the amount of the gain/loss in the system that causes the PT symmetry to break. The results show that the type of the modulation along the unit cell can significantly affect the position of the threshold point of the PT system. In all cases the lowest threshold is achieved near the end of the Brillouin zone. In the case of finite PT-chains, and for a particular type of modulation, early PT symmetry breaking is observed and shown to be caused by the presence of termination states localized at the edges of the finite chain resulting in localized lasing and dissipative modes at each end of the chain. PMID:26848095
Extension of the frequency-domain pFFT method for wave structure interaction in finite depth
NASA Astrophysics Data System (ADS)
Teng, Bin; Song, Zhi-jie
2017-06-01
To analyze wave interaction with a large scale body in the frequency domain, a precorrected Fast Fourier Transform (pFFT) method has been proposed for infinite depth problems with the deep water Green function, as it can form a matrix with Toeplitz and Hankel properties. In this paper, a method is proposed to decompose the finite depth Green function into two terms, which can form matrices with the Toeplitz and a Hankel properties respectively. Then, a pFFT method for finite depth problems is developed. Based on the pFFT method, a numerical code pFFT-HOBEM is developed with the discretization of high order elements. The model is validated, and examinations on the computing efficiency and memory requirement of the new method have also been carried out. It shows that the new method has the same advantages as that for infinite depth.
NASA Astrophysics Data System (ADS)
Hosseini, Kasra; Sigloch, Karin; Staehler, Simon C.
2014-05-01
In its lowermost 200-300 km, the mantle has a complex structure resulting from accumulations of downwellings (subducted slabs), upwellings (LLSVPs and plumes), and probably phase transitions; seismic velocities and density show large variations but are not tightly constrained. Core-diffracted body waves are the seismic phases that sample the lowermost mantle extensively and are prime candidates to be used in tomography for enhancing resolution in this depth range. Since they are diffracted along the core-mantle boundary, their behavior is highly dispersive and cannot be modeled satisfactory using ray theory, nor early versions of finite-frequency modeling. Hence they have rarely been used for tomography so far, and where they have been, large imaging blur can be expected. We present a processing scheme to measure finite-frequency travel-time anomalies of arbitrary seismic body-wave phases in a fully automated way, with an initial focus on core-diffracted P waves. The aim is to extract a maximum of information from observed broadband seismograms using multi-frequency techniques. Using a matched-filtering approach, predicted and observed waveforms are compared in a cross-correlation sense in eight overlapping frequency passbands, with dominant periods ranging between 30 and 2.7sec. This method was applied to a global data set of ≡2000 teleseismic events in our waveform archive, which resulted in 1,616,184 P and 536,190 Pdiff usable multi-frequency measurements of high cross-correlation coefficient (≥ 0.8). The measurements are analyzed statistically in terms of goodness of fit, effects of epicentral distance, and frequency-dependent behavior of P and Pdiff phases. The results for Pdiff waves are displayed by projecting the measured travel time anomalies onto the phase's nominal grazing segments along the core-mantle boundary.
Zonal flow energy ratio evolution during L-H and H-L transitions in EAST plasmas
NASA Astrophysics Data System (ADS)
Hailin, ZHAO; Tao, LAN; Adi, LIU; Defeng, KONG; Huagang, SHEN; Jie, WU; Wandong, LIU; Changxuan, YU; Wei, ZHANG; Guosheng, XU; Baonian, WAN
2017-03-01
The essential role of zonal flow in the L-H transition and the suppression of turbulence have been studied with a long range correlation technique using Langmuir probe arrays in EAST tokamak. Two toroidally localized probe arrays are used to measure the zonal flow during L-H transition and H-L back transition. The energy ratio of the low frequency zonal flow to the total drift wave turbulence is calculated. During ELM-free H mode, the energy ratio is higher than that in L mode, which reveals the important role of zonal flows in regulating turbulence amplitude in L-H transition.
Nonlinear Generation of Zonal Fields by the Beta-Induced Alfvén Eigenmode in Tokamak
NASA Astrophysics Data System (ADS)
Zhang, Huasen; Lin, Zhihong
2013-10-01
The zonal fields effect on the beta-induced Alfvén eigenmode (BAE) destabilized by the energetic particles in toroidal plasmas is studied through the gyrokinetic particle simulations. It is found that the localized zonal fields with a negative value around the mode rational surface are generated by the nonlinear BAE. In the weakly driven case, the zonal fields with a strong geodesic acoustic mode (GAM) component have weak effects on the nonlinear BAE evolution. In the strongly driven case, the zonal fields are dominated by a more significant zero frequency component and have stronger effects on the nonlinear BAE evolution.
NASA Astrophysics Data System (ADS)
Joglekar, D. M.; Mitra, M.
2015-11-01
A breathing crack, due to its bilinear stiffness characteristics, modifies the frequency spectrum of a propagating dual-frequency elastic wave, and gives rise to sidebands around the probing frequency. This paper presents an analytical-numerical method to investigate such nonlinear frequency mixing resulting from the modulation effects induced by a breathing crack in 1D waveguides, such as axial rods and the Euler-Bernoulli beams. A transverse edge-crack is assumed to be present in both the waveguides, and the local flexibility caused by the crack is modeled using an equivalent spring approach. A simultaneous treatment of both the waveguides, in the framework of the Fourier transform based spectral finite element method, is presented for analyzing their response to a dual frequency excitation applied in the form of a tone-burst signal. The intermittent contact between the crack surfaces is accounted for by introducing bilinear contact forces acting at the nodes of the damage spectral element. Subsequently, an iterative approach is outlined for solving the resulting system of nonlinear simultaneous equations. Applicability of the proposed method is demonstrated by considering several test cases. The existence of sidebands and the higher order harmonics is confirmed in the frequency domain response of both the waveguides under investigation. A qualitative comparison with the previous experimental observations accentuates the utility of the proposed solution method. Additionally, the influence of the two constituent frequencies in the dual frequency excitation is assessed by varying the relative strengths of their amplitudes. A brief parametric study is performed for bringing out the effects of the relative crack depth and crack location on the degree of modulation, which is quantified in terms of the modulation parameter. Results of the present investigation can find their potential use in providing an analytical-numerical support to the studies geared towards the
Jonsson, Ulf; Lindahl, Olof; Andersson, Britt
2014-12-01
To gain an understanding of the high-frequency elastic properties of silicone rubber, a finite element model of a cylindrical piezoelectric element, in contact with a silicone rubber disk, was constructed. The frequency-dependent elastic modulus of the silicone rubber was modeled by a fourparameter fractional derivative viscoelastic model in the 100 to 250 kHz frequency range. The calculations were carried out in the range of the first radial resonance frequency of the sensor. At the resonance, the hyperelastic effect of the silicone rubber was modeled by a hyperelastic compensating function. The calculated response was matched to the measured response by using the transitional peaks in the impedance spectrum that originates from the switching of standing Lamb wave modes in the silicone rubber. To validate the results, the impedance responses of three 5-mm-thick silicone rubber disks, with different radial lengths, were measured. The calculated and measured transitional frequencies have been compared in detail. The comparison showed very good agreement, with average relative differences of 0.7%, 0.6%, and 0.7% for the silicone rubber samples with radial lengths of 38.0, 21.4, and 11.0 mm, respectively. The average complex elastic moduli of the samples were (0.97 + 0.009i) GPa at 100 kHz and (0.97 + 0.005i) GPa at 250 kHz.
Numerical analysis of curved frequency selective surface by finite-difference time-domain
NASA Astrophysics Data System (ADS)
Chen, Xin-yi; Wang, Jian-bo; Chen, Gui-bo; Sun, Guan-cheng; Lu, Jun
2011-08-01
Frequency selective surface is a monolayer or multilayer 2D periodic structure which is composed of multiple resonance units scattering by a two-dimensional periodic array on dielectric layer. FSS can't absorb radio frequency energy, but can filter the frequency which is therefore applied in microwave technique or stealth technology. The relative research on curved FSS is relatively scarce since the curved FSS structure can be obtained only when FSS is attached on the materials surfaces of curved structures in engineering application. However, curved FSS is widely applied in practical engineering; therefore, the research on curved FSS structure has important significance. In this paper, a curved FSS structure model of Y-pore unit is established and numerical simulated by means of FDTD. The influence of curvature on FSS transmission characteristics is studied according to the analysis on the changing of radar cross section (RCS). The results show: the center frequency point of the plane band pass FSS structure drifts after the curve surface deformation of the structure; the center frequency point of the curved band pass FSS structure drifts with the changing of the curvature radius, i. e. with the decreasing of curvature radius, the frequency point drifts towards high points and the transmittance decreases. The design of FSS radome demands of accurate and stable center resonance frequency; therefore, the actual situation of curved surface should be considered in practical engineering application when band pass FSS is made into frequency selection filtering radome. The curvature radius should be long enough to avoid center frequency drifting and transmittance deceasing.
Zareian Jahromi, S Abdolali; Salomons, Mark; Sun, Qiao; Wolkow, Robert A
2008-07-01
In this paper, we study the resonant behavior of a piezoelectric tube scanner used in scanning probe microscopes. In particular, we use a finite element model to allow the inclusion of boundary effects, i.e., nonrigid bonding layers and elastic tip holder, on the dynamic response of the scanner. We show that although existing analytical models provide a good estimation of the axial resonant frequency, their predictions of the first bending resonance may have up to a 100% error. In addition, a simple procedure is proposed that combines some precalculated factors to predict the lowest resonant frequency for a wide range of typical scanner dimensions. An experiment is carried out to illustrate the procedure and validate the prediction.
Effects of Landau damping on finite amplitude low-frequency nonlinear waves in a dusty plasma
NASA Astrophysics Data System (ADS)
Sikdar, Arnab; Khan, Manoranjan
2017-06-01
The effect of linear ion Landau damping on weakly nonlinear as well as weakly dispersive low-frequency waves in a dusty plasma is investigated. The standard perturbative approach leads to the Korteweg-de Vries (KdV) equation with a linear Landau damping term for the dynamics of the low-frequency nonlinear wave. Landau damping causes the wave amplitude to decay with time and the dust charge variation enhances the damping rate.
Kohno, H.; Myra, J. R.
2017-07-24
A finite element code that solves self-consistent radio-frequency (RF) sheath-plasma interaction problems is improved by incorporating a generalized sheath boundary condition in the macroscopic solution scheme. This sheath boundary condition makes use of a complex sheath impedance including both the sheath capacitance and resistance, which enables evaluation of not only the RF voltage across the sheath but also the power dissipation in the sheath. The newly developed finite element procedure is applied to cases where the background magnetic field is perpendicular to the sheath surface in one- and two-dimensional domains filled by uniform low- and high-density plasmas. The numerical resultsmore » are compared with those obtained by employing the previous capacitive sheath model at a typical frequency for ion cyclotron heating used in fusion experiments. It is shown that for sheaths on the order of 100 V in a high-density plasma, localized RF power deposition can reach a level which causes material damage. It is also shown that the sheath-plasma wave resonances predicted by the capacitive sheath model do not occur when parameters are such that the generalized sheath impedance model substantially modifies the capacitive character of the sheath. Here, possible explanations for the difference in the maximum RF sheath voltage depending on the plasma density are also discussed.« less
Wareing, Robin R; Davy, John L; Pearse, John R
2016-01-01
Current theories for predicting the sound insulation of orthotropic materials are limited to a small range of infinite panels. This paper presents a method that allows for the prediction of the sound insulation of a finite size orthotropic panel. This method uses an equation for the forced radiation impedance of a finite size rectangular panel. This approach produces an equation that has three nested integrals. The long numerical calculation times were reduced by using approximate formulas for the azimuthally averaged forced radiation impedance. This reduced the number of nested integrals from three to two. The resulting predictions are compared to results measured using two sample sizes of four different thicknesses of plywood and one sample size of another three different thicknesses of plywood. Plywood was used for all the tests because it is somewhat orthotropic. It was found during testing that the Young's moduli of the plywood were dependent on the frequency of excitation. The influence of the frequency dependent Young's moduli was then included in the prediction method. The experimental results were also compared with a simple isotropic prediction method.
NASA Astrophysics Data System (ADS)
Liu, Yang; D'Angelo, Ralph M.; Sinha, Bikash K.; Zeroug, Smaine
2017-02-01
Modeling and understanding the complex elastic-wave physics prevalent in solid-fluid cylindrically-layered structures is of importance in many NDE fields, and most pertinently in the domain of well integrity evaluation of cased holes in the oil and gas industry. Current sonic measurements provide viable techniques for well integrity evaluation yet their practical effectiveness is hampered by the current lack of knowledge of acoustic wave fields particularly in complicated cased-hole geometry where for instance two or more nested steel strings are present in the borehole. In this article, we propose and implement a Sweeping Frequency Finite Element Method (SFFEM) for acoustic guided waves simulation in complex geometries that include double steel strings cemented to each other and to the formation and where the strings may be non-concentric. Transient dynamic finite element models are constructed with sweeping frequency signals being applied as the excitation sources. The sources and receivers disposition simulate current sonic measurement tools deployed in the oilfield. Synthetic wavetrains are recorded and processed with modified matrix pencil method to isolate both the dispersive and non-dispersive propagating guided wave modes. Scaled experiments of fluid-filled double strings with dimensions mimicking the real ones encountered in the field have also been carried out to generate reference data. A comparison of the experimental and numerical results indicates that the SFFEM is capable of accurately reproducing the rich and intricate higher-order multiple wave fields observed experimentally in the fluid-filled double string geometries.
NASA Astrophysics Data System (ADS)
Li, Y.; Han, B.; Métivier, L.; Brossier, R.
2016-09-01
We investigate an optimal fourth-order staggered-grid finite-difference scheme for 3D frequency-domain viscoelastic wave modeling. An anti-lumped mass strategy is incorporated to minimize the numerical dispersion. The optimal finite-difference coefficients and the mass weighting coefficients are obtained by minimizing the misfit between the normalized phase velocities and the unity. An iterative damped least-squares method, the Levenberg-Marquardt algorithm, is utilized for the optimization. Dispersion analysis shows that the optimal fourth-order scheme presents less grid dispersion and anisotropy than the conventional fourth-order scheme with respect to different Poisson's ratios. Moreover, only 3.7 grid-points per minimum shear wavelength are required to keep the error of the group velocities below 1%. The memory cost is then greatly reduced due to a coarser sampling. A parallel iterative method named CARP-CG is used to solve the large ill-conditioned linear system for the frequency-domain modeling. Validations are conducted with respect to both the analytic viscoacoustic and viscoelastic solutions. Compared with the conventional fourth-order scheme, the optimal scheme generates wavefields having smaller error under the same discretization setups. Profiles of the wavefields are presented to confirm better agreement between the optimal results and the analytic solutions.
NASA Astrophysics Data System (ADS)
Herrmann, Jan; Koreck, Jürgen; Maess, Matthias; Gaul, Lothar; von Estorff, Otto
2011-04-01
The integration of a model for longitudinal hydroacoustic fluid damping in thin hydraulic pipes in 3D finite element models is presented in this paper. In order to perform quantitative prediction of the vibroacoustic behavior and resulting noise levels of such fluid-structure coupled system due to hydraulic excitation, an accurate frequency-dependent fluid damping model including friction effects near the pipe wall is required. This step is achieved by matching complex wave numbers from analytical derivation into a parameterized damped wave equation and consecutive translation into finite element modeling. Since the friction effect close to the pipe wall changes locally with the inner pipe radius, the fluid damping model is applied segment-wise in order to model the influence of cross-sectional discontinuity, such as orifices, on the oscillating pressure pulsations. A component synthesis approach, which uses pipe segments as substructures, allows a simple model generation and fast computation times. The numerical harmonic results are compared to experimental frequency response functions, which are performed on a hydraulic test bench driven by a dynamic pressure source in the kHz-range.
Finite Difference Time Domain Electromagnetic Scattering from Frequency-Dependent Lossy Materials
NASA Technical Reports Server (NTRS)
Luebbers, Raymond J.; Beggs, John H.
1991-01-01
During this effort the tasks specified in the Statement of Work have been successfully completed. The extension of Finite Difference Time Domain (FDTD) to more complicated materials has been made. A three-dimensional FDTD code capable of modeling interactions with both dispersive dielectric and magnetic materials has been written, validated, and documented. This code is efficient and is capable of modeling interesting targets using a modest computer work station platform. However, in addition to the tasks in the Statement of Work, a significant number of other FDTD extensions and calculations have been made. RCS results for two different plate geometries have been reported. The FDTD method has been extended to computing far zone time domain results in two dimensions. Finally, the capability to model nonlinear materials has been incorporated into FDTD and validated. The FDTD computer codes developed have been supplied, along with documentation, and preprints describing the other FDTD advances have been included with this report as attachments.
Low frequency eddy current finite element model validation and benchmark studies
Cherry, M.; Knopp, J.; Mooers, R.; Boehnlein, T.; Aldrin, J. C.; Sabbagh, H. A.
2011-06-23
A finite element method (FEM) model was created to calculate the change in impedance of a coil due to the presence of a notch in a plate. The rectangular notches were created via electrical discharge machining (EDM) in a thick aluminum plate and were positioned at normal and oblique angles (10, 20, and 30 degrees) with respect to the vertical axis of the coil. The FEM method was chosen for this model due to its ability to solve problems in complicated geometries with the use of irregular mesh elements to discretize the solution domain. The change in impedance was calculated from the field variables in the simulation for each probe position along the parallel axis of the plate. The error between the model and the experimental data was approximately 5% for the majority of cases. The validated model was used to investigate more complex problems.
Low Frequency Eddy Current Finite Element Model Validation and Benchmark Studies
NASA Astrophysics Data System (ADS)
Cherry, M.; Mooers, R.; Knopp, J.; Aldrin, J. C.; Sabbagh, H. A.; Boehnlein, T.
2011-06-01
A finite element method (FEM) model was created to calculate the change in impedance of a coil due to the presence of a notch in a plate. The rectangular notches were created via electrical discharge machining (EDM) in a thick aluminum plate and were positioned at normal and oblique angles (10, 20, and 30 degrees) with respect to the vertical axis of the coil. The FEM method was chosen for this model due to its ability to solve problems in complicated geometries with the use of irregular mesh elements to discretize the solution domain. The change in impedance was calculated from the field variables in the simulation for each probe position along the parallel axis of the plate. The error between the model and the experimental data was approximately 5% for the majority of cases. The validated model was used to investigate more complex problems.
ITG sideband coupling models for zonal flows
Stransky, M.
2011-05-15
Four-wave interaction model between ITG mode and zonal flow was derived using fluid equations. In this model, the zonal flow is excited non-linearly by ITG turbulence via Reynolds stress. Numerical simulations show that the system allows for a small range above the ITG threshold where the zonal flow can stabilize an unstable ITG mode, effectively increasing {eta}{sub i} threshold, an effect which has been called the Dimits shift. However, the shift is smaller than in known cases such that in the Cyclone base.
Frisch, Matthias; Melchinger, Albrecht E
2008-01-01
Random intermating of F2 populations has been suggested for obtaining precise estimates of recombination frequencies between tightly linked loci. In a simulation study, sampling effects due to small population sizes in the intermating generations were found to abolish the advantages of random intermating that were reported in previous theoretical studies considering an infinite population size. We propose a mating scheme for intermating with planned crosses that yields more precise estimates than those under random intermating.
Sensitivity kernels of finite-frequency travel times in ocean acoustic tomography
NASA Astrophysics Data System (ADS)
Skarsoulis, Emmanuel K.; Cornuelle, Bruce D.
2004-05-01
Wave theoretic modeling is applied to obtain travel-time sensitivity kernels representing the amount by which travel times are affected by localized sound-speed variations anywhere in the medium. In the ray approximation travel times are sensitive to medium changes only along the corresponding eigenrays. In the wave-theoretic approach the perturbations of peak arrival times are expressed in terms of pressure perturbations, which are further related with the underlying sound-speed perturbations using the first Born approximation. In this way, an integral representation of travel-time perturbations is obtained in terms of sound-speed perturbations; the associated kernel represents the spatial sensitivity of travel times to sound-speed perturbations. The application of the travel-time sensitivity kernel to an ocean acoustic waveguide gives a picture close to the ray-theoretic one in the high-frequency case but significantly differs at lower frequencies. Low-frequency travel times are sensitive to sound-speed changes in areas surrounding the eigenrays, but not on the eigenrays themselves, where the sensitivity is zero. Further, there are areas of positive sensitivity, where, e.g., a sound-speed increase results in a counter-intuitive increase of arrival times. These findings are confirmed by independent forward calculations.
Localization of finite frequency inertial Alfvén wave and turbulent spectrum in low beta plasmas
NASA Astrophysics Data System (ADS)
Rinawa, M. L.; Sharma, R. P.; Modi, K. V.
2015-05-01
In the present paper, we have investigated nonlinear interaction of inertial Alfvén wave with ion acoustic wave, for low β-plasma ( β≪ m e / m i ) where β is the thermal to magnetic pressure ratio. We have developed the dynamical equation of inertial Alfvén wave by considering the finite frequency as well as finite ion temperature correction. The dynamical equation of ion acoustic wave, propagating at an angle with respect to the background magnetic field, in the presence of ponderomotive nonlinearity due to inertial Alfvén wave is also derived. Numerical simulation has been carried out to study the effect of nonlinear coupling between these waves which results in the formation of localized structures and turbulent spectrum, applicable to auroral region. The result reveals that the localized structures become complex and intense in nature (quasi-steady state). Further, we have studied the turbulent spectrum which follows spectral index (˜ k -4.46) at smaller scales. Relevance of the obtained results has been shown with the observations reported by various spacecrafts like Hawkeye and HEOS-2 (Highly Eccentric Orbiting Satellite-2).
NASA Astrophysics Data System (ADS)
Onishchenko, O. G.; Pokhotelov, O. A.; Astafieva, N. M.
2008-06-01
The review deals with a theoretical description of the generation of zonal winds and vortices in a turbulent barotropic atmosphere. These large-scale structures largely determine the dynamics and transport processes in planetary atmospheres. The role of nonlinear effects on the formation of mesoscale vortical structures (cyclones and anticyclones) is examined. A new mechanism for zonal wind generation in planetary atmospheres is discussed. It is based on the parametric generation of convective cells by finite-amplitude Rossby waves. Weakly turbulent spectra of Rossby waves are considered. The theoretical results are compared to the results of satellite microwave monitoring of the Earth's atmosphere.
EQUATORIAL ZONAL JETS AND JUPITER's GRAVITY
Kong, D.; Liao, X.; Zhang, K.; Schubert, G.
2014-08-20
The depth of penetration of Jupiter's zonal winds into the planet's interior is unknown. A possible way to determine the depth is to measure the effects of the winds on the planet's high-order zonal gravitational coefficients, a task to be undertaken by the Juno spacecraft. It is shown here that the equatorial winds alone largely determine these coefficients which are nearly independent of the depth of the non-equatorial winds.
NASA Technical Reports Server (NTRS)
2000-01-01
This movie is a manipulated sequence showing motions in Jupiter's atmosphere over the course of five days beginning Oct. 1, 2000, as seen by a camera on NASA's Cassini spacecraft, using a blue filter.
Beginning with seven images taken at uneven time intervals, this sequence was made by using information on wind speeds derived from actual Jupiter images to create evenly spaced time steps throughout. The final result is a smooth movie sequence consisting of both real and false frames.
The view is of the opposite side of the planet from Jupiter's Great Red Spot. The region shown reaches from 50 degrees north to 50 degrees south of Jupiter's equator, and extends 100 degrees east-to-west, about one-quarter of Jupiter's circumference. The smallest features are about 500 kilometers (about 300 miles) across.
Towards the end of the sequence, a shadow appears from one of Jupiter's moons, Europa.
The movie shows the remains of a historic merger that began several years ago, when three white oval storms that had existed for 60 years merged into two, then one. The resulting oval is visible in the lower left portion of the movie.
The movie also shows zonal jets that circle the planet on constant latitudes. Winds seen moving toward the left (westward) correspond to features that are rotating a little slower than Jupiter's magnetic field, and winds moving the opposite direction correspond to features that are rotating a little faster than the magnetic field. Since Jupiter has no solid surface, the rotation of the magnetic field is the point of reference for the rotation of the planet.
Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.
NASA Technical Reports Server (NTRS)
2000-01-01
This movie is a manipulated sequence showing motions in Jupiter's atmosphere over the course of five days beginning Oct. 1, 2000, as seen by a camera on NASA's Cassini spacecraft, using a blue filter.
Beginning with seven images taken at uneven time intervals, this sequence was made by using information on wind speeds derived from actual Jupiter images to create evenly spaced time steps throughout. The final result is a smooth movie sequence consisting of both real and false frames.
The view is of the opposite side of the planet from Jupiter's Great Red Spot. The region shown reaches from 50 degrees north to 50 degrees south of Jupiter's equator, and extends 100 degrees east-to-west, about one-quarter of Jupiter's circumference. The smallest features are about 500 kilometers (about 300 miles) across.
Towards the end of the sequence, a shadow appears from one of Jupiter's moons, Europa.
The movie shows the remains of a historic merger that began several years ago, when three white oval storms that had existed for 60 years merged into two, then one. The resulting oval is visible in the lower left portion of the movie.
The movie also shows zonal jets that circle the planet on constant latitudes. Winds seen moving toward the left (westward) correspond to features that are rotating a little slower than Jupiter's magnetic field, and winds moving the opposite direction correspond to features that are rotating a little faster than the magnetic field. Since Jupiter has no solid surface, the rotation of the magnetic field is the point of reference for the rotation of the planet.
Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.
Degirmenci, Elif; Landais, Pascal
2013-10-20
Photonic band gap and transmission characteristics of 2D metallic photonic crystals at THz frequencies have been investigated using finite element method (FEM). Photonic crystals composed of metallic rods in air, in square and triangular lattice arrangements, are considered for transverse electric and transverse magnetic polarizations. The modes and band gap characteristics of metallic photonic crystal structure are investigated by solving the eigenvalue problem over a unit cell of the lattice using periodic boundary conditions. A photonic band gap diagram of dielectric photonic crystal in square lattice array is also considered and compared with well-known plane wave expansion results verifying our FEM approach. The photonic band gap designs for both dielectric and metallic photonic crystals are consistent with previous studies obtained by different methods. Perfect match is obtained between photonic band gap diagrams and transmission spectra of corresponding lattice structure.
Chan, T V Chow Ting; Tang, J; Younce, F
2004-01-01
This paper presents a new, yet simple and effective approach to modeling industrial Radio Frequency heating systems, using the wave equation applied in three dimensions instead of the conventional electrostatics method. The central idea is that the tank oscillatory circuit is excited using an external source. This then excites the applicator circuit which is then used to heat or dry the processed load. Good agreement was obtained between the experimental and numerical data, namely the S11-parameter, phase, and heating patterns for different sized loads and positions.
Finite size effect on spread of resonance frequencies in arrays of coupled vortices
Vogel, Andreas; Drews, André; Im, Mi-Young; Fischer, Peter; Meier, Guido
2011-01-25
Dynamical properties of magnetic vortices in arrays of magnetostatically coupled ferromagnetic disks are studied by means of a broadband ferromagnetic-resonance (FMR) setup. Magnetic force microscopy and magnetic transmission soft X-ray microscopy are used to image the core polarizations and the chiralities which are both found to be randomly distributed. The resonance frequency of vortex-core motion strongly depends on the magnetostatic coupling between the disks. The parameter describing the relative broadening of the absorption peak observed in the FMR transmission spectra for a given normalized center-to-center distance between the elements is shown to depend on the size of the array.
P and S Wave Finite-frequency Imaging of the Cordillera-craton Boundary Zone in Western Canada
NASA Astrophysics Data System (ADS)
Gu, Y. J.; Chen, Y.; Hung, S. H.
2016-12-01
The Western Canada Sedimentary Basin (WCSB) marks a boundary zone and a strong seismic lateral velocity gradient in the upper mantle between the Precambrian North American craton and the Phanerozoic Cordillera. While much of the tectonic imprints are buried below thick sediments, seismic data coverage in this region has been greatly improved to unravel the underlying structure, owing to a growing number of regional broadband arrays. In this study we conduct a high-resolution survey of the mantle P- and S-wave velocities in the WCSB using a multi-scale parameterization and the finite-frequency theory. Our models suggest respective increases of 4% and 6% of Vp and Vs velocities across the Cordilleran Deformation Front (CDF) toward the craton interior. This sharp gradient resides to the west of the CDF, which may imply the over-thrusting of the crustal terranes of the Cordillera onto the craton edge. Significant along-strike variation in the lithospheric basal geometry and dip could reflect secular tectonic modifications such as episodic shortening/extension and convective erosion. The results of our finite-frequency tomography indicate vertically continuous high velocities at least down to 200 km beneath the crustal domains of the Precambrian Buffalo Head Terrane (BHT), Hearne craton and Medicine Hat Block (MHB). The lithosphere beneath the southern Hearne province could extend down to 280 km, nearly 70 km deeper than those of its neighboring cratons of similar ages. The velocity anomalies and their intricate variations/reversals within the mantle lithosphere may be evidence for a multi-stage formation of western Laurentia during Precambrian plate convergence. On the other hand, destruction processes since formation, e.g., convective removal and thermomagmatic erosion, may also have played key roles in shaping the mantle lithosphere beneath the western margin of the North American craton.
Zonal-flow-driven nonlinear energy transfer in experiment and simulation
Holland, C.; Tynan, G. R.; Fonck, R. J.; McKee, G. R.; Candy, J.; Waltz, R. E.
2007-05-15
Using a newly developed algorithm, the nonlinear transfer of internal fluctuation energy vertical bar n-tilde vertical bar{sup 2} due to convection of drift-wave turbulence by a geodesic acoustic mode (GAM, a finite-frequency zonal flow) has now been measured directly in a high-temperature plasma. By combining spatially resolved density fluctuation measurements obtained via an upgraded beam emission spectroscopy system in the edge region of the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] with a velocity inference algorithm, the convection of turbulent fluctuations by the GAM has been measured. Taken together, the results strongly suggest that GAM convection of turbulence leads to a transfer of internal fluctuation energy from low to high frequencies, in agreement with expectations from theory and simulation. In addition, the GAM is found to modulate the intensity of the density fluctuations. Calculations of the measured nonlinear interactions in the gyrokinetic code GYRO are found to be in good qualitative agreement with the experimental observations.
Finite-frequency structural sensitivities of short-period compressional body waves
NASA Astrophysics Data System (ADS)
Fuji, Nobuaki; Chevrot, Sébastien; Zhao, Li; Geller, Robert J.; Kawai, Kenji
2012-07-01
We present an extension of the method recently introduced by Zhao & Chevrot for calculating Fréchet kernels from a precomputed database of strain Green's tensors by normal mode summation. The extension involves two aspects: (1) we compute the strain Green's tensors using the Direct Solution Method, which allows us to go up to frequencies as high as 1 Hz; and (2) we develop a spatial interpolation scheme so that the Green's tensors can be computed with a relatively coarse grid, thus improving the efficiency in the computation of the sensitivity kernels. The only requirement is that the Green's tensors be computed with a fine enough spatial sampling rate to avoid spatial aliasing. The Green's tensors can then be interpolated to any location inside the Earth, avoiding the need to store and retrieve strain Green's tensors for a fine sampling grid. The interpolation scheme not only significantly reduces the CPU time required to calculate the Green's tensor database and the disk space to store it, but also enhances the efficiency in computing the kernels by reducing the number of I/O operations needed to retrieve the Green's tensors. Our new implementation allows us to calculate sensitivity kernels for high-frequency teleseismic body waves with very modest computational resources such as a laptop. We illustrate the potential of our approach for seismic tomography by computing traveltime and amplitude sensitivity kernels for high frequency P, PKP and Pdiff phases. A comparison of our PKP kernels with those computed by asymptotic ray theory clearly shows the limits of the latter. With ray theory, it is not possible to model waves diffracted by internal discontinuities such as the core-mantle boundary, and it is also difficult to compute amplitudes for paths close to the B-caustic of the PKP phase. We also compute waveform partial derivatives for different parts of the seismic wavefield, a key ingredient for high resolution imaging by waveform inversion. Our computations
NASA Astrophysics Data System (ADS)
Raychaudhuri, Pratap
2015-03-01
The notion of spontaneous formation of an inhomogeneous superconducting state is at the heart of most theories attempting to understand the superconducting state in the presence of strong disorder. Using a combination of low-temperature scanning tunneling spectroscopy and high resolution scanning transmission electron microscopy, we experimentally demonstrate that under the competing effects of strong homogeneous disorder and superconducting correlations, the superconducting state of a conventional superconductor, NbN, spontaneously segregates into domains. Tracking the superconducting state as a function of temperature we show that these superconducting domains persist across the bulk superconducting transition, Tc, and disappear close to the pseudogap temperature, T*, where signatures of superconducting correlations disappear from the tunneling spectrum and the superfluid response of the system. These results along with complementary measurements of the superfluid stiffness at microwave frequencies underpins the importance of phase fluctuations in strongly disordered s-wave superconductors.
Long-range correlations induced by the self-regulation of zonal flows and drift-wave turbulence
Manz, P.; Ramisch, M.; Stroth, U.
2010-11-15
By means of a unique probe array, the interaction between zonal flows and broad-band drift-wave turbulence has been investigated experimentally in a magnetized toroidal plasma. Homogeneous potential fluctuations on a magnetic flux surface, previously reported as long range correlations, could be traced back to a predator-prey-like interaction between the turbulence and the zonal flow. At higher frequency the nonlocal transfer of energy to the zonal flow is dominant and the low-frequency oscillations are shown to result from the reduced turbulence activity due to this energy loss. This self-regulation process turns out to be enhanced with increased background shear flows.
Luo, Y.; Xia, J.; Xu, Y.; Zeng, C.; Liu, J.
2010-01-01
Love-wave propagation has been a topic of interest to crustal, earthquake, and engineering seismologists for many years because it is independent of Poisson's ratio and more sensitive to shear (S)-wave velocity changes and layer thickness changes than are Rayleigh waves. It is well known that Love-wave generation requires the existence of a low S-wave velocity layer in a multilayered earth model. In order to study numerically the propagation of Love waves in a layered earth model and dispersion characteristics for near-surface applications, we simulate high-frequency (>5 Hz) Love waves by the staggered-grid finite-difference (FD) method. The air-earth boundary (the shear stress above the free surface) is treated using the stress-imaging technique. We use a two-layer model to demonstrate the accuracy of the staggered-grid modeling scheme. We also simulate four-layer models including a low-velocity layer (LVL) or a high-velocity layer (HVL) to analyze dispersive energy characteristics for near-surface applications. Results demonstrate that: (1) the staggered-grid FD code and stress-imaging technique are suitable for treating the free-surface boundary conditions for Love-wave modeling, (2) Love-wave inversion should be treated with extra care when a LVL exists because of a lack of LVL information in dispersions aggravating uncertainties in the inversion procedure, and (3) energy of high modes in a low-frequency range is very weak, so that it is difficult to estimate the cutoff frequency accurately, and "mode-crossing" occurs between the second higher and third higher modes when a HVL exists. ?? 2010 Birkh??user / Springer Basel AG.
NASA Astrophysics Data System (ADS)
Luo, Yinhe; Xia, Jianghai; Xu, Yixian; Zeng, Chong; Liu, Jiangping
2010-12-01
Love-wave propagation has been a topic of interest to crustal, earthquake, and engineering seismologists for many years because it is independent of Poisson's ratio and more sensitive to shear (S)-wave velocity changes and layer thickness changes than are Rayleigh waves. It is well known that Love-wave generation requires the existence of a low S-wave velocity layer in a multilayered earth model. In order to study numerically the propagation of Love waves in a layered earth model and dispersion characteristics for near-surface applications, we simulate high-frequency (>5 Hz) Love waves by the staggered-grid finite-difference (FD) method. The air-earth boundary (the shear stress above the free surface) is treated using the stress-imaging technique. We use a two-layer model to demonstrate the accuracy of the staggered-grid modeling scheme. We also simulate four-layer models including a low-velocity layer (LVL) or a high-velocity layer (HVL) to analyze dispersive energy characteristics for near-surface applications. Results demonstrate that: (1) the staggered-grid FD code and stress-imaging technique are suitable for treating the free-surface boundary conditions for Love-wave modeling, (2) Love-wave inversion should be treated with extra care when a LVL exists because of a lack of LVL information in dispersions aggravating uncertainties in the inversion procedure, and (3) energy of high modes in a low-frequency range is very weak, so that it is difficult to estimate the cutoff frequency accurately, and "mode-crossing" occurs between the second higher and third higher modes when a HVL exists.
NASA Astrophysics Data System (ADS)
Panayappan, Kadappan
With the advent of sub-micron technologies and increasing awareness of Electromagnetic Interference and Compatibility (EMI/EMC) issues, designers are often interested in full- wave solutions of complete systems, taking to account a variety of environments in which the system operates. However, attempts to do this substantially increase the complexities involved in computing full-wave solutions, especially when the problems involve multi- scale geometries with very fine features. For such problems, even the well-established numerical methods, such as the time domain technique FDTD and the frequency domain methods FEM and MoM, are often challenged to the limits of their capabilities. In an attempt to address such challenges, three novel techniques have been introduced in this work, namely Dipole Moment (DM) Approach, Recursive Update in Frequency Domain (RUFD) and New Finite Difference Time Domain ( vFDTD). Furthermore, the efficacy of the above techniques has been illustrated, via several examples, and the results obtained by proposed techniques have been compared with other existing numerical methods for the purpose of validation. The DM method is a new physics-based approach for formulating MoM problems, which is based on the use of dipole moments (DMs), as opposed to the conventional Green's functions. The absence of the Green's functions, as well as those of the vector and scalar potentials, helps to eliminate two of the key sources of difficulties in the conventional MoM formulation, namely the singularity and low-frequency problems. Specifically, we show that there are no singularities that we need to be concerned with in the DM formulation; hence, this obviates the need for special techniques for integrating these singularities. Yet another salutary feature of the DM approach is its ability to handle thin and lossy structures, or whether they are metallic, dielectric-type, or even combinations thereof. We have found that the DM formulation can handle these
The Galileo probe Doppler wind experiment: Measurement of the deep zonal winds on Jupiter
NASA Astrophysics Data System (ADS)
Atkinson, David H.; Pollack, James B.; Seiff, Alvin
1998-09-01
During its descent into the upper atmosphere of Jupiter, the Galileo probe transmitted data to the orbiter for 57.5 min. Accurate measurements of the probe radio frequency, driven by an ultrastable oscillator, allowed an accurate time history of the probe motions to be reconstructed. Removal from the probe radio frequency profile of known Doppler contributions, including the orbiter trajectory, the probe descent velocity, and the rotation of Jupiter, left a measurable frequency residual due to Jupiter's zonal winds, and microdynamical motion of the probe from spin, swing under the parachute, atmospheric turbulence, and aerodynamic buffeting. From the assumption of the dominance of the zonal horizontal winds, the frequency residuals were inverted and resulted in the first in situ measurements of the vertical profile of Jupiter's deep zonal winds. A number of error sources with the capability of corrupting the frequency measurements or the interpretation of the frequency residuals were considered using reasonable assumptions and calibrations from prelaunch and in-flight testing. It is found that beneath the cloud tops (about 700 mbar) the winds are prograde and rise rapidly to 170 m/s at 4 bars. Beyond 4 bars to the depth at which the link with the probe was lost, nearly 21 bars, the winds remain constant and strong. Corrections for the high temperatures encountered by the probe have recently been completed and provide no evidence of diminishing or strengthening of the zonal wind profile in the deeper regions explored by the Galileo probe.
Electromagnetic corrections to the zonal flow residual
NASA Astrophysics Data System (ADS)
Pusztai, Istvan; Catto, Peter J.; Parra, Felix I.
2014-10-01
The axisymmetric zonal flow residual calculation in tokamak plasmas is generalized to include electromagnetic perturbations. Instead of imposing magnetic perturbations externally, we formulate and solve a description retaining the fully self-consistent temporal and spatial perturbations in the electric and magnetic fields. Simple expressions for the electrostatic, shear and compressional magnetic residual responses derived provide a fully electromagnetic test of the zonal flow residual in gyrokinetic codes. We find that at β ~ O (1) the most easily testable quantity is the compressional magnetic perturbation generated by the density perturbation corresponding to the zonal flow potential, while at small values of β, the electrostatic and shear magnetic responses to an initial compressional magnetic perturbation can also be detectable. Without collisions any initial magnetic perturbation remain completely undamped. Supported by US Department of Energy grant at DE-FG02-91ER-54109 at MIT. IP is supported by the International Postdoc grant of Vetenskapsradet.
Dynamics of zonal flow saturation in strong collisionless drift wave turbulence
NASA Astrophysics Data System (ADS)
Kim, Eun-jin; Diamond, P. H.
2002-11-01
Generalized Kelvin-Helmholtz (GKH) instability is examined as a mechanism for the saturation of zonal flows in the collisionless regime. By focusing on strong turbulence regimes, GKH instability is analyzed in the presence of a background of finite-amplitude drift waves. A detailed study of a simple model with cold ions shows that nonlinear excitation of GKH modes via modulational instability can be comparable to their linear generation. Furthermore, it is demonstrated that zonal flows are likely to grow faster than GKH mode near marginality, with insignificant turbulent viscous damping by linear GKH. The effect of finite ion temperature fluctuations is incorporated in a simple toroidal ion temperature gradient model, within which both zonal flow and temperature are generated by modulational instability. The phase between the two is calculated self-consistently and shown to be positive. Furthermore, the correction to nonlinear generation of GKH modes appears to be small, being of order O(ρi2k2). Thus, the role of linear GKH instability in the saturation of collisionless zonal flows, in general, seems dubious.
Zonal function network frames on the sphere.
Mhaskar, H N; Narcowich, F J; Ward, J D
2003-03-01
We introduce a class of zonal function network frames suitable for analyzing data collected at scattered sites on the surface of the unit sphere of a Euclidean space. Our frames consist of zonal function networks and are well localized. The frames belonging to higher and higher scale wavelet spaces have more and more vanishing polynomial moments. The main technique is applicable in the general setting of separable Hilbert spaces, in which context, we study the construction of new frames by perturbing an orthonormal basis.
NASA Astrophysics Data System (ADS)
Li, Gang; Li, Yuguo; Han, Bo
2017-05-01
We present an accurate interpolating method for calculating electric and magnetic fields at the seafloor with a resistivity contrast. This method is applied to the three-dimensional (3D) frequency-domain marine controlled-source electromagnetic (CSEM) modeling with the towed transmitters and receivers located at the seafloor. We simulate the 3D marine CSEM responses by the staggered finite-difference method with a direct solver. The secondary-field approach is used for avoiding the source singularities and the primary fields excited by the electric dipole source could be calculated quasi-analytically for the one-dimensional layered background. Therefore, in this study, we focus on interpolating of electric and magnetic fields to the receiver locations at the seafloor interface between the conductive seawater and resistive seafloor formation. Considering the discontinuity of the normal electric fields, we use the normal current electric density for interpolation. The secondary electric and magnetic fields are also used for interpolation instead of the total fields for high numerical accuracy. The proposed interpolation only utilizes the nodes below/above the seafloor interface and is approved to be much more accurate than other tested interpolating methods, i.e., the conventional linear interpolation and the rigorous interpolation.
NASA Astrophysics Data System (ADS)
Obayashi, M.; Yoshimitsu, J.; Sugioka, H.; Ito, A.; Isse, T.; Shiobara, H.; Reymond, D.; Suetsugu, D.
2016-11-01
We present a new tomographic image beneath the South Pacific superswell, using finite frequency P wave travel time tomography with global and regional data. The regional stations include broadband ocean-bottom seismograph stations. The tomographic image shows slow anomalies of 200-300 km in diameter beneath most hot spots in the studied region, extending continuously from the shallow upper mantle to 400 km depth. Narrow and weak slow anomalies are detected at depths of 500-1000 km, connecting the upper mantle slow anomalies with large-scale slow anomalies with lateral dimension of 1000-2000 km prevailing below 1000 km depth down to the core-mantle boundary. There are two slow anomalies around the Society hot spot at depths shallower than 400 km, which both emerge from the same slow anomaly at 500 km depth. One of them is located beneath the Society hot spot and the other underlies 500 km east of the Society hot spot, where no volcanism is observed.
Tungjitkusolmun, S; Woo, E J; Cao, H; Tsai, J Z; Vorperian, V R; Webster, J G
2000-09-01
Finite element (FE) analysis has been utilised as a numerical tool to determine the temperature distribution in studies of radio frequency (RF) cardiac ablation. However, none of the previous FE analyses clarified such computational aspects as software requirements, computation time or convergence test. In addition, myocardial properties included in the previous models vary greatly. A process of FE modelling of a system that included blood, myocardium, and an ablation catheter with a thermistor embedded at the tip is described. The bio-heat equation is solved to determine the temperature distribution in myocardium using a commercial software application (ABAQUS). A Cauchy convergence test (epsilon = 0.1 degree C) was performed and it is concluded that the optimal number of elements for the proposed system is 24610. The effects of changes in myocardial properties (+/- 50% electric conductivity, +100%/-50% thermal conductivity, and +100%/-50% specific heat capacity) in both power-controlled (PCRFA) and temperature-controlled RF ablation (TCRFA) were studied. Changes in myocardial properties affect the results of the FE analyses of PCRFA more than those of TCRFA, and the maximum changes in lesion volumes were -58.6% (-50% electric conductivity), -60.7% (+100% thermal conductivity), and +43.2% (-50% specific heat).
NASA Astrophysics Data System (ADS)
Chevrot, Sébastien; Martin, Roland; Komatitsch, Dimitri
2012-12-01
Wavelets are extremely powerful to compress the information contained in finite-frequency sensitivity kernels and tomographic models. This interesting property opens the perspective of reducing the size of global tomographic inverse problems by one to two orders of magnitude. However, introducing wavelets into global tomographic problems raises the problem of computing fast wavelet transforms in spherical geometry. Using a Cartesian cubed sphere mapping, which grids the surface of the sphere with six blocks or 'chunks', we define a new algorithm to implement fast wavelet transforms with the lifting scheme. This algorithm is simple and flexible, and can handle any family of discrete orthogonal or bi-orthogonal wavelets. Since wavelet coefficients are local in space and scale, aliasing effects resulting from a parametrization with global functions such as spherical harmonics are avoided. The sparsity of tomographic models expanded in wavelet bases implies that it is possible to exploit the power of compressed sensing to retrieve Earth's internal structures optimally. This approach involves minimizing a combination of a ℓ2 norm for data residuals and a ℓ1 norm for model wavelet coefficients, which can be achieved through relatively minor modifications of the algorithms that are currently used to solve the tomographic inverse problem.
NASA Astrophysics Data System (ADS)
Guiroy, Axel; Certon, Dominique; Boy, Philippe; Lethiecq, Marc; Levassort, Franck
A 2D numerical model based on a hybrid finite-difference (FD) and pseudospectral (PS) method adapted to high frequency linear arrays is presented. This model, coupled with the DREAM toolbox, was used to simulate the 1-way radiation pattern in water of a 50 MHz linear array with 64 elements (at a focal distance of 10 mm). The influence of several parameters of the internal structure of the array on the radiation pattern was studied. The variation of element widths, kerf widths and kerf depths was evaluated on the main properties of the pressure field (i.e. spatial resolutions, sensitivity and depth of field) in the focal zone. These simulations were performed using experimental data previously measured for materials used and in particular for the PZT piezoelectric thick film. Results show that a trade-off can be found between the technological aspects (width of elements and kerf) and performance of the array. Finally, a kerfless configuration was evaluated and it is shown that this is also a viable option.
Self-organized zonal flow in the flute-mode turbulence of a plasma
Kodama, Y.; Pavlenko, V.P.
1988-04-11
Flute-mode turbulence has a forward spectral cascade unlike the case of drift-wave turbulence. Therefore the linear flute instability may be reduced by this energy cascading toward large wave numbers. As a consequence of three-wave cascade processes derivable from model equations including the effects of density gradient and finite ion Larmor radius the formation of zonal flows in flute mode turbulence is predicted.
Stability of Shallow Jovian Atmospheric Zonal Jets
NASA Astrophysics Data System (ADS)
Sayanagi, Kunio M.; Dowling, T. E.; Showman, A. P.
2007-10-01
Jupiter's cloud-level zonal jets are remarkably steady in time despite their sharp curvature (i.e., second latitudinal derivative of the zonal wind profile). The stable jets must be supported by a proper sub-cloud wind and thermal structure; however, the large-scale deep structure of the zonal jets and temperature remain a major unknown in the gas-giant planet atmospheres. Past studies suggest two end-point scenarios of deep wind structures that allow stable cloud-level jets. The first shows that the jets are stable if they penetrate through the molecular hydrogen layer (Ingersoll and Pollard, 1982), although they do not address how the deep flow may be coupled to the cloud-level wind. Many other studies, though they may not directly address the shear instabilities, support this "deep jet” scenario (e.g. Heimpel and Aurnou, 2007); however, they do not rule out the possibility that the jets are shallow. Gierasch (2004) introduced a notable alternative to this "deep” picture. Through linear stability analysis, he showed that an isolated eastward jet that reaches a point of zero motion at 100-bar level, with Jupiter-like speeds and widths at the top, can be stable under certain conditions. However, his analysis contained several untested assumptions, and whether such flows are actually stable in a more realistic setting remains an open question. The possibility of stable shallow zonal jets on Jupiter remains largely unexplored, and this possibility deserves a thorough consideration. We present full-3D nonlinear simulations that test the stability of shallow zonal jets. We use Richardson number as a measure of vertical flow scale, and aim to show whether shallow jets are consistent with the observed jets and place theoretical constraints on the sub-cloud wind structure. Our study uses the EPIC model (Dowling et al., 1998, 2006). The research has been supported by NASA Planetary Atmosphere grants to APS and TED.
NASA Astrophysics Data System (ADS)
Mackay, Robert Malcolm
The two-dimensional statistical dynamical climate model that has recently been developed at the Global Change Research Center and the Oregon Graduate Institute of Science & Technology (GCRC 2D climate model) is presented and several new results obtained using the model are discussed. The model solves the 2-D primitive equations in finite difference form (mass continuity, Newton's second law, and the first law of thermodynamics) for the prognostic variables zonal mean density, zonal mean zonal velocity, zonal mean meridional velocity, and zonal mean temperature on a grid that has 18 nodes in latitude and 9 vertical nodes (plus the surface). The equation of state, p=rho RT and an assumed hydrostatic atmosphere, Delta p = -rho gDelta z, are used to diagnostically calculate the zonal mean pressure and vertical velocity for each grid node, and the moisture balance equation is used to estimate the precipitation rate. The performance of the model at simulating the two-dimensional temperature, zonal winds, and mass stream function is explored. The strengths and weaknesses of the model are highlighted and suggestions for future model improvements are given. The parameterization of the transient eddy fluxes of heat and momentum developed by Stone and Yao (1987 and 1990) are used with small modifications. These modifications are shown to help the performance of the model at simulating the observed climate system as well as increase the model's computational stability. Following earlier work that analyzed the response of the zonal wind fields predicted by three GCM simulations for a doubling of atmospheric CO_2, the response of the GCRC 2D model's zonal wind fields is also explored for the same experiment. Unlike the GCM simulations, our 2D model results in distinct patterns of change. It is suggested that the observed changes in zonal winds for the 2xCO_2 experiment are related to the increase in the upper level temperature gradients predicted by our model and most climate
Gyrokinetic simulations in general geometry and applications to collisional damping of zonal flows
Lin, Z.; Hahm, T.S.; Lee, W.W.; Tang, W.M.; White, R.B.
2000-02-15
A fully three-dimensional gyrokinetic particle code using magnetic coordinates for general geometry has been developed and applied to the investigation of zonal flows dynamics in toroidal ion-temperature-gradient turbulence. Full torus simulation results support the important conclusion that turbulence-driven zonal flows significantly reduce the turbulent transport. Linear collisionless simulations for damping of an initial poloidal flow perturbation exhibit an asymptotic residual flow. The collisional damping of this residual causes the dependence of ion thermal transport on the ion-ion collision frequency even in regimes where the instabilities are collisionless.
NASA Astrophysics Data System (ADS)
Böhm, Sigrid
2013-04-01
The reaction of the Earth-ocean system to zonal tidal forcing is characterized by the so-called zonal response coefficient κ defined by Agnew & Farrell (1978). The frequency dependent zonal response coefficient is an extension to the concept of the Love number k2 which allows for a response of the Earth to tidal forcing, deviating from purely elastic behavior and thus taking into account effects of ocean tides, a fluid core and mantle anelasticity. A change of the rotation rate of the Earth and consequently of UT1 induced by zonal body and ocean tides is proportional to the tide-generating potential through the zonal response coefficient κ. Variations of UT1 can be obtained directly from VLBI observations. If atmospheric and oceanic variations of UT1 are considered accordingly, the proportionality factor κ can be estimated within a VLBI global solution. A global solution is a common adjustment of the observations of several sessions with a simultaneous estimation of global parameters, such as station positions and velocities. The global solution of the Vienna VLBI Software (VieVS) was employed to simultaneously adjust the observations of selected sessions spanning 1984-2012 and derive the zonal response coefficients for periods up to 35 days. The directly estimated fortnightly and monthly zonal response coefficients are discussed in comparison with theoretical values and the corresponding results of a straight time series approach.
Isotope effect on gyro-fluid edge turbulence and zonal flows
NASA Astrophysics Data System (ADS)
Meyer, O. H. H.; Kendl, A.
2016-11-01
The role of ion polarisation and finite Larmor radius on the isotope effect on turbulent tokamak edge transport and flows is investigated by means of local electromagnetic multi-species gyro-fluid computations. Transport is found to be reduced with the effective plasma mass for protium, deuterium and tritium mixtures. This isotope effect is found for both cold and warm ion models, but significant influence of finite Larmor radius and polarisation effects are identified. Sheared flow reduction of transport through self generated turbulent zonal flows and geodesic acoustic modes in the present model (not including neoclassical flows) is found to play only a minor role on regulating isotopically improved confinement.
Zonal scales of Madden-Julian Oscillation in model experiments with and without continents
NASA Astrophysics Data System (ADS)
Das, Surajit; Sengupta, Debasis; Chakraborty, Arindam; Sukhatme, Jai; Murtugudde, Raghu
2015-04-01
The low-frequency eastward propagating Madden-Julian Oscillation (MJO) impacts weather and climate around the globe. MJO has zonal wavenumber 1-5, but the reason why these characteristic spatial scales arise are not clearly understood. We use the aquaplanet version of the Community Atmospheric Model (CAM-5), with perpetual spring equinox forcing and zonally symmetric sea surface temperature (SST), to study tropical intraseasonal oscillations (ISO), including MJO. In the first two experiments, we specify zonally symmetric SST profiles that mimic observed climatological July and January conditions. In the January SST simulation, we find a zonal wavenumber 1 mode with dominant period of 60 days, moving east at about 6 m/s. This mode, which resembles the Madden-Julian Oscillation (MJO), is absent when the model was forced by July SST. This shows the importance of the meridional gradient of SST on generation of MJO in this model. For further investigation of the influence of tropical SST on ISO and convectively coupled equatorial waves (CCEW), we conduct experiments with idealized symmetric SST profiles having different widths of warm ocean centered at the equator. When the latitudinal extent of warm SST is comparable to or larger than the equatorial Rossby radius, we find a dominant low frequency (50-80 days) eastward mode that resembles the MJO, as in the January SST experiment. Our study shows that wider, meridionally symmetric SST profiles are necessary for a stronger MJO-like mode. In contrast to many other aquaplanet studies, a significant finding is the existence of westward propagating 30-120 day Rossby waves with zonal wavenumber 1 to 3, and meridional wavenumber 1, 3 and 5. However, in all the aquaplanet simulations, the MJO variance occurs at zonal wavenumber one. To understand the role of land-sea distribution on zonal wavenumber of MJO, we perform a third set of experiments by introducing continents with realistic orography in the model. These experiments
A Multi-layered Model for the Shape, Zonal Winds and Gravitational Field of Jupiter
NASA Astrophysics Data System (ADS)
Schubert, G.; Zhang, K.; Kong, D.
2016-12-01
We have developed a three-dimensional, finite-element, multi-layered, non-spheroidal model of Jupiter consisting of an inner core, a metallic dynamo region and an outer molecular electrically insulating envelope. Different polytropic equations of state are used in the metallic and molecular regions. The zonal winds are on cylinders parallel to the rotation axis and are confined within the molecular envelope by magnetic braking. The effect of rotational distortion is fully accounted for; it is not treated as simply a small perturbation on a spherically symmetric state. The model determines the density, size and shape of the inner core, the irregular shape of the 1-bar pressure level, and the internal structure of Jupiter. It produces the known mass, the known equatorial and polar radii, and the known zonal gravitational coefficient J2 of Jupiter within their error bars; it also yields the coefficients J4 and J6 with an accuracy of a few percent. The variation of the gravitational field caused solely by the effect of the zonal winds on the rotationally distorted Jupiter is also determined. Different cases, ranging from a deep wind profile to a very shallow profile, are considered. The model enables accurate interpretation of the zonal gravitational coefficients expected from the Juno mission.
Structures and Zonal Flows in Magnetized Plasmas
Jovanovic, D.; Shukla, P. K.
2010-12-14
The numerical study of the zonal flows (transport barriers) in the drift-wave turbulence in magnetically confined plasmas is presented. The existence of two distinct mechanisms for their generation is demonstrated. The evolution of a drift wave-zonal flow system, nonlinearly coupled via the Reynolds stress, is described by a nonlinear equation for the slowly varying envelope of the drift waves, and the nonlinear dispersion relation for the modulational instability of a drift wave pump is derived and analyzed. First, an arbitrary spatial distribution of strictly poloidally propagating drift waves is shown to rapidly decay into the array of localized soliton-like structures moving with different speeds. The corresponding zonal flow potential evolves into the sequence of shocks that produces a strong shearing, with many alternating plasma flows. Next, it is demonstrated that the coherent dipolar vortices, that constitute the building blocks of the strong drift-wave turbulence, are unstable in the presence of an electron temperature gradient. The dipolar vortices (or modons) undergo a qualitative modification by the action of the scalar nonlinearity arising from the magnetic {beta} effect. The modons propagating in the direction of the electron diamagnetic drift rapidly topple, disintegrating into two monopoles that propagate independently and rapidly disperse. Conversely, for the modons that initially moved in the direction of the ion diamagnetic drift, the {beta}-effect produces the change of the direction of the propagation, followed by the stretching in the poloidal direction. On a long time scale, such modons expand to a length equal to the size of the computational box, and essentially an one-dimensional zonal flow is created, whose transverse scale is determined by the initial modon size.
Semiautomatic Design Of Zonal Computational Grids
NASA Technical Reports Server (NTRS)
Vogel, Alison Andrews
1991-01-01
EZGrid is knowledge-based computer program semiautomatically generating zonal computational grids for use in numerical simulations of two-dimensional flows. Zoning necessary because of limitations imposed by size of available computer memory and by topological complexity of typical flow field. Complexity and amount of required memory reduced by dividing flow field into zones, within each of which computational grid refined only to extent necessary to resolve local high gradients. Developed to speed and systematize zoning.
The dynamics of baroclinic zonal jets
NASA Astrophysics Data System (ADS)
Williams, Paul
2015-04-01
Multiple alternating zonal jets are a ubiquitous feature of planetary atmospheres and oceans. However, most studies to date have focused on the special case of barotropic jets. Here we investigate the dynamics of freely evolving baroclinic jets, using a two-layer quasi-geostrophic annulus model with sloping topography. In a suite of 15 numerical simulations, the baroclinic Rossby radius and baroclinic Rhines scale are sampled by varying the stratification and root-mean-square eddy velocity, respectively. Small-scale eddies in the initial state evolve through geostrophic turbulence and accelerate zonally as they grow in horizontal scale, first isotropically and then anisotropically. This process leads ultimately to the formation of jets, which take about 2,500 rotation periods to equilibrate. The kinetic energy spectrum of the equilibrated baroclinic zonal flow steepens from a -3 power law at small scales to a -5 power law near the jet scale. The conditions most favorable for producing multiple alternating baroclinic jets are large baroclinic Rossby radius (i.e., strong stratification) and small baroclinic Rhines scale (i.e., weak root-mean-square eddy velocity). The baroclinic jet width is diagnosed objectively and found to be 2.2-2.8 times larger than the baroclinic Rhines scale, with a best estimate of 2.5 times larger. This finding suggests that Rossby wave motions must be moving at speeds of approximately 6 times the turbulent eddy velocity in order to be capable of arresting the isotropic inverse energy cascade. Reference Williams PD and Kelsall CW (2015) The dynamics of baroclinic zonal jets. Journal of the Atmospheric Sciences, in press. DOI: 10.1175/JAS-D-14-0027.1
Laboratory Exploration of Multiple Zonal Jet Regimes
NASA Astrophysics Data System (ADS)
Smith, C. A.; Speer, K. G.; Griffiths, R. W.
2012-12-01
The differentially heated, rotating annulus has classically been used to study wave interactions within a single, baroclinic jet. At high rotation rates, the baroclinic instability of the flow leads to a transition to a turbulent, eddy-dominated regime. In the presence of a topographic beta effect, the flow has been observed to produce multiple, meandering zonal jets that are qualitatively similar to those found in planetary atmospheres and in the Antarctic Circumpolar Current (ACC). Our study builds on previous annulus experiments [1] by making observations further within this new regime. We observe with PIV and other techniques how the structure of the flow responds to changes in various parameters such as tank geometry, gradient in the Coriolis parameter, rotation rate, and differential thermal forcing. By not employing the more typical direct forcing of small scales, but by applying a large scale forcing over the annulus gap width, this study allows the varying effects of eddy scale selection, enstrophy cascade, etc. to naturally generate flow that more closely resembles planetary atmospheres and the ACC. We seek nondimensional parameters that significantly control zonation in a real fluid. These observations will provide a metric for the comparison of various theoretical models for multiple zonal jet formation. Other properties of the jets, such as their migration, meandering, bifurcation, and merging, can also be observed in an idealized situation and compared to numerical simulations. Ultimately, this will aid the testing and development of sub-grid-scale parameterizations for the multiple zonal jet regime that remain robust in the face of multiple forcing parameters. [1] Wordsworth, R. D., Read, P. L., & Yamazaki, Y. H. (2008). Turbulence, waves, and jets in a differentially heated rotating annulus experiment Physics of Fluids, 20(12), 126602.Streak photograph of suspended particles visualizing the flow representative of multiple zonal jets
Building an anisotropic meniscus with zonal variations.
Higashioka, Michael M; Chen, Justin A; Hu, Jerry C; Athanasiou, Kyriacos A
2014-01-01
Toward addressing the difficult problems of knee meniscus regeneration, a self-assembling process has been used to re-create the native morphology and matrix properties. A significant problem in such attempts is the recapitulation of the distinct zones of the meniscus, the inner, more cartilaginous and the outer, more fibrocartilaginous zones. In this study, an anisotropic and zonally variant meniscus was produced by self-assembly of the inner meniscus (100% chondrocytes) followed by cell seeding the outer meniscus (coculture of chondrocytes and meniscus cells). After 4 weeks in culture, the engineered, inner meniscus exhibited a 42% increase in both instantaneous and relaxation moduli and a 62% increase in GAG/DW, as compared to the outer meniscus. In contrast, the circumferential tensile modulus and collagen/DW of the outer zone was 101% and 129% higher, respectively, than the values measured for the inner zone. Furthermore, there was no difference in the radial tensile modulus between the control and zonal engineered menisci, suggesting that the inner and outer zones of the engineered zonal menisci successfully integrated. These data demonstrate that not only can biomechanical and biochemical properties be engineered to differ by the zone, but they can also recapitulate the anisotropic behavior of the knee meniscus.
The Dynamics of Baroclinic Zonal Jets
NASA Astrophysics Data System (ADS)
Williams, P. D.
2015-12-01
Multiple alternating zonal jets are a ubiquitous feature of planetary atmospheres and oceans. However, most studies to date have focused on the special case of barotropic jets. Here, the dynamics of freely evolving baroclinic jets are investigated using a two-layer quasigeostrophic annulus model with sloping topography. In a suite of 15 numerical simulations, the baroclinic Rossby radius and baroclinic Rhines scale are sampled by varying the stratification and root-mean-square eddy velocity, respectively. Small-scale eddies in the initial state evolve through geostrophic turbulence and accelerate zonally as they grow in horizontal scale, first isotropically and then anisotropically. This process leads ultimately to the formation of jets, which take about 2500 rotation periods to equilibrate. The kinetic energy spectrum of the equilibrated baroclinic zonal flow steepens from a -3 power law at small scales to a -5 power law near the jet scale. The conditions most favorable for producing multiple alternating baroclinic jets are large baroclinic Rossby radius (i.e., strong stratification) and small baroclinic Rhines scale (i.e., weak root-mean-square eddy velocity). The baroclinic jet width is diagnosed objectively and found to be 2.2-2.8 times larger than the baroclinic Rhines scale, with a best estimate of 2.5 times larger. This finding suggests that Rossby wave motions must be moving at speeds of approximately 6 times the turbulent eddy velocity in order to be capable of arresting the isotropic inverse energy cascade.
NASA Astrophysics Data System (ADS)
Valentova, L.; Gallovic, F.; Ruzek, B.; de la Puente, J.
2012-04-01
In recent years, great emphasis has been laid on finite-frequency tomography. The inverted observables are considered to be dependent not only on model parameters along infinitely thin raypaths but to exhibit more complicated spatial dependency represented by so-called sensitivity kernels. Efficient tool for the calculation of the sensitivity kernels is adjoint method. It is based on two calculations: forward calculation of wavefield propagating from source to receivers in an initial model, and adjoint calculation where the residuals between observed data and synthetics backpropagate from the receivers to the source (so-called adjoint wavefield). The aim of the presented work is obtaining surface wave group velocity maps of the Czech Republic for specific periods in the range of 2 - 20 s. Data used in the inversion consist of crosscorrelation traveltimes of Love waves between stations located in the Czech Republic and adjacent areas acquired from ambient seismic noise band-pass filtered around the specific periods. The inverse problem for the L2 crosscorrelation traveltime misfit is solved by the conjugate gradient technique, with misfit gradients calculated using the adjoint method. Assuming that propagation of surface waves along Earth's surface can be approximated by membrane wave problem, the computations are reduced to only 2D domain. Therefore, the calculations could be performed using adjoint version of SeisSol, elastodynamic equation solver using Discontinuous Galerkin method with Arbitrary High Order time Derivatives (ADER-DG). More attention is paid to the inversion of data of the highest periods i.e. 16s and 20s. The main advantage are lower computational demands. Moreover, 16s and 20s Love waves have similar depth sensitivities, thus the travel times and the resulting models are expected to exhibit only very minor differences. However, in real application this may not be valid, as the data and their processing are subject to various kinds of errors
NASA Technical Reports Server (NTRS)
Vlahopoulos, Nickolas
2005-01-01
The Energy Finite Element Analysis (EFEA) is a finite element based computational method for high frequency vibration and acoustic analysis. The EFEA solves with finite elements governing differential equations for energy variables. These equations are developed from wave equations. Recently, an EFEA method for computing high frequency vibration of structures either in vacuum or in contact with a dense fluid has been presented. The presence of fluid loading has been considered through added mass and radiation damping. The EFEA developments were validated by comparing EFEA results to solutions obtained by very dense conventional finite element models and solutions from classical techniques such as statistical energy analysis (SEA) and the modal decomposition method for bodies of revolution. EFEA results have also been compared favorably with test data for the vibration and the radiated noise generated by a large scale submersible vehicle. The primary variable in EFEA is defined as the time averaged over a period and space averaged over a wavelength energy density. A joint matrix computed from the power transmission coefficients is utilized for coupling the energy density variables across any discontinuities, such as change of plate thickness, plate/stiffener junctions etc. When considering the high frequency vibration of a periodically stiffened plate or cylinder, the flexural wavelength is smaller than the interval length between two periodic stiffeners, therefore the stiffener stiffness can not be smeared by computing an equivalent rigidity for the plate or cylinder. The periodic stiffeners must be regarded as coupling components between periodic units. In this paper, Periodic Structure (PS) theory is utilized for computing the coupling joint matrix and for accounting for the periodicity characteristics.
ZonalMetrics - a Python toolbox for zonal landscape structure analysis
NASA Astrophysics Data System (ADS)
Adamczyk, Joanna; Tiede, Dirk
2017-02-01
We present a Python toolbox for the calculation of zonal landscape metrics. Instead of global calculations focusing on the whole landscape, the proposed ZonalMetrics toolbox allows the calculation of landscape metrics for user-defined zones. Such zones can be defined through regular units (e.g. hexagons, grids) that can be created within the toolbox. In addition, any polygonal set specified by the user (e.g. administrative units) can be used. The implemented set of landscape metrics is specifically selected and valid for calculations within zones. The tool is demonstrated based on a case study for the Warsaw metropolitan area and the possibilities of applying the toolbox for different zonal layers are illustrated. The implementation is based on the Python toolbox introduced in ArcGIS 10.1, offering an easy to use graphical user interface and batch calculation possibilities. The source code is free and open to the community and extendable to specific needs.
NASA Technical Reports Server (NTRS)
Young, Donald R.; Orne, David
1976-01-01
The influence of pretwist, nonuniformities in mass and flexural stiffness, rotatory inertia and shear deformation on the natural frequencies of intact bones is evaluated by means of a linear elastic, finite-element model which has been programmed for solution on the digital computer. Theoretical results are compared to the results on the forced vibration of intact canine radii obtained experimentally by Thompson. Surprisingly, inclusion of fairly large pretwist angles (from -14 to 12 deg for one specimen) had little affect on the first three frequencies of transverse vibration in either the cranial or lateral directions. Inclusion of shear deformation reduced the third-mode frequency in the stiffest (lateral) direction by about six percent, otherwise shear deformation played a minor role in determining natural frequencies. Similarly. rotatory inertia had negligible influence up to the third natural frequency. The predominant influence on the first three natural frequencies of transverse vibration could be attributed to the variations in mass and flexural stiffness along the length of the test specimens. Different effective moduli of elasticity are required to yield correct absolute values for the frequencies which correspond to experimental findings. thus implying the presence of some inhomogeneities in material properties around the bone cross-section and/or along its length.
Gyroaverage effects on chaotic transport by drift waves in zonal flows
Martinell, J.; Del-Castillo-Negrete, Diego B
2013-01-01
Finite Larmor radius (FLR) effects on E x B test particle chaotic transport in the presence of zonal flows is studied. The FLR effects are introduced by the gyro-average of a simplified E x B guiding center model consisting of the linear superposition of a non-monotonic zonal flow and drift waves. Non-monotonic zonal flows play a critical role on transport because they exhibit robust barriers to chaotic transport in the region(s) where the shear vanishes. In addition, the non-monotonicity gives rise to nontrivial changes in the topology of the orbits of the E x B Hamiltonian due to separatrix reconnection. The present study focuses on the role of FLR effects on these two signatures of non-monotonic zonal flows: shearless transport barriers and separatrix reconnection. It is shown that, as the Larmor radius increases, the effective zonal flow profile bifurcates and multiple shearless regions are created. As a result, the topology of the gyro-averaged Hamiltonian exhibits very complex separatrix reconnection bifurcations. It is also shown that FLR effects tend to reduce chaotic transport. In particular, the restoration of destroyed transport barriers is observed as the Larmor radius increases. A detailed numerical study is presented on the onset of global chaotic transport as function of the amplitude of the drift waves and the Larmor radius. For a given amplitude, the threshold for the destruction of the shearless transport barrier, as function of the Larmor radius, exhibits a fractal-like structure. The FLR effects on a thermal distribution of test particles are also studied. In particular, the fraction of confined particles with a Maxwellian distribution of gyroradii is computed, and an effective transport suppression is found for high enough temperatures.
Gyroaverage effects on chaotic transport by drift waves in zonal flows
Martinell, Julio J.; Castillo-Negrete, Diego del
2013-02-15
Finite Larmor radius (FLR) effects on E Multiplication-Sign B test particle chaotic transport in the presence of zonal flows is studied. The FLR effects are introduced by the gyro-average of a simplified E Multiplication-Sign B guiding center model consisting of the linear superposition of a non-monotonic zonal flow and drift waves. Non-monotonic zonal flows play a critical role on transport because they exhibit robust barriers to chaotic transport in the region(s) where the shear vanishes. In addition, the non-monotonicity gives rise to nontrivial changes in the topology of the orbits of the E Multiplication-Sign B Hamiltonian due to separatrix reconnection. The present study focuses on the role of FLR effects on these two signatures of non-monotonic zonal flows: shearless transport barriers and separatrix reconnection. It is shown that, as the Larmor radius increases, the effective zonal flow profile bifurcates and multiple shearless regions are created. As a result, the topology of the gyro-averaged Hamiltonian exhibits very complex separatrix reconnection bifurcations. It is also shown that FLR effects tend to reduce chaotic transport. In particular, the restoration of destroyed transport barriers is observed as the Larmor radius increases. A detailed numerical study is presented on the onset of global chaotic transport as function of the amplitude of the drift waves and the Larmor radius. For a given amplitude, the threshold for the destruction of the shearless transport barrier, as function of the Larmor radius, exhibits a fractal-like structure. The FLR effects on a thermal distribution of test particles are also studied. In particular, the fraction of confined particles with a Maxwellian distribution of gyroradii is computed, and an effective transport suppression is found for high enough temperatures.
NASA Astrophysics Data System (ADS)
Yin, Shengwen; Yu, Dejie; Yin, Hui; Lü, Hui; Xia, Baizhan
2017-09-01
Considering the epistemic uncertainties within the hybrid Finite Element/Statistical Energy Analysis (FE/SEA) model when it is used for the response analysis of built-up systems in the mid-frequency range, the hybrid Evidence Theory-based Finite Element/Statistical Energy Analysis (ETFE/SEA) model is established by introducing the evidence theory. Based on the hybrid ETFE/SEA model and the sub-interval perturbation technique, the hybrid Sub-interval Perturbation and Evidence Theory-based Finite Element/Statistical Energy Analysis (SIP-ETFE/SEA) approach is proposed. In the hybrid ETFE/SEA model, the uncertainty in the SEA subsystem is modeled by a non-parametric ensemble, while the uncertainty in the FE subsystem is described by the focal element and basic probability assignment (BPA), and dealt with evidence theory. Within the hybrid SIP-ETFE/SEA approach, the mid-frequency response of interest, such as the ensemble average of the energy response and the cross-spectrum response, is calculated analytically by using the conventional hybrid FE/SEA method. Inspired by the probability theory, the intervals of the mean value, variance and cumulative distribution are used to describe the distribution characteristics of mid-frequency responses of built-up systems with epistemic uncertainties. In order to alleviate the computational burdens for the extreme value analysis, the sub-interval perturbation technique based on the first-order Taylor series expansion is used in ETFE/SEA model to acquire the lower and upper bounds of the mid-frequency responses over each focal element. Three numerical examples are given to illustrate the feasibility and effectiveness of the proposed method.
Predictability of Zonal Means During Boreal Summer
NASA Technical Reports Server (NTRS)
Schubert, Siegfried; Suarez, Max J.; Pegion, Philip J.; Kistler, Michael A.; Kumar, Arun; Einaudi, Franco (Technical Monitor)
2001-01-01
This study examines the predictability of seasonal means during boreal summer. The results are based on ensembles of June-July-August (JJA) simulations (started in mid May) carried out with the NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) atmospheric general circulation model (AGCM) forced with observed sea surface temperatures (SSTS) and sea ice for the years 1980-1999. We find that the predictability of the JJA extra-tropical height field is primarily in the zonal mean component of the response to the SST anomalies. This contrasts with the cold season (January-February-March) when the predictability of seasonal means in the boreal extratropics is primarily in the wave component of the El Nino/Southern Oscillation (ENSO) response. Two patterns dominate the interannual variability of the ensemble mean JJA zonal mean height field. One has maximum variance in the tropical/subtropical upper troposphere, while the other has substantial variance in middle latitudes of both hemispheres. Both are symmetric with respect to the equator. A regression analysis suggests that the tropical/subtropical pattern is associated with SST anomalies in the far eastern tropical Pacific and the Indian Ocean, while the middle latitude pattern is forced by SST anomalies in the tropical Pacific just east of the dateline. The two leading zonal height patterns are reproduced in model runs forced with the two leading JJA SST patterns of variability. A comparison with observations shows a signature of the middle latitude pattern that is consistent with the occurrence of dry and wet summers over the United States. We hypothesize that both patterns, while imposing only weak constraints on extratropical warm season continental-scale climates, may play a role in the predilection for drought or pluvial conditions.
Baroclinic Multiple Zonal Jets on the Sphere.
NASA Astrophysics Data System (ADS)
Lee, Sukyoung
2005-07-01
Multiple zonal jets are investigated with a two-level primitive equation model on the sphere in which both baroclinicity and planetary radius are varied. As in the case for a two-layer quasigeostrophic model on a β-plane channel, it is found both that the Rhines scale successfully predicts the meridional scale of the multiple zonal jets, and that these jets are maintained in part by an eddy momentum flux divergence associated with slow baroclinic waves at the interjet minimum.A scaling analysis suggests that njets (a/θm)1/2, with the constraints e 8 sin2f (θm/θ ) > 1 and njets 1, where njets is the number of the jets, a the planetary radius, θm one-half of the pole-to-equator potential temperature difference, e the supercriticality of the two-layer Phillips model, Δθ the potential temperature difference between the two levels, and the latitude. The number of jets simulated by the model agrees with this scaling, provided that Ljet a, where Ljet is the jet scale.In model runs with a large planet where multiple zonal jets exist, the time-mean eddy heat flux is found to be consistent with the diffusive picture of Held and Larichev. In contrast, for the model runs with the planetary size equal to that of Earth, baroclinic adjustment is found to be more relevant. These results are consistent with the finding that in the large-planet (Earth-like) model runs, the jet/eddy scale is smaller than (comparable to) the corresponding planetary radius.
ZASPE: Zonal Atmospheric Stellar Parameters Estimator
NASA Astrophysics Data System (ADS)
Brahm, Rafael; Jordan, Andres; Hartman, Joel; Bakos, Gaspar
2016-07-01
ZASPE (Zonal Atmospheric Stellar Parameters Estimator) computes the atmospheric stellar parameters (Teff, log(g), [Fe/H] and vsin(i)) from echelle spectra via least squares minimization with a pre-computed library of synthetic spectra. The minimization is performed only in the most sensitive spectral zones to changes in the atmospheric parameters. The uncertainities and covariances computed by ZASPE assume that the principal source of error is the systematic missmatch between the observed spectrum and the sythetic one that produces the best fit. ZASPE requires a grid of synthetic spectra and can use any pre-computed library minor modifications.
NASA Astrophysics Data System (ADS)
Yang, Qingjie; Mao, Weijian
2017-01-01
The poroelastodynamic equations are used to describe the dynamic solid-fluid interaction in the reservoir. To obtain the intrinsic properties of reservoir rocks from geophysical data measured in both laboratory and field, we need an accurate solution of the wave propagation in porous media. At present, the poroelastic wave equations are mostly solved in the time domain, which involves a difficult and complicated time convolution. In order to avoid the issues caused by the time convolution, we propose a frequency-space domain method. The poroelastic wave equations are composed of a linear system in the frequency domain, which easily takes into account the effects of all frequencies on the dispersion and attenuation of seismic wave. A 25-point weighted-averaging finite different scheme is proposed to discretize the equations. For the finite model, the perfectly matched layer technique is applied at the model boundaries. We validated the proposed algorithm by testing three numerical examples of poroelastic models, which are homogenous, two-layered and heterogeneous with different fluids, respectively. The testing results are encouraging in the aspects of both computational accuracy and efficiency.
NASA Astrophysics Data System (ADS)
Kong, Dali; Zhang, Keke; Schubert, Gerald
2017-02-01
It is expected that the Juno spacecraft will provide an accurate spectrum of the Jovian zonal gravitational coefficients that would be affected by both the deep zonal flow, if it exists, and the basic rotational distortion. We derive the first analytical solution, under the spheroidal-shape approximation, for the density anomaly induced by an internal zonal flow in rapidly rotating Jupiter-like planets. We compare the density anomaly of the analytical solution to that obtained from a fully numerical solution based on a three-dimensional finite element method; the two show excellent agreement. We apply the analytical solution to a rapidly rotating Jupiter-like planet and show that there exists a close relationship between the spatial structure of the zonal flow and the spectrum of zonal gravitational coefficients. We check the accuracy of the spheroidal-shape approximation by computing both the spheroidal and non-spheroidal solutions with exactly the same physical parameters. We also discuss implications of the new analytical solution for interpreting the future high-precision gravitational measurements of the Juno spacecraft.
Titan's zonal winds in its lower stratosphere
NASA Astrophysics Data System (ADS)
Flasar, F. Michael; Schinder, Paul J.
2016-10-01
Titan's atmosphere near 80 km (20 mbar) marks the transition between lower altitudes, where radiative damping times are large and seasonal variations are muted, and higher higher altitudes, where the damping times are much smaller and temperatures and winds vary significantly over the year. Cassini radio occultation soundings at high northern latitudes in winter have indicated a sharp transition from a highly stable temperature profile in the lower stratosphere to a layer between 80 and 100 km where temperatures decrease with altitude. The cause of this destabilization may be associated with the enhanced infrared opacity of a cloud of organic ices. It is curious that 20 mbar is also the level where the Doppler Wind Experiment on the Huygens Probe at 10° S observed a deep minimum in the zonal wind profile. Application of the gradient wind relation to the altitude-pressure profiles obtained from the Cassini radio occultation soundings have shown that this minimum is global. More recent soundings, obtained as Titan's southern hemisphere moves toward winter, indicate that this structure persists. The cause of this peculiar behavior is not really understood, but the the deceleration of the zonal winds observed in the lower stratosphere may be caused by radiative damping of vertically propagating atmospheric waves in a region where the damping time decreases rapidly with altitude.
Zonal flow formation in the presence of ambient mean shear
Hsu, Pei-Chun; Diamond, P. H.
2015-02-15
The effect of mean shear flows on zonal flow formation is considered in the contexts of plasma drift wave turbulence and quasi-geostrophic turbulence models. The generation of zonal flows by modulational instability in the presence of large-scale mean shear flows is studied using the method of characteristics as applied to the wave kinetic equation. It is shown that mean shear flows reduce the modulational instability growth rate by shortening the coherency time of the wave spectrum with the zonal shear. The scalings of zonal flow growth rate and turbulent vorticity flux with mean shear are determined in the strong shear limit.
Zonal flow generation in parallel flow shear driven turbulence
NASA Astrophysics Data System (ADS)
Kosuga, Y.; Itoh, S.-I.; Itoh, K.
2017-03-01
Generation of zonal flow in parallel flow shear driven turbulence is discussed. Nonlinear dynamics is formulated by calculating energy transfer in the wave number space. It is shown that zonal flows can be generated (gain energy) from the primary mode which is driven by parallel flow shear. As a result, helical flow pattern can develop in turbulent plasmas. Our results imply that zonal flow can be generated in 3D parallel flow shear driven turbulence, which indicates that zonal flows are ubiquitous in turbulent plasmas, either 2D or 3D. Implications for turbulent momentum transport in laboratory and astrophysical plasmas are discussed.
NASA Astrophysics Data System (ADS)
Kozlov, V. G.; Subbotin, S. V.
2017-09-01
The paper is devoted to the experimental study of the dynamics of a free solid core and a liquid in a spherical cavity rotating about a horizontal axis. The cavity rotation rate consists of two components: constant and oscillating ones (librations). Under the action of centrifugal force the core with the density less than the density of liquid is located near the rotation axis. The gravity field causes a small stationary displacement of the core from the cavity center. In turn, this displacement induces mean retrograde differential rotation of the core and the fluid. It is found that the librations generate the mean effects (zonal flow and the retrograde differential rotation of the core), which manifest themselves in sum with the ones caused by gravity. The intensity of zonal flow and the core differential rotation is proportional to the square of the libration amplitude. The additivity of mean effects connected with librations and gravity is observed in a wide range of the libration frequency excluding the areas of very low-frequency librations and resonant (close to the rotation frequency and natural frequencies of the core translational oscillations) ones. At low-frequency librations, the core rotation rate changes periodically with the libration frequency and is accompanied by the periodic variation of the core position in the cavity. At some part of the libration period, the relaxation oscillations of the core with natural frequency are excited. Librations with the frequency equal to the cavity rotation exert the strongest resonant effect on the core, generating the core translational oscillations with large amplitude and substantial change of the structure of mean zonal flows. In this case and when the libration frequency coincides with the natural frequency of the core oscillations, the dependence of the differential rotational rate on the libration amplitude is different from the quadratic. This specific response of the system on the librations is caused
Combining zonal refractive and diffractive aspheric multifocal intraocular lenses.
Muñoz, Gonzalo; Albarrán-Diego, César; Javaloy, Jaime; Sakla, Hani F; Cerviño, Alejandro
2012-03-01
To assess visual performance with the combination of a zonal refractive aspheric multifocal intraocular lens (MIOL) (Lentis Mplus, Oculentis GmbH) and a diffractive aspheric MIOL (Acri.Lisa 366, Acri.Tech GmbH). This prospective interventional cohort study comprised 80 eyes from 40 cataract patients (mean age: 65.5±7.3 years) who underwent implantation of the Lentis Mplus MIOL in one eye and Acri.Lisa 366 MIOL in the fellow eye. The main outcome measures were refraction; monocular and binocular uncorrected and corrected distance, intermediate, and near visual acuities; monocular and binocular defocus curves; binocular photopic contrast sensitivity function compared to a monofocal intraocular lens (IOL) control group (40 age-matched pseudophakic patients implanted with the AR-40e [Abbott Medical Optics]); and quality of vision questionnaire. Binocular uncorrected visual acuities were 0.12 logMAR (0.76 decimal) or better at all distances measured between 6 m and 33 cm. The Lentis Mplus provided statistically significant better vision than the Acri.Lisa at distances between 2 m and 40 cm, and the Acri.Lisa provided statistically significant better vision than the Lentis Mplus at 33 cm. Binocular defocus curve showed little drop-off at intermediate distances. Photopic contrast sensitivity function for distance and near were similar to the monofocal IOL control group except for higher frequencies. Moderate glare (15%), night vision problems (12.5%), and halos (10%) were reported. Complete independence of spectacles was achieved by 92.5% of patients. The combination of zonal refractive aspheric and diffractive aspheric MIOLs resulted in excellent uncorrected binocular distance, intermediate, and near vision, with low incidence of significant photic phenomena and high patient satisfaction. Copyright 2012, SLACK Incorporated.
NASA Technical Reports Server (NTRS)
Picaut, Joel; Camusat, Bruno; Busalacchi, Antonio J.; Mcphaden, Michael J.
1990-01-01
The applicability of satellite altimeter data for estimating zonal current variability at the equator is assessed using the meriodionally differenced form of the geostrophic balance. Estimates of geostrophic zonal flow anomalies in the equatorial Pacific have been deduced from 17-day collinear altimeter data during the first year of the Geosat Exact Repeat Mission. Altimeter-derived geostrophic estimates agree well with in situ zonal current variability. Comparison of flow-frequency near-surface zonal current observed from equatorial moorings at 165 deg E, 140 deg W, and 110 deg W yield correlations of 0.83, 0.85, and 0.51, respectively, with a mean rms difference of 23 cm/sec. The inclusion of up to 11 ascending and descending Geosat tracks within the 9-deg band for every 17-day repeat effectively reduced the temporal sampling interval to 1.5 days at 165 deg E and 140 deg W. The 6.8-km along track spacing of the altimeter measurements provides sufficient resolution for the effective filtering of small-scale meridional noise, both instrumental and oceanic.
NASA Technical Reports Server (NTRS)
Picaut, Joel; Camusat, Bruno; Busalacchi, Antonio J.; Mcphaden, Michael J.
1990-01-01
The applicability of satellite altimeter data for estimating zonal current variability at the equator is assessed using the meriodionally differenced form of the geostrophic balance. Estimates of geostrophic zonal flow anomalies in the equatorial Pacific have been deduced from 17-day collinear altimeter data during the first year of the Geosat Exact Repeat Mission. Altimeter-derived geostrophic estimates agree well with in situ zonal current variability. Comparison of flow-frequency near-surface zonal current observed from equatorial moorings at 165 deg E, 140 deg W, and 110 deg W yield correlations of 0.83, 0.85, and 0.51, respectively, with a mean rms difference of 23 cm/sec. The inclusion of up to 11 ascending and descending Geosat tracks within the 9-deg band for every 17-day repeat effectively reduced the temporal sampling interval to 1.5 days at 165 deg E and 140 deg W. The 6.8-km along track spacing of the altimeter measurements provides sufficient resolution for the effective filtering of small-scale meridional noise, both instrumental and oceanic.
Zonal Flow Growth Rates: Modulational Instability vs Statistical Steady States.
NASA Astrophysics Data System (ADS)
Krommes, J. A.; Kolesnikov, R. A.
2002-11-01
The nonlinear growth rate of zonal flows has been the subject of various investigations. The calculations can be grouped into two major classes: those based on modulational instability of a fixed pump wave;(L. Chen et al., Phys. Plasmas 7), 3129 (2000); P. N. Guzdar et al., Phys. Rev. Lett. 87, 015001 (2001); C. N. Lashmore-Davies et al., Phys. Plasmas 8, 5121 (2001). and those employing statistical formalism to describe a self-consistent, energy-conserving steady state.(J. A. Krommes and C.--B. Kim, Phys. Rev. E 62), 8508 (2000), and references therein. The results from these two approaches do not necessarily agree either in their dependence on parameters like the plasma pressure β, on the threshold for instability, or even, in some cases, on the sign. The reasons for such disagreements are isolated, and it is shown to what extent the steady-state statistical approach can be reconciled with a generic modulational instability calculation. Generalizations of the statistical formalism to the multifield systems appropriate for finite β are described. Specific calculations based on model systems are used to illustrate the general arguments.
Zonal Jets on the Giant Planets
NASA Astrophysics Data System (ADS)
Showman, A. P.; Lian, Y.; Gierasch, P. J.
2006-12-01
The question of what causes the numerous east-west zonal jets on the giant planets has remained a mystery since high-resolution Pioneer and Voyager images were returned in the 1970s. A probable hypothesis is that small-scale turbulence undergoes an inverse energy cascade that reorganizes the energy into zonal jets, but whether this turbulence results from deep penetrative convection or shallow cloud-layer processes (e.g., thunderstorms) remains unknown. Here I provide a broad summary of this problem and proceed to describe several results on the effect of cloud-layer turbulence on the flow. I present 3D numerical simulations showing that cloud-layer thermal contrasts (resulting from sunlight or latent-heat variations in the upper troposphere) can drive numerous Jupiter-like zonal jets at the cloud level, in some cases including a superrotating equatorial jet resembling that on Jupiter. Furthermore, these simulations -- as well as linear, analytic calculations -- show that such shallow forcing can produce deep jets that extend far below the level of the forcing. This disproves the common assumption that jets produced by cloud-layer processes would be confined to these shallow layers. An implication is that, contrary to the claims of many publications, the winds measured by the Galileo probe to pressures of 22 bars might just as easily result from shallow forcing as from deep convective forcing. Detailed diagnostics show that the deep jets result from Coriolis accelerations acting on deep meridional circulations that are induced by the upper-level forcing. I also show that, under some conditions, vertical stretching of atmospheric columns can inhibit the standard jet-formation mechanism and lead to vortices instead of jets. Cloud-layer turbulence can also substantially modify pre-existing deep jets, leading to different jet patterns at the 1-bar cloud level than exist in the interior. On balance, these simulations support the idea that cloud-level forcing plays an
Acute Zonal Cone Photoreceptor Outer Segment Loss.
Aleman, Tomas S; Sandhu, Harpal S; Serrano, Leona W; Traband, Anastasia; Lau, Marisa K; Adamus, Grazyna; Avery, Robert A
2017-05-01
The diagnostic path presented narrows down the cause of acute vision loss to the cone photoreceptor outer segment and will refocus the search for the cause of similar currently idiopathic conditions. To describe the structural and functional associations found in a patient with acute zonal occult photoreceptor loss. A case report of an adolescent boy with acute visual field loss despite a normal fundus examination performed at a university teaching hospital. Results of a complete ophthalmic examination, full-field flash electroretinography (ERG) and multifocal ERG, light-adapted achromatic and 2-color dark-adapted perimetry, and microperimetry. Imaging was performed with spectral-domain optical coherence tomography (SD-OCT), near-infrared (NIR) and short-wavelength (SW) fundus autofluorescence (FAF), and NIR reflectance (REF). The patient was evaluated within a week of the onset of a scotoma in the nasal field of his left eye. Visual acuity was 20/20 OU, and color vision was normal in both eyes. Results of the fundus examination and of SW-FAF and NIR-FAF imaging were normal in both eyes, whereas NIR-REF imaging showed a region of hyporeflectance temporal to the fovea that corresponded with a dense relative scotoma noted on light-adapted static perimetry in the left eye. Loss in the photoreceptor outer segment detected by SD-OCT co-localized with an area of dense cone dysfunction detected on light-adapted perimetry and multifocal ERG but with near-normal rod-mediated vision according to results of 2-color dark-adapted perimetry. Full-field flash ERG findings were normal in both eyes. The outer nuclear layer and inner retinal thicknesses were normal. Localized, isolated cone dysfunction may represent the earliest photoreceptor abnormality or a distinct entity within the acute zonal occult outer retinopathy complex. Acute zonal occult outer retinopathy should be considered in patients with acute vision loss and abnormalities on NIR-REF imaging, especially if
Mackay, R.M.
1994-12-31
The two-dimensional statistical dynamical climate model that has recently been developed at the Global Change Research Center and the Oregon Graduate Institute of Science & Technology (GCRC 2D climate model) is presented and several new results obtained using the model are discussed. The model solves the 2-D primitive equations in finite difference form (mass continuity, Newton`s second law, and the first law of thermodynamics) for the prognostic variables zonal mean density, zonal mean zonal velocity, zonal mean meridional velocity, and zonal mean temperature on a grid that has 18 nodes in latitude and 9 vertical nodes (plus the surface). The equation of state, p = (rho RT) and an assumed hydrostatic atmosphere, Delta(p) = -(rho g Delta z) are used to diagnostically calculate the zonal mean pressure and vertical velocity for each grid node, and the moisture balance equation is used to estimate the precipitation rate. The performance of the model at simulating the two-dimensional temperature, zonal winds, and mass stream function is explored. The strengths and weaknesses of the model are highlighted and suggestions for future model improvements are given. The parameterization of the transient eddy fluxes of heat and momentum developed by Stone and Yao are used with small modifications. These modifications are shown to help the performance of the model at simulating the observed climate system as well as increase the model`s computational stability. Following earlier work that analyzed the response of the zonal wind fields predicted by three GCM simulations for a doubling of atmospheric CO2, the response of the GCRC 2D model`s zonal wind fields is also explored for the same experiment. Unlike the GCM simulations, this 2D model results in distinct patterns of change.
NASA Technical Reports Server (NTRS)
Win, Moe Z.; Bartman, Randy
1994-01-01
Frequency stabilization plays a very critical role in diverse applications such as long distanc fiber and free space optical communications, interferometric sensing, optical gyroscopes, squeezed states of light, atomic beam trapping, and gravity wave detection.
Geomagnetic equatorial anomaly in zonal plasma flow
NASA Technical Reports Server (NTRS)
Aggson, T. L.; Herrero, F. A.; Mayr, H. G.; Brace, L. H.; Maynard, N. C.
1987-01-01
The observation of a geomagnetic signature in the zonal eastward plasma flow, which is a striking feature of the equatorial ionosphere in the evening quadrant is reported. These observations were derived fronm (E x B)/B-squared measurements made with the cylindrical double-floating-probe experiment carried on the Dynamics Explorer 2 satellite. The signature consists of a crest-trough-crest effect in the latitude dependence of the eastward plasma flow with the crests at + or - 8 dip latitude and the trough nearly centered at the dip equator at all geographic longitudes. This phenomenon can be readily interpreted in terms of the altitude dependence of the F region dynamo electric field, and it is related to dip equator signatures in the plasma density and the magnetic declination which have been reported earlier.
EXPERIMENTAL CHARACTERIZATION OF COHERENT, RADIALLY-SHEARED ZONAL FLOWS IN THE DIII-D TOKAMAK
MCKEE,GR; FONCK,RJ; JAKUBOWSKI,M; BURRELL,KH; HALLATSCHEK,K; MOYER,RA; NEVINS,W; PORTER,GD; RUDAKOV,DL; XU,X
2002-11-01
A271 EXPERIMENTAL CHARACTERIZATION OF COHERENT, RADIALLY-SHEARED ZONAL FLOWS IN THE DIII-D TOKAMAK. Application of time-delay-estimation techniques to two-dimensional measurements of density fluctuations, obtained with beam emission spectroscopy in DIII-D plasmas, has provided temporally and spatially resolved measurements of the turbulence flow-field. Features that are characteristic of self-generated zonal flows are observed in the radial region near 0.85 {<=} r/a {<=} 1.0. These features include a coherent oscillation (approximately 15 kHz) in the poloidal flow of density fluctuations that has a long poloidal wavelength, possibly m = 0, narrow radial extent (k{sub r}{rho}{sub I} < 0.2), and whose frequency varies monotonically with the local temperature. The approximate effective shearing rate, dv{sub {theta}}/dr, of the flow is of the same order of magnitude as the measured nonlinear decorrelation rate of the turbulence, and the density fluctuation amplitude is modulated at the frequency of the observed flow oscillation. Some phase coherence is observed between the higher wavenumber density fluctuations and low frequency poloidal flow fluctuations, suggesting a Reynolds stress contribution. These characteristics are consistent with predicted features of zonal flows, specifically identified as geodesic acoustic modes, observed in 3-D Braginskii simulations of core/edge turbulence.
Collisionless Zonal Flow Saturation for Weak Magnetic Shear
NASA Astrophysics Data System (ADS)
Lu, Zhixin; Wang, Weixing; Diamond, Patrick; Ashourvan, Arash; Tynan, George
2015-11-01
The damping of the zonal flow, either collisional or collisionless, plays an important role in regulating the drift wave-zonal flow system, and can affect the transport and confinement. The tertiary instability, e.g., a generalized Kelvin-Helmholtz (KH) instability driven by flow shear, has been suggested theoretically as a possible damping mechanism [Rogers 2000 PRL, Diamond 2005 PPCF]. The sensitivity of the tertiary mode to magnetic shear has not been quantified, especially in weak magnetic shear regimes. In this work, parametric scans using gyrokinetic simulation demonstrate that the zonal electric field energy normalized by the turbulence electric field energy decreases as magnetic shear decreases. With ITG drive artificially eliminated, the time evolution of the zonal structure indicates that the zonal electric field damps more rapidly at weak shear. This suggests larger collisionless zonal flow damping or larger effective turbulent viscosity at weak magnetic shear. The effects of the zonal components of specific variables, e.g., the parallel shear flow and the radial electric field, on tertiary instability, are also studied. Quantitative studies on the magnetic shear scaling of tertiary instability excitation and the collisionless zonal flow saturation are ongoing.
Zonal-flow dynamics and size scaling of anomalous transport.
Chen, Liu; White, Roscoe B; Zonca, F
2004-02-20
Nonlinear equations for the slow space-time evolution of the radial drift-wave envelope and zonal flow amplitude have been self-consistently derived for a model nonuniform tokamak equilibrium within the coherent four-wave drift wave-zonal flow modulation interaction model of Chen, Lin, and White [Phys. Plasmas 7, 3129 (2000)
B-spline methods and zonal grids for numerical simulations of turbulent flows
NASA Astrophysics Data System (ADS)
Kravchenko, Arthur Grigorievich
1998-12-01
A novel numerical technique is developed for simulations of complex turbulent flows on zonal embedded grids. This technique is based on the Galerkin method with basis functions constructed using B-splines. The technique permits fine meshes to be embedded in physically significant flow regions without placing a large number of grid points in the rest of the computational domain. The numerical technique has been tested successfully in simulations of a fully developed turbulent channel flow. Large eddy simulations of turbulent channel flow at Reynolds numbers up to Rec = 110,000 (based on centerline velocity and channel half-width) show good agreement with the existing experimental data. These tests indicate that the method provides an efficient information transfer between zones without accumulation of errors in the regions of sudden grid changes. The numerical solutions on multi-zone grids are of the same accuracy as those on a single-zone grid but require less computer resources. The performance of the numerical method in a generalized coordinate system is assessed in simulations of laminar flows over a circular cylinder at low Reynolds numbers and three-dimensional simulations at ReD = 300 (based on free-stream velocity and cylinder diameter). The drag coefficients, the size of the recirculation region, and the vortex shedding frequency all agree well with the experimental data and previous simulations of these flows. Large eddy simulations of a flow over a circular cylinder at a sub-critical Reynolds number, ReD = 3900, are performed and compared with previous upwind-biased and central finite-difference computations. In the very near-wake, all three simulations are in agreement with each other and agree fairly well with the PIV experimental data of Lourenco & Shih (1993). Farther downstream, the results of the B- spline computations are in better agreement with the hot- wire experiment of Ong & Wallace (1996) than those obtained in finite-difference simulations
The Linear Study of Zonally Asymmetric Barotropic Flows.
NASA Astrophysics Data System (ADS)
Zhang, Zuojun
Available from UMI in association with The British Library. The loss of orthogonality between unstable normal modes is general for any kind of eigen-analysis. In particular for an observed climatological mean flow this is found to be very significant for the development of perturbations. A small perturbation can have a very large projection onto the most unstable normal mode. The adjoint eigenmode is most efficient at exciting the normal mode. The "gain" on projection is described by the projectibility. In general, growthrate and frequency information should be augmented with the projectibility and eigenvectors should be augmented by the corresponding adjoint eigenvectors. For the 300mb January climatological mean flow, the maximum projectibility is found to be 7.8 and the adjoint mode corresponding to the most unstable normal mode has large amplitude over the subtropical Indian Ocean and southeast Asia. The adjoint mode when used as an initial perturbation yields an energy increase of a factor of 50 within 10 days even when a damping is added to make the system stable. Both the initial value problems and forcing problems show that the linear barotropic vorticity equation gives important ideas on atmospheric low-frequency variability and the role of the tropics. The sensitivity of linear analysis to details of flow is studied. It is found that the instability is much more sensitive to the strength of the zonal flow component than to that of the wave components. The variation of leading unstable modes with respect to the strength of the waves is easily traced, as it is also in a simple system which contains only a zonal flow and a wave. Instability depends upon the assumption of the maintenance of the basic state. The sensitivity to basic states maintained by a divergent wind forcing and an equivalent orographic forcing are studied. It is found that the instability is more sensitive to the equivalent orographic forcing than to the divergent wind forcing. The
ON THE VARIATION OF ZONAL GRAVITY COEFFICIENTS OF A GIANT PLANET CAUSED BY ITS DEEP ZONAL FLOWS
Kong Dali; Zhang Keke; Schubert, Gerald E-mail: kzhang@ex.ac.uk
2012-04-01
Rapidly rotating giant planets are usually marked by the existence of strong zonal flows at the cloud level. If the zonal flow is sufficiently deep and strong, it can produce hydrostatic-related gravitational anomalies through distortion of the planet's shape. This paper determines the zonal gravity coefficients, J{sub 2n}, n = 1, 2, 3, ..., via an analytical method taking into account rotation-induced shape changes by assuming that a planet has an effective uniform density and that the zonal flows arise from deep convection and extend along cylinders parallel to the rotation axis. Two different but related hydrostatic models are considered. When a giant planet is in rigid-body rotation, the exact solution of the problem using oblate spheroidal coordinates is derived, allowing us to compute the value of its zonal gravity coefficients J-bar{sub 2n}, n=1,2,3,..., without making any approximation. When the deep zonal flow is sufficiently strong, we develop a general perturbation theory for estimating the variation of the zonal gravity coefficients, {Delta}J{sub 2n}=J{sub 2n}-J-bar{sub 2n}, n=1,2,3,..., caused by the effect of the deep zonal flows for an arbitrarily rapidly rotating planet. Applying the general theory to Jupiter, we find that the deep zonal flow could contribute up to 0.3% of the J{sub 2} coefficient and 0.7% of J{sub 4}. It is also found that the shape-driven harmonics at the 10th zonal gravity coefficient become dominant, i.e., {Delta}J{sub 2n}>=J-bar{sub 2n} for n {>=} 5.
NASA Astrophysics Data System (ADS)
Satriano, C.; Ruiz, J. A.; Bernard, P.; Vilotte, J. P.
2015-12-01
Back projection (BP) has recently emerged as a tool for imaging the spatio-temporal distribution of high-frequency (HF) emission during the earthquake rupture. BP images are typically constructed from HF-filtered, far field velocity waveforms, shifted and stacked according to the predicted travel-time from each node of a source grid. The underlying assumption is that the radiated wave field is coherent across the recording array, so that waveforms sum up constructively when the correct source point is selected. For regional arrays, at teleseismic distance, this assumption is generally valid up to 2-3 Hz. BP is an inherently HF method (resolution degrades at lower frequencies), and has been often used in conjunction with kinematic slip modeling (inherently low-frequency) to discuss the variability of rupture behavior with frequency. Many studies have evidenced that HF emissions occur at the border of large slip asperities and/or are associated with abrupt changes in rupture velocity. Here we perform a systematic investigation of the relationship between rupture properties and BP images of HF emission through the analysis of synthetic finite-source models, using a kinematic k-2 source model. This approach is based on a composite source description, with sub-events following a fractal distribution of sizes. Each elementary source is activated by the macro scale rupture front, with rupture duration proportional to its size. This approach generates, in the far-field approximation, ground displacements that follow the ω-2 model with frequency-dependent directivity effects. For a large earthquake rupture (M~9), synthetic far field recordings can be generated up to 4 Hz, with reasonable computing time. We study several scenarios, exploring the spatial variability of rupture velocity, fractal properties (slip heterogeneity) and source directivity, and analyze the effect of the relative position between the recording teleseismic array and the fault.
NASA Astrophysics Data System (ADS)
Shi, Yu; Cerjan, Alexander; Fan, Shanhui
2017-02-01
We introduce a finite-difference frequency-domain algorithm for coupled acousto-optic simulations. First-principles acousto-optic simulation in time domain has been challenging due to the fact that the acoustic and optical frequencies differ by many orders of magnitude. We bypass this difficulty by formulating the interactions between the optical and acoustic waves rigorously as a system of coupled nonlinear equations in frequency domain. This approach is particularly suited for on-chip devices that are based on a variety of acousto-optic interactions such as the stimulated Brillouin scattering. We validate our algorithm by simulating a stimulated Brillouin scattering process in a suspended waveguide structure and find excellent agreement with coupled-mode theory. We further provide an example of a simulation for a compact on-chip resonator device that greatly enhances the effect of stimulated Brillouin scattering. Our algorithm should facilitate the design of nanophotonic on-chip devices for the harnessing of photon-phonon interactions.
Wear, Keith A; Harris, Gerald R
2008-11-01
A model is presented for the echo from a thin, oblique, finite-length cylinder. The echo is calculated from the line integral of the transducer directivity pattern along the cylinder axis. The model was validated with broadband pulse-echo measurements from (1) a perpendicular (to the ultrasound beam) nylon wire as a function of lateral displacement from the beam center, (2) a tilted nylon wire as a function of the angle of inclination relative to the ultrasound beam, and (3) a quasi-parallel-nylon-wire phantom, which mimicked the scattering properties of cancellous bone. The transducer directivity pattern (as a function of position and frequency) was measured with a membrane hydrophone. The model predicts an approximately cubic frequency dependence of backscatter coefficient from the phantom, as has been observed experimentally in cancellous bone. The model also predicts the relationship between the cylinder length and the exponent of a power law fit to backscatter coefficient versus frequency, which is 4 for very short (compared to a wavelength) cylinders and asymptotically approaches 3 for very long cylinders.
Zonal wavefront reconstruction in quadrilateral geometry for phase measuring deflectometry
Huang, Lei; Xue, Junpeng; Gao, Bo; ...
2017-06-14
There are wide applications for zonal reconstruction methods in slope-based metrology due to its good capability of reconstructing the local details on surface profile. It was noticed in the literature that large reconstruction errors occur when using zonal reconstruction methods designed for rectangular geometry to process slopes in a quadrilateral geometry, which is a more general geometry with phase measuring deflectometry. In this paper, we present a new idea for the zonal methods for quadrilateral geometry. Instead of employing the intermediate slopes to set up height-slope equations, we consider the height increment as a more general connector to establish themore » height-slope relations for least-squares regression. The classical zonal methods and interpolation-assisted zonal methods are compared with our proposal. Results of both simulation and experiment demonstrate the effectiveness of the proposed idea. In implementation, the modification on the classical zonal methods is addressed. Finally, the new methods preserve many good aspects of the classical ones, such as the ability to handle a large incomplete slope dataset in an arbitrary aperture, and the low computational complexity comparable with the classical zonal method. Of course, the accuracy of the new methods is much higher when integrating the slopes in quadrilateral geometry.« less
Generation of zonal flows by coupled electrostatic drift and ion-acoustic waves
NASA Astrophysics Data System (ADS)
Kaladze, T. D.; Kahlon, L. Z.; Tsamalashvili, L. V.
2017-07-01
Generation of sheared zonal flow by low-frequency coupled electrostatic drift and ion-acoustic waves is presented. Primary waves of different (small, intermediate, and large) scales are considered, and the appropriate system of equations consisting of generalized Hasegawa-Mima equation for the electrostatic potential (involving both vector and scalar nonlinearities) and equation of parallel to magnetic field ions motion is obtained. It is shown that along with the mean poloidal flow with strong variation in minor radius mean sheared toroidal flow can also be generated. According to laboratory plasma experiments, main attention to large scale drift-ion-acoustic wave is given. Peculiarities of the Korteweg-de Vries type scalar nonlinearity due to the electrons temperature non-homogeneity in the formation of zonal flow by large-scale turbulence are widely discussed. Namely, it is observed that such type of flows need no generation condition and can be spontaneously excited.
Zonal winds near Venus' cloud top level - An analytic model of the equatorial wind speed
NASA Technical Reports Server (NTRS)
Leovy, Conway B.
1987-01-01
A consequence of the presently hypothesized maintenance of the equatorial wind speed near the cloud top level of Venus by a balance between the semidiurnal tide's pumping and the Hadley circulation's vertical advection (both integrated across the thermal driving region) is that the maximum equatorial zonal wind speed is proportional to the product of the buoyancy frequency and the magnitude of the driving region's thickness. The proportionality constant is characterized as a weakly increasing function of the heating rate, and a decreasing function of the product of an inverse length, expressing the mean zonal wind shear, and the driving region thickness. For the class of solutions thus treated, there is a threshold heating rate value below which no equilibrium satisfies the prescribed balance.
NASA Astrophysics Data System (ADS)
Mukherjee, Sushovan; Gopalakrishnan, S.
2016-04-01
The class of fabricated materials known as metamaterials, with its promises for unconventional material properties or characteristics, has opened up a whole new paradigm of possibilities and challenges. The primary enablers have been capabilities at the very low length scale and novel design configurations. Pentamode metamaterials, having fluid like properties, is one such idea to have been realized in recent past. This type of fabricated materials show high bulk modulus but low shear modulus. The fundamental constituent element is a rod like structure tapered down on both ends. Four of such elements meet at any joint, two of which in a plane orthogonal to that of the other two. The dynamics and wave propagation characteristics of such structures have been studied with an aim to obtain band structures formed because of their periodic nature. Here, a methodology has been developed to compute the wave propagation characteristics of such pentamode structures using spectrally formulated finite elements based on frequency domain Ritz method. Bloch theory has also been used to represent the dynamics of an infinite structure through that of a unit cell. The proposed method is computationally more efficient compared to one using conventional finite element. A few variants of pentamodes are also analyzed to arrive at configurations with superior wave propagation characteristics.
Choi, M.; Chan, V. S.; Lao, L. L.; Pinsker, R. I.; Green, D.; Berry, L. A.; Jaeger, F.; Park, J. M.; Heidbrink, W. W.; Liu, D.; Podesta, M.; Harvey, R.; Smithe, D. N.; Bonoli, P.
2010-05-15
The five-dimensional finite-orbit Monte Carlo code ORBIT-RF[M. Choi et al., Phys. Plasmas 12, 1 (2005)] is successfully coupled with the two-dimensional full-wave code all-orders spectral algorithm (AORSA) [E. F. Jaeger et al., Phys. Plasmas 13, 056101 (2006)] in a self-consistent way to achieve improved predictive modeling for ion cyclotron resonance frequency (ICRF) wave heating experiments in present fusion devices and future ITER [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)]. The ORBIT-RF/AORSA simulations reproduce fast-ion spectra and spatial profiles qualitatively consistent with fast ion D-alpha [W. W. Heidbrink et al., Plasma Phys. Controlled Fusion 49, 1457 (2007)] spectroscopic data in both DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 41, 1435 (2001)] high harmonic ICRF heating experiments. This work verifies that both finite-orbit width effect of fast-ion due to its drift motion along the torus and iterations between fast-ion distribution and wave fields are important in modeling ICRF heating experiments.
Choi, M.; Green, David L; Heidbrink, W. W.; Harvey, R. W.; Liu, D.; Chan, V. S.; Berry, Lee A; Jaeger, Erwin Frederick; Lao, L.L.; Pinsker, R. I.; Podesta, M.; Smithe, D. N.; Park, J. M.; Bonoli, P.
2010-01-01
The five-dimensional finite-orbit Monte Carlo code ORBIT-RF [M. Choi , Phys. Plasmas 12, 1 (2005)] is successfully coupled with the two-dimensional full-wave code all-orders spectral algorithm (AORSA) [E. F. Jaeger , Phys. Plasmas 13, 056101 (2006)] in a self-consistent way to achieve improved predictive modeling for ion cyclotron resonance frequency (ICRF) wave heating experiments in present fusion devices and future ITER [R. Aymar , Nucl. Fusion 41, 1301 (2001)]. The ORBIT-RF/AORSA simulations reproduce fast-ion spectra and spatial profiles qualitatively consistent with fast ion D-alpha [W. W. Heidbrink , Plasma Phys. Controlled Fusion 49, 1457 (2007)] spectroscopic data in both DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and National Spherical Torus Experiment [M. Ono , Nucl. Fusion 41, 1435 (2001)] high harmonic ICRF heating experiments. This work verifies that both finite-orbit width effect of fast-ion due to its drift motion along the torus and iterations between fast-ion distribution and wave fields are important in modeling ICRF heating experiments. (C) 2010 American Institute of Physics. [doi:10.1063/1.3314336
Asakura, T; Ishizuka, T; Miyajima, T; Toyoda, M; Sakamoto, S
2014-09-01
Due to limitations of computers, prediction of structure-borne sound remains difficult for large-scale problems. Herein a prediction method for low-frequency structure-borne sound transmissions on concrete structures using the finite-difference time-domain scheme is proposed. The target structure is modeled as a composition of multiple plate elements to reduce the dimensions of the simulated vibration field from three-dimensional discretization by solid elements to two-dimensional discretization. This scheme reduces both the calculation time and the amount of required memory. To validate the proposed method, the vibration characteristics using the numerical results of the proposed scheme are compared to those measured for a two-level concrete structure. Comparison of the measured and simulated results suggests that the proposed method can be used to simulate real-scale structures.
Potravkin, N N; Perezhogin, I A; Makarov, V A
2012-11-01
We propose an alternative method of integration of Maxwell equations. This method is the generalization of a finite-difference time-domain method with an auxiliary differential equation for the case of a linear optical medium with a frequency dispersion and an arbitrary source of spatial dispersion. We apply this method to the problem of the propagation of short plane-wave linearly polarized light pulses in such a medium. It is shown that some features of their propagation are completely different from those that are generally recognized for the linear optical activity phenomenon. For example, in some cases an initially linearly polarized light pulse becomes elliptically polarized during the propagation. This effect is more prominent in the front part of the pulse.
Bounded relative motion under zonal harmonics perturbations
NASA Astrophysics Data System (ADS)
Baresi, Nicola; Scheeres, Daniel J.
2017-04-01
The problem of finding natural bounded relative trajectories between the different units of a distributed space system is of great interest to the astrodynamics community. This is because most popular initialization methods still fail to establish long-term bounded relative motion when gravitational perturbations are involved. Recent numerical searches based on dynamical systems theory and ergodic maps have demonstrated that bounded relative trajectories not only exist but may extend up to hundreds of kilometers, i.e., well beyond the reach of currently available techniques. To remedy this, we introduce a novel approach that relies on neither linearized equations nor mean-to-osculating orbit element mappings. The proposed algorithm applies to rotationally symmetric bodies and is based on a numerical method for computing quasi-periodic invariant tori via stroboscopic maps, including extra constraints to fix the average of the nodal period and RAAN drift between two consecutive equatorial plane crossings of the quasi-periodic solutions. In this way, bounded relative trajectories of arbitrary size can be found with great accuracy as long as these are allowed by the natural dynamics and the physical constraints of the system (e.g., the surface of the gravitational attractor). This holds under any number of zonal harmonics perturbations and for arbitrary time intervals as demonstrated by numerical simulations about an Earth-like planet and the highly oblate primary of the binary asteroid (66391) 1999 KW4.
NASA Technical Reports Server (NTRS)
Chaderjian, Neal M.
1986-01-01
A computer code is under development whereby the thin-layer Reynolds-averaged Navier-Stokes equations are to be applied to realistic fighter aircraft configurations. This transonic Navier-Stokes code (TNS) utilizes a zonal approach in order to treat complex geometries and satisfy in-core computer memory constraints. The zonal approach was applied to isolated wing geometries in order to facilitate code development. The TNS finite difference algorithm, zonal methodology, and code validation with experimental data is addressed. Also addressed are some numerical issues such as code robustness, efficiency, and accuracy at high angles of attack. Special free-stream-preserving metrics proved an effective way to treat H-mesh singularities over a large range of severe flow conditions, including strong leading edge flow gradients, massive shock induced separation, and stall. Furthermore, lift and drag coefficients were computed for a wing up through CLmax. Numerical oil flow patterns and particle trajectories are presented both for subcritical and transonic flow. These flow simulations are rich with complex separated flow physics and demonstrate the efficiency and robustness of the zonal approach.
NASA Technical Reports Server (NTRS)
Chaderjian, N. M.
1986-01-01
A computer code is under development whereby the thin-layer Reynolds-averaged Navier-Stokes equations are to be applied to realistic fighter-aircraft configurations. This transonic Navier-Stokes code (TNS) utilizes a zonal approach in order to treat complex geometries and satisfy in-core computer memory constraints. The zonal approach has been applied to isolated wing geometries in order to facilitate code development. Part 1 of this paper addresses the TNS finite-difference algorithm, zonal methodology, and code validation with experimental data. Part 2 of this paper addresses some numerical issues such as code robustness, efficiency, and accuracy at high angles of attack. Special free-stream-preserving metrics proved an effective way to treat H-mesh singularities over a large range of severe flow conditions, including strong leading-edge flow gradients, massive shock-induced separation, and stall. Furthermore, lift and drag coefficients have been computed for a wing up through CLmax. Numerical oil flow patterns and particle trajectories are presented both for subcritical and transonic flow. These flow simulations are rich with complex separated flow physics and demonstrate the efficiency and robustness of the zonal approach.
NASA Astrophysics Data System (ADS)
Borgeaud, Anselme F. E.; Konishi, Kensuke; Kawai, Kenji; Geller, Robert J.
2016-10-01
We conduct a numerical experiment to investigate potential bias in measurements of S-wave splitting (apparent differences between the arrival times of SH and SV phases) for waves propagating close to the core-mantle boundary (CMB) in the D″ layer. The bias is defined as the discrepancy between shear wave splitting measured from finite frequency synthetic seismograms (`apparent splitting') and the splitting predicted by ray theory, which is a high-frequency approximation. For simple isotropic models, we find biases which are typically between 0.5 and 4 s, depending on the model, the Q structure and the dominant period of the synthetics. The bias increases for lower frequencies or lower Q values. The epicentral distance at which the bias starts depends on the frequency and the Q structure. We also compute synthetics for models based on mineral physics (using the elastic constants under lower-mantle pressure and temperature conditions, taking into account the phase transition from Mg-perovskite to Mg-post-perovskite) and geodynamics (the thermal boundary layer) and find that the depth of the positive velocity jump associated with the phase transition and the depth range over which the velocity decreases (due to temperature increases) in the thermal boundary layer significantly influence the wavefield in the lowermost mantle. For example, in cold regions beneath subduction zones, wavefields for SH and SV differ greatly due to the steep velocity decrease close to the CMB. For complex models, apparent splitting can also arise from the possibility that low amplitude direct phases might be overlooked, and larger amplitude later phases might instead incorrectly be picked as the direct arrival. Biases of the type investigated in this study combine with other sources of uncertainty for splitting in D″ (e.g. the correction for upper-mantle anisotropy and the difference between SH and SV ray paths) to make a precise evaluation of the anisotropy in D″ difficult.
Mondal, Mintu; Kamlapure, Anand; Ganguli, Somesh Chandra; Jesudasan, John; Bagwe, Vivas; Benfatto, Lara; Raychaudhuri, Pratap
2013-01-01
The persistence of a soft gap in the density of states above the superconducting transition temperature Tc, the pseudogap, has long been thought to be a hallmark of unconventional high-temperature superconductors. However, in the last few years this paradigm has been strongly revised by increasing experimental evidence for the emergence of a pseudogap state in strongly-disordered conventional superconductors. Nonetheless, the nature of this state, probed primarily through scanning tunneling spectroscopy (STS) measurements, remains partly elusive. Here we show that the dynamic response above Tc, obtained from the complex ac conductivity, is highly modified in the pseudogap regime of strongly disordered NbN films. Below the pseudogap temperature, T*, the superfluid stiffness acquires a strong frequency dependence associated with a marked slowing down of critical fluctuations. When translated into the length-scale of fluctuations, our results suggest a scenario of thermal phase fluctuations between superconducting domains in a strongly disordered s-wave superconductor. PMID:23446946
NASA Astrophysics Data System (ADS)
Miller, Nathaniel C.; Lizarralde, Daniel
2016-08-01
Effects of serpentine-filled fault zones on seismic wave propagation in the upper mantle at the outer rise of subduction zones are evaluated using acoustic wave propagation models. Modeled wave speeds depend on azimuth, with slowest speeds in the fault-normal direction. Propagation is fastest along faults, but, for fault widths on the order of the seismic wavelength, apparent wave speeds in this direction depend on frequency. For the 5-12 Hz Pn arrivals used in tomographic studies, joint-parallel wavefronts are slowed by joints. This delay can account for the slowing seen in tomographic images of the outer rise upper mantle. At the Middle America Trench, confining serpentine to fault zones, as opposed to a uniform distribution, reduces estimates of bulk upper mantle hydration from 3.5 wt % to as low as 0.33 wt % H2O.
Miller, Nathaniel; Lizarralde, Daniel
2016-01-01
Effects of serpentine-filled fault zones on seismic wave propagation in the upper mantle at the outer rise of subduction zones are evaluated using acoustic wave propagation models. Modeled wave speeds depend on azimuth, with slowest speeds in the fault-normal direction. Propagation is fastest along faults, but, for fault widths on the order of the seismic wavelength, apparent wave speeds in this direction depend on frequency. For the 5–12 Hz Pn arrivals used in tomographic studies, joint-parallel wavefronts are slowed by joints. This delay can account for the slowing seen in tomographic images of the outer rise upper mantle. At the Middle America Trench, confining serpentine to fault zones, as opposed to a uniform distribution, reduces estimates of bulk upper mantle hydration from ~3.5 wt % to as low as 0.33 wt % H2O.
A modified zonal index and its physical sense
NASA Astrophysics Data System (ADS)
Li, Jianping; Wang, Julian X. L.
2003-06-01
A modified zonal index (ZI) for the Northern Hemisphere (NH) general circulation is defined as the normalized difference in zonal-averaged sea level pressure anomalies between 35°N and 65°N. The ZI is a measure of hemispheric-wide fluctuations in air mass between two annular belts of action (ABAs) over middle and high latitudes, centered near 35°N and 65°N, respectively. The spatial structure of the NH general circulation represented by the ZI is a zonally symmetric pattern, similar to the NH annular mode. Some physical features associated with the ZI are discussed and summarized as a concept model, and the analysis indicates that the Ferrel cell stands out as a dominant signal in the zonal-mean circulation anomalies related to the ZI, implying a strong dynamical property of the general circulation in the mid-high latitudes.
NASA Astrophysics Data System (ADS)
Kong, D. F.; Liu, A. D.; Lan, T.; Cui, Z. Y.; Yu, D. L.; Yan, L. W.; Zhao, H. L.; Sheng, H. G.; Chen, R.; Xie, J. L.; Li, H.; Liu, W. D.; Yu, C. X.; Ding, W. X.; Sun, X.; Hong, W. Y.; Cheng, J.; Zhao, K. J.; Dong, J. Q.; Duan, X. R.
2013-12-01
Geodesic acoustic mode (GAM) and low-frequency zonal flow (LFZF) are both observed through Langmuir probe arrays during electron cyclotron resonance heating (ECRH) on the HL-2A tokamak edge. The radial distributions of the amplitude and peak frequency of GAM in floating potential fluctuations are investigated through rake probe arrays under different ECRH powers. It is observed that the GAM frequency would decrease and the intensity of carbon line emission would increase as the ECRH power exceeds a certain threshold. The analyses suggest that the impurity ions may play an important role in the GAM frequency at the edge region. It is also found that during the ECRH phase besides the mean flow, both GAM and LFZF are strengthened. The total fluctuation power and the fraction of that power associated with zonal flows both increase with the ECRH power, consistent with a predator-prey model. The auto- and cross-bicoherence analyses show the coupling between GAM and its second harmonic during the ECRH phase. Moreover, the results also suggest that the couplings between GAM and the components with multiple GAM frequency are strengthened. These couplings may be important for GAM saturation during the ECRH phase.
Variable threshold zonal filtering. [in nonlinear image enhancement
NASA Technical Reports Server (NTRS)
Schwartz, A. A.; Soha, J. M.
1977-01-01
Variable threshold zonal filtering is an active nonlinear image enhancement technique designed to avoid ringing artifacts which filtering can introduce near sharp brightness transitions in the original scene. The filtering procedure can be implemented in the Fourier domain or by subtractive box filtering. It is shown, in reference to a Landsat scene of Iceland, that while conventional box filtering produces severe ringing, zonal filtering results in a more uniform display of local detail.
Zonal analysis - The final step in system safety assessment
NASA Astrophysics Data System (ADS)
Caldwell, Richard E.; Merdgen, David B.
The unexpected interaction of unrelated systems has often been implicated in design-related aircraft accidents. Zonal analysis, which is definable as the systematic inspection of geographical locations of components and interconnections in a system with a view to potential system-to-system interactions, is highly relevant to the consequences of high rotational energy systems (such as turbofan engines), corrosive liquids, and pressure vessels. Attention is presently given to the course of formal zonal analysis for the MD-11 airliner.
The total containment of a batch-type zonal centrifuge.
Webb, N L; Richards, B M; Gooders, A P
1975-09-01
A batch-type zonal centrifuge has been modified and totally contained for use with biologically hazardous materials. A sealed cabinet encloses the centrifuge and the ancilliary equipment. It is operated with a flow of filtered air when the zonal system is on, decontaminated with ethylene oxide, and maintained at a negative pressure throughout. The centrifuge subsystems can be drained, flushed, and decontaminated with ethylene oxide before an engineer services the machine. The sample handling system within the cabinet is remotely controlled.
Deriving Saturn's Zonal Winds from Cassini Radio Occultations
NASA Astrophysics Data System (ADS)
Flasar, F. Michael; Schinder, Paul J.
2015-11-01
Tracking cloud features from visible images have provided detailed maps of the meridional variation of the mean zonal winds on the giant planets, including Saturn. Filters at different wavelengths can provide information on the vertical structure of the zonal winds, but that is approximate, and the altitudes of winds observed with a given filter generally vary with location, because cloud heights do. Radio occultations provide vertical profiles of refractivity, pressure, and temperature vs. altitude. Zonal winds can be derived from the assumption of gradient wind balance, which relates the zonal wind to the change of geopotential height with latitude along an isobar. Occultations have the advantage that vertical profiles of winds can be obtained in the troposphere and stratosphere. There are, however, complicating factors. In general, the meridional distribution of occultation soundings is limited and unevenly distributed. Moreover, one needs to know the geometry of the occulting atmosphere to correctly account for the path of the refracted radio signal. The zonal winds matter, because they distort isobaric surfaces. For example, an inversion that includes Saturn's oblateness from uniform rotation, based on the Voyager System III period, would yield equatorial temperature profiles that are shifted by ~ 2 K relative to one that also includes the differential rotation associated with the cloud-tracked zonal winds. In retrieving vertical profiles of atmospheric variables from occultation soundings, one also needs an additional symmetry assumption to make the inversions tractable. Typically one uses the zonal winds based on cloud-tracking studies, and assumes they are axisymmetric and barotropic, so that both the gravitational and centrifugal forces are derivable from a potential, and the surfaces of constant geopotential height, pressure, and temperature coincide. This forms the basis for an iterative approach. The pressures and temperatures so retrieved from the
Unsteady airfoil flow solutions on moving zonal grids
NASA Technical Reports Server (NTRS)
Cricelli, Antonio S.; Ekaterinaris, John A.; Platzer, Max F.
1992-01-01
Euler and Navier-Stokes solutions for airfoil flows on zonal grids are presented. The governing equations are solved with an implicit, iterative, factorized numerical scheme. The inviscid fluxes are examined with a third-order accurate upwind method. Zonal grid solutions are compared with experimental measurements for flows over airfoils at fixed angles of incidence. The computed unsteady solutions for rapidly pitching and oscillating airfoils are in good agreement with experiments.
Kinefuchi, K.; Funaki, I.; Shimada, T.; Abe, T.
2012-10-15
Under certain conditions during rocket flights, ionized exhaust plumes from solid rocket motors may interfere with radio frequency transmissions. To understand the relevant physical processes involved in this phenomenon and establish a prediction process for in-flight attenuation levels, we attempted to measure microwave attenuation caused by rocket exhaust plumes in a sea-level static firing test for a full-scale solid propellant rocket motor. The microwave attenuation level was calculated by a coupling simulation of the inviscid-frozen-flow computational fluid dynamics of an exhaust plume and detailed analysis of microwave transmissions by applying a frequency-dependent finite-difference time-domain method with the Drude dispersion model. The calculated microwave attenuation level agreed well with the experimental results, except in the case of interference downstream the Mach disk in the exhaust plume. It was concluded that the coupling estimation method based on the physics of the frozen plasma flow with Drude dispersion would be suitable for actual flight conditions, although the mixing and afterburning in the plume should be considered depending on the flow condition.
NASA Astrophysics Data System (ADS)
Xu, Fuming; Wang, Bin; Wei, Yadong; Wang, Jian
2013-10-01
Orbital-free density functional theory (OFDFT) replaces the wavefunction in the kinetic energy by an explicit energy functional and thereby speeds up significantly the calculation of ground state properties of the solid state systems. So far, the application of OFDFT has been centered on closed systems and less attention is paid on the transport properties in open systems. In this paper, we use OFDFT and combine it with non-equilibrium Green's function to simulate equilibrium electronic transport properties in silicon nanostructures from first principles. In particular, we study ac transport properties of a silicon atomic junction consisting of a silicon atomic chain and two monoatomic leads. We have calculated the dynamic conductance of this atomic junction as a function of ac frequency with one to four silicon atoms in the central scattering region. Although the system is transmissive with dc conductance around 4 to 5 e2/h, capacitive-like behavior was found in the finite frequency regime. Our analysis shows that, up to 0.1 THz, this behavior can be characterized by a classic RC circuit consisting of two resistors and a capacitor. One resistor gives rise to dc resistance and the other one accounts for the charge relaxation resistance with magnitude around 0.2 h/e2 when the silicon chain contains two atoms. It was found that the capacitance is around 5 aF for the same system.
NASA Astrophysics Data System (ADS)
Kinefuchi, K.; Funaki, I.; Shimada, T.; Abe, T.
2012-10-01
Under certain conditions during rocket flights, ionized exhaust plumes from solid rocket motors may interfere with radio frequency transmissions. To understand the relevant physical processes involved in this phenomenon and establish a prediction process for in-flight attenuation levels, we attempted to measure microwave attenuation caused by rocket exhaust plumes in a sea-level static firing test for a full-scale solid propellant rocket motor. The microwave attenuation level was calculated by a coupling simulation of the inviscid-frozen-flow computational fluid dynamics of an exhaust plume and detailed analysis of microwave transmissions by applying a frequency-dependent finite-difference time-domain method with the Drude dispersion model. The calculated microwave attenuation level agreed well with the experimental results, except in the case of interference downstream the Mach disk in the exhaust plume. It was concluded that the coupling estimation method based on the physics of the frozen plasma flow with Drude dispersion would be suitable for actual flight conditions, although the mixing and afterburning in the plume should be considered depending on the flow condition.
NASA Astrophysics Data System (ADS)
Lu, Yujie; Zhu, Banghe; Shen, Haiou; Rasmussen, John C.; Wang, Ge; Sevick-Muraca, Eva M.
2011-03-01
Fluorescence-enhanced optical imaging/tomography may play an important role in preclinical research and clinical diagnostics as a type of optical molecular. Time- and frequency-domain measurement can acquire more measurement information, reducing the ill-posedness and improving the reconstruction quality of fluorescence-enhanced optical tomography. Although the diffusion approximation (DA) theory has been extensively in optical imaging, high-order photon migration models must be further investigated for application to complex and small tissue volumes. In this paper, a frequency-domain fully parallel adaptive finite element solver is developed with the simplified spherical harmonics (SPN) approximations. To fully evaluate the performance of the SPN approximations, a fast tetrahedron-based Monte Carlo simulator suitable for complex heterogeneous geometries is developed using the convolution strategy to realize the simulation of the fluorescence excitation and emission. With simple and real digital mouse phantoms, the results show that the significant precision and speed improvements are obtained from the parallel adaptive mesh evolution strategy.
Investigation of zonal flows by using the collective scattering measurement of density fluctuations
NASA Astrophysics Data System (ADS)
Shen, H. G.; Yu, Y.; Lan, T.; Li, Y. D.; Liu, A. D.; Xie, J. L.; Liu, W. D.; Yu, C. X.; Zhang, W. Y.; Ti, A.; Li, J. G.
2015-09-01
The poloidal {{E}r}× {{B}\\text{T}} rotation velocities in the core plasma region are studied using the instantaneous frequency method (IFM) with the density fluctuations measured by the CO2 laser collective scattering diagnostics on the HT-7 tokamak. A coherent mode is observed in the fluctuations of poloidal velocities with the mode frequency from 10 to 20 kHz. It is identified as geodesic acoustic mode (GAM) zonal flow with poloidal symmetry (m = 0) and its mode frequency coinciding with the theoretical expected GAM frequency. The nonlinear interactions are investigated by applying the envelope analysis on the density fluctuations. The results confirm that the envelope modulation in the high frequency density fluctuations only comes from the shearing by GAM. The comparison between IFM and envelope analysis is also discussed.
Role of stable modes in zonal flow regulated ITG turbulence
NASA Astrophysics Data System (ADS)
Makwana, Kirit; Terry, Paul; Hatch, David; Pueschel, M. J.
2012-10-01
Stable modes are studied in zonal flow regulated ITG turbulence using the gyrokinetic code GENE. Proper orthogonal decomposition (POD) modes are employed to investigate the eigenmode space of the distribution function. Both the unstable and stable POD modes show strong nonlinear energy transfer via three wave interactions that include zonal modes. The zonal mode itself absorbs a small fraction of the energy injected by the unstable mode. The remaining energy is deposited in the stable modes of non-zonal wavenumbers that are involved in the three wave coupling. These stable modes lie mostly within the wavenumber range of the instability. This indicates that zonal flows mediate energy transfer from unstable to stable modes, leading to saturation. The amplitude attenuation rate (AAR) of POD modes shows an equipartition across a large range of stable modes. This rate is balanced by three wave correlations of the POD modes and their time dependent amplitudes. These correlations are large if they involve zonal modes and they also show an equipartition for higher mode numbers. A similar analysis using linear eigenmodes also shows rough equipartition among the linear modes. Thus, AAR provides a handle to collectively describe the multitude of stable modes in a gyrokinetic simulation.
Zhang, Hai-Feng; Ding, Guo-Wen; Lin, Yi-Bing; Chen, Yu-Qing
2015-05-15
In this paper, the properties of acceptor mode in two-dimensional plasma photonic crystals (2D PPCs) composed of the homogeneous and isotropic dielectric cylinders inserted into nonmagnetized plasma background with square lattices under transverse-magnetic wave are theoretically investigated by a modified finite-difference frequency-domain (FDFD) method with supercell technique, whose symmetry of every supercell is broken by removing a central rod. A new FDFD method is developed to calculate the band structures of such PPCs. The novel FDFD method adopts a general function to describe the distribution of dielectric in the present PPCs, which can easily transform the complicated nonlinear eigenvalue equation to the simple linear equation. The details of convergence and effectiveness of proposed FDFD method are analyzed using a numerical example. The simulated results demonstrate that the enough accuracy of the proposed FDFD method can be observed compared to the plane wave expansion method, and the good convergence can also be obtained if the number of meshed grids is large enough. As a comparison, two different configurations of photonic crystals (PCs) but with similar defect are theoretically investigated. Compared to the conventional dielectric-air PCs, not only the acceptor mode has a higher frequency but also an additional photonic bandgap (PBG) can be found in the low frequency region. The calculated results also show that PBGs of proposed PPCs can be enlarged as the point defect is introduced. The influences of the parameters for present PPCs on the properties of acceptor mode are also discussed in detail. Numerical simulations reveal that the acceptor mode in the present PPCs can be easily tuned by changing those parameters. Those results can hold promise for designing the tunable applications in the signal process or time delay devices based on the present PPCs.
NASA Astrophysics Data System (ADS)
Tsekhmistrenko, Maria; Sigloch, Karin; Hosseini, Kasra; Barruol, Guilhem
2016-04-01
From 2011 to 2014, the RHUM-RUM project (Reunion Hotspot Upper Mantle - Reunions Unterer Mantel) instrumented a 2000x2000km2 area of Indian Ocean seafloor, islands and Madagascar with broadband seismometers and hydrophones. The central component was a 13-month deployment of 57 German and French Ocean Bottom Seismometers (OBS) in 2300-5600 m depth. This was supplemented by 2-3 year deployments of 37 island stations on Reunion, Mauritius, Rodrigues, the southern Seychelles, the Iles Eparses and southern Madagascar. Two partner projects contributed another 30+ stations on Madagascar. Our ultimate objective is multifrequency waveform tomography of the entire mantle column beneath the Reunion hotspot. Ideally we would use all passbands that efficiently transmit body waves but this meets practical limits in the noise characteristics of ocean-bottom recordings in particular. Here we present the preliminary data set of frequency-dependent P-wave traveltime measurements on seismometers and hydrophones, obtained by cross-correlation of observed with predicted waveforms. The latter are synthesized from fully numerical Green's functions and carefully estimated, broadband source time functions. More than 200 teleseismic events during the 13-month long deployment yielded usable P-waveform measurements. We present our methods and discuss data yield and quality of ocean-bottom versus land seismometers, and of OBS versus broadband hydrophones. Above and below the microseismic noise band, data yields are higher than within it, especially for OBS. The 48 German OBS, equipped with Guralp 60 s sensors, were afflicted by relatively high self-noise compared to the 9 French instruments equipped with Nanometrics Trillium 240 s sensors. The HighTechInc (model HTI-01 and HTI-04-PCA/ULF) hydrophones (100 s corner period) functioned particularly reliably but their waveforms are relatively more challenging to model due to reverberations in the water column. We obtain ~15000 combined cross
Rossby wave, drift wave and zonal flow turbulence
NASA Astrophysics Data System (ADS)
Quinn, Brenda E.
An extensive qualitative and quantitative study of Rossby wave, drift wave and zonal flow turbulence in the Charney-Hasegawa-Mima model is presented. This includes details of two generation mechanisms of the zonal flows, evidence of the nonlocal nature of this turbulence and of the energy exchange between the small and large scales. The modulational instability study shows that for strong primary waves the most unstable modes are perpendicular to the primary wave, which corresponds to the generation of a zonal flow if the primary wave is purely meridional. For weak waves, the maximum growth occurs for off-zonal modulations that are close to being in three-wave resonance with the primary wave. Nonlinear jet pinching is observed for all nonlinearity levels but the subsequent dynamics differ between strong and weak primary waves. The jets of the former further roll up into Karman-like vortex streets and saturate, while for the latter, the growth of the unstable mode reverses and the system oscillates between a dominant jet and a dominant primary wave. A critical level of nonlinearity is defined which separates the two regimes. Some of these characteristics are captured by truncated models. Numerical proof of the extra invariant in Rossby and drift wave turbulence is presented. While the theoretical derivations of this invariant stem from the wave kinetic equation which assumes weak wave amplitudes, it is shown to be relatively-well conserved for higher nonlinearities also. Together with the energy and enstrophy, these three invariants cascade into anisotropic sectors in the k-space as predicted by the Fjortoft argument. The cascades are characterised by the zonostrophy pushing the energy to the zonal scales. A small scale instability forcing applied to the model has demonstrated the wellknown drift wave - zonal flow feedback loop. The drift wave turbulence is generated from this primary instability. The zonal flows are then excited by either one of the generation
Shape, zonal winds and gravitational field of Jupiter: a fully self-consistent, multi-layered model
NASA Astrophysics Data System (ADS)
Schubert, Gerald; Kong, Dali; Zhang, Keke
2016-10-01
We construct a three-dimensional, finite-element, fully self-consistent, multi-layered,non-spheroidal model of Jupiter consisting of an inner core, a metallic electrically conducting dynamo region and an outer molecular electrically insulating envelope. We assume that the Jovian zonal winds are on cylinders parallel to the rotation axis but, due to the effect of magnetic braking, are confined within the outer molecular envelope. Two related calculations are carried out. The first provides an accurate description of the shape and internal density profile of Jupiter; the effect of rotational distortion is not treated as a small perturbation on a spherically symmetric state. This calculation determines the density, size and shape of the inner core, the irregular shape of the 1-bar pressure level, and the internal structure of Jupiter; the full effect of rotational distortion, without the influence of the zonal winds, is accounted for. Our multi-layered model is able to produce the known mass, the known equatorial and polar radii, and the known zonal gravitational coefficient J2 of Jupiter within their error bars; it also yields the coefficients J4 and J6 within about 5% accuracy, and the core equatorial radius 0.09RJ containing 3.73 Earth masses.The second calculation determines the variation of the gravitational field caused solely by the effect of the zonal winds on the rotationally distorted non-spheroidal Jupiter. Four different cases, ranging from a deep wind profile to a very shallow profile, are considered and implications for accurate interpretation of the zonal gravitational coefficients expected from the Juno mission are discussed.
Agarwal, Aakash; Zakeri, Amanda; Agarwal, Anand K; Jayaswal, Arvind; Goel, Vijay K
2015-08-01
Growth rods are used to limit the progression of scoliosis without restraining the opportunity for the spine to grow. However, major complications like rod breakage, screw loosening, and altered sagittal contour have been encountered. To analyse the effect of the magnitude of distraction forces on the T1-S1 growth, maximum von Mises stresses on the rods, sagittal contours, and load at the pedicle screw-bone interface and quantify the maximum stresses on the rod for a period of 24 months using different frequencies of distraction in a representative scoliotic spine model. A representative finite element model of a juvenile scoliotic spine was used to study the effect of magnitude and frequency of distraction on growth rods. A representative scoliotic model was developed and instrumented using proximal foundation, distal foundation, and rods. Part 1: simulation steps comprised 6 months of growth under various distraction forces to analyze effects of distraction force on the biomechanics of the spine and instrument. Part 2: simulation steps comprised 24 months of growth under various intervals of distraction to analyze effects of distraction interval on the propensity of rod fracture. Part 1: an optimal distraction force exists for which the growth is sustained with minimum stress on the rod, lower loads at screw-bone interface, and unaltered sagittal contours. Part 2: the stresses on the rods were highest for 12-month distraction (2 distractions in 2 years) and lowest for 2-month distraction (12 distractions in 2 years). The data and trend suggest that as the distraction forces vary so do the effects on spinal growth. The results of this study also signify the importance of shorter distraction period in reducing the stresses on the rods. Published by Elsevier Inc.
NASA Astrophysics Data System (ADS)
Youssof, M.; Thybo, H.; Levander, A.; Yuan, X.; Bezada, M. J.
2011-12-01
We present a seismic model of the South-African cratonic region obtained by combining receiver functions and teleseismic P and S traveltime tomography. We determined receiver functions (RFs) for 82 stations by iterative deconvolution. Based on HK analysis (Zhou and Kananmori, JGR,2001), we measure a relatively standard crustal thickness (~38 km) with a flat and sharp Moho discontinuity within the Kaapvaal and Zimbabwe cratons. The lowest Vp/Vs values ~1.69, are found near the locations of diamondiferous kimberlite pipes in the heart of the Kaapvaal craton. We also observe strong crustal anisotropy in the lower crust. Our best-fit RF model has an average fast polarization oriented at 30° to 40° and a crustal fabric that produces, in some cases, around 50% of the total anisotropy inferred from SKS splitting (Paul G. Silver et al., GRL,2001). We also performed finite-frequency tomography in 3 frequency bands (1, 0.5 and 0.25 Hz for P and 0.1, 0.05 and 0.02 Hz for S) to obtain 3-D P- and S-wave perturbation models for the upper mantle. Crustal corrections are based on the RF models. Tests showed that our dataset is able to resolve structure of 3°x3° up to 400 km depth. The high-velocity cratonic roots extend to 300-350 km depth. Lower velocities are detected below the Bushveld complex and the mobile belts. The model also suggests a stratified structure, since we found a low velocity zone (LVZ) at about 170 km depth in the cratonic areas. SdP RFs and surface-wave tomography are in progress and should improve imaging of the LVZ and resolving the unusual structures within the cratonic lithosphere.
NASA Astrophysics Data System (ADS)
Chen, Yunfeng; Gu, Yu Jeffrey; Hung, Shu-Huei
2017-02-01
The lithosphere beneath the Western Canada Sedimentary Basin has potentially undergone Precambrian subduction and collisional orogenesis, resulting in a complex network of crustal domains. To improve the understanding of its evolutionary history, we combine data from the USArray and three regional networks to invert for P-wave velocities of the upper mantle using finite-frequency tomography. Our model reveals distinct, vertically continuous high (> 1%) velocity perturbations at depths above 200 km beneath the Precambrian Buffalo Head Terrane, Hearne craton and Medicine Hat Block, which sharply contrasts with those beneath the Canadian Rockies (<- 1%) at comparable depths. The P velocity increases from - 0.5% above 70 km depth to 1.5% at 330 km depth beneath southern Alberta, which provides compelling evidence for a deep, structurally complex Hearne craton. In comparison, the lithosphere is substantially thinner beneath the adjacent Buffalo Head Terrane (160 km) and Medicine Hat Block (200 km). These findings are consistent with earlier theories of tectonic assembly in this region, which featured distinct Archean and Proterozoic plate convergences between the Hearne craton and its neighboring domains. The highly variable, bimodally distributed craton thicknesses may also reflect different lithospheric destruction processes beneath the western margin of Laurentia.
Rate zonal sedimentation of proteins in one hour or less.
Basi, N S; Rebois, R V
1997-08-15
Rate zonal sedimentation gives information about the shape and size of proteins, and is useful for investigating protein-protein interactions. However, rate zonal sedimentation experiments typically last approximately 1 day. In contrast, this report describes a rate zonal sedimentation method requiring 1 h or less. This was accomplished by centrifuging small density gradients (200 microliters) prepared with sucrose or OptiPrep in a fixed-angle rotor at high relative centrifugal force. By using small gradient volumes, the sample dilution that occurs with larger gradients and with many chromatographic techniques was also avoided. For a variety of proteins, plots of S20,w versus distance sedimented during centrifugation in a TLA 120.2 rotor were linear. As a practical application, sedimentation of the heterotrimeric stimulatory G protein and its dissociated alpha-subunit were determined. The results were similar to those obtained with 17- to 22-h centrifugations in an SW 50.1 rotor and agreed with previously published values. Long periods of centrifugation might preclude the study of some unstable proteins or the investigation of protein-protein interactions whose affinities are to low to survive the lengthy centrifugations required to carry out traditional rate zonal sedimentation experiments. A rate zonal sedimentation technique that rivals many chromatographic methods in celerity will help to circumvent these problems.
Numerical Simulation on Zonal Disintegration in Deep Surrounding Rock Mass
Chen, Xuguang; Wang, Yuan; Mei, Yu; Zhang, Xin
2014-01-01
Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration phenomenon was confirmed and its mechanism is revealed. It is found to be the result of circular fracture which develops within surrounding rock mass under the high geostress. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The numerical results were in accordance with the model test findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic-plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks. PMID:24592166
Numerical simulation on zonal disintegration in deep surrounding rock mass.
Chen, Xuguang; Wang, Yuan; Mei, Yu; Zhang, Xin
2014-01-01
Zonal disintegration have been discovered in many underground tunnels with the increasing of embedded depth. The formation mechanism of such phenomenon is difficult to explain under the framework of traditional rock mechanics, and the fractured shape and forming conditions are unclear. The numerical simulation was carried out to research the generating condition and forming process of zonal disintegration. Via comparing the results with the geomechanical model test, the zonal disintegration phenomenon was confirmed and its mechanism is revealed. It is found to be the result of circular fracture which develops within surrounding rock mass under the high geostress. The fractured shape of zonal disintegration was determined, and the radii of the fractured zones were found to fulfill the relationship of geometric progression. The numerical results were in accordance with the model test findings. The mechanism of the zonal disintegration was revealed by theoretical analysis based on fracture mechanics. The fractured zones are reportedly circular and concentric to the cavern. Each fracture zone ruptured at the elastic-plastic boundary of the surrounding rocks and then coalesced into the circular form. The geometric progression ratio was found to be related to the mechanical parameters and the ground stress of the surrounding rocks.
Parallel numerical simulations of axisymmetric projectile flows using zonal-overlapped grids
NASA Astrophysics Data System (ADS)
Patel, Nisheeth R.; Sturek, Walter B.
1990-05-01
Recent developments in vector and parallel computer architectures provide the potential for achieving greatly enhanced computational speed in the execution of fluid dynamic flow solvers. In order to explore techniques for efficient use of these computer architectural features and to develop an improved capability for modeling highly irregular projectile geometries, the development of a zonal Navier-Stokes computational code was undertaken. This report documents the initial development and validation of this code. The code employs a multi-zone overlapped grid technique and uses MacCormack's explicit finite-differences numerical algorithm. Parallel execution features are incorporated within the code that permit implementation on both distributed and shared memory multiprocessors. The code has been applied to several challenging test problems, in particular, the application to a ramjet configuration with a highly complex internal flow which is discussed in detail. The computational results are compared with experimental measurements. The code has been found to provide for efficient utilization of vector/parallel computer architectures. Also, the zonal flow field topology has proven to be well suited for configurations with irregular geometries.
Type B cyclogenesis in a zonally varying flow
NASA Technical Reports Server (NTRS)
Whitaker, Jeffrey S.; Barcilon, Albert
1992-01-01
An earlier formulated hypothesis that surface cyclogenesis in the Northern-Hemisphere storm-track regions can be described by the structural modification of baroclinic wave packets traversing a zonally varying flow field was tested using a linear quasi-geostrophic model with a zonally varying basic state and a zonally varying Ekman layer eddy viscosity. The results of eigenvalue calculations and initial value integrations confirm the proposed mechanism for Type B cyclogenesis. It is shown that a disturbance initiated upstream of the midchannel baroclinic zone rapidly evolves into a wave packet with the maximum amplitude near the tropopause; the wave packet undergoes a structural modification upon entering the low-level baroclinic zone, developing maximum amplitude at the surface. The proposed model of Type B cyclogenesis is consistent with numerous case studies.
Impact of zonal flows on edge pedestal collapse
NASA Astrophysics Data System (ADS)
Jhang, Hogun; Kaang, Helen H.; Kim, S. S.; Rhee, T.; Singh, R.; Hahm, T. S.
2017-02-01
We perform a computational study of the role of zonal flows in edge pedestal collapse on the basis of a nonlinear three-field reduced magnetohydrodynamic (MHD) model. A dramatic change of dynamics takes place when ideal ballooning modes are completely stabilized. Analyses show that a new instability is developed due to a strong excitation of zonal vorticity, resulting in a series of secondary crashes. The presence of subsidiary bursts after a main crash increases the effective crash time and energy loss. These simulation results resemble the behavior of compound edge localized modes (ELMs). Analyses in this paper indicate that a complete understanding of ELM crash dynamics requires the self-consistent inclusion of nonlinear zonal flows-MHD interaction and transport physics.
Jovian winds from Voyager 2. I - Zonal mean circulation
NASA Technical Reports Server (NTRS)
Limaye, S. S.; Revercomb, H. E.; Sromovsky, L. A.; Krauss, R. J.; Santek, D. A.; Suomi, V. E.; Collins, S. A.; Avis, C. C.
1982-01-01
Independent measurements of Jovian cloud motions confirm previously published results on the general structure of Jupiter's zonal mean circulation. The new results are based on Voyager 2 images and measurement techniques which are different from those used in previous studies. The latitudes of the zonal jets agree with previous results, but there are some differences in the measured speed of the jets which exceed uncertainty estimates. These differences may be due to differences in sampling strategies. The structure of the zonal mean meridional velocity profile has still not been clearly resolved: mean meridional velocities generally differ from zero by no more than their estimated uncertainty. An analysis of successive measurements of the same cloud targets shows that most of the variance of individual velocity measurements is due to true variability of the winds.
NASA Astrophysics Data System (ADS)
Kharshiladze, O. A.; Chargazia, Kh.
2017-03-01
A theoretical-numerical description of zonal flow generation in the turbulent ionosphere by controlled inhomogeneous background wind is given. The generalized Charney-Obukhov equation, which describes the nonlinear interaction of five different-scale modes (primary modes, relatively short-wave ultra-low frequency (ULF) magnetized Rossby waves (MRWs) (pumping waves), two satellites of these MRWs, long-wave zonal mode, and large-scale background shear flows (inhomogeneous wind)) is used. New features of energy transfer from relatively small-scale waves and the background shear flow into that of largescale zonal flows and nonlinear self-organization of the five-wave collective activity in the ionospheric medium are identified based on the numerical solution of the corresponding system of equations for perturbation amplitudes (generalized eigenvalue problems). It is shown that if there is the background shear flow with a moderate amplitude growth the modulation instability increment and intensifies the zonal flow generation, while a very strong shear flow significantly reduces the modulation instability increment and can even suppress the generation process.
A dynamo driven by zonal winds at the upper surface
NASA Astrophysics Data System (ADS)
Guervilly, C.; Cardin, P.
2009-12-01
In a first approximation, Jupiter is made of two fluid layers: a deep metallic hydrogen layer where the jovian dynamo is generated and a superficial “atmospheric” non metallic envelope of approximately 10,000 km depth (10-20% of the total radius of the planet). Recent numerical simulations of three-dimensional rotating convection in a relatively thin spherical shell modelling the atmospheric layer of Jupiter reproduce zonal winds similar to the bands visible on Jupiter’s surface [1]. The simulated flow displays a quasi two-dimensional structure aligned with axis of rotation. Thus [1] suggests that the zonal winds may be “deep rooted” within Jupiter’s interior. These zonal winds are believed to be damped within the deep metallic hydrogen layer [2]. The main question that leads to our work is simple: can the external forcing created by the zonal winds at the top of the metallic hydrogen region drive a dynamo? The external zonal winds generate geostrophic shear layers inside which may lead to non-axisymmetric hydrodynamic instabilities. Such instabilities are known to excite dynamo action [3], [4] and the jovian dynamo will be discussed following these ideas. [1] Heimpel, M.H., Aurnou, J.M., Wicht, J., 2005. Simulation of equatorial and high-latitude jets on Jupiter in a deep convection model. Nature 438, 193-196. [2] Kirk, R.L., Stevenson, D.J., 1987. Hydromagnetic constraints on deep zonal flow in the giant planets. Astrophys. J. 316, 816-846 [3] Guervilly C. and Cardin P., 2009. Numerical simulations of dynamos generated in spherical Couette flows, submitted to Geophys. Astrophys. Fluid Dyn. [4] Schaeffer, N. and Cardin, P., 2006. Quasi-geostrophic kinematic dynamos at low magnetic Prandtl number. Earth Planet. Sci. Lett., 245, 595-604.
Magnetic Field Generation and Zonal Flows in the Gas Giants
NASA Astrophysics Data System (ADS)
Duarte, L.; Wicht, J.; Gastine, T.
2013-12-01
The surface dynamics of Jupiter and Saturn is dominated by a banded system of fierce zonal winds. The depth of these winds remains unclear but they are thought to be confined to the very outer envelopes where hydrogen remains molecular and the electrical conductivity is negligible. The dynamo responsible for the dipole dominated magnetic fields of both Gas Giants, on the other hand, likely operates in the deeper interior where hydrogen assumes a metallic state. We present numerical simulations that attempt to model both the zonal winds and the interior dynamo action in an integrated approach. Using the anelastic version of the MHD code MagIC, we explore the effects of density stratification and radial electrical conductivity variations. The electrical conductivity is assumed to remain constant in the thicker inner metallic region and decays exponentially towards the outer boundary throughout the molecular envelope. Our results show that the combination of stronger density stratification (Δρ≈55) and a weaker conducting outer layer is essential for reconciling dipole dominated dynamo action and a fierce equatorial zonal jet. Previous simulations with homogeneous electrical conductivity show that both are mutually exclusive, with solutions either having strong zonal winds and multipolar magnetic fields or weak zonal winds and dipole dominated magnetic fields. The particular setup explored here allows the equatorial jet to remain confined to the weaker conducting region where is does not interfere with the deeper seated dynamo action. The equatorial jet can afford to remain geostrophic and reaches throughout the whole shell. This is not an option for the additional mid to higher latitude jets, however. In dipole dominated dynamo solutions, appropriate for the Gas Giants, zonal flows remain very faint in the deeper dynamo region but increase in amplitude in the weakly conducting outer layer in some of our simulations. This suggests that the mid to high latitude jets
Zonal modes of Cosmic Microwave Background temperature maps
NASA Astrophysics Data System (ADS)
Short, Jo; Coles, Peter
2010-02-01
All-sky maps of the cosmic microwave background temperature fluctuations are usually represented by a spherical harmonic decomposition, involving modes labelled by their degree l and order m (where -l <= m <= +l). The zonal modes (i.e. those with m = 0) are of particular interest because they vary only with galactic latitude; any anomalous behaviour in them might therefore be an indication of erroneous foreground substraction. We perform a simple statistical analysis of the modes with low l for sky maps derived via different cleaning procedures from the Wilkinson Microwave Anisotropy Probe, and show that the zonal modes provide a useful diagnostic of possible systematics.
Coherent structures in ion temperature gradient turbulence-zonal flow
NASA Astrophysics Data System (ADS)
Singh, Rameswar; Singh, R.; Kaw, P.; Gürcan, Ã.-. D.; Diamond, P. H.
2014-10-01
Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG)-zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of the ITG mode, and the longer scale zonal mode is described by a dynamic equation for the m = n = 0 component of the potential. Two populations of trapped and untrapped drift wave trajectories are shown to exist in a moving frame of reference. This novel effect leads to the formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radially propagating modulation envelope structures such as solitons, shocks, and nonlinear wave trains.
Coherent nonlinear structures in ITG-Zonal flow system
NASA Astrophysics Data System (ADS)
Singh, Rameswar; Singh, Raghvendra; Kaw, Predhiman; Diamond, Patrick H.
2013-10-01
Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG) - Zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of ITG mode and the longer scale zonal mode is described by a dynamical equation for the m = n = 0 component of the potential. In a moving frame, two populations of trappped and untrapped drift wave trajectories are shown to exist. This novel effect leads to formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radialy propagating modulation envelope structures such as solitons, shocks, nonlinear wave trains, etc.
A zonally symmetric model for volcanic influence upon atmospheric circulation
NASA Technical Reports Server (NTRS)
Schatten, K. H.; Mayr, H. G.; Harris, I.; Taylor, H. A., Jr.
1984-01-01
The effects of volcanic activity upon zonal wind flow in a model atmosphere are considered. A low latitude volcanic eruption could lower the tropospheric pole to equator temperature difference and thereby affect the atmospheric motions. When the temperature contrast decreases, the zonal wind velocities at high altitudes are reduced. To conserve angular momentum, the velocities in the lower atmosphere near the surface must increase, thus providing a momentum source for ocean currents. It is suggested that this momentum source may have played a role as a trigger for inducing the 1982-83 anomalous El Nino and possibly other climate changes.
A zonally symmetric model for volcanic influence upon atmospheric circulation
NASA Astrophysics Data System (ADS)
Schatten, K. H.; Mayr, H. G.; Harris, I.; Taylor, H. A., Jr.
1984-04-01
The effects of volcanic activity upon zonal wind flow in a model atmosphere are considered. A low latitude volcanic eruption could lower the tropospheric pole to equator temperature difference and thereby affect the atmospheric motions. When the temperature contrast decreases, the zonal wind velocities at high altitudes are reduced. To conserve angular momentum, the velocities in the lower atmosphere near the surface must increase, thus providing a momentum source for ocean currents. It is suggested that this momentum source may have played a role as a trigger for inducing the 1982-83 anomalous El Nino and possibly other climate changes.
Observations of zonal flows in electrode biasing experiments on the Joint Texas Experimental tokamak
NASA Astrophysics Data System (ADS)
Shen, H. G.; Lan, T.; Chen, Z. P.; Kong, D. F.; Zhao, H. L.; Wu, J.; Sun, X.; Liu, A. D.; Xie, J. L.; Li, H.; Ding, W. X.; Liu, W. D.; Yu, C. X.; Xu, M.; Sun, Y.; Liu, H.; Wang, Z. J.; Zhuang, G.
2016-04-01
Zonal flows (ZFs) are observed during the electrode biasing (EB) high confinement mode (H-mode) using Langmuir probe arrays on the edge of J-TEXT tokamak. The long-distance correlation characteristics of floating potentials and interactions with turbulence are studied. During positive biasing H-mode, either the geodesic acoustic mode or low frequency ZF increases. Strong suppression of radial transport by ZFs is found in the low frequency region. The components of the radial particle flux without and with EB are compared in the frequency domain. The interaction between ZFs and ambient turbulence is also discussed. The results show that the rate of ZFs' shear is comparable with that of E × B shear, suggesting that ZFs could be the trigger of the biasing H-mode.
Measurement of a zonal wind profile on Titan by Doppler tracking of the Cassini entry probe
NASA Technical Reports Server (NTRS)
Atkinson, D. H.; Pollack, J. B.; Seiff, A.
1990-01-01
A program, called the Cassini mission, intended to study the Saturn system by utilizing a Saturn orbiter and a probe descending to the surface of Titan, is discussed. Winds are expected to cause perturbations to the probe local horizontal velocity, resulting in an anomalous drift in the probe location and a shift in the frequency of the probe telemetry, due to the Doppler effect. By using an iterative algorithm, in which the time variation of the probe telemetry frequency is monitored throughout the descent, and the probe trajectory is updated to reflect the effect of wind on the probe location, a highly accurate relative wind profile can be recovered. By adding a single wind velocity, measured by independent means, an absolute wind profile can be obtained. However, the accuracy of the zonal winds recovery is limited by errors in trajectory, and frequency.
Navier-Stokes simulation of transonic wing flow fields using a zonal grid approach
NASA Technical Reports Server (NTRS)
Chaderjian, Neal M.
1988-01-01
The transonic Navier-Stokes code was used to simulate flow fields about isolated wings for workshop wind-tunnel and free-air cases using the thin-layer Reynolds-averaged Navier-Stokes equations. An implicit finite-difference scheme based on a diagonal version of the Beam-Warming algorithm was used to integrate the governing equations. A zonal grid approach was used to allow efficient grid refinement near the wing surface. The flow field was sensitive to the turbulent transition model, and flow unsteadiness was observed for a wind-tunnel case but not for the corresponding free-air case. The specification of experimental pressure at the wind-tunnel exit plane is the primary reason for the difference of these two numerical solutions.
NASA Astrophysics Data System (ADS)
Portner, D. E.; Biryol, C. B.; Delph, J. R.; Beck, S. L.; Zandt, G.; Özacar, A.; Sandvol, E. A.; Turkelli, N.
2016-12-01
The eastern Mediterranean region is characterized by active subduction of Tethyan lithosphere beneath the Anatolian sub-continent at the Aegean and Cyprean trenches. The subduction system is historically characterized by slab roll-back, detachment, and slab settling in the mantle transition zone. Prior mantle tomography studies reveal segmentation of the subducted Tethyan lithosphere, which is thought to have a strong control on surface volcanism and uplift across Anatolia. However, tomographic resolution, particularly in central Anatolia, has been limited, thus making detailed delineations of the subducted slab segments difficult. To improve resolution, we combine two years of seismic data from the recent Continental Dynamics - Central Anatolia Tectonics (CD-CAT) seismic deployment and Turkey's national seismic network ( 33,000 residuals) to 33,000 travel time residuals from Biryol et al. (2011, GJI) in a new finite-frequency teleseismic P-wave tomographic inversion. Our new images reveal with detail a complicated geometry of fast velocity anomalies associated with subducted Tethyan lithosphere. At shallow depths, slow velocities separate the fast anomalies connected to the Aegean and Cyprean trenches. The fast anomaly connected to the Cyprean trench has an arcuate shape in map view, following the trace of the Central Taurus Mountains. This anomaly is separated from a high-amplitude block to the north that appears to dip sub-vertically throughout the upper mantle (200-660 km depth). Other blocks of fast material that may represent subducted Tethyan lithosphere appear down-dip of the vertical block. Additionally, our images indicate that some of the fast velocity anomalies previously seen to flatten in the mantle transition zone may continue into the lower mantle. Thus, our new images provide a more detailed picture of the fate of the Cyprean slab and suggest that some of the fast anomalies associated with the slab continue into the lower mantle, bringing to
Li, Yuan; Lewis, Gladius
2010-01-01
For patients who are suffering debilitating and persistent pain due to vertebral compression fracture(s) and for whom conservative therapies have not provided relief, balloon kyphoplasty (BKP) is used as a surgical option. There are only a very few literature reports on the use of the finite element analysis (FEA) method to obtain biomechanical parameters of models of spine segments that include BKP augmentation at a given level. In each of these studies, the applied loading used was quasi-static. During normal activities of daily living, the patient's spine would be subject to dynamically-applied loading. Thus, the question of the influence of the characteristics of a dynamically-applied loading cycle on biomechanical parameters of a spine that includes BKP-augmented segment(s) is germane; however, a study of this issue is lacking. We investigated this issue in the present FEA work, with the spine segment model being the L1-L3 motion segment units (MSUs) (a segment that is commonly augmented using BKP) and prophylactic BKP simulated at L2. The dynamic load was the compressive load-versus-time cycle to which the L3-L4 MSU is subjected during gait. Four cases of the cycle were considered, corresponding to slow-, normal-, fast- and very fast-paced gait. The loading cycle was applied to the superior surface of L1 while the inferior surface of L3 was fully constrained. It was found that (1) the global mean von Mises stress during the loading cycle (σVMG), in each tissue in the model increased in going from a slow-paced gait cycle to a very fast-paced gait cycle; and (2) for the slow-paced gait cycle, with increase in frequency of the cycle, f (1 ≤ f ≤ 3 Hz), σVMG in each of these tissues increased. Potential uses of the present findings are identified.
NASA Astrophysics Data System (ADS)
Fukao, Y.; Obayashi, M.
2012-12-01
We constructed a new P-wave tomographic model of the mantle using more than ten millions of travel time data. The finite frequency effect of seismic ray was taken into account by calculating banana-donut kernels at 2 Hz for all the first arrival data and at 0.1 Hz for the broadband differential travel time data. Based on this model, a systematic survey was made for subducted slab images around the circum Pacific including Kurile, Honshu, Izu-Bonin, Mariana, Java, Tonga-Kermadec, southern and northern South America, and Central America. This survey clarified a progressive lateral variation of slab configuration along the arc or through the arc to arc, where a subducted slab is in general in one or two of the following four stages: I. slab stagnant above the 660, II. slab penetrating the 660, III. slab trapped in the uppermost lower mantle (660 to ˜1000 km in depth), and IV. slab descending well into the deep lower mantle. The majority of the slab images are either at stage I or III. We interpret I to IV as the successive stages of slab subduction through the transition region with the 660 at the middle, where I and III are relatively stable or neutral stages and II and IV are relatively unstable, transient stages. In particular, we emphasize III as a distinct stage of slab subduction, through which the slab once softened by the phase transition may progressively recover its hardness. Alternatively, the mantle viscosity may not increase stepwise across the 660 but increase gradually throughout the uppermost lower mantle. Plots of hypocentral distribution on tomographic slab images show that deep shocks at depths greater than ˜620 km are a good measure of slab penetration at stage either II or III.
NASA Astrophysics Data System (ADS)
Chang, Y.; Hung, S.; Kuo, B.; Kuochen, H.
2012-12-01
Taiwan is one of the archetypical places for studying the active orogenic process in the world, where the Luzon arc has obliquely collided into the southwest China continental margin since 5 Ma ago. Because of the lack of convincing evidence for the structure in the lithospheric mantle and at even greater depths, several competing models have been proposed for the Taiwan mountain-building process. With the deployment of ocean-bottom seismometers (OBSs) on the seafloor around Taiwan from the TAIGER (TAiwan Integrated GEodynamic Research) and IES seismic experiments, the aperture of the seismic network is greatly extended to improve the depth resolution of tomographic imaging, which is critical to illuminate the nature of the arc-continent collision and accretion in Taiwan. In this study, we use relative travel-time residuals between a collection of teleseismic body wave arrivals to tomographically image the velocity structure beneath Taiwan. In addition to those from common distant earthquakes observed across an array of stations, we take advantage of dense seismicity in the vicinity of Taiwan and the source and receiver reciprocity to augment the data coverage from clustered earthquakes recorded by global stations. As waveforms are dependent of source mechanisms, we carry out the cluster analysis to group the phase arrivals with similar waveforms into clusters and simultaneously determine relative travel-time anomalies in the same cluster accurately by a cross correlation method. The combination of these two datasets would particularly enhance the resolvability of the tomographic models offshore of eastern Taiwan, where the two subduction systems of opposite polarity are taking place and have primarily shaped the present tectonic framework of Taiwan. On the other hand, our inversion adopts an innovation that invokes wavelet-based, multi-scale parameterization and finite-frequency theory. Not only does this approach make full use of frequency-dependent travel
NASA Technical Reports Server (NTRS)
Lou, Y. Q.
1987-01-01
This paper considers two-dimensional nonlinear MHD waves of large horizontal spatial scales for a thin magnetofluid layer on the surface of a rotating sphere. The 'shallow fluid' hydrodynamic equations are generalized to include the effects of magnetic fields, and it is shown that the resulting MHD equations can be reduced to a single scalar equation for a stream function involving several free functions. For special choices of these free functions, two kinds of finite-amplitude MHD waves are obtained, propagating in the azimuthal direction relative to the uniformly rotating background atmosphere in the presence of a background zonal magnetic field and a steady differential zonal flow. These two kinds of MHD waves are fundamentally due to the joint effects of the uniform rotation of the background atmosphere and background magnetic field; the first is an inertial wave of the Rossby (1939) and Haurwitz (1940) type, modified by the presence of the background zonal magnetic field, while the second is a magnetic Alfven-like wave which is modified by the uniform rotation of the background atmosphere.
Impact of Stratospheric Ozone Zonal Asymmetries on the Tropospheric Circulation
NASA Technical Reports Server (NTRS)
Tweedy, Olga; Waugh, Darryn; Li, Feng; Oman, Luke
2015-01-01
The depletion and recovery of Antarctic ozone plays a major role in changes of Southern Hemisphere (SH) tropospheric climate. Recent studies indicate that the lack of polar ozone asymmetries in chemistry climate models (CCM) leads to a weaker and warmer Antarctic vortex, and smaller trends in the tropospheric mid-latitude jet and the surface pressure. However, the tropospheric response to ozone asymmetries is not well understood. In this study we report on a series of integrations of the Goddard Earth Observing System Chemistry Climate Model (GEOS CCM) to further examine the effect of zonal asymmetries on the state of the stratosphere and troposphere. Integrations with the full, interactive stratospheric chemistry are compared against identical simulations using the same CCM except that (1) the monthly mean zonal mean stratospheric ozone from first simulation is prescribed and (2) ozone is relaxed to the monthly mean zonal mean ozone on a three day time scale. To analyze the tropospheric response to ozone asymmetries, we examine trends and quantify the differences in temperatures, zonal wind and surface pressure among the integrations.
Can zonally symmetric inertial waves drive an oscillating mean flow?
NASA Astrophysics Data System (ADS)
Seelig, Torsten; Harlander, Uwe
2016-04-01
In the presentation [5] zonal mean flow excitation by inertial waves is studied in analogy to mean flow excitation by gravity waves [3] that plays an important role for the quasi-biennial oscillation in the equatorial atmosphere. In geophysical flows that are stratified and rotating, pure gravity and inertial waves correspond to the two limiting cases: gravity waves neglect rotation, inertial waves neglect stratification. The former are more relevant for fluids like the atmosphere, where stratification is dominant, the latter for the deep oceans or planet cores, where rotation dominates. In the present study a hierarchy of simple analytical and numerical models of zonally symmetric inertial wave-mean flow interactions is considered and the results are compared with data from a laboratory experiment [4]. The main findings can be summarised as follows: (i) when the waves are decoupled from the mean flow they just drive a retrograde (eastward) zonal mean flow, independent of the sign of the meridional phase speed; (ii) when coupling is present and the zonal mean flow is assumed to be steady, the waves can drive vertically alternating jets, but still, in contrast to the gravity wave case, the structure is independent of the sign of the meridional phase speed; (iii) when coupling is present and time-dependent zonal mean flows are considered the waves can drive vertically and temporarily oscillating mean flows. The comparison with laboratory data from a rotating annulus experiment shows a qualitative agreement. It appears that the experiment captures the basic elements of the inertial wave mean flow coupling. The results might be relevant to understand how the Equatorial Deep Jets can be maintained against dissipation [1, 2], a process currently discussed controversially. [1] Greatbatch, R., Brandt, P., Claus, M., Didwischus, S., Fu, Y.: On the width of the equatorial deep jets. J. Phys. Oceanogr. 42, 1729-1740 (2012) [2] Muench, J.E., Kunze, E.: Internal wave
The Formation of Non-Zonal Jets over Sloped Topography
NASA Astrophysics Data System (ADS)
Boland, E.; Thompson, A. F.; Shuckburgh, E.; Haynes, P. H.
2012-04-01
We present the results of an investigation into the effect of a spatially uniform slope in bottom topography in a quasi-geostrophic, doubly periodic, two-layer model. A slope in the meridional direction results in the enhancement of the 'beta' effect, producing zonal jets, familiar from many previous studies. The novel aspect of this investigation is that the bottom slope has arbitrary orientation. Jets continue to form but they are non-zonal and tilted relative to layer-wise potential vorticity gradients. We show that these non-zonal jets follow the barotropic potential vorticity gradient, and we find that eddy energies are larger when the barotropic potential vorticity gradient is aligned with the direction of the shear in the system. The tilted jets are also demonstrated to be weaker barriers to transport than their zonal counterparts using an effective diffusivity diagnostic. These results are shown to be independent of the ratio of layer depths and to carry over to more complicated topographies containing slopes. We also interpret these results in the light of linear Rossby wave theory, showing the extent to which the jet orientation can be explained by the alteration of the linear dispersion relation by the presence of sloped topography, and the extent to which a Rhines scale can explain the separation of such jets. This work is of relevance to the many regions of the oceans where strong non-zonal jets are present, and is a significant step towards understanding the influence of topography on the dynamical properties of jets.
Zonal flow generation from trapped electron mode turbulence
NASA Astrophysics Data System (ADS)
Wang, Lu; Hahm, T. S.
2009-11-01
Most existing zonal flow generation theory [1,2] has been developed with a usual assumption of qrρiθ<<1 (qr is the radial wave number of zonal flow, and ρiθ is the ion poloidal gyroradius). However, recent nonlinear gyrokinetic simulations of trapped electron mode (TEM) turbulence exhibit a relatively short radial scale of the zonal flows with qrρiθ˜1 [3,4,5]. This work reports an extension of zonal flow growth calculation to this short wavelength regime via the wave kinetics approach. A generalized expression for the polarization shielding for arbitrary radial wavelength [6] which extends the Rosenbluth-Hinton formula in the long wavelength limit [7] is applied. The electron nonlinearity effects on zonal flow are investigated by using GTC simulation. This work was supported by the China Scholarship Council (LW), U.S. DoE Contract No. DE--AC02--09CH11466 (TSH, LW), the U. S. DOE SciDAC center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas, and the U. S. DOE SciDAC-FSP Center for Plasma Edge Simulation (TSH). [1] P. H. Diamond et al., IAEA-CN-69/TH3/1 (1998). [2] L. Chen, Z. Lin, and R. White, Phys. Plasmas 7, 3129 (2000). [3] Z. Lin et al., IAEA-CN-138/TH/P2-8 (2006). [4] D. Ernst et al., Phys. Plasmas 16, 055906 (2009). [5] Y. Xiao and Z. Lin, ``Turbulent transport of trapped electron modes in collisionless plasmas'', submitted to Phys. Rev. Lett. (2009). [6] Lu Wang and T.S. Hahm, Phys. Plasmas 16, 062309 (2009). [7] M. N. Rosenbluth and F. L. Hinton, Phys. Rev. Lett. 80, 724 (1998).
NASA Astrophysics Data System (ADS)
Rao, R. R.; Horii, T.; Masumoto, Y.; Mizuno, K.
2017-08-01
The observed variability of zonal currents (ZC) at the Equator, 90°E shows a strong seasonal cycle in the near-surface 40-350 m water column with periodic east-west reversals most pronounced at semiannual frequency. Superposed on this, a strong intraseasonal variability of 30-90 day periodicity is also prominently seen in the near-surface layer (40-80 m) almost throughout the year with the only exception of February-March. An eastward flowing equatorial undercurrent (EUC) is present in the depth range of 80-160 m during March-April and October-November. The observed intraseasonal variability in the near-surface layer is primarily determined by the equatorial zonal westerly wind bursts (WWBs) through local frictional coupling between the zonal flow in the surface layer and surface zonal winds and shows large interannual variability. The eastward flowing EUC maintained by the ZPG set up by the east-west slope of the thermocline remotely controlled by the zonal wind (ZW) and zonally propagating wave fields also shows significant interannual variability. This observed variability on interannual time scales appears to be controlled by the corresponding variability in the alongshore winds off the Somalia coast during the preceding boreal winter, the ZW field along the equator, and the associated zonally propagating Kelvin and Rossby waves. The salinity induced vertical stratification observed in the near-surface layer through barrier layer thickness (BLT) effects also shows a significant influence on the ZC field on intraseasonal time scale. Interestingly, among all the 8 years (2001-2008), relatively weaker annual cycle is seen in both ZC in the 40-350 m water column and boreal spring sea surface temperature (SST) only during 2001 and 2008 along the equator caused through propagating wave dynamics.
NASA Astrophysics Data System (ADS)
Rao, R. R.; Horii, T.; Masumoto, Y.; Mizuno, K.
2016-06-01
The observed variability of zonal currents (ZC) at the Equator, 90°E shows a strong seasonal cycle in the near-surface 40-350 m water column with periodic east-west reversals most pronounced at semiannual frequency. Superposed on this, a strong intraseasonal variability of 30-90 day periodicity is also prominently seen in the near-surface layer (40-80 m) almost throughout the year with the only exception of February-March. An eastward flowing equatorial undercurrent (EUC) is present in the depth range of 80-160 m during March-April and October-November. The observed intraseasonal variability in the near-surface layer is primarily determined by the equatorial zonal westerly wind bursts (WWBs) through local frictional coupling between the zonal flow in the surface layer and surface zonal winds and shows large interannual variability. The eastward flowing EUC maintained by the ZPG set up by the east-west slope of the thermocline remotely controlled by the zonal wind (ZW) and zonally propagating wave fields also shows significant interannual variability. This observed variability on interannual time scales appears to be controlled by the corresponding variability in the alongshore winds off the Somalia coast during the preceding boreal winter, the ZW field along the equator, and the associated zonally propagating Kelvin and Rossby waves. The salinity induced vertical stratification observed in the near-surface layer through barrier layer thickness (BLT) effects also shows a significant influence on the ZC field on intraseasonal time scale. Interestingly, among all the 8 years (2001-2008), relatively weaker annual cycle is seen in both ZC in the 40-350 m water column and boreal spring sea surface temperature (SST) only during 2001 and 2008 along the equator caused through propagating wave dynamics.
Modeling the Interaction of Moist Convection with the Zonal Jets of Jupiter
NASA Astrophysics Data System (ADS)
Li, L.; Ingersoll, A. P.
2004-11-01
We use a reduced-gravity quasi-geostrophic model with a parameterization of moist convection that is based on Galileo and Cassini observations of lightning and convective storms (Little et al., 1999; Gierasch et al., 2000; Porco et al., 2003). The features of the jets we want to reproduce in the model include: (1) the curvature of the zonal jet profile, which violates the barotropic stability criterion near many of the westward jets (Ingersoll et al., 1981; Li et al., 2004), (2) the speed of the zonal jets, which is related to their width, given that the jets marginally violate the barotropic stability criterion, and (3) the sign of the eddy momentum flux, which is into the jets and tends to sustain them (Beebe et al., 1979; Ingersoll et al., 1981; Salyk et al., 2004). The features of moist convective storms that are taken from observation include: (1) the tendency of the storms to occur in the cyclonic belts, (2) the rapid divergence of horizontal velocity near the cloud tops, and (3) the lifetime of the storms, which is on average 4-5 days (Li et al., 2004). We find that moist convection leads to zonal jets in the upper layer, but the jets violate the barotropic stability criterion only if the flow in the deep underlying layer is westward. We can reproduce the chevron shape on the sides of the jets if we postulate that the clouds persist longer than the storms that produce them. We can reproduce the number and frequency of moist convection storms by assuming that they carry most of the planet's vertical heat flux (Gierasch et al., 2000). The NASA Planetary Atmospheres Program supported this research.
Shen, Ming; Hu, Bingwen; Lafon, Oliver; Trébosc, Julien; Chen, Qun; Amoureux, Jean-Paul
2012-10-01
We demonstrate that inter-residue (13)C-(13)C proximities (of about 380 pm) in uniformly (13)C-labeled proteins can be probed by applying robust first-order recoupling during several milliseconds in single-quantum single-quantum dipolar homo-nuclear correlation (SQ-SQ D-HOMCOR) 2D experiments. We show that the intensity of medium-range homo-nuclear correlations in these experiments is enhanced using broadband first-order finite-pulse radio-frequency-driven recoupling (fp-RFDR) NMR sequence with a nested (XY8)4(1) super-cycling. The robustness and the efficiency of the fp-RFDR-(XY8)4(1) method is demonstrated at high magnetic field (21.1T) and high Magic-Angle Spinning (MAS) speeds (up to 60 kHz). The introduced super-cycling, formed by combining phase inversion and a global four-quantum phase cycle, improves the robustness of fp-RFDR to (i) chemical shift anisotropy (CSA), (ii) spread in isotropic chemical shifts, (iii) rf-inhomogeneity and (iv) hetero-nuclear dipolar couplings for long recoupling times. We show that fp-RFDR-(XY8)4(1) is efficient sans (1)H decoupling, which is beneficial for temperature-sensitive biomolecules. The efficiency and the robustness of fp-RFDR-(XY8)4(1) is investigated by spin dynamics numerical simulations as well as solid-state NMR experiments on [U-(13)C]-L-histidine·HCl, a tetra-peptide (Fmoc-[U-(13)C,(15)N]-Val-[U-(13)C,(15)N]-Ala-[U-(13)C,(15)N]-Phe-Gly-t-Boc) and Al(PO(3))(3).
Xu, G. S.; Wang, H. Q.; Wan, B. N.; Guo, H. Y.; Zhang, W.; Chang, J. F.; Wang, L.; Chen, R.; Liu, S. C.; Ding, S. Y.; Shao, L. M.; Xiong, H.; Naulin, V.; Diamond, P. H.; Tynan, G. R.; Xu, M.; Yan, N.; Zhao, H. L.
2012-12-15
A new turbulence-flow cycle state has been discovered after the formation of a transport barrier in the H-mode plasma edge during a quiescent phase on the EAST superconducting tokamak. Zonal-flow modulation of high-frequency-broadband (0.05-1 MHz) turbulence was observed in the steep-gradient region leading to intermittent transport events across the edge transport barrier. Good confinement (H{sub 98y,2} {approx} 1) has been achieved in this state, even with input heating power near the L-H transition threshold. A novel model based on predator-prey interaction between turbulence and zonal flows reproduced this state well.
NASA Astrophysics Data System (ADS)
Liang, X.; Chen, Y.; Tian, X.; Chen, Y. J.; Ni, J.; Gallegos, A. C.; Klemperer, S. L.; Wang, M.; Xu, T.; Teng, J.
2015-12-01
Combining the new teleseismic body waves recorded by TIBET-31N passive seismic array with waveforms from several previous temporary seismic arrays, we carried out finite-frequency tomographic inversions to image three-dimensional velocity structures beneath southern and central Tibetan Plateau to examine the roles of the upper mantle in the formation of the Tibetan Plateau. Continuous high velocities are observed beneath the Himalayas and Lhasa Terrane with a moderate northward inclining angle. We interpret this high velocity anomaly as the subducting Indian continental lithosphere, which shows a slight east-west variation of northern extent, reaching ~31°N along 85°E and ~30°N along 91°E to 350-km depth. Strong low P- and S-wave velocity anomalies that extend from lower crust to about 200 km depth beneath the Cona rift, Yadong-Gulu rift, Tangra Yum Co rift, suggesting that rifting in southern Tibet is probably a process that involves the entire lithosphere. And these upper mantle low velocities also show east-west variations of depth extent. The one beneath Tangra Yum Co extends shallower to about 180 km, and the ones west of Yadong-Gulu rift and east of Cona rift have extended more than 300 km. The low velocity west of Yadong-Gulu rift extends further north and appears to connect with the massive upper mantle low velocity beneath central Tibet. We propose a three-dimensional dynamic model for Indian continental lithosphere that is consistent with these important observations. The most importrant features of this 3-D dynamic model are: the northward moving Indian continental lithosphere is currently subducting beneath the southern Tibetan Plateau with a moderate angle of 40 degrees, reaching to Bangong-Nujiang Suture at depth of 350 km; the subducting Indian continental lithosphere is fragmented beneath the surface rifts with the largest gap beneath the Yadong-Gulu rift; and the fragmentation induced local upwelling asthenosphere beneath the Yadong-Gulu rift
Anelastic models of the zonal winds in gas giants
NASA Astrophysics Data System (ADS)
Gastine, T.; Wicht, J.
2012-12-01
The banded structures observed at the surfaces of Jupiter and Saturn are associated with eastward and westward zonal flows. In both gas giants, we observe a large amplitude prograde equatorial jet, which is flanked by multiple alternating zonal winds of weaker amplitudes. The depth of these jets is however poorly known and highly debated. Theoretical scenarios encompass "shallow models", that assume that these zonal flows are restricted to the outer weather layer; as well as "deep models" that suppose that the jets penetrate deeper down in the molecular envelope. The latter idea has been supported by 3-D numerical simulations using the so-called "Boussinesq approximation", that assumes the reference state to be constant with radius (e.g. Heimpel et al., 2005). While this approximation is well-adapted to weakly-stratified fluids (e.g. iron cores of Earth-like planets), it becomes more questionable in the gas giants interiors, where the density contrast is huge (ρ bot/ρ top ˜ 104). The "anelastic approximation", already employed in recent models of the gas giants (e.g. Jones & Kuzanyan 2009; Gastine & Wicht 2012), thus provides a more realistic framework to simulate the interior dynamics of such planets. We present here the results of a systematic parameter study where we explore the dependence of convection and zonal flows on density stratification. While the density contrast affects the convective flow amplitude and the typical lengthscale of convection, global quantities and zonal jets properties are found to be fairly independent of the density contrast. Notwithstanding these common properties, compressibility effects also yield interesting differences to Boussinesq approaches. For instance, in the strongly stratified models, the main force balance can significantly vary with depth. While the flow in the deep interior is dominated by rotation, buoyancy can indeed become larger than Coriolis force close to the surface. This "transitional regime" has a visible
Changes in the zonal propagation of El Niño-related SST anomalies: a possible link to the PDO
NASA Astrophysics Data System (ADS)
Antico, Pablo L.; Barros, Vicente R.
2016-03-01
Long-term variability of El Niño (EN) cycle has been the topic of several studies, mainly because of its impacts on climate around the globe. This variability has been mainly described by changes in the intensity and frequency of EN events. In this study, interdecadal changes in the zonal evolution of EN-related sea surface temperature anomalies (SSTA) and their possible link with a well-known mode of Pacific interdecadal variability are analyzed. EN events are classified according to the sense of zonal propagation of SSTA along the equatorial Pacific during the period 1900-2012. As a result, two types of EN are defined: eastward-directed and westward-directed EN. It is found that EN-related SSTA preferably evolves to the east (west) during the warm (cold) phase of the Pacific Decadal Oscillation. Hence, this study offers new insights into the possible causes of long-term EN changes.
Changes in the zonal propagation of El Niño-related SST anomalies: a possible link to the PDO
NASA Astrophysics Data System (ADS)
Antico, Pablo L.; Barros, Vicente R.
2017-07-01
Long-term variability of El Niño (EN) cycle has been the topic of several studies, mainly because of its impacts on climate around the globe. This variability has been mainly described by changes in the intensity and frequency of EN events. In this study, interdecadal changes in the zonal evolution of EN-related sea surface temperature anomalies (SSTA) and their possible link with a well-known mode of Pacific interdecadal variability are analyzed. EN events are classified according to the sense of zonal propagation of SSTA along the equatorial Pacific during the period 1900-2012. As a result, two types of EN are defined: eastward-directed and westward-directed EN. It is found that EN-related SSTA preferably evolves to the east (west) during the warm (cold) phase of the Pacific Decadal Oscillation. Hence, this study offers new insights into the possible causes of long-term EN changes.
NASA Technical Reports Server (NTRS)
Wang, P.-H.; Mccormick, M. P.
1985-01-01
The behavior of the zonal mean aerosol extinction ratio in the lower stratosphere near 75 deg N and its relationship with the zonal mean temperature during the January-February 1979 stratospheric sudden warming have been investigated based on the satellite sensor SAM II (Stratospheric Aerosol Measurement) and auxiliary meteorological measurements. The results indicate that distinct changes in the zonal mean aerosol extinction ratio occurred during this stratospheric sudden warming. It is also found that horizontal eddy transport due to planetary waves may have played a significant role in determining the distribution of the zonal mean aerosol extinction ratio.
NASA Astrophysics Data System (ADS)
Fetzer, Eric J.; Gille, John C.
1996-02-01
Zonal-mean gravity wave variance in the Limb Infrared Monitor of the Stratosphere (LIMS) temperature data is seen to correlate strongly with the residual term in the LIMS zonal-mean momentum budget throughout much of the observed mesosphere. This momentum residual is attributed to gravity wave momentum transport at scales that cannot be directly sampled by the LIMS instrument Correlation is highest in the vicinity of the fall and winter mesospheric jets, where both gravity wave variance and momentum residual reach their largest values. Correlation is also high in the Southern Hemisphere subtropical mesophere, where gravity wave variance and the momentum residual have broad temporal maxima during the easterly acceleration of the stratopause semi-annual oscillation (SAO). This subtropical correlation has important implications for the SAO eastward acceleration, which several studies suggest is forced by gravity wave momentum flux divergence. Correlation between gravity wave variance and inferred gravity wave momentum flux divergence is unexpected because variance is dominated by large scales and long periods (inertio-gravity waves), while both theoretical arguments and ground-based observations indicate that momentum transport is dominated by periods under 1 h. The results of this study suggest a broadband gravity wave field experiencing forcing and loss processes, which are largely independent of frequency.
Global variations of zonal mean ozone during stratospheric warming events
NASA Technical Reports Server (NTRS)
Randel, William J.
1993-01-01
Eight years of Solar Backscatter Ultraviolet (SBUV) ozone data are examined to study zonal mean variations associated with stratospheric planetary wave (warming) events. These fluctuations are found to be nearly global in extent, with relatively large variations in the tropics, and coherent signatures reaching up to 50 deg in the opposite (summer) hemisphere. These ozone variations are a manifestation of the global circulation cells associated with stratospheric warming events; the ozone responds dynamically in the lower stratosphere to transport, and photochemically in the upper stratosphere to the circulation-induced temperature changes. The observed ozone variations in the tropics are of particular interest because transport is dominated by zonal-mean vertical motions (eddy flux divergences and mean meridional transports are negligible), and hence, substantial simplifications to the governing equations occur. The response of the atmosphere to these impulsive circulation changes provides a situation for robust estimates of the ozone-temperature sensitivity in the upper stratosphere.
Coherent structures in ion temperature gradient turbulence-zonal flow
Singh, Rameswar; Singh, R.; Kaw, P.; Gürcan, Ö. D.; Diamond, P. H.
2014-10-15
Nonlinear stationary structure formation in the coupled ion temperature gradient (ITG)-zonal flow system is investigated. The ITG turbulence is described by a wave-kinetic equation for the action density of the ITG mode, and the longer scale zonal mode is described by a dynamic equation for the m = n = 0 component of the potential. Two populations of trapped and untrapped drift wave trajectories are shown to exist in a moving frame of reference. This novel effect leads to the formation of nonlinear stationary structures. It is shown that the ITG turbulence can self-consistently sustain coherent, radially propagating modulation envelope structures such as solitons, shocks, and nonlinear wave trains.
Global variations of zonal mean ozone during stratospheric warming events
Randel, W.J. )
1993-10-01
Eight years of Solar Backscatter Ultraviolet ozone data are examined to study zonal mean ozone variations associated with stratospheric planetary wave (warming) events. These fluctuations are found to be nearly global in extent, with relatively large variations in the tropics, and coherent signatures reaching up to 50[degrees] in the opposite (summer) hemisphere. These ozone variations are a manifestation of the global circulation cells associated with stratospheric warming events; the ozone responds dynamically in the lower stratosphere to transport, and photochemically in the upper stratosphere to the circulation-induced temperature changes. The observed ozone variations in the tropics are of particular interest because transport is dominated by zonal-mean vertical motions (eddy flux divergences and mean meridional transports are negligible), and hence, substantial simplifications to the governing equations occur. The response of the atmosphere to these impulsive circulation changes provides a situation for robust estimates of ozone-temperature sensitivity in the upper stratosphere. 39 refs., 16 rigs.
Global variations of zonal mean ozone during stratospheric warming events
NASA Technical Reports Server (NTRS)
Randel, William J.
1993-01-01
Eight years of Solar Backscatter Ultraviolet (SBUV) ozone data are examined to study zonal mean variations associated with stratospheric planetary wave (warming) events. These fluctuations are found to be nearly global in extent, with relatively large variations in the tropics, and coherent signatures reaching up to 50 deg in the opposite (summer) hemisphere. These ozone variations are a manifestation of the global circulation cells associated with stratospheric warming events; the ozone responds dynamically in the lower stratosphere to transport, and photochemically in the upper stratosphere to the circulation-induced temperature changes. The observed ozone variations in the tropics are of particular interest because transport is dominated by zonal-mean vertical motions (eddy flux divergences and mean meridional transports are negligible), and hence, substantial simplifications to the governing equations occur. The response of the atmosphere to these impulsive circulation changes provides a situation for robust estimates of the ozone-temperature sensitivity in the upper stratosphere.
Role of Zonal Flow in Turbulent Transport Scaling
Z. Lin; T.S. Hahm; J.A. Krommes; W.W. Lee; J. Lewandowski; H. Mynick; H. Qin; G. Rewoldt; W.M. Tang; R. White
2000-11-15
Transport scalings with respect to collisionality (n*) and device size (r*) are obtained from massively parallel gyrokinetic particle simulations of toroidal ion-temperature-gradient (ITG) turbulence in the presence of zonal flows. Simulation results show that ion thermal transport from electrostatic ITG turbulence depends on ion-ion collisions due to the neo-classical damping of self-generated EXB zonal flows that regulate the turbulence. Fluctuations and heat transport levels exhibit bursting behavior with a period corresponding to the collisional damping time of poloidal flows. Results from large-scale full torus simulations with device-size scans for realistic parameters show that Bohm-like transport can be driven by microscopic scale fluctuations in the ITG turbulence with isotropic spectra. These simulation results resolve some apparent physics contradictions between experimental observations and turbulent transport theories.
Statistical properties of Charney-Hasegawa-Mima zonal flows
Anderson, Johan; Botha, G. J. J.
2015-05-15
A theoretical interpretation of numerically generated probability density functions (PDFs) of intermittent plasma transport events in unforced zonal flows is provided within the Charney-Hasegawa-Mima (CHM) model. The governing equation is solved numerically with various prescribed density gradients that are designed to produce different configurations of parallel and anti-parallel streams. Long-lasting vortices form whose flow is governed by the zonal streams. It is found that the numerically generated PDFs can be matched with analytical predictions of PDFs based on the instanton method by removing the autocorrelations from the time series. In many instances, the statistics generated by the CHM dynamics relaxes to Gaussian distributions for both the electrostatic and vorticity perturbations, whereas in areas with strong nonlinear interactions it is found that the PDFs are exponentially distributed.
Statistical properties of Charney-Hasegawa-Mima zonal flows
NASA Astrophysics Data System (ADS)
Anderson, Johan; Botha, G. J. J.
2015-05-01
A theoretical interpretation of numerically generated probability density functions (PDFs) of intermittent plasma transport events in unforced zonal flows is provided within the Charney-Hasegawa-Mima (CHM) model. The governing equation is solved numerically with various prescribed density gradients that are designed to produce different configurations of parallel and anti-parallel streams. Long-lasting vortices form whose flow is governed by the zonal streams. It is found that the numerically generated PDFs can be matched with analytical predictions of PDFs based on the instanton method by removing the autocorrelations from the time series. In many instances, the statistics generated by the CHM dynamics relaxes to Gaussian distributions for both the electrostatic and vorticity perturbations, whereas in areas with strong nonlinear interactions it is found that the PDFs are exponentially distributed.
Zonal isolation and evaluation for cemented horizontal liners
Gai, H; Summers, T.D.; Cocking, D.A.; Greaves, C.
1996-12-01
This paper discusses the novel application of technology in the cementing and bond evaluation from the world-record breaking extended-reach drilling (ERD) wells in Wytch Farm, where horizontal liners of the order of 800 to 1,300 m at TVD of approximately 1,600 m have been successfully cemented and perforated. Detailed analysis of the conditions by a multidisciplinary team provided some practical procedures that enabled the authors to achieve their objectives of zonal isolation and cement bond evaluation successfully. Important aspects of zonal isolation, such as the use of spiral-blade centralizers, rotating the liner, and trials of the external casing packer (ECP), are discussed in detail. Cement bond evaluation is also detailed, involving coiled tubing (CT) deployment and various bond-logging tools, including ultrasonic tools. The cement bond log (CBL) was found to be surprisingly reliable if used correctly.
Cloud Radiative Feedback and Zonal Surface Temperature Gradient
NASA Astrophysics Data System (ADS)
Liu, Y.; Yang, J.; Peltier, W. R.; Hu, Y.
2013-12-01
Two fully coupled atmosphere--ocean general circulation models, CCSM3 and CCSM4 are employed to investigate the response of the mean climate state of the tropics to a sequence of CO2 concentrations (pCO2) from 17.5 to 4576 ppmv. Analyses based upon both of thes models demonstrate that the zonal surface temperature gradient across the equatorial Pacific is a monotonic function of pCO2, decreasing as pCO2 is increased. It is found that increased pCO2 enhances both the strength of convection and the area of the western and central Pacific over which it occurs thereby leading to increased cloudiness, an increase in shortwave reflection, and therefore a diminution of surface temperature in the region. The opposite tendencies are realized in response to deacreasing pCO2. This study demonstrates that cloud radiative feedback promotes a weakening (strengthening) of the zonal surface temperature gradient as greenhouse gas concentrations increase (decrease), which has important implications for future climate change and also for the understanding of past warm and cold climates. Long-term mean sea surface temperature and and zonal SST gradient along the equatorial Pacific in CCSM3 (a and c) and CCSM4 (b and d). The CO2 level in CCSM3 is between 35 and 4576 ppmv while in CCSM4 it is between 17.5 and 2288 ppmv. The zonal SST gradient is defined by the maximum minus the minimum (red dots), or the area-averaged value of 145E--165E minus that of 120W--100W (blue squares).
Interaction of Moist Convection With Jupiter's Zonal Jets
NASA Astrophysics Data System (ADS)
Li, L.; Ingersoll, A. P.; Huang, X.
2004-12-01
Since Voyager times, observations have suggested that Jupiter's zonal jets violate the barotropic stability criterion (BSTC) (Ingersoll et al., 1981; Limaye, 1986; Li et al., in press). Recently, images from the Cassini Imaging Science System (ISS) (Porco et al., 2003; Li et al., in press) and from the Galileo imaging system (Little et al., 1999; Gierasch et al., 2000) have revealed important features of moist convection on Jupiter and suggest that moist convection may be driving the zonal jets. Here we investigate the interaction of moist convection with the zonal jets in a reduced-gravity quasi-geostrophic model using a moist convection parameterization that is based on the new observations. Our study shows that moist convection can excite multiple jets when the velocity of the flow in the deep underlying layer is zero, but these jets never violate the BSTC. However, based on a model of the interaction between the magnetic field and the zonal flow, Liu and Stevenson (2003, DPS 35th meeting) predict that there are easterly flows in the deep underlying layer at middle latitudes. With easterly flows in the deep underlying layer we can get stable multiple jets that violate the BSTC. Furthermore, the modeled jets have almost same width and amplitude as the observed jets. An easterly flow in the lower layer provides a simple explanation for why the upper layer jets are stable even though they violate the BSTC. The model reproduces the tilted, chevron-shaped cloud features provided we assume that the clouds persist longer than the moist convective storms that produce them.
First zonal harmonic component of cosmic ray neutron intensity
NASA Technical Reports Server (NTRS)
Takahashi, H.; Yahagi, N.; Chiba, T.
1985-01-01
Cosmic ray neutron data from the cosmic ray stations from the worldwide network in 1966, 1967 and 1969 are analyzed by means of the three dimensional analysis method by Nagashima. The variations of the north-south anisotropy, which is the first zonal harmonic component obtained from the analysis are studied. The result obtained confirms earlier findings. Relationship of the anisotropy to the interplanetary magnetic field sector polarity is also studied.
Dynamic Stall Computations Using a Zonal Navier-Stokes Model
1988-06-01
COMPUTATIONS USING A ZONAL NAVIER-STOKES MODEL OfOSONA, AUTWOR(S) Conrovd, Jack H. r. __ _ I, ,3 , iOR co T’M( COVERED DATE Of REPORT (Yea, Month Oy) IS PAGE...48 computer and is used to calculate the flow field about a NACA 0012 airfoil oscillating in pitch. Surface pressure distributions and integrated...lift, pitching moment, and drag coefficient versus angle of attack are compared to existing experimental data for four cases and existing computational
The residual zonal flows in anisotropic tokamak plasmas
Ren, Haijun
2016-06-15
The gyro-kinetic equation is analytically solved based on the anisotropic two-temperature distribution, in which the ions' parallel temperature is a flux function while the perpendicular temperature depends on the poloidal angle. The residual level of collisionless zonal flows (ZFs) is derived and calculated in the large aspect circular limit. Our result shows that the anisotropy plays a remarkable role in determining the residual value of ZFs. Even weak anisotropy can significantly change the residual level.
Analysis of Venusian Zonal Winds Using Venus Express Data
NASA Astrophysics Data System (ADS)
McCabe, Ryan M.; Sayanagi, Kunio M.; Blalock, John J.; Peralta, Javier; Gray, Candace L.; McGouldrick, Kevin; Imamura, Takeshi
2016-10-01
We measure the zonal mean wind structure of Venus between 2006 and 2013 in the ultraviolet images captured by the Venus Monitoring Camera (VMC) onboard the ESA Venus Express spacecraft. Our wind measurements employ the digital two-dimensional Correlation Imaging Velocimetry method to track cloud motions. Our current focus is on understanding the short- and long-term dynamics of Venus's atmospheric superrotation, in which the equatorial atmosphere rotates with a period of approximately 4-5 days (~60 times faster than the solid planet). The Venusian atmospheric superrotation's forcing and maintenance mechanisms remain to be explained. A number of studies have been published on the cloud-tracking wind measurements on Venus, however, those different measurements have not reached a consensus on the temporal evolution of the zonal wind structure (e.g., Kouyama et al 2013, Khatuntsev et al 2013, Patsaeva et al. 2015). Temporal evolution of the zonal wind could reveal the transport of energy and momentum and eventually shed a light on mechanisms that maintain the superrotation. Our first goal is to characterize the temporal dynamics of Venus's zonal wind profile and two-dimensional wind field, in which we will search for equatorial waves (in particular the so-called "Y-feature") that may force the Venusian atmospheric superrotation.Kouyama, T. et al (2013), J. Geophys. Res. Planets, 118, 37-46, doi:10.1029/2011JE004013.Khatuntsev et al. (2013), Icarus, 226, 140-158, doi:10.1016/j.icarus.2013.05.018.Patsaeva,M.V.,et al. (2015), Planetary and Space Science, 113, 100-108, doi:10.1016/j.pss.2015.01.013.
Nonstationary Gravity Wave Forcing of the Stratospheric Zonal Mean Wind
NASA Technical Reports Server (NTRS)
Alexander, M. J.; Rosenlof, K. H.
1996-01-01
The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non-zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity-wave-driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.
Longitudinal variation in zonal winds at subauroral regions: Possible mechanisms
NASA Astrophysics Data System (ADS)
Wang, Hui; Luehr, Hermann; Zheng, Zhichao
2017-04-01
Longitudinal differences in thermospheric zonal winds (Uy) were investigated in the subauroral region for different seasons and under solar maximum and medium conditions by using CHAMP observations. Prominent wave-1 longitudinal and diurnal variations of Uy were observed, along with an anti-phase relationship between the Northern and Southern Hemispheres. These structures persisted over the whole year and were independent of solar activity. Uy values were greater at nighttime than at daytime, and values in the south were greater than those in the north in local summer and winter. Model simulations confirmed the observed results in large-scale structures, and the nonzero dipole tilt was vital for the longitudinal variation of the zonal winds. The neutral air pressure gradient caused by the day-night difference in solar heating was a major contributor to the observed Uy. The pressure effects were larger at nighttime than at daytime and were larger in the Southern Hemisphere than in the Northern Hemisphere. Ion drag reduced the compatibility between the modeled and observed Uy as expected, with larger effects at nighttime than at daytime. Viscous force reduced the compatibility between the modeled and observed Uy with greater effects at daytime, except at nighttime in the Southern Hemisphere. Coriolis force reduced the compatibility between the modeled and observed Uy. The sum of these factors can explain the observed local time and the hemispheric asymmetries in the longitudinal variations of the zonal wind.
Zonal organization of the mammalian main and accessory olfactory systems.
Mori, K; von Campenhause, H; Yoshihara, Y
2000-01-01
Zonal organization is one of the characteristic features observed in both main and accessory olfactory systems. In the main olfactory system, most of the odorant receptors are classified into four groups according to their zonal expression patterns in the olfactory epithelium. Each group of odorant receptors is expressed by sensory neurons distributed within one of four circumscribed zones. Olfactory sensory neurons in a given zone of the epithelium project their axons to the glomeruli in a corresponding zone of the main olfactory bulb. Glomeruli in the same zone tend to represent similar odorant receptors having similar tuning specificity to odorants. Vomeronasal receptors (or pheromone receptors) are classified into two groups in the accessory olfactory system. Each group of receptors is expressed by vomeronasal sensory neurons in either the apical or basal zone of the vomeronasal epithelium. Sensory neurons in the apical zone project their axons to the rostral zone of the accessory olfactory bulb and form synaptic connections with mitral tufted cells belonging to the rostral zone. Signals originated from basal zone sensory neurons are sent to mitral tufted cells in the caudal zone of the accessory olfactory bulb. We discuss functional implications of the zonal organization in both main and accessory olfactory systems. PMID:11205342
What maintains the zonal circulation in planetary atmospheres
Mayr, H.G.; Chan, K.L.; Harris, I.; Schatten, K. )
1991-01-01
The latest Voyager observations have shown large zonal velocities in Neptune's atmosphere, with some indication of alternating jets. Similar wind velocities have also been observed on Venus and are characteristic of planetary atmospheres in general, which is remarkable considering that the available solar or internal heating varies by more than a factor of 1000. A simplified model of the planetary circulation which provides some qualitative understanding is discussed. The basic assumption is that the source driving the circulation is also generating the dissipating eddies which are simulated by diffusion. Thus, the magnitude and structure of the zonal circulation are independent both of the source and the dissipation rate. The zonal velocities are related to the speed of sound and are of comparable magnitude in different atmospheres; although the available heating varies by a large factor, and the planetary parameters vary over a wide range. The alternating jets are described by a convective eigenmode which develops when energy transport out of the planetary interior is important, as is the case on Jupiter, Neptune, and Saturn. 26 refs.
What maintains the zonal circulation in planetary atmospheres?
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Chan, K. L.; Harris, I.; Schatten, K.
1991-01-01
The latest Voyager observations have shown large zonal velocities in Neptune's atmosphere, with some indication of alternating jets. Similar wind velocities have also been observed on Venus and are characteristic of planetary atmospheres in general, which is remarkable considering that the available solar or internal heating varies by more than a factor of 1000. A simplified model of the planetary circulation which provides some qualitative understanding is discussed. The basic assumption is that the source driving the circulation is also generating the dissipating eddies which are simulated by diffusion. Thus, the magnitude and structure of the zonal circulation are independent both of the source and the dissipation rate. The zonal velocities are related to the speed of sound and are of comparable magnitude in different atmospheres; although the available heating varies by a large factor, and the planetary parameters vary over a wide range. The alternating jets are described by a convective eigenmode which develops when energy transport out of the planetary interior is important, as is the case on Jupiter, Neptune, and Saturn.
Cerebellar Zonal Patterning Relies on Purkinje Cell Neurotransmission
White, Joshua J.; Arancillo, Marife; Stay, Trace L.; George-Jones, Nicholas A.; Levy, Sabrina L.; Heck, Detlef H.
2014-01-01
Cerebellar circuits are patterned into an array of topographic parasagittal domains called zones. The proper connectivity of zones is critical for motor coordination and motor learning, and in several neurological diseases cerebellar circuits degenerate in zonal patterns. Despite recent advances in understanding zone function, we still have a limited understanding of how zones are formed. Here, we focused our attention on Purkinje cells to gain a better understanding of their specific role in establishing zonal circuits. We used conditional mouse genetics to test the hypothesis that Purkinje cell neurotransmission is essential for refining prefunctional developmental zones into sharp functional zones. Our results show that inhibitory synaptic transmission in Purkinje cells is necessary for the precise patterning of Purkinje cell zones and the topographic targeting of mossy fiber afferents. As expected, blocking Purkinje cell neurotransmission caused ataxia. Using in vivo electrophysiology, we demonstrate that loss of Purkinje cell communication altered the firing rate and pattern of their target cerebellar nuclear neurons. Analysis of Purkinje cell complex spike firing revealed that feedback in the cerebellar nuclei to inferior olive to Purkinje cell loop is obstructed. Loss of Purkinje neurotransmission also caused ectopic zonal expression of tyrosine hydroxylase, which is only expressed in adult Purkinje cells when calcium is dysregulated and if excitability is altered. Our results suggest that Purkinje cell inhibitory neurotransmission establishes the functional circuitry of the cerebellum by patterning the molecular zones, fine-tuning afferent circuitry, and shaping neuronal activity. PMID:24920627
Zonal subdivision of marine sequences: achievements and discrepancies
NASA Astrophysics Data System (ADS)
Gladenkov, Yuri
2010-05-01
It was 150 years ago when a notion of zone was introduced into stratigraphy. By the present time zonal units with a duration of 0.3-3.0 M.y. in average have been established virtually for all systems and stages of the Phanerozoic. Their quantity reached 300. It is not a chance that zonal stratigraphy is considered to be one of the most significant achievement of the modern geology. There are different interpretations of essence and goals of zonal stratigraphy, techniques of separation of zones, and evaluation of zones as stratigraphic units. Particularly it is reflected in International Stratigraphic Guide (Murphy, Salvador, 1999), Russian Stratigraphic Code (Zhamoida, 2006), and a number of stratigraphic reports of the last years. It concerns different approaches to: (a) establishment of different types of zones (biostratigraphic zones and chronozones, oppel-zones and biohorizons, etc.); (b) assessment of spatial distribution of zones (global or provincial) and a role of sedimentological factor; (c) definition of zones as stratigraphic units (relationships with geostratigraphic units of the standard and regional scales). The latest publications show that because of the different interpretations of zones, authors should explain usage of certain type of zone (for example, when they use the terms "interval-zone" or "assemblage-zone", what limitations stem from application of datum-levels, and others). It is common opinion, that biostratigraphic zones used widely by paleontologists and stratigraphers cannot be a final goal of stratigraphy although they provide a base for solution of many important problems (definition of certain stratigraphic levels, correlation of different biofacies, and others). At the same time, the most important stratigraphic units are chronozones, which correspond to stages or phases of geological evolutio of basins and are marked by distinct fossil assemblages and other properties (magnetic and other characteristics) in the type sections
Toroidal symmetry of the geodesic acoustic mode zonal flow in a tokamak plasma.
Zhao, K J; Lan, T; Dong, J Q; Yan, L W; Hong, W Y; Yu, C X; Liu, A D; Qian, J; Cheng, J; Yu, D L; Yang, Q W; Ding, X T; Liu, Y; Pan, C H
2006-06-30
The toroidal symmetry of the geodesic acoustic mode (GAM) zonal flows is identified with toroidally distributed three step Langmuir probes at the edge of the HuanLiuqi-2A (commonly referred to as HL-2A) tokamak plasmas for the first time. High coherence of both the GAM and the ambient turbulence for the toroidally displaced measurements along a magnetic field line is observed, in contrast with the high coherence of the GAM but low coherence of the ambient turbulence when the toroidally displaced measurements are not along the same field line. The radial and poloidal features of the flows are also simultaneously determined. The nonlinear three wave coupling between the high frequency turbulent fluctuations and the flows is demonstrated to be a plausible formation mechanism of the flows.
Atmospheric tidal forcing of the zonal-mean circulation - The Martian dusty atmosphere
NASA Technical Reports Server (NTRS)
Zurek, R. W.
1986-01-01
Classical atmospheric tidal theory has been used to compute the bilinear tidal zonal-mean forcing per unit mass of the zonal-mean meridional and zonal winds, together with the tidal zonal-mean heating per unit mass for the dusty Martian atmosphere. The convergences of the tidal Eliassen-Palm (EP) flux have been computed for both clear and dusty atmospheric conditions, including the special case of a 'dusty corridor' in the summer southern subtropics that is meant to simulate the early stages of a planetary-scale Martian dust storm. The calculation of the tidal EP zonal forcing differs from Hamilton in that more realistic thermotidal forcings and basic state temperatures are used. The zonal-mean convergences of the tidal fluxes of heat and momentum are large during a Martian great dust storm and should alter significantly the zonal-mean circulation and its residual component driven by the zonal-mean heating. In particular, the tidal forcing of the meridional wind, which is an order of magnitude greater than its zonal counterpart, is likely to give rise to a complex pattern of significantly ageostrophic zonal-mean flow in the Martian tropics.
Potential Vorticity Dynamics and Models of Zonal Flow Formation
NASA Astrophysics Data System (ADS)
Hsu, Pei-Chun
We describe the general theory of anisotropic flow formation in quasi two- dimensional turbulence from the perspective on the potential vorticity (PV) trans- port in real space. The aim is to calculate the vorticity or PV flux. In Chapter 2, the general structure of PV flux is deduced non-perturbatively using two relaxation models: the first is a mean field theory for the dynamics of minimum enstrophy relaxation based on the requirement that the mean flux of PV dissipates total po- tential enstrophy but conserves total fluid kinetic energy. The analyses show that the structure of PV flux has the form of a sum of a positive definite hyper-viscous and a negative or positive viscous flux of PV. Turbulence spreading is shown to be related to PV mixing via the link of turbulence energy flux to PV flux. In the relaxed state, the ratio of the PV gradient to zonal flow velocity is homogenized. This structure of the relaxed state is consistent with PV staircases. The homog- enized quantity sets a constraint on the amplitudes of PV and zonal flow in the relaxed state. The second relaxation model is derived from a joint reflection symmetry principle, which constrains the PV flux driven by the deviation from the self- organized state. The form of PV flux contains a nonlinear convective term in addition to viscous and hyper-viscous terms. The nonlinear convective term, how- ever, can be viewed as a generalized diffusion, on account of the gradient-dependent ballistic transport in avalanche-like systems. For both cases, the detailed transport coefficients can be calculated using perturbation theory in Chapter 3. For a broad turbulence spectrum, a modula- tional calculation of the PV flux gives both a negative viscosity and a positive hyper-viscosity. For a narrow turbulence spectrum, the result of a parametric in- stability analysis shows that PV transport is also convective. In both relaxation and perturbative analyses, it is shown that turbulent PV transport is sensitive to
Effects of Zonal Wind on Stratospheric Ozone Variations over Nigeria
NASA Astrophysics Data System (ADS)
Chidinma Okoro, Eucharia,
2016-07-01
The effects of zonal wind on stratospheric ozone variation over Nigeria have been studied. The areas covered in this study include; Maiduguri, Ikeja, Port-Harcourt, Calabar, Makurdi, Ilorin, Akure, Yola, Minna, Jos, Kano and Enugu in Nigeria, from 1986 to 2008. Zonal wind was computed from the iso-velocity map employing MATLAB software. The mean monthly variations of AAM and LOD at pressure levels of 20, 30 and 50 mb in the atmosphere depict a trend of maximum amplitude between April and September, and minimum amplitude between December and March. The trend observed in seasonal variation of O3 column data in the low latitude had maximum amount from May through August and minimum values from December through February. The mean monthly maximum O3 concentrations was found to be 284.70 Du (Kano) occurring in May 1989 while, an average monthly minimum O3 concentration was found to be 235.60 Du (Port-Harcourt and Calabar) occurring in January 1998. It has been established in this study that, the variation in atmospheric angular momentum (AAM) caused by variation of the universal time or length of day (LOD) transfer ozone (O3) by means of zonal wind from the upper troposphere to the lower stratosphere in the stations understudy. The strong effect of the pressure levels of the atmosphere on O3 variation could be attributed to its effect on the AAM and LOD. Variation in the LOD is significant in the tropics, suggesting that, the effects of the extra-tropical suction pump (ETSP) action is not the only driver responsible for O3 transportation from the tropics to extra-tropical zones. Consequently, these findings lead to a deduction that weather pattern alteration observed due to these changes could lead to climate change. Keywords: ozone variations; dynamical processes; harmattan wind; ETSP; and climatic variability
Zonal flow generation in inertial confinement fusion implosions
Peterson, J. L.; Humbird, K. D.; Field, J. E.; ...
2017-03-06
A supervised machine learning algorithm trained on a multi-petabyte dataset of inertial confinement fusion simulations has identified a class of implosions that robustly achieve high yield, even in the presence of drive variations and hydrodynamic perturbations. These implosions are purposefully driven with a time-varying asymmetry, such that coherent flow generation during hotspot stagnation forces the capsule to self-organize into an ovoid, a shape that appears to be more resilient to shell perturbations than spherical designs. Here this new class of implosions, whose configurations are reminiscent of zonal flows in magnetic fusion devices, may offer a path to robust inertial fusion.
Wind-driven zonal jets in the South Pacific Ocean
NASA Astrophysics Data System (ADS)
Kessler, William S.; Gourdeau, Lionel
2006-02-01
Zonal jets west of the large islands of the South Pacific Ocean are predicted by theory, commonly seen in ocean models with sufficiently high resolution, and are beginning to be observed. These jets are often taken to reflect the blocking effect of the islands in the South Equatorial Current through ``Island Rule'' dynamics. Here it is shown that quasi-permanent structures of the basin-wide wind field imply the existence of jets formed independently of the islands. Evidence for the existence of the wind-driven jets is found in climatological geostrophic currents. The hydrographic structures that produce the jets occur well below the thermocline.
Zonal flow regimes in rotating anelastic spherical shells (Invited)
NASA Astrophysics Data System (ADS)
Gastine, T.; Wicht, J.; Aurnou, J. M.; Heimpel, M. H.
2013-12-01
The surface zonal winds observed in the giant planets form a complex jet pattern with alternating prograde and retrograde direction. While the main equatorial band is prograde on the gas giants, both ice giants have a pronounced retrograde equatorial jet. The depth of these jets is however poorly known and highly debated. Theoretical scenarios range from "shallow models", that assume that these zonal flows are restricted to the outer stably stratified layer; to "deep models" that hypothesise that the surface winds are the signature of deep-seated convection. Most of the numerical models supporting the latter idea employed the Boussinesq approximation where compressibility effects are ignored. While this approximation is suitable for modelling the liquid iron core of terrestrial planets, this becomes questionable in the gas giants interiors, where density increases by several orders of magnitude. To tackle this problem, several numerical models using the "anelastic approximation" have been recently developed to study the compressibility effects while filtering out the fast acoustic waves. Here, we consider such anelastic models of rapidly-rotating spherical shells to explore the properties of the zonal winds in different regimes where either rotation or buoyancy dominates the force balance. We conduct several parameter studies to quantify the dependence of zonal flows on the background density stratification and the driving of convection. We find that the direction of the equatorial wind is controlled by the ratio of buoyancy and Coriolis force. The prograde equatorial band maintained by Reynolds stresses is found in the rotation-dominated regime. At low Ekman numbers, several alternating jets form at high latitude in a similar way to some previous Boussinesq calculations. In cases where buoyancy dominates Coriolis force, the angular momentum per unit mass is homogenised and the equatorial band is retrograde, reminiscent to those observed in the ice giants
Zonal drifts of irregularities imparted by meridional winds.
NASA Technical Reports Server (NTRS)
Waldman, H.; Da Rosa, A. V.
1973-01-01
In a uniform ionosphere, meridional winds cause only meridional motions of irregularities. It is shown, however, that, if F-region irregularities are considered in a real ionosphere in which there is a highly conductive E-layer, zonal motions occur. During the day a substantial westward drift takes place, while at night the drift is eastward but smaller, owing to the much smaller E-layer conductivity. Thus, the effect of meridional winds is to impart a net westward drift to small irregularities in the ionization, provided such irregularities persist long enough.
A simple inertial model for Neptune's zonal circulation
NASA Technical Reports Server (NTRS)
Allison, Michael; Lumetta, James T.
1990-01-01
Voyager imaging observations of zonal cloud-tracked winds on Neptune revealed a strongly subrotational equatorial jet with a speed approaching 500 m/s and generally decreasing retrograde motion toward the poles. The wind data are interpreted with a speculative but revealingly simple model based on steady gradient flow balance and an assumed global homogenization of potential vorticity for shallow layer motion. The prescribed model flow profile relates the equatorial velocity to the mid-latitude shear, in reasonable agreement with the available data, and implies a global horizontal deformation scale L(D) of about 3000 km.
Response of zonal chondrocytes to extracellular matrix-hydrogels.
Hwang, Nathaniel S; Varghese, Shyni; Lee, H Janice; Theprungsirikul, Parnduangjai; Canver, Adam; Sharma, Blanka; Elisseeff, Jennifer
2007-09-04
We investigated the biological response of chondrocytes isolated from different zones of articular cartilage and their cellular behaviors in poly (ethylene glycol)-based (PEG) hydrogels containing exogenous type I collagen, hyaluronic acid (HA), or chondroitin sulfate (CS). The cellular morphology was strongly dependent on the extracellular matrix component of hydrogels. Additionally, the exogenous extracellular microenvironment affected matrix production and cartilage specific gene expression of chondrocytes from different zones. CS-based hydrogels showed the strongest response in terms of gene expression and matrix accumulation for both superficial and deep zone chondrocytes, but HA and type I collagen-based hydrogels demonstrated zonal-dependent cellular responses.
RESPONSE OF ZONAL CHONDROCYTES TO EXTRACELLULAR MATRIX-HYDROGELS
Hwang, Nathaniel S.; Varghese, Shyni; Lee, H. Janice; Theprungsirikul, Parnduangjai; Canver, Adam; Sharma, Blanka; Elisseeff, Jennifer
2009-01-01
We investigated the biological response of chondrocytes isolated from different zones of articular cartilage and their cellular behaviors in poly (ethylene glycol)-based (PEG) hydrogels containing exogenous type I collagen, hyaluronic acid (HA), or chondroitin sulfate (CS). The cellular morphology was strongly dependent on the extracellular matrix component of hydrogels. Additionally, the exogenous extracellular microenvironment affected matrix production and cartilage specific gene expression of chondrocytes from different zones. CS-based hydrogels showed the strongest response in terms of gene expression and matrix accumulation for both superficial and deep zone chondrocytes, but HA and type I collagen-based hydrogels demonstrated zonal-dependent cellular responses. PMID:17692846
Zonal flow generation in inertial confinement fusion implosions
NASA Astrophysics Data System (ADS)
Peterson, J. L.; Humbird, K. D.; Field, J. E.; Brandon, S. T.; Langer, S. H.; Nora, R. C.; Spears, B. K.; Springer, P. T.
2017-03-01
A supervised machine learning algorithm trained on a multi-petabyte dataset of inertial confinement fusion simulations has identified a class of implosions that robustly achieve high yield, even in the presence of drive variations and hydrodynamic perturbations. These implosions are purposefully driven with a time-varying asymmetry, such that coherent flow generation during hotspot stagnation forces the capsule to self-organize into an ovoid, a shape that appears to be more resilient to shell perturbations than spherical designs. This new class of implosions, whose configurations are reminiscent of zonal flows in magnetic fusion devices, may offer a path to robust inertial fusion.
Non-linear Paradigm for Drift Wave - Zonal Flow interplay: coherence, chaos and turbulence
NASA Astrophysics Data System (ADS)
Zonca, Fulvio
2003-10-01
Non-linear equations for the slow space-time evolution of the radial drift wave (DW) envelope and zonal flow (ZF) amplitude have been self-consistently derived for a model nonuniform tokamak equilibrium within the coherent 4-wave drift wave-zonal flow modulation interaction model of Chen, Lin and White(chen00). For the sake of simplicity, in this work we assume electrostatic fluctuations; but our formalism is readily extended to electromagnetic fluctuations(chen01). In the local limit, i.e. neglecting equilibrium profile variations, the coherent 4-wave DW-ZF modulation interaction model has successfully demonstrated spontaneous generation of ZFs and non-linear DW/ITG-ZF dynamics in toroidal plasmas(chen00). The present work is an extension of previous analyses to allow both (slow) temporal and spatial variations of the DW/ITG radial envelope; thus, it naturally incorporates the effects of equilibrium variations; i.e., turbulence spreading and size-dependence of the saturated wave intensities and transport coefficients(lin99). This approach makes it possible to treat equilibrium profile variations and non-linear interactions on the same footing, assuming that coupling among different DWs on the shortest non-linear time scale is mediated by ZF only. At this level, the competition between linear drive/damping, DW spreading due to finite linear (and nonlinear) group velocity(lin02,chen02,kim02) and non-linear energy transfer between DWs and ZF, determines the saturation levels of the fluctuating fields. Despite the coherence of the underlying non-linear dynamics at this level, this system exhibits both chaotic behavior and intermittency, depending on system size and proximity to marginal stability(chen02). The present model can be further extended to include longer time-scale physics such as 3-wave interactions and collisionless damping of zonal flows. 9 chen00 Liu Chen, Zhihong Lin and Roscoe White, Phys. Plasmas 7, 3129, (2000). chen01 L. Chen, Z. Lin, R.B. White and
Overview of gyrokinetic studies of finite-β microturbulence
NASA Astrophysics Data System (ADS)
Terry, P. W.; Carmody, D.; Doerk, H.; Guttenfelder, W.; Hatch, D. R.; Hegna, C. C.; Ishizawa, A.; Jenko, F.; Nevins, W. M.; Predebon, I.; Pueschel, M. J.; Sarff, J. S.; Whelan, G. G.
2015-10-01
Recent results on electromagnetic turbulence from gyrokinetic studies in different magnetic configurations are overviewed, detailing the physics of electromagnetic turbulence and transport, and the effect of equilibrium magnetic field scale lengths. Ion temperature gradient (ITG) turbulence is shown to produce magnetic stochasticity through nonlinear excitation of linearly stable tearing-parity modes. The excitation, which is catalyzed by the zonal flow, produces an electron heat flux proportional to β2 that deviates markedly from quasilinear theory. Above a critical beta known as the non-zonal transition (NZT), the magnetic fluctuations disable zonal flows by allowing electron streaming that shorts zonal potential between flux surfaces. This leads to a regime of very high transport levels. Kinetic ballooning mode (KBM) saturation is described. For tokamaks saturation involves twisted structures arising from magnetic shear; for helical plasmas oppositely inclined convection cells interact by mutual shearing. Microtearing modes are unstable in the magnetic geometry of tokamaks and the reversed field pinch (RFP). In NSTX instability requires finite collisionality, large beta, and is favored by increasing magnetic shear and decreasing safety factor. In the RFP, a new branch of microtearing with finite growth rate at vanishing collisionality is shown from analytic theory to require the electron grad-B/curvature drift resonance. However, gyrokinetic modeling of experimental MST RFP discharges at finite beta reveals turbulence that is electrostatic, has large zonal flows, and a large Dimits shift. Analysis shows that the shorter equilibrium magnetic field scale lengths increase the critical gradients associated with the instability of trapped electron modes, ITG and microtearing, while increasing beta thresholds for KBM instability and the NZT.
Flexible Finite-Element Modeling of Global Geomagnetic Depth Sounding
NASA Astrophysics Data System (ADS)
Ribaudo, Joseph Thomas
Time-varying primary magnetic fields generated outside Earth by the magnetospheric ring current induce electrical currents in Earth's interior, which give rise to secondary magnetic fields with a complementary geometry. Geomagnetic depth sounding involves the analysis of magnetic field data to compute frequency-dependent response functions which yield information about the electrical conductivity of Earth's interior. I explore methods and results of forward-modeling global electromagnetic induction under a variety of assumptions about Earth conductivity and the spatial structure of the primary field. I begin by developing computational tools to perform time- and frequency-domain simulations of global induction in models with arbitrary conductivity and primary field structure using FlexPDE, a general-purpose software package that employs the finite-element method to solve partial differential equations. The method is shown to produce solutions with better than 1% accuracy when the simulated fields and response functions are compared to analytic solutions for a variety of problems in electromagnetic induction, and to qualitatively reproduce fields and response functions measured by satellites and observatories. The technique is employed in combination with analytic methods to explore the effect on the response of Earth models to primary fields with asymmetric structure. Standard methods of producing response functions from scalar and vector magnetic data are compared, and scalar methods are found to generate responses with significantly greater spatial bias for models with non-zonal fields. I develop the mathematical formulation for including Earth-rotation in the forward models, and use it to calculate frequency-dependent estimates of the amount of non-zonal structure required to produce previously reported local-time bias in empirical satellite response functions. Because it is difficult to validate solutions to induction problems that lack analytic solutions, we
Experimental studies of zonal flow and field in compact helical system plasmaa)
NASA Astrophysics Data System (ADS)
Fujisawa, A.; Itoh, K.; Shimizu, A.; Nakano, H.; Ohshima, S.; Iguchi, H.; Matsuoka, K.; Okamura, S.; Minami, T.; Yoshimura, Y.; Nagaoka, K.; Ida, K.; Toi, K.; Takahashi, C.; Kojima, M.; Nishimura, S.; Isobe, M.; Suzuki, C.; Akiyama, T.; Ido, T.; Nagashima, Y.; Itoh, S.-I.; Diamond, P. H.
2008-05-01
The experimental studies on zonal flows and turbulence have been carried out in Compact Helical System [K. Matsuoka, S. Kubo, M. Hosokawa et al., in Plasma Physics and Controlled Nuclear Fusion Research, Proc. 12th Int. Conf., Nice, 1988 (International Atomic Energy Agency, Vienna, 1989, Vol. 2, p. 411] using twin heavy ion beam probes. The paper presents the experimental observations of stationary zonal flow, nonlinear couplings between zonal flow and turbulence, and the role of zonal flow in the improved confinement, together with the recent discovery of zonal magnetic field. The presented experimental results strongly support the new paradigm that the plasma transport should be considered as a system of drift wave and zonal flows, and provides the first direct evidence for turbulence dynamo that the structured magnetic field can be really generated by turbulence.
Kesar, Amit S.; Hess, Mark; Korbly, Stephen E.; Temkin, Richard J.
2005-01-01
Smith-Purcell radiation (SPR), formed by an electron beam traveling above a grating, is a very promising source of coherent radiation from the THz to the optical regime. We present two theoretical calculations of the SPR from a two-dimensional bunch of relativistic electrons passing above a grating of finite length. The first calculation uses the finite-difference time-domain approach with the total-field/scattered-field procedure for fields incident on the grating. This calculation allows good physical insight into the radiation process and also allows arbitrary geometries to be treated. The second calculation uses an electric-field integral equation method. Good agreement is obtained between these two calculations. The results of these theoretical calculations are then compared with a theoretical formalism based on an infinite-length grating. The latter formalism allows periodic boundary conditions to be rigorously applied. For gratings with less than {approx}50 periods, a significant error in the strength of the radiated field is introduced by the infinite-grating approximation. It is shown that this error disappears asymptotically as the number of periods increases. The Wood-Rayleigh anomalies, predicted in the infinite-grating approximation, were not seen in our finite-grating calculations. The SPR resonance condition is the same in all three formalisms. Numerical examples are presented for an {approx}18 MeV, 50 nC/m, 200 {mu}m bunch traveling 0.6 mm above a ten-period echelle grating having a 2.1-mm periodicity.
NASA Astrophysics Data System (ADS)
2015-10-01
The world has agreed on 17 Sustainable Development Goals, to be adopted this week. This is great progress towards acknowledging that the planet's finite resources need to be managed carefully in the face of humanity's unlimited aspirations.
Implementing Multidisciplinary and Multi-Zonal Applications Using MPI
NASA Technical Reports Server (NTRS)
Fineberg, Samuel A.
1995-01-01
Multidisciplinary and multi-zonal applications are an important class of applications in the area of Computational Aerosciences. In these codes, two or more distinct parallel programs or copies of a single program are utilized to model a single problem. To support such applications, it is common to use a programming model where a program is divided into several single program multiple data stream (SPMD) applications, each of which solves the equations for a single physical discipline or grid zone. These SPMD applications are then bound together to form a single multidisciplinary or multi-zonal program in which the constituent parts communicate via point-to-point message passing routines. Unfortunately, simple message passing models, like Intel's NX library, only allow point-to-point and global communication within a single system-defined partition. This makes implementation of these applications quite difficult, if not impossible. In this report it is shown that the new Message Passing Interface (MPI) standard is a viable portable library for implementing the message passing portion of multidisciplinary applications. Further, with the extension of a portable loader, fully portable multidisciplinary application programs can be developed. Finally, the performance of MPI is compared to that of some native message passing libraries. This comparison shows that MPI can be implemented to deliver performance commensurate with native message libraries.
Variations in Nimbus-7 cloud estimates. Part I: Zonal averages
Weare, B.C. )
1992-12-01
Zonal averages of low, middle, high, and total cloud amount estimates derived from measurements from Nimbus-7 have been analyzed for the six-year period April 1979 through March 1985. The globally and zonally averaged valued of six-year annual means and standard deviations of total cloud amount and a proxy of cloudtop height are illustrated. Separate means for day and night and land and sea are also shown. The globally averaged value of intra-annual variability of total cloud amount is greater than 7%, and that for cloud height is greater than 0.3 km. Those of interannual variability are more than one-third of these values. Important latitudinal differences in variability are illustrated. The dominant empirical orthogonal analyses of the intra-annual variations of total cloud amount and heights show strong annual cycles, indicating that in the tropics increases in total cloud amount of up to about 30% are often accompanied by increases in cloud height of up to 1.2 km. This positive link is also evident in the dominant empirical orthogonal function of interannual variations of a total cloud/cloud height complex. This function shows a large coherent variation in total cloud cover of about 10% coupled with changes in cloud height of about 1.1 km associated with the 1982-83 El Ni[tilde n]o-Southern Oscillation event. 14 refs. 12 figs., 2 tabs.
Zonal structure of unbounded external-flow and aerodynamics
NASA Astrophysics Data System (ADS)
Liu, L. Q.; Kang, L. L.; Wu, J. Z.
2017-08-01
This paper starts from the far-field behaviors of velocity field in externally unbounded flow. We find that the well-known algebraic decay of disturbance velocity as derived kinematically is too conservative. Once the kinetics are taken into account by working on the fundamental solutions of far-field linearized Navier-Stokes equations, it is proven that the furthest far-field zone adjacent to the uniform fluid at infinity must be unsteady, viscous and compressible, where all disturbances degenerate to sound waves that decay exponentially. But this optimal rate does not exist in some commonly used simplified flow models, such as steady flow, incompressible flow and inviscid flow, because they actually work in true subspaces of the unbounded free space, which are surrounded by further far fields of different nature. This finding naturally leads to a zonal structure of externally unbounded flow field. The significance of the zonal structure is demonstrated by its close relevance to existing theories of aerodynamic force and moment in external flows, including the removal of the difficulties or paradoxes inherent in the simplified models.
Application of zonal model on indoor air sensor network design
NASA Astrophysics Data System (ADS)
Chen, Y. Lisa; Wen, Jin
2007-04-01
Growing concerns over the safety of the indoor environment have made the use of sensors ubiquitous. Sensors that detect chemical and biological warfare agents can offer early warning of dangerous contaminants. However, current sensor system design is more informed by intuition and experience rather by systematic design. To develop a sensor system design methodology, a proper indoor airflow modeling approach is needed. Various indoor airflow modeling techniques, from complicated computational fluid dynamics approaches to simplified multi-zone approaches, exist in the literature. In this study, the effects of two airflow modeling techniques, multi-zone modeling technique and zonal modeling technique, on indoor air protection sensor system design are discussed. Common building attack scenarios, using a typical CBW agent, are simulated. Both multi-zone and zonal models are used to predict airflows and contaminant dispersion. Genetic Algorithm is then applied to optimize the sensor location and quantity. Differences in the sensor system design resulting from the two airflow models are discussed for a typical office environment and a large hall environment.
Finite element model and identification procedure
NASA Technical Reports Server (NTRS)
How, Jonathan P.; Blackwood, Gary; Anderson, Eric; Balmes, Etienne
1992-01-01
Viewgraphs on finite element model and identification procedure are presented. Topics covered include: interferometer finite element model; testbed mode shapes; finite element model update; identification procedure; shaker locations; data analysis; modal frequency and damping comparison; computational procedure; fit comparison; residue analysis; typical residues; identification/FEM residual comparison; and pathlength control using isolation mounts.
Mesoscale electric fluctuations interacting with zonal flows, magnetic fluctuations and turbulence
NASA Astrophysics Data System (ADS)
Zhao, K. J.; Nagashima, Y.; Diamond, P. H.; Dong, J. Q.; Itoh, K.; Itoh, S.-I.; Yan, L. W.; Cheng, J.; Fujisawa, A.; Inagaki, S.; Kosuga, Y.; Sasaki, M.; Huang, Z. H.; Yu, D. L.; Li, Q.; Ji, X. Q.; Song, X. M.; Huang, Y.; Liu, Yi.; Yang, Q. W.; Ding, X. T.; Duan, X. R.; HL-2A Team
2017-07-01
New mesoscale electric fluctuations (MSEFs) are identified in the edge plasmas of the HL-2A tokamak using multiple Langmuir probe arrays. The MSEFs, resulting from the synchronization and having components of dominant geodesic acoustic mode (GAM) and m/n = 6/2 potential fluctuations, are found at the same frequency as that of the magnetic fluctuations of m/n = 6/2 (m and n are poloidal and toroidal mode numbers, respectively). The temporal evolutions of the MSEFs and the magnetic fluctuations clearly show the frequency entrainment and the phase lock between the GAM and the m/n = 6/2 magnetic fluctuations. The results indicate that GAMs and magnetic fluctuations can transfer energy through nonlinear synchronization. The nonlinear coupling analyses show that the MSEFs couple to turbulence and low frequency zonal flows (LFZFs). This suggests that the MSEFs may contribute to the LFZF formation, reduction of turbulence level, and thus confinement regime transitions. The analysis of the envelope modulation demonstrates that both the MSEFs and the LFZFs modulate the turbulence while the MSEFs are modulated by the LFZFs.
Northern hemisphere teleconnection patterns during extreme phases of the zonal-mean circulation
Mingfang Ting; Hoerling, M.P.; Taiyi Xu
1996-10-01
Regional climate anomalies associated with year-to-year changes in the tropospheric zonal-mean zonal wind ({mu}) are examined. This study focuses on the wintertime Northern Hemisphere extratronics and compares seasonal mean anomalies associated with {mu} to those associated with the El Nino-Southern Oscillation during the 1947-94 period. Dynamical model experiments indicate that a single zonal index, characterized by out-of-phase {mu} anomalies at 35{degrees} and 55{degrees}N, is of primary importance for zonal flow/stationary wave interactions in the Northern Hemisphere extratropics. Such fluctuations in the zonal-mean zonal flow are shown to occur independently of tropical SST variability, consistent with earlier studies. Dynamical model experiments and regression analyses of the historical data indicate that such a zonal index explains a significant fraction of the wintertime stationary wave variability in several regions. The principal centers of action reside within wave trains over the North Pacific-North American region and the North Atlantic-Eurasian region where locally 30%-40% of the eddy height variability is explained by the zonal index. Only over the North Pacific does the stationary wave signal related to ENSO appreciably exceed that associated with the zonal index. Only over the North Pacific does the stationary wave signal related to ENSO appreciably exceed that associated with the zonal index. The surface climate associated with the zonal index is described by a wavenumber 1 pattern, which has out-of-phase temperature anomalies between Eurasia and North America and amplitudes considerably larger than those experienced during ENSO. 35 refs., 10 figs.
Chen, Z.
2001-01-01
The Spallation Neutron Source (SNS) is an accelerator-based neutron scattering research facility. The linear accelerator (linac) is the principal accelerating structure and divided into a room-temperature linac and a superconducting linac. The normal conducting linac system that consists of a Drift Tube Linac (DTL) and a Coupled Cavity Linac (CCL) is to be built by Los Alamos National Laboratory. The CCL structure is 55.36-meters long. It accelerates H- beam from 86.8 Mev to 185.6 Mev at operating frequency of 805 MHz. This side coupled cavity structure has 8 cells per segment, 12 segments and 11 bridge couplers per module, and 4 modules total. A 5-MW klystron powers each module. The number 3 and number 9 bridge coupler of each module are connected to the 5-MW RF power supply. The bridge coupler with length of 2.5 {beta}{gamma} is a three-cell structure and located between the segments and allows power flow through the module. The center cell of each bridge coupler is excited during normal operation. To obtain a uniform electromagnetic filed and meet the resonant frequency shift, the RF induced heat must be removed. Thus, the thermal deformation and frequency shift studies are performed via numerical simulations in order to have an appropriate cooling design and predict the frequency shift under operation. The center cell of the bridge coupler also contains a large 4-inch slug tuner and a tuning post that used to provide bulk frequency adjustment and field intensity adjustment, so that produce the proper total field distribution in the module assembly.
On radiating baroclinic instability of zonally varying flow
NASA Technical Reports Server (NTRS)
Finley, Catherine A.; Nathan, Terrence R.
1993-01-01
A quasi-geostrophic, two-layer, beta-plane model is used to study the baroclinic instability characteristics of a zonally inhomogeneous flow. It is assumed that the disturbance varied slowly in the cross-stream direction, and the stability problem was formulated as a 1D initial value problem. Emphasis is placed on determining how the vertically averaged wind, local maximum in vertical wind shear, and length of the locally supercritical region combine to yield local instabilities. Analysis of the local disturbance energetics reveals that, for slowly varying basic states, the baroclinic energy conversion predominates within the locally unstable region. Using calculations of the basic state tendencies, it is shown that the net effect of the local instabilities is to redistribute energy from the baroclinic to the barotropic component of the basic state flow.
Biohazards Assessment in Large-Scale Zonal Centrifugation
Baldwin, C. L.; Lemp, J. F.; Barbeito, M. S.
1975-01-01
A study was conducted to determine the biohazards associated with use of the large-scale zonal centrifuge for purification of moderate risk oncogenic viruses. To safely and conveniently assess the hazard, coliphage T3 was substituted for the virus in a typical processing procedure performed in a National Cancer Institute contract laboratory. Risk of personnel exposure was found to be minimal during optimal operation but definite potential for virus release from a number of centrifuge components during mechanical malfunction was shown by assay of surface, liquid, and air samples collected during the processing. High concentration of phage was detected in the turbine air exhaust and the seal coolant system when faulty seals were employed. The simulant virus was also found on both centrifuge chamber interior and rotor surfaces. Images PMID:1124921
Biohazards assessment in large-scale zonal centrifugation.
Baldwin, C L; Lemp, J F; Barbeito, M S
1975-04-01
A study was conducted to determine the biohazards associated with use of the large-scale zonal centrifuge for purification of moderate risk oncogenic viruses. To safely and conveniently assess the hazard, coliphage T3 was substituted for the virus in a typical processing procedure performed in a National Cancer Institute contract laboratory. Risk of personnel exposure was found to be minimal during optimal operation but definite potential for virus release from a number of centrifuge components during mechanical malfunction was shown by assay of surface, liquid, and air samples collected during the processing. High concentration of phage was detected in the turbine air exhaust and the seal coolant system when faulty seals were employed. The simulant virus was also found on both the centrifuge chamber interior and rotor surfaces.
A Zonal Approach for Prediction of Jet Noise
NASA Technical Reports Server (NTRS)
Shih, S. H.; Hixon, D. R.; Mankbadi, Reda R.
1995-01-01
A zonal approach for direct computation of sound generation and propagation from a supersonic jet is investigated. The present work splits the computational domain into a nonlinear, acoustic-source regime and a linear acoustic wave propagation regime. In the nonlinear regime, the unsteady flow is governed by the large-scale equations, which are the filtered compressible Navier-Stokes equations. In the linear acoustic regime, the sound wave propagation is described by the linearized Euler equations. Computational results are presented for a supersonic jet at M = 2. 1. It is demonstrated that no spurious modes are generated in the matching region and the computational expense is reduced substantially as opposed to fully large-scale simulation.
Decomposition method for zonal resource allocation problems in telecommunication networks
NASA Astrophysics Data System (ADS)
Konnov, I. V.; Kashuba, A. Yu
2016-11-01
We consider problems of optimal resource allocation in telecommunication networks. We first give an optimization formulation for the case where the network manager aims to distribute some homogeneous resource (bandwidth) among users of one region with quadratic charge and fee functions and present simple and efficient solution methods. Next, we consider a more general problem for a provider of a wireless communication network divided into zones (clusters) with common capacity constraints. We obtain a convex quadratic optimization problem involving capacity and balance constraints. By using the dual Lagrangian method with respect to the capacity constraint, we suggest to reduce the initial problem to a single-dimensional optimization problem, but calculation of the cost function value leads to independent solution of zonal problems, which coincide with the above single region problem. Some results of computational experiments confirm the applicability of the new methods.
Effect of chlorofluoromethane infrared radiation on zonal atmospheric temperatures
NASA Technical Reports Server (NTRS)
Dickinson, R. E.; Donahue, T. M.; Liu, S. C.
1978-01-01
Estimates are made of changes in the atmospheric climate due to the radiative effects of 10 ppb of chlorofluoromethanes (CFM's). The estimates are derived on the basis of a 12-layer stratospheric general circulation model with a specified change of ocean temperature. Two tropical maxima in zonal average temperature change were observed: one in the upper troposphere and one centered at the tropopause. The temperature change exceeds the surface temperature change by a factor of at least two. If the 1975 CFM emission rate were to continue indefinitely, stratospheric water-vapor concentrations would increase by up to 60% due to CFM radiative effects. This would reduce ozone concentrations by an additional 4% of the natural ozone column.
A time Fourier analysis of zonal averaged ozone heating rates
NASA Technical Reports Server (NTRS)
Wang, P.-H.; Wu, M.-F.; Deepak, A.; Hong, S.-S.
1981-01-01
A time-Fourier analysis is presented for the yearly variation of the zonal averaged ozone heating rates in the middle atmosphere based on a model study. The ozone heating rates are determined by utilizing two-dimensional ozone distributions, the altitude and latitude, and by including the effect of the curved earth's atmosphere. In addition, assumptions are introduced to the yearly variations of the ozone distributions due to the lack of sufficient existing ozone data. Among other results, it is shown that the first harmonic component indicates that the heating rates are completely out of phase between the northern and southern hemispheres. The second Fourier component shows a symmetric pattern with respect to the equator, as well as five distinct local extreme values of the ozone heating rate. The third harmonic component shows a pattern close to that of the first component except in the regions above 70 deg between 45-95 km in both hemispheres.
Zonal analysis of two high-speed inlets
NASA Technical Reports Server (NTRS)
Dilley, A. D.; Switzer, G. F.; Eppard, W. M.
1991-01-01
Using a zonal technique, thin layer Navier-Stokes solutions for two high speed inlet geometries are presented and compared with experimental data. The first configuration consists of a 3-D inlet preceded by a sharp flat plate. Results with two different grids demonstrate the importance of adequate grid refinement in high speed internal flow computations. The fine grid solution has reasonably good agreement with experimental heat transfer and pressure values inside the inlet. The other configuration consists of a 3-D inlet mounted on a research hypersonic forebody. Numerical results for this configuration have good agreement with experimental pressure data along the forebody, but not inside the inlet. A more refined grid calculation is currently being done to better predict the flowfield in the inlet.
Residual zonal flows in tokamaks and stellarators at arbitrary wavelengths
NASA Astrophysics Data System (ADS)
Monreal, Pedro; Calvo, Iván; Sánchez, Edilberto; Parra, Félix I.; Bustos, Andrés; Könies, Axel; Kleiber, Ralf; Görler, Tobias
2016-04-01
In the linear collisionless limit, a zonal potential perturbation in a toroidal plasma relaxes, in general, to a non-zero residual value. Expressions for the residual value in tokamak and stellarator geometries, and for arbitrary wavelengths, are derived. These expressions involve averages over the lowest order particle trajectories, that typically cannot be evaluated analytically. In this work, an efficient numerical method for the evaluation of such expressions is reported. It is shown that this method is faster than direct gyrokinetic simulations performed with the Gene and EUTERPE codes. Calculations of the residual value in stellarators are provided for much shorter wavelengths than previously available in the literature. Electrons must be treated kinetically in stellarators because, unlike in tokamaks, kinetic electrons modify the residual value even at long wavelengths. This effect, that had already been predicted theoretically, is confirmed by gyrokinetic simulations.
A PV view of the zonal mean distribution of temperature and wind in the extratropical troposphere
NASA Technical Reports Server (NTRS)
Sun, De-Zheng; Lindzen, Richard S.
1994-01-01
The dependence of the temperature and wind distribution of the zonal mean flow in the extratropical troposphere on the gradient of pontential vorticity along isentropes is examined. The extratropics here refer to the region outside the Hadley circulation. Of particular interest is whether the distribution of temperature and wind corresponding to a constant potential vorticity (PV) along isentropes resembles the observed, and the implications of PV homogenization along isentropes for the role of the tropics. With the assumption that PV is homogenized along isentropes, it is found that the temperature distribution in the extratropical troposphere may be determined by a linear, first-order partial differential equation. When the observed surface temperature distribution and tropical lapse rate are used as the boundary conditions, the solution of the equation is close to the observed temperature distribution except in the upper troposphere adjacent to the Hadley circulation, where the troposphere with no PV gradient is considerably colder. Consequently, the jet is also stronger. It is also found that the meridional distribution of the balanced zonal wind is very sensitive to the meridional distribution of the tropopause temperature. The result may suggest that the requirement of the global momentum balance has no practical role in determining the extratropical temperature distribution. The authors further investigated the sensitivity of the extratropical troposphere with constant PV along isentropes to changes in conditions at the tropical boundary (the edge of the Hadley circulation). It is found that the temperature and wind distributions in the extratropical troposphere are sensitive to the vertical distribution of PV at the tropical boundary. With a surface distribution of temperature that decreases linearly with latitude, the jet maximum occurs at the tropical boundary and moves with it. The overall pattern of wind distribution is not sensitive to the change of
Fine-Scale Zonal Flow Suppression of Electron Temperature Gradient Turbulence
Parker, S. E.; Kohut, J. J.; Chen, Y.; Lin, Z.; Hinton, F. L.; Lee, W. W.
2006-11-30
It is found in collisionless Electron Temperature Gradient (ETG) turbulence simulations that, while zonal flows are weak at early times, the zonal flows continue to grow algebraically (proportional to time). These fine-scale zonal flows have a radial wave number such that kr{rho}i > 1 and kr{rho}e < 1. Eventually, the zonal flows grow to a level that suppresses the turbulence due to ExB shearing. The final electron energy flux is found to be relatively low. These conclusions are based on particle convergence studies with adiabatic ion electrostatic flux-tube gyrokinetic {delta}f particle simulations run for long times. The Rosenbluth-Hinton random walk mechanism is given as an explanation for the long time build up of the zonal flow in ETG turbulence and it is shown that the generation is (k perpendicular {rho}e)2 smaller than for isomorphic Ion Temperature Gradient (ITG) problem. This mechanism for zonal flow generation here is different than the modulational instability mechanism for ITG turbulence. These results are important because previous results indicated zonal flows were unimportant for ETG turbulence. Weak collisional damping of the zonal flow is also shown to be a n important effect.
NASA Astrophysics Data System (ADS)
Li, Deyu; Zhang, Xiao-Hong; Cheng, Li; Yu, Ganghua
2010-10-01
Double-panel partitions are widely used for sound insulation purposes. Their insulation efficiency is, however, deteriorated at low frequencies due to the structural and acoustic resonances. To tackle this problem, this paper proposes the use of long T-shaped acoustic resonators in a double-panel partition embedded along the edges. In order to facilitate the design and assess the performance of the structure, a general vibro-acoustic model, characterizing the interaction between the panels, air cavity, and integrated acoustic resonators, is developed. The effectiveness of the technique as well as the optimal locations of the acoustic resonators is examined at various frequencies where the system exhibits different coupling characteristics. The measured optimal locations are also compared with the predicted ones to verify the developed theory. Finally, the performance of the acoustic resonators in broadband sound transmission control is demonstrated.
NASA Astrophysics Data System (ADS)
Grigoryan, Artyom M.; John, Aparna; Agaian, Sos S.
2017-03-01
2-D quaternion discrete Fourier transform (2-D QDFT) is the Fourier transform applied to color images when the color images are considered in the quaternion space. The quaternion numbers are four dimensional hyper-complex numbers. Quaternion representation of color image allows us to see the color of the image as a single unit. In quaternion approach of color image enhancement, each color is seen as a vector. This permits us to see the merging effect of the color due to the combination of the primary colors. The color images are used to be processed by applying the respective algorithm onto each channels separately, and then, composing the color image from the processed channels. In this article, the alpha-rooting and zonal alpha-rooting methods are used with the 2-D QDFT. In the alpha-rooting method, the alpha-root of the transformed frequency values of the 2-D QDFT are determined before taking the inverse transform. In the zonal alpha-rooting method, the frequency spectrum of the 2-D QDFT is divided by different zones and the alpha-rooting is applied with different alpha values for different zones. The optimization of the choice of alpha values is done with the genetic algorithm. The visual perception of 3-D medical images is increased by changing the reference gray line.
NASA Astrophysics Data System (ADS)
Carrano, Charles S.; Groves, Keith M.; Rino, Charles L.; Doherty, Patricia H.
2016-08-01
The zonal drift of ionospheric irregularities at low latitudes is most commonly measured by cross-correlating observations of a scintillating satellite signal made with a pair of closely spaced antennas. The Air Force Research Laboratory-Scintillation Network Decision Aid (AFRL-SCINDA) network operates a small number of very high frequency (VHF) spaced-receiver systems at low latitudes for this purpose. A far greater number of Global Navigation Satellite System (GNSS) scintillation monitors are operated by the AFRL-SCINDA network (25-30) and the Low-Latitude Ionospheric Sensor Network (35-50), but the receivers are too widely separated from each other for cross-correlation techniques to be effective. In this paper, we present an alternative approach that leverages the weak scatter scintillation theory to infer the zonal irregularity drift from single-station GNSS measurements of S4, σφ, and the propagation geometry. Unlike the spaced-receiver technique, this approach requires assumptions regarding the height of the scattering layer (which introduces a bias in the drift estimates) and the spectral index of the irregularities (which affects the spread of the drift estimates about the mean). Nevertheless, theory and experiment suggest that the ratio of σφ to S4 is less sensitive to these parameters than it is to the zonal drift. We validate the technique using VHF spaced-receiver measurements of zonal irregularity drift obtained from the AFRL-SCINDA network. While the spaced-receiver technique remains the preferred way to monitor the drift when closely spaced antenna pairs are available, our technique provides a new opportunity to monitor zonal irregularity drift using regional or global networks of widely separated GNSS scintillation monitors.
Collisionless kinetic-fluid simulation of zonal flows in non-circular tokamaks
Yamagishi, Osamu; Sugama, Hideo
2012-09-15
Fluid simulation of linear zonal flow damping is done with a closure model based on the collisionless gyrokinetics [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. Simulation results of residual zonal flow for low radial wavenumbers are compared with theoretical formulas for circular and non-circular tokamaks. The effects of the elongation and the triangularity are shown to be properly treated in the closure model. Effects of initial parallel flows on zonal flow evolution are also clarified. An appropriate choice of the initial parallel flow gives a much higher residual level than the conventional result with no initial parallel flow. Besides, the zonal flow simulations are done with the E Multiplication-Sign B nonlinearity as initial sources, which is evaluated from linear gyrokinetic microinstabilities such as ion temperature gradient modes, trapped electron modes, and electron temperature gradient modes, in order to estimate efficiency of zonal flow generation by the source instabilities.
Zonal mean wind, the Indian monsoon, and July drying in the western Atlantic subtropics
NASA Astrophysics Data System (ADS)
Kelly, Patrick; Mapes, Brian
2011-11-01
A fully closed zonal momentum budget is decomposed to explain the occurrence of zonal mean easterlies at subtropical latitudes in July. Eddy momentum fluxes from stationary eddies, most prominently the western sector of the Indian monsoon Tibetan High, are the primary mechanism governing the negative tendency of zonal mean momentum near 20°N-30°N. This strengthening of the zonal mean easterlies in July is significantly correlated with the concurrent strengthening of the North Atlantic Subtropical High (NASH) and the rainfall deficit in the western North Atlantic (WATL). Interannual variations of the Indian monsoon reflect changes in the strength of these zonal mean easterlies, with downstream teleconnections on the westward displacement of the NASH and precipitation in the WATL. An increase in rainfall in India from June to July corresponds to a decrease in rainfall in the WATL.
Constraining the depth of Saturn’s zonal winds by measuring thermal and gravitational signals
NASA Astrophysics Data System (ADS)
Liu, Junjun; Schneider, Tapio; Fletcher, Leigh N.
2014-09-01
Based on straightforward dynamical considerations, we show how available and upcoming measurements of Saturn’s thermal and gravitational signals can be used to constrain the depth to which its zonal winds penetrate. The dynamical considerations issue from the facts that Saturn has a strong intrinsic heat flux, rotates rapidly, and has negligible atmospheric viscosity. As a result, convective motions align with surfaces of constant specific angular momentum, which are, away from the equator, approximately cylinders concentric with the planet’s spin axis. Convective motions in the interior therefore tend to homogenize entropy in the direction of the spin axis, but not necessarily perpendicular to it. Using the assumption of interior entropy homogenization in the direction of the spin axis, we determine the zonal winds and their associated thermal and gravitational signals by combining thermal wind balance, the equation of state, the observed zonal winds at the cloud level, and estimates of the strength of the magnetohydrodynamic (MHD) drag that zonal winds experience in the deep interior. We find zonal winds likely extend deeply into Saturn, to a depth between about 0.63 and 0.83RS (with Saturn’s radius RS), or to pressures between 1.4 and 0.3 Mbar. The equation of state of hydrogen constrains zonal winds with strengths similar to the cloud level winds to be confined within the outer few percent of Saturn’s radius, with substantially weaker winds below, irrespective of where in the range of plausible estimates Saturn’s imprecisely known rotation rate falls. Depending on the rotation rate and the precise depth to which zonal winds penetrate, we estimate that the meridional equator-to-pole temperature contrasts in thermal wind balance with the inferred zonal winds increase with depth and reach 1-2 K at 1 bar and 2-4 K at 5 bar. They would be much larger if the cutoff radii of the zonal winds were much shallower than we estimate, but thermal observations by
The residual zonal flow in tokamak plasmas toroidally rotating at arbitrary velocity
Zhou, Deng
2014-08-15
Zonal flows, initially driven by ion-temperature-gradient turbulence, may evolve due to the neoclassic polarization in a collisionless tokamak plasma. In our previous work [D. Zhou, Nucl. Fusion 54, 042002 (2014)], the residual zonal flow in a tokamak plasma rotating toroidally at sonic speed is found to have the same form as that of a static plasma. In the present work, the form of the residual zonal flow is presented for tokamak plasmas rotating toroidally at arbitrary velocity. The gyro-kinetic equation is analytically solved for low speed rotation to give the expression of residual zonal flows, and the expression is then generalized for cases with arbitrary rotating velocity through interpolation. The zonal flow level decreases as the rotating velocity increases. The numerical evaluation is in good agreement with the former simulation result for high aspect ratio tokamaks.
NASA Astrophysics Data System (ADS)
Veljović-Jovanović, S.; Vidović, M.; Morina, F.; Prokić, Lj.; Todorović, D. M.
2016-09-01
Green-white variegated leaves of Pelargonium zonale were studied using the photoacoustic method. Our aim was to characterize photosynthetically active green tissue and nonphotosynthetically active white tissue by the photoacoustic amplitude signals. We observed lower stomatal conductance and higher leaf temperature in white tissue than in green tissue. Besides these thermal differences, significantly higher absorbance in green tissue was based on chlorophyll and carotenoids which were absent in white tissue. However, optical properties of epidermal layers of both tissues were equal. The photoacoustic amplitude of white tissue was over four times higher compared to green tissue, which was correlated with lower stomatal conductance. In addition, at frequencies >700 Hz, the significant differences between the photoacoustic signals of green and white tissue were obtained. We identified the photoacoustic signal deriving from photosynthetic oxygen evolution in green tissue, using high intensity of red light modulated at 10 Hz. Moreover, the photoacoustic amplitude of green tissue increased progressively with time which corresponded to the period of induction of photosynthetic oxygen evolution. For the first time, very high frequencies (1 kHz to 5 kHz) were applied on leaf material.
NASA Astrophysics Data System (ADS)
Ortland, David A.
2017-04-01
Satellites provide a global view of the structure in the fields that they measure. In the mesosphere and lower thermosphere, the dominant features in these fields at low zonal wave number are contained in the zonal mean, quasi-stationary planetary waves, and tide components. Due to the nature of the satellite sampling pattern, stationary, diurnal, and semidiurnal components are aliased and spectral methods are typically unable to separate the aliased waves over short time periods. This paper presents a data processing scheme that is able to recover the daily structure of these waves and the zonal mean state. The method is validated by using simulated data constructed from a mechanistic model, and then applied to Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature measurements. The migrating diurnal tide extracted from SABER temperatures for 2009 has a seasonal variability with peak amplitude (20 K at 95 km) in February and March and minimum amplitude (less than 5 K at 95 km) in early June and early December. Higher frequency variability includes a change in vertical structure and amplitude during the major stratospheric warming in January. The migrating semidiurnal tide extracted from SABER has variability on a monthly time scale during January through March, minimum amplitude in April, and largest steady amplitudes from May through September. Modeling experiments were performed that show that much of the variability on seasonal time scales in the migrating tides is due to changes in the mean flow structure and the superposition of the tidal responses to water vapor heating in the troposphere and ozone heating in the stratosphere and lower mesosphere.
Recent pollen spectra and zonal vegetation in the western USSR
NASA Astrophysics Data System (ADS)
Peterson, G. M.
The relationship of modern pollen spectra to present-day vegetation is critical to the reconstruction of vegetation and climate from fossil pollen spectra. This study uses isopoll maps to illustrate the pollen-vegetation relationships in the Soviet Union west of 100°E and presents descriptive statistics for 544 modern samples of arboreal pollen and for 370 samples of herb pollen obtained from the Soviet palynological literature. Data are assembled from this large geographic region and presented in a standardized form on a scale which can be used to relate quantitative pollen data to zonal vegetation and climatic variables and to make comparisons with other regions. In order to show the relationship between pollen types and major ecotones in forested and non-forested areas, the pollen data are presented as percentages of a sum including both arboreal and non-arboreal pollen. Major pollen types which attain values of 10% or more in at least one vegetation zone include Betula (birch), Cyperaceae (sedges), Picea (spruce), Pinus (total pine), Pinus sibirica, Ericaceae (heath family), Gramineae (grasses), Artemisia (sage), and Chenopodiaceae (i.e., saltbush, Russian thistle, pigweed family). Samples from the tundra and forest-tundra have high values of Ericaceae (heath family), birch, alder, and sedge pollen. In the boreal forest, pine, spruce, and birch pollen predominate. In the mixed and deciduous forests, Tilia (linden), Quercus (oak), Ulmus (elm), and Corylus (hazel) pollen attain maximum values. In the forest-steppe and steppe zones, arboreal pollen decreases in importance and is replaced by non-arboreal pollen types. Pollen of Artemisia and Chenopodiaceae predominates in the semi-desert zones. In spite of variation in the pollen spectra arising from the use of different sediment types (soil, peat, and river sediments), and human disturbance of vegetation, the pollen spectra are clearly related to zonal vegetation. Pollen spectra from the western USSR show
Titan's Temperature and Zonal Wind Structure and Seasonal Behavior
NASA Astrophysics Data System (ADS)
Flasar, F.; Achterberg, Richard; Schinder, Paul
2016-06-01
Titan's atmosphere near 80 km (20 mbar) marks the transition between large radiative damping times at lower altitudes, where seasonal variations are muted, and small damping times higher up, where temperatures and winds vary significantly over the year. Cassini CIRS and Radio-Occultation measurements obtained in 2004-2016 have tracked the evolution of temperatures and winds in Titan's atmosphere from early northern winter to late spring. In winter, the northern hemisphere was characterized by cold temperatures at high latitudes in the lower stratosphere and a strong circumpolar vortex that extended to subtropical northern latitudes. At high altitudes over the north pole, there was an elevated stratopause with a temperature roughly 30 K above the seasonal average, associated with subsidence and adiabatic warming. As the northern hemisphere has moved toward summer the dissolution of the circumpolar vortex has been gradual, and there is no evidence of rapid distortion and disruption forced by planetary waves like that seen on Earth. During this time, the southern hemisphere has cooled fairly abruptly at high latitudes. A circumpolar vortex has formed in the stratosphere, but it is more compact than seen in the north, with maximum winds at 60°S. Potential vorticity maps now indicate steep meridional gradients at high southern latitudes, implying a barrier to efficient mixing between the polar region and lower latitudes. One of the curious features of Titan's temperatures has been the destabilization seen in the winter north polar region, where negative temperature gradients were observed between 80 and 100 km. As the southern hemisphere moves toward winter, temperatures retrieved from radio occultation soundings have shown the early development this phenomenon at high southernlatitudes. The cause of the destabilization in winter may be associated with a cloud of organic ices. However, the transition region near 80 km is also where the zonal winds exhibit a sharp
Response of zonal winds and atmospheric angular momentum to a doubling of CO[sub 2
Rosen, R.D.; Gutowski, W.J. Jr. )
1992-12-01
The possible impact of doubling CO[sub 2] on the zonal-mean zonal winds and the angular momentum of the atmosphere is examined using general circulation model output archived by the Goddard Institute for Space Studies, the National Center for Atmospheric Research, and the Geophysical Fluid Dynamics Laboratory. Whereas the emphasis in most previous studies with these models has been placed on the temperature and precipitation changes expected from a doubled-CO[sub 2] scenario, the intent here is to investigate some of the dynamical consequences predicted by these model, especially within the tropics where the zonal-wind and temperature changes are less tightly coupled than elsewhere. Comparisons among the three models of the difference in zonal-mean zonal winds between 2 [times] CO[sub 2] and 1 [times] CO[sub 2] simulations indicate a common tendency when CO[sub 2] is doubled for winds to become more easterly in much of the tropics during June-July-August. Less of a consensus for the tropics emerges for December-January-February, perhaps as a result of differences among the models' basic climatologies for the zonal-wind field. In general, however, changes predicted for the zonal winds in the tropics and elsewhere are comparable to the interannual variability currently observed, suggesting that these changes ought to becomes detectable eventually. 24 refs., 6 figs.
Zonal Flow Magnetic Field Interaction in the Semi-Conducting Region of Giant Planets
NASA Astrophysics Data System (ADS)
Cao, H.; Stevenson, D. J.
2016-12-01
All four giant planets in the Solar System feature zonal flows on the order of 100 m/s in the cloud deck, and large-scale intrinsic magnetic fields on the order of 1 Gauss near the surface. The vertical structure of the zonal flows remains obscure. The end-member scenarios are shallow flows confined in the radiative atmosphere and deep flows throughout the planet with constant velocity along the direction of the spin-axis. The electrical conductivity increases smoothly as a function of depth inside Jupiter and Saturn, while a discontinuity of electrical conductivity inside Uranus and Neptune cannot be ruled out. Deep zonal flows will inevitably interact with the magnetic field, at depth with even modest electrical conductivity. We first investigate the kinematic interaction between zonal flows and magnetic fields in the semi-conducting region of giant planets. Employing mean-field electrodynamics, we show that the kinematic interaction will generate detectable poloidal magnetic field perturbations spatially correlated with the deep zonal flows. These poloidal perturbations should be detectable with the in-situ magnetic field measurements from the Juno mission and the Cassini Grand Finale. This implies that magnetic field measurements can be employed to constrain the properties of deep zonal flows in the semi-conducting region of giant planets. We then investigate the role of magnetic field in establishing the global property of deep zonal flows inside giant planet. By solving the Reynolds-averaged magnetohydrodynamics (MHD) equation, we show that the meridional circulation driven by the Reynolds stress and the Lorentz force in mid-to-high latitude will give rise to latitudinal thermal gradient acting to decrease the zonal wind velocity along the direction of the spin-axis (the thermal wind shear). Furthermore, we evaluate the modified Taylor integral, which takes into account the contribution from the Reynolds stress, to assess its role in determining the amplitude
Diligent, O; Grahn, T; Boström, A; Cawley, P; Lowe, M J S
2002-12-01
A study of the interaction of the S0 Lamb wave with a circular through-thickness hole in a plate is presented. The study is limited to the nondispersive frequency range of this wave, in which the distributions of stress and displacement are simple. This allows a Finite Element analysis to be undertaken using a two-dimensional membrane discretization. Predictions of the direct reflection of the S0 mode and the lateral scattering of the SH0 mode are made for a range of diameters of the hole. At the same time, an analytical solution based on modal superposition is developed, and this is also used to predict the reflection and scattering coefficients. Both sets of predictions are validated by experimental measurements. It is found that the trends of the reflection coefficients for different hole diameters, frequencies and distances from the hole satisfy a simple normalization. On a detailed scale, the functions exhibit undulations which are shown to result from the interference of the direct reflection with secondary reflections which arrive slightly later.
Dynamics of zonal flows: failure of wave-kinetic theory, and new geometrical optics approximations
NASA Astrophysics Data System (ADS)
Parker, Jeffrey B.
2016-12-01
The self-organisation of turbulence into regular zonal flows can be fruitfully investigated with quasi-linear methods and statistical descriptions. A wave-kinetic equation that assumes asymptotically large-scale zonal flows leads to ultraviolet divergence. From an exact description of quasi-linear dynamics emerges two better geometrical optics approximations. These involve not only the mean flow shear but also the second and third derivative of the mean flow. One approximation takes the form of a new wave-kinetic equation, but is only valid when the zonal flow is quasi-static and wave action is conserved.
Fluid simulation of tokamak ion temperature gradient turbulence with zonal flow closure model
NASA Astrophysics Data System (ADS)
Yamagishi, Osamu; Sugama, Hideo
2016-03-01
Nonlinear fluid simulation of turbulence driven by ion temperature gradient modes in the tokamak fluxtube configuration is performed by combining two different closure models. One model is a gyrofluid model by Beer and Hammett [Phys. Plasmas 3, 4046 (1996)], and the other is a closure model to reproduce the kinetic zonal flow response [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. By including the zonal flow closure, generation of zonal flows, significant reduction in energy transport, reproduction of the gyrokinetic transport level, and nonlinear upshift on the critical value of gradient scale length are observed.
Fluid simulation of tokamak ion temperature gradient turbulence with zonal flow closure model
Yamagishi, Osamu Sugama, Hideo
2016-03-15
Nonlinear fluid simulation of turbulence driven by ion temperature gradient modes in the tokamak fluxtube configuration is performed by combining two different closure models. One model is a gyrofluid model by Beer and Hammett [Phys. Plasmas 3, 4046 (1996)], and the other is a closure model to reproduce the kinetic zonal flow response [Sugama et al., Phys. Plasmas 14, 022502 (2007)]. By including the zonal flow closure, generation of zonal flows, significant reduction in energy transport, reproduction of the gyrokinetic transport level, and nonlinear upshift on the critical value of gradient scale length are observed.
Barotropic instability of midlatitude zonal jets on Mars, earth and Venus
NASA Technical Reports Server (NTRS)
Michelangeli, Diane V.; Zurek, Richard W.; Elson, Lee S.
1987-01-01
A linearized, nondivergent, barotropic vorticity model on a sphere is used to intercompare the fastest growing, barotropically unstable wave modes computed for zonal jets at high latitudes in the middle atmospheres of Venus, earth, and Mars. The model is briefly described, and the choice of a range of zonal jet parameters - primarily Rossby numbers and the jet width - appropriate to Venus and Mars is discussed. The results are presented and compared with those found by Elson (1982) and Hartmann (1983) for nondivergent, barotropically unstable modes in relatively broad, midlatitude zonal jets in planetary atmospheres. Some specific examples appropriate to Venus and Mars are presented.
Evolution of the zonal mean state in the equatorial middle atmosphere during October 1978-May 1979
NASA Technical Reports Server (NTRS)
Hitchman, Matthew H.; Leovy, Conway B.
1986-01-01
The week-to-week evolution of the zonal mean state of the equatorial middle atmosphere is studied using daily mapped temperatures derived with the Limb Infrared Monitor of the Stratosphere (LIMS) instrument on Nimbus 7. The characteristics of the LIMS instrument and rocket data are described. The development of the zonal mean state at low latitudes, and the relation between the evolution of the zonal mean state and extratropical changes are examined. The residual circulation is estimated using a radiative algorithm. Advection by the residual mean circulation, and the role of inertial acceleration in mean meridional circulations are discussed.
Zonal Flow as Pattern Formation: Merging Jets and the Ultimate Jet Length Scale
Jeffrey B. Parker and John A. Krommes
2013-01-30
Zonal flows are well known to arise spontaneously out of turbulence. It is shown that for statisti- cally averaged equations of quasigeostrophic turbulence on a beta plane, zonal flows and inhomoge- neous turbulence fit into the framework of pattern formation. There are many implications. First, the zonal flow wavelength is not unique. Indeed, in an idealized, infinite system, any wavelength within a certain continuous band corresponds to a solution. Second, of these wavelengths, only those within a smaller subband are linearly stable. Unstable wavelengths must evolve to reach a stable wavelength; this process manifests as merging jets.
Advances and Current Challenges in the Theory of Zonal-Flow Generation
NASA Astrophysics Data System (ADS)
Krommes, John A.
2010-11-01
Some remarks are made about the use of modern statistical formalism in the calculation of the zonal-flow growth rate and the backreaction of zonal flows on drift waves. The intimate connection between the zonal growth-rate calculation and the derivation of a statistical formula for eddy viscosity in two-dimensional neutral fluids is emphasized, as is the the role of Casimir invariants in disparate-scale expansion. Also stressed is the importance of random Galilean invariance in the calculation of the triad interaction time between short-wavelength drift waves and long-wavelength flows.
Advances and Current Challenges in the Theory of Zonal-Flow Generation
Krommes, John A.
2010-11-23
Some remarks are made about the use of modern statistical formalism in the calculation of the zonal-flow growth rate and the backreaction of zonal flows on drift waves. The intimate connection between the zonal growth-rate calculation and the derivation of a statistical formula for eddy viscosity in two-dimensional neutral fluids is emphasized, as is the the role of Casimir invariants in disparate-scale expansion. Also stressed is the importance of random Galilean invariance in the calculation of the triad interaction time between short-wavelength drift waves and long-wavelength flows.
Zonal-flow dynamics from a phase-space perspective
Ruiz, D. E.; Parker, J. B.; Shi, E. L.; Dodin, I. Y.
2016-12-16
The wave kinetic equation (WKE) describing drift-wave (DW) turbulence is widely used in the studies of zonal flows (ZFs) emerging from DW turbulence. But, this formulation neglects the exchange of enstrophy between DWs and ZFs and also ignores effects beyond the geometrical-optics limit. Furthermore, we derive a modified theory that takes both of these effects into account, while still treating DW quanta (“driftons”) as particles in phase space. The drifton dynamics is described by an equation of the Wigner–Moyal type, which is commonly known in the phase-space formulation of quantum mechanics. In the geometrical-optics limit, this formulation features additional terms missing in the traditional WKE that ensure exact conservation of the total enstrophy of the system, in addition to the total energy, which is the only conserved invariant in previous theories based on the WKE. We present numerical simulations to illustrate the importance of these additional terms. The proposed formulation can be considered as a phase-space representation of the second-order cumulant expansion, or CE2.
Zonal-flow dynamics from a phase-space perspective
Ruiz, D. E.; Parker, J. B.; Shi, E. L.; ...
2016-12-16
The wave kinetic equation (WKE) describing drift-wave (DW) turbulence is widely used in the studies of zonal flows (ZFs) emerging from DW turbulence. But, this formulation neglects the exchange of enstrophy between DWs and ZFs and also ignores effects beyond the geometrical-optics limit. Furthermore, we derive a modified theory that takes both of these effects into account, while still treating DW quanta (“driftons”) as particles in phase space. The drifton dynamics is described by an equation of the Wigner–Moyal type, which is commonly known in the phase-space formulation of quantum mechanics. In the geometrical-optics limit, this formulation features additional termsmore » missing in the traditional WKE that ensure exact conservation of the total enstrophy of the system, in addition to the total energy, which is the only conserved invariant in previous theories based on the WKE. We present numerical simulations to illustrate the importance of these additional terms. The proposed formulation can be considered as a phase-space representation of the second-order cumulant expansion, or CE2.« less
Combinatorial scaffold morphologies for zonal articular cartilage engineering☆
Steele, J.A.M.; McCullen, S.D.; Callanan, A.; Autefage, H.; Accardi, M.A.; Dini, D.; Stevens, M.M.
2014-01-01
Articular cartilage lesions are a particular challenge for regenerative medicine strategies as cartilage function stems from a complex depth-dependent organization. Tissue engineering scaffolds that vary in morphology and function offer a template for zone-specific cartilage extracellular matrix (ECM) production and mechanical properties. We fabricated multi-zone cartilage scaffolds by the electrostatic deposition of polymer microfibres onto particulate-templated scaffolds produced with 0.03 or 1.0 mm3 porogens. The scaffolds allowed ample space for chondrocyte ECM production within the bulk while also mimicking the structural organization and functional interface of cartilage’s superficial zone. Addition of aligned fibre membranes enhanced the mechanical and surface properties of particulate-templated scaffolds. Zonal analysis of scaffolds demonstrated region-specific variations in chondrocyte number, sulfated GAG-rich ECM, and chondrocytic gene expression. Specifically, smaller porogens (0.03 mm3) yielded significantly higher sGAG accumulation and aggrecan gene expression. Our results demonstrate that bilayered scaffolds mimic some key structural characteristics of native cartilage, support in vitro cartilage formation, and have superior features to homogeneous particulate-templated scaffolds. We propose that these scaffolds offer promise for regenerative medicine strategies to repair articular cartilage lesions. PMID:24370641
Equatorial superrotation in a thermally driven zonally symmetric circulation
NASA Technical Reports Server (NTRS)
Mayr, H. G.; Harris, I.
1981-01-01
Near the equator where the Coriolis force vanishes, the momentum balance for the axially symmetric circulation is established between horizontal and vertical diffusion, which, a priori, does not impose constraints on the direction or magnitude of the zonal winds. Solar radiation absorbed at low latitudes is a major force in driving large scale motions with air rising near the equator and falling at higher latitudes. In the upper leg of the meridional cell, angular momentum is redistributed so that the atmosphere tends to subrotate (or corotate) at low latitudes and superrotate at high latitudes. In the lower leg, however, the process is reversed and produces a tendency for the equatorial region to superrotate. The outcome depends on the energy budget which is closely coupled to the momentum budget through the thermal wind equation; a pressure (temperature) maximum is required to sustain equatorial superrotation. Such a condition arises in regions which are convectively unstable and the temperature lapse rate is superadiabatic. It should arise in the tropospheres of Jupiter and Saturn; planetary energy from the interior is carried to higher altitudes where radiation to space becomes important. Upward equatorial motions in the direct and indirect circulations (Ferrel-Thomson type) imposed by insolation can then trap dynamic energy for equatorial heating which can sustain the superrotation of the equatorial region.
The Wave Zonal Mean Flow Interaction in the Southern Hemisphere.
NASA Astrophysics Data System (ADS)
Kim, Hyun-Kyung; Lee, Sukyoung
2004-05-01
This study examines the wave zonal mean flow interaction in the Southern Hemisphere (SH) and in an SH- like model atmosphere. During the SH winter, when there exist both subtropical and polar front jets, growing baroclinic waves are found between the two jets as well as along the polar front jet. These baroclinic waves between the two jets pump westerly momentum into the interjet region flanked by the subtropical and polar front jets. As a result, these baroclinic waves blend the two jets, preventing the longtime occurrence or establishment of two well-defined jets. It is also shown that during the SH winter, the deceleration of the westerlies on the equatorward side of the subtropical jet is mostly associated with the above baroclinic waves in the interjet region, rather than with eddies that originate along the polar front jet.A set of idealized numerical model experiments shows that as the value of the surface friction is increased, the direction of the baroclinic wave momentum flux in the interjet region changes, resulting in a drastically different climatological flow.
Zonal Flow Velocimetry in Spherical Couette Flow using Acoustic Modes
NASA Astrophysics Data System (ADS)
Adams, Matthew M.; Mautino, Anthony R.; Stone, Douglas R.; Triana, Santiago A.; Lekic, Vedran; Lathrop, Daniel P.
2015-11-01
We present studies of spherical Couette flows using the technique of acoustic mode Doppler velocimetry. This technique uses rotational splittings of acoustic modes to infer the azimuthal velocity profile of a rotating flow, and is of special interest in experiments where direct flow visualization is impractical. The primary experimental system consists of a 60 cm diameter outer spherical shell concentric with a 20 cm diameter sphere, with air or nitrogen gas serving as the working fluid. The geometry of the system approximates that of the Earth's core, making these studies geophysically relevant. A turbulent shear flow is established in the system by rotating the inner sphere and outer shell at different rates. Acoustic modes of the fluid volume are excited using a speaker and measured via microphones, allowingdetermination of rotational splittings. Preliminary results comparing observed splittings with those predicted by theory are presented. While the majority of these studies were performed in the 60 cm diameter device using nitrogen gas, some work has also been done looking at acoustic modes in the 3 m diameter liquid sodium spherical Couette experiment. Prospects for measuring zonal velocity profiles in a wide variety of experiments are discussed.
Comments on "extended zonal dislocations mediating ? ? twinning in titanium"
NASA Astrophysics Data System (ADS)
El Kadiri, Haitham; Barrett, Christopher D.
2013-09-01
In a recent paper, Li et al. (Philos. Mag. 92 (2012) p.1006) used results of atomistic simulations to advance a growth mechanism of ? ? twinning in titanium based on the concept of two elementary twinning dislocations which nucleate and glide in pairs but separately and sequentially on two neighbouring planes. This new Comment was stimulated after A. Serra, D.J. Bacon and R.C. Pond privately raised concerns on this growth model to one of the present authors, H. El Kadiri, who This was a co-author of the original paper (Philos. Mag. 92 (2012) p.1006). We repeated the simulations and obtained nearly the same simulations results as Li et al. However, after re-analysing these results, we have concluded that the extended extrinsic zonal dislocation mechanism claimed to be that for twin growth in titanium is in fact false, confirming the accuracy of the Comment by Serra et al that results of Li and co-authors were misinterpreted.
Investigating the zonal wind response to SST warming using transient ensemble AGCM experiments
NASA Astrophysics Data System (ADS)
Palipane, Erool; Lu, Jian; Staten, Paul; Chen, Gang; Schneider, Edwin K.
2017-01-01
The response of the atmospheric circulation to greenhouse gas-induced SST warming is investigated using large ensemble experiments with two AGCMs, with a focus on the robust feature of the poleward shift of the eddy driven jet. In these experiments, large ensembles of simulations are conducted by abruptly switching the SST forcing on from January 1st to focus on the wintertime circulation adjustment. A hybrid, finite amplitude wave activity budget analysis is performed to elucidate the nonlinear and irreversible aspects of the eddy-mean flow interaction during the adjustment of the zonal wind towards a poleward shifted state. The results confirm the results from earlier more idealized studies, particularly the importance of reduced dissipation of wave activity, in which the midlatitude decrease of effective diffusivity appears to be dominant. This reduction in dissipation increases the survival of midlatitude waves. These surviving waves, when reaching the upper propagation level in the upper troposphere, are subject to the influence of the increase of reflection phase speed at the poleward side of the mean jet, and thus more waves are reflected equatorward across the jet, giving rise to a poleward transport of momentum and thus an eddy momentum flux convergence for the poleward shift. The relative importance of wave breaking-induced PV mixing versus diabatic PV source in the evolution of the Lagrangian PV gradient is also investigated. The former plays the dominant role in the PV gradient formation during the initial phase of the jet shift, while the latter actually opposes the evolution of the Lagrangian PV gradient at times.
Zonal Flow Velocimetry using Acoustic Modes in Experimental Models of a Planetary Core
NASA Astrophysics Data System (ADS)
Adams, M. M.; Mautino, A. R.; Stone, D.; Triana, S. A.; Lekic, V.; Lathrop, D. P.
2015-12-01
Rotating hydromagnetic experiments can serve as models of planetary cores, matching some of the dimensionless parameters relevant to planets. One challenge with such experiments is determining the flows present. The opacity of the fluids used in these experiments (e.g. liquid sodium) prevents direct flow visualization techniques from being employed. One method allowing determination of zonal flows in such experiments is acoustic mode velocimetry. In this technique, the rotational splittings of acoustic mode spectra are used to infer the azimuthal velocity profile of the flow. Here we present the use of this technique to study flows in experimental models of the Earth's core. Most of these results were obtained in a 60 cm diameter spherical Couette device, with a 20 cm diameter inner sphere, and using nitrogen gas as the working fluid. Turbulent flow is driven in the system via differential rotation of the outer shell and inner sphere. Acoustic modes are excited in the fluid volume using a speaker, and microphones are used to measure the frequencies and rotational splittings of the modes. We compare the observed splittings with those predicted by theory as a way of validating the method, and infer mean flows from these observations. We also present some preliminary results of acoustic studies in the 3 m diameter liquid sodium spherical Couette experiment. Finally, we discuss future prospects for this experimental technique.
NASA Astrophysics Data System (ADS)
Li, K. F.; Yao, K.; Taketa, C.; Zhang, X.; Liang, M. C.; Jiang, X.; Newman, C. E.; Tung, K. K.; Yung, Y. L.
2015-12-01
With the advance of modern computers, studies of planetary atmospheres have heavily relied on general circulation models (GCMs). Because these GCMs are usually very complicated, the simulations are sometimes difficult to understand. Here we develop a semi-analytic zonally averaged, cyclostrophic residual Eulerian model to illustrate how some of the large-scale structures of the middle atmospheric circulation can be explained qualitatively in terms of simple thermal (e.g. solar heating) and mechanical (the Eliassen-Palm flux divergence) forcings. This model is a generalization of that for fast rotating planets such as the Earth, where geostrophy dominates (Andrews and McIntyre 1987). The solution to this semi-analytic model consists of a set of modified Hough functions of the generalized Laplace's tidal equation with the cyclostrohpic terms. As examples, we apply this model to Titan and Venus. We show that the seasonal variations of the temperature and the circulation of these slowly-rotating planets can be well reproduced by adjusting only three parameters in the model: the Brunt-Väisälä bouyancy frequency, the Newtonian radiative cooling rate, and the Rayleigh friction damping rate. We will also discuss the application of this model to study the meridional transport of photochemically produced tracers that can be observed by space instruments.
NASA Astrophysics Data System (ADS)
Li, King-Fai; Yao, Kaixuan; Taketa, Cameron; Zhang, Xi; Liang, Mao-Chang; Jiang, Xun; Newman, Claire; Tung, Ka-Kit; Yung, Yuk L.
2016-04-01
With the advance of modern computers, studies of planetary atmospheres have heavily relied on general circulation models (GCMs). Because these GCMs are usually very complicated, the simulations are sometimes difficult to understand. Here we develop a semi-analytic zonally averaged, cyclostrophic residual Eulerian model to illustrate how some of the large-scale structures of the middle atmospheric circulation can be explained qualitatively in terms of simple thermal (e.g. solar heating) and mechanical (the Eliassen-Palm flux divergence) forcings. This model is a generalization of that for fast rotating planets such as the Earth, where geostrophy dominates (Andrews and McIntyre 1987). The solution to this semi-analytic model consists of a set of modified Hough functions of the generalized Laplace's tidal equation with the cyclostrohpic terms. As an example, we apply this model to Titan. We show that the seasonal variations of the temperature and the circulation of these slowly-rotating planets can be well reproduced by adjusting only three parameters in the model: the Brunt-Väisälä bouyancy frequency, the Newtonian radiative cooling rate, and the Rayleigh friction damping rate. We will also discuss an application of this model to study the meridional transport of photochemically produced tracers that can be observed by space instruments.
Fundamental Scalings of Zonal Flows in a Basic Plasma Physics Experiment
NASA Astrophysics Data System (ADS)
Sokolov, Vladimir; Wei, Xiao; Sen, Amiya K.
2007-11-01
A basic physics experimental study of zonal flows (ZF) associated with ITG (ion temperature gradient) drift modes has been performed in the Columbia Linear Machine (CLM) and ZF has been definitively identified [1]. However, in contrast to most tokamak experiments, the stabilizing effect of ZF shear to ITG appears to be small in CLM. We now report on the study of important scaling behavior of ZF. First and most importantly, we report on the collisional damping scaling of ZF, which is considered to be its saturation mechanism [2]. By varying the sum of ion-ion and ion-neutral collision frequency over nearly half an order of magnitude, we find no change in the amplitude of ZF. Secondly, we study the scaling of ZF amplitude with ITG amplitude via increasing ITG drive though ηi, as well as feedback (stabilizing / destabilizing). We have observed markedly different scaling near and far above marginal stability. [1] V. Sokolov, X. Wei, A.K. Sen and K. Avinash, Plasma Phys.Controlled Fusion 48, S111 (2006). [2] P.H. Diamond, S.-I. Itoh, K.Itoh and T.S. Hahm, Plasma Phys.Controlled Fusion 47, R35 (2005).
Novel design for zonal flow probe arrays in the HL-2A tokamak
NASA Astrophysics Data System (ADS)
Yan, Longwen; Hong, Wenyu; Zhao, Kaijun; Dong, Jiaqi; Cheng, Jun; Qian, Jun; Yu, Deliang; Luo, Cuiwen; Xu, Zhengyu; Huang, Yuan; Yang, Qingwei; Ding, Xuantong
2006-11-01
A novel design of three-step Langmuir probe (TSLP) array has been developed for zonal flow (ZF) studies in the HL-2A tokamak. Three TSLP arrays are used to determine three-dimensional (3D) features of the ZFs. Two TSLP arrays are located in the same poloidal plane at a 6.5cm separation, while the third TSLP array is separated toroidally by 80cm. A fourth TSLP array driven by pneumatically reciprocating system is applied for boundary parameter profile measurements within 8cm. The TSLP structure is described in detail. The measured 3D properties of the geodesic acoustic mode (GAM) ZFs are described and the poloidal and toroidal mode numbers (m<2,n˜0) are simultaneously determined in the HL-2A tokamak for the first time. The radial wave vector at the GAM frequency is estimated as 2.6±0.2cm-1, corresponding to radial scale length of 2.4cm.
The importance of wave break events for synoptic scale buildups of zonal available potential energy
NASA Astrophysics Data System (ADS)
Bowley, K.; Gyakum, J. R.; Atallah, E.
2016-12-01
to zonally elongate the jet, reduce baroclinic conversions to kinetic energy, and to regionally generate ZAPE. Finally, the importance of ZAPE buildup events in creating an environment prone to significant cyclogenesis will be examined by exploring the frequency of LC2 (cyclonic) wave break events in the days following a ZAPE buildup event.
Futatani, S.; Horton, W.; Kahlon, L. Z.; Kaladze, T. D.
2015-01-15
Nonlinear simulations of electromagnetic Rossby and Khantadze planetary waves in the presence of a shearless and sheared zonal flows in the weakly ionized ionospheric E-layer are carried out. The simulations show that the nonlinear action of the vortex structures keeps the solitary character in the presence of shearless zonal winds as well as the ideal solutions of solitary vortex in the absence of zonal winds. In the presence of sheared zonal winds, the zonal flows result in breaking into separate multiple smaller pieces. A passively convected scalar field is shown to clarify the transport associated with the vortices. The work shows that the zonal shear flows provide an energy source into the vortex structure according to the shear rate of the zonal winds.
Quasi-Stationary Zonally Asymmetric Circulations in the Equatorial Lower Mesosphere.
NASA Astrophysics Data System (ADS)
Hitchman, Matthew H.; Leovy, Conway B.; Gille, John C.; Bailey, Paul L.
1987-08-01
Data from the Limb Infrared Monitor of the Stratosphere (LIMS) are used to identify a new type of planetary scale disturbance in the equatorial lower mesosphere during northern winter 1978/79. The disturbances consist of two or three vertically stacked temperature extrema of alternating sign. They persist for as long as two weeks and do not propagate. Their occurrence is confined to regions of very weak or negative inertial stability, and their meridional to vertical aspect ratio, meridional structure and zonal spectrum are consistent with disturbances predicted by inertial instability theory. However, they are found only when there is strong forcing of the subtropical mesosphere by zonal wavenumber one and two Rossby waves. This fact, together with the absence of zonal propagation, suggests that stationary Rossby waves determine their occurrence and longitudinal structure. These structures can significantly modify the zonal mean flow and should be taken into account in dynamical models of the equatorial mesosphere.
Stationary zonal flows during the formation of the edge transport barrier in the JET tokamak
Hillesheim, J. C.; Meyer, H.; Maggi, C. F.; ...
2016-02-10
In this study, high spatial resolution Doppler backscattering measurements in JET have enabled new insights into the development of the edge Er. We observe fine-scale spatial structures in the edge Er well with a wave number krρi ≈ 0.4-0.8, consistent with stationary zonal flows, the characteristics of which vary with density. The zonal flow amplitude and wavelength both decrease with local collisionality, such that the zonal flow E x B shear increases. Above the minimum of the L-H transition power threshold dependence on density, the zonal flows are present during L mode and disappear following the H-mode transition, while belowmore » the minimum they are reduced below measurable amplitude during L mode, before the L-H transition.« less
Stationary zonal flows during the formation of the edge transport barrier in the JET tokamak
Hillesheim, J. C.; Meyer, H.; Maggi, C. F.; Meneses, L.; Poli, E.; Delabie, E.
2016-02-10
In this study, high spatial resolution Doppler backscattering measurements in JET have enabled new insights into the development of the edge E_{r}. We observe fine-scale spatial structures in the edge E_{r} well with a wave number k_{rρi} ≈ 0.4-0.8, consistent with stationary zonal flows, the characteristics of which vary with density. The zonal flow amplitude and wavelength both decrease with local collisionality, such that the zonal flow E x B shear increases. Above the minimum of the L-H transition power threshold dependence on density, the zonal flows are present during L mode and disappear following the H-mode transition, while below the minimum they are reduced below measurable amplitude during L mode, before the L-H transition.
Asahi, Y. Tsutsui, H.; Tsuji-Iio, S.; Ishizawa, A.; Watanabe, T.-H.
2014-05-15
Turbulent transport caused by electron temperature gradient (ETG) modes was investigated by means of gyrokinetic simulations. It was found that the ETG turbulence can be regulated by meso-scale zonal flows driven by trapped electron modes (TEMs), which are excited with much smaller growth rates than those of ETG modes. The zonal flows of which radial wavelengths are in between the ion and the electron banana widths are not shielded by trapped ions nor electrons, and hence they are effectively driven by the TEMs. It was also shown that an E × B shearing rate of the TEM-driven zonal flows is larger than or comparable to the growth rates of long-wavelength ETG modes and TEMs, which make a main contribution to the turbulent transport before excitation of the zonal flows.
Stationary Zonal Flows during the Formation of the Edge Transport Barrier in the JET Tokamak
NASA Astrophysics Data System (ADS)
Hillesheim, J. C.; Delabie, E.; Meyer, H.; Maggi, C. F.; Meneses, L.; Poli, E.; JET Contributors; EUROfusion Consortium, JET, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom
2016-02-01
High spatial resolution Doppler backscattering measurements in JET have enabled new insights into the development of the edge Er. We observe fine-scale spatial structures in the edge Er well with a wave number krρi≈0.4 -0.8 , consistent with stationary zonal flows, the characteristics of which vary with density. The zonal flow amplitude and wavelength both decrease with local collisionality, such that the zonal flow E ×B shear increases. Above the minimum of the L -H transition power threshold dependence on density, the zonal flows are present during L mode and disappear following the H -mode transition, while below the minimum they are reduced below measurable amplitude during L mode, before the L -H transition.
Studies of Zonal Flows Driven by Drift Mode Turbulence in Laboratory and Space Plasmas
NASA Astrophysics Data System (ADS)
Bingham, R.; Trines, R.; Mendonça, J. T.; Silva, L. O.; Shukla, P. K.; Dunlop, M. W.; Vaivads, A.; Davies, J. A.; Bamford, R. A.; Mori, W. B.; Tynan, G.
2008-10-01
The interaction between broadband drift mode turbulence and zonal flows is an important topic associated with transport at plasma boundaries. The generation of zonal flows by the modulational instability of broad band drift waves has resulted in the observation of self organized solitary wave structures at the magnetopause. To understand these structures and their importance to future burning plasmas and space plasmas we have developed a unique numerical simulation code that describes drift wave—zonal flow turbulence. We show that observations by cluster spacecraft confirms the role of drift wave zonal flow turbulence at the Earth's magnetopause and further demonstrates that the magnetopause boundary acts in a s similar manner to transport barriers in tokamak fusion devices. Thus cementing the relationship between the plasma physics of laboratory devices and space plasmas.
NASA Technical Reports Server (NTRS)
Hou, Arthur Y.; Goody, Richard M.; Fels, Stephen B.
1990-01-01
The equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the Venus cloud base were calculated. The results show that the tidal mechanism proposed by Fels and Lindzen (1974) can account for a substantial fraction (and possibly all) of the increase of the equatorial wind speed above the cloud base. Above the cloud tops, tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data. Tidal forcing does not explain the superrotation below the clouds, and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes.
NASA Technical Reports Server (NTRS)
Hou, Arthur Y.; Goody, Richard M.; Fels, Stephen B.
1990-01-01
The equilibrium zonal wind structure resulting from the interaction of the semidiurnal tide and the mean meridional circulation driven by the zonally averaged solar heating above the Venus cloud base were calculated. The results show that the tidal mechanism proposed by Fels and Lindzen (1974) can account for a substantial fraction (and possibly all) of the increase of the equatorial wind speed above the cloud base. Above the cloud tops, tidal deceleration may be too small to produce the zonal wind decrease with height inferred from thermal data. Tidal forcing does not explain the superrotation below the clouds, and additional eddy sources are needed to account for the zonal wind structure at mid and high latitudes.
Two- and three-dimensional natural and mixed convection simulation using modular zonal models
Wurtz, E.; Nataf, J.M.; Winkelmann, F.
1996-07-01
We demonstrate the use of the zonal model approach, which is a simplified method for calculating natural and mixed convection in rooms. Zonal models use a coarse grid and use balance equations, state equations, hydrostatic pressure drop equations and power law equations of the form {ital m} = {ital C}{Delta}{sup {ital n}}. The advantage of the zonal approach and its modular implementation are discussed. The zonal model resolution of nonlinear equation systems is demonstrated for three cases: a 2-D room, a 3-D room and a pair of 3-D rooms separated by a partition with an opening. A sensitivity analysis with respect to physical parameters and grid coarseness is presented. Results are compared to computational fluid dynamics (CFD) calculations and experimental data.
Theory of Fine-scale Zonal Flow Generation From Trapped Electron Mode Turbulence
Lu Wang and T.S. Hahm
2009-06-11
Most existing zonal flow generation theory has been developed with a usual assumption of qrρθ¡ << 1 (qr is the radial wave number of zonal flow, and ρθ¡ is the ion poloidal gyrora- dius). However, recent nonlinear gyrokinetic simulations of trapped electron mode (TEM) turbulence exhibit a relatively short radial scale of the zonal flows with qrρθ¡ ~ 1 [Z. Lin et al., IAEA-CN/TH/P2-8 (2006); D. Ernst et al., Phys. Plasmas 16, 055906 (2009)]. This work reports an extension of zonal flow growth calculation to this short wavelength regime via the wave kinetics approach. A generalized expression for the polarization shielding for arbitrary radial wavelength [Lu Wang and T.S. Hahm, to appear in Phys. Plasmas (2009)] which extends the Rosenbluth-Hinton formula in the long wavelength limit is applied.
Thermodynamic and dynamic controls on changes in the zonally anomalous hydrological cycle
NASA Astrophysics Data System (ADS)
Wills, Robert C.; Byrne, Michael P.; Schneider, Tapio
2016-05-01
The wet gets wetter, dry gets drier paradigm explains the expected moistening of the extratropics and drying of the subtropics as the atmospheric moisture content increases with global warming. Here we show, using precipitation minus evaporation (P - E) data from climate models, that it cannot be extended to apply regionally to deviations from the zonal mean. Wet and dry zones shift substantially in response to shifts in the stationary-eddy circulations that cause them. Additionally, atmospheric circulation changes lead to a smaller increase in the zonal variance of P - E than would be expected from atmospheric moistening alone. The P - E variance change can be split into dynamic and thermodynamic components through an analysis of the atmospheric moisture budget. This reveals that a weakening of stationary-eddy circulations and changes in the zonal variation of transient-eddy moisture fluxes moderate the strengthening of the zonally anomalous hydrological cycle with global warming.
Dynamics of zonal-mean flow assimilation and implications for winter circulation anomalies
DeWeaver, E.; Nigam, S.
1997-07-01
Seasonally averaged 200-mb circulations for recent winters (1987/88 and 1988/89) that represent opposite phases of El Nino and a zonal-mean zonal flow index cycle are diagnosed using data assimilated by the Goddard Earth Observing System (GEOS) and operational analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF). The comparison is undertaken to determine whether there are significant differences in the 200-mb vorticity dynamics implied by the mean meridional circulations in the two datasets and whether these differences can be related to the Incremental Analysis Update (IAU) method used in the GEOS assimilation. The two datasets show a high degree of similarity in their depictions of the large-scale rotational flow, but there are substantial differences in the associated divergent circulations. For the zonal-mean flow, the zonal winds are substantially the same, but the meridional wind in the Tropics and subtropics is considerably weaker in the GEOS assimilation than its counterparts in both the ECMWF data and the GEOS analyses used to produce the assimilation. The authors examine the assimilation of the Hadley circulation using a zonally symmetric f-plane model. For this model, the IAU method easily assimilates the rotational flow but fails to assimilate the divergent circulation. This deficiency of the IAU method may explain the weakness of the Hadley cell in the GEOS assimilation. For this simple model, an alternative assimilation method, based on constraints imposed by the analyzed potential vorticity and mean meridional circulation fields, is proposed that simultaneously assimilates both rotational and divergent flow components. Barotropic modeling suggests that an accurate representation of mean meridional flow anomalies can be important for the diagnosis of both zonal-mean and eddy rotational flow perturbations, particularly during extreme phases of the zonal-mean zonal flow fluctuation. 22 refs., 10 figs.
Ion Layer Separation and Equilibrium Zonal Winds in Midlatitude Sporadic E
NASA Technical Reports Server (NTRS)
Earle, G. D.; Kane, T. J.; Pfaff, R. F.; Bounds, S. R.
2000-01-01
In-situ observations of a moderately strong mid-latitude sporadic-E layer show a separation in altitude between distinct sublayers composed of Fe(+), Mg(+), and NO(+). From these observations it is possible to estimate the zonal wind field consistent with diffusive equilibrium near the altitude of the layer. The amplitude of the zonal wind necessary to sustain the layer against diffusive effects is less than 10 meters per second, and the vertical wavelength is less than 10 km.
Monsoons over an idealized zonally-symmetric continent
NASA Astrophysics Data System (ADS)
Bordoni, S.; Laraia, A.
2016-12-01
Idealized modeling studies have provided the basis for significant progress on our conceptual and theoretical understanding of the fundamental dynamics of ITCZ and monsoon convergence zones. In this work, we study monsoons over an idealized zonally symmetric, fully-saturated continent north of 10N in a model with simplified physics. The use of such an idealized model allows us to identify essential dynamical mechanisms of monsoons in the absence of uncertain feedbacks, which can be used as a reference for evaluation of more complex simulations. Our results show that adding a hemispheric asymmetry in surface heat capacity between land and ocean is sufficient to cause symmetric breaking in both the spatial and temporal distribution of precipitation. The spatial symmetry breaking is manifest in a poleward displaced ITCZ over the continent during NH summer. Interestingly, while the ITCZ is further displaced poleward during NH summer, the cross-equatorial energy transport maximizes in the opposite season, when the ITCZ remains closer to the equator over the ocean. This seems at odd with previous work that has correlated the ITCZ position with the cross-equatorial energy transport, but arises because the energy input into the equatorial atmosphere, which acts as a sensitivity factor of the ITCZ position to cross-equatorial energy transport, is smaller in JJA than it is in DJF. The temporal symmetric breaking appears in an asymmetry between a rapid NH monsoon onset and a much more gradual retreat. This asymmetry results from the tropical overturning circulation being in different dynamical regimes at the beginning and end of the NH summer, which causes a fundamentally different response to the insolation forcing. Interestingly, the seasonal cycle of this idealized monsoon bears resemblance to that of the Indian monsoon, suggesting that fundamental mechanisms emerging from this study might be indeed relevant for observed monsoons.
Theoretical studies of interaction between drift waves and zonal flows
NASA Astrophysics Data System (ADS)
Guo, Zehua
The size scaling of confinement properties in magnetized plasmas is one of the crucial and challenging problems of fusion energy research. It has been pointed out [64] that turbulence spreading is responsible for the local turbulence intensity dependence on the global equilibrium properties, i.e. the system size, and, ultimately, for the size scaling of turbulent transport coefficients. In the present work, first we investigate the slab analysis [46] for the spatio-temporal evolution of the drift wave(DW) radial envelope and zonal flow(ZF) amplitude. The derived two-field DW-ZF description reduces to the well-known coherent four-wave modulation interaction model [13] when separating the pump wave and its side bands. Stationary solution of the resulting coupled partial differential equations in a simple limit suggests formation of DW-ZF solitons, due to competition between DW dispersion and nonlinear ZF modulation. It is shown that the hyperbolic-secant DW soliton structure can propagate at group velocity which depends on the envelope peak amplitude. Additional interesting physics, i.e. birth and death, collision, reflection of solitons, can be produced by effects of linear growth/damping, dissipation and equilibrium nonuniformities. Turbulence bursting or intermittency can also be understood within soliton dynamics. The propagation of soliton causes significant radial spreading of initially localized DW turbulence and therefore can affect transport scaling by increasing the radial turbulent region. Further discussion about the correspondence to the two-field DW-ZF description in toroidal geometry [14] will also be presented.
NASA Astrophysics Data System (ADS)
Fedorov, Alexey V.; Burls, Natalie J.; Lawrence, Kira T.; Peterson, Laura C.
2015-12-01
The climate of the tropics and surrounding regions is defined by pronounced zonal (east-west) and meridional (equator to mid-latitudes) gradients in sea surface temperature. These gradients control zonal and meridional atmospheric circulations, and thus the Earth’s climate. Global cooling over the past five million years, since the early Pliocene epoch, was accompanied by the gradual strengthening of these temperature gradients. Here we use records from the Atlantic and Pacific oceans, including a new alkenone palaeotemperature record from the South Pacific, to reconstruct changes in zonal and meridional sea surface temperature gradients since the Pliocene, and assess their connection using a comprehensive climate model. We find that the reconstructed zonal and meridional temperature gradients vary coherently over this time frame, showing a one-to-one relationship between their changes. In our model simulations, we systematically reduce the meridional sea surface temperature gradient by modifying the latitudinal distribution of cloud albedo or atmospheric CO2 concentration. The simulated zonal temperature gradient in the equatorial Pacific adjusts proportionally. These experiments and idealized modelling indicate that the meridional temperature gradient controls upper-ocean stratification in the tropics, which in turn controls the zonal gradient along the equator, as well as heat export from the tropical oceans. We conclude that this tight linkage between the two sea surface temperature gradients posits a fundamental constraint on both past and future climates.
Model test of anchoring effect on zonal disintegration in deep surrounding rock masses.
Chen, Xu-Guang; Zhang, Qiang-Yong; Wang, Yuan; Liu, De-Jun; Zhang, Ning
2013-01-01
The deep rock masses show a different mechanical behavior compared with the shallow rock masses. They are classified into alternating fractured and intact zones during the excavation, which is known as zonal disintegration. Such phenomenon is a great disaster and will induce the different excavation and anchoring methodology. In this study, a 3D geomechanics model test was conducted to research the anchoring effect of zonal disintegration. The model was constructed with anchoring in a half and nonanchoring in the other half, to compare with each other. The optical extensometer and optical sensor were adopted to measure the displacement and strain changing law in the model test. The displacement laws of the deep surrounding rocks were obtained and found to be nonmonotonic versus the distance to the periphery. Zonal disintegration occurs in the area without anchoring and did not occur in the model under anchoring condition. By contrasting the phenomenon, the anchor effect of restraining zonal disintegration was revealed. And the formation condition of zonal disintegration was decided. In the procedure of tunnel excavation, the anchor strain was found to be alternation in tension and compression. It indicates that anchor will show the nonmonotonic law during suppressing the zonal disintegration.
Model Test of Anchoring Effect on Zonal Disintegration in Deep Surrounding Rock Masses
Chen, Xu-Guang; Zhang, Qiang-Yong; Wang, Yuan; Liu, De-Jun; Zhang, Ning
2013-01-01
The deep rock masses show a different mechanical behavior compared with the shallow rock masses. They are classified into alternating fractured and intact zones during the excavation, which is known as zonal disintegration. Such phenomenon is a great disaster and will induce the different excavation and anchoring methodology. In this study, a 3D geomechanics model test was conducted to research the anchoring effect of zonal disintegration. The model was constructed with anchoring in a half and nonanchoring in the other half, to compare with each other. The optical extensometer and optical sensor were adopted to measure the displacement and strain changing law in the model test. The displacement laws of the deep surrounding rocks were obtained and found to be nonmonotonic versus the distance to the periphery. Zonal disintegration occurs in the area without anchoring and did not occur in the model under anchoring condition. By contrasting the phenomenon, the anchor effect of restraining zonal disintegration was revealed. And the formation condition of zonal disintegration was decided. In the procedure of tunnel excavation, the anchor strain was found to be alternation in tension and compression. It indicates that anchor will show the nonmonotonic law during suppressing the zonal disintegration. PMID:23997683
Dynamics of Zonal FLow Instability and Saturation in Drift Wave Turbulence
NASA Astrophysics Data System (ADS)
Katt, S. T.; Kim, E.; Diamond, P. H.
2001-10-01
We study generalized Kelvin-Helmholtz (GKH) instability as a saturation mechanism for a collisionless zonal flow in the background of drift waves. By treating drift waves as adiabatically modified by GKH, we investigate the modulation instability of drift waves due to GKH modes as well as the linear inflection-type instability of zonal flow. In the case where zonal flows evolve on the time scale much larger than GKH mode, GKH mode is shown to become destabilized not only by the linear instability of zonal flow but also by coupling to drift waves, with a growth rate which is enhanced over the linear value. Furthermore, the nonlinear (modulational) generation of a zonal flow is estimated to dominate over that of GKH. Our results indicate that GKH may not play an important role in a collisionless saturation of zonal flow, in contrast to [1] and [2]. The effect of temperature fluctuation will be discussed. [1] B.N. Rogers, W. Dorland, and M. Kotschenreuther, PRL, 85, 5336, (2000). [2] Y. Idomura, M. Wakatani, and S. Tokuda, PoP, 7, 3551, (2000).
NASA Astrophysics Data System (ADS)
Inatsu, Masaru; Mukougawa, Hitoshi; Xie, Shang-Ping
2003-10-01
Midwinter storm track response to zonal variations in midlatitude sea surface temperatures (SSTs) has been investigated using an atmospheric general circulation model under aquaplanet and perpetual-January conditions. Zonal wavenumber-1 SST variations with a meridionally confined structure are placed at various latitudes. Having these SST variations centered at 30°N leads to a zonally localized storm track, while the storm track becomes nearly zonally uniform when the same SST forcing is moved farther north at 40° and 50°N. Large (small) baroclinic energy conversion north of the warm (cold) SST anomaly near the axis of the storm track (near 40°N) is responsible for the large (small) storm growth. The equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction.Significant stationary eddies form in the upper troposphere, with a ridge (trough) northeast of the warm (cold) SST anomaly at 30°N. Heat and vorticity budget analyses indicate that zonally localized condensational heating in the storm track is the major cause for these stationary eddies, which in turn exert a positive feedback to maintain the localized storm track by strengthening the vertical shear near the surface. These results indicate an active role of synoptic eddies in inducing deep, tropospheric-scale response to midlatitude SST variations. Finally, the application of the model results to the real atmosphere is discussed.
Fluctuating zonal flows in the I-mode regime in Alcator C-Moda)
NASA Astrophysics Data System (ADS)
Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C.
2013-05-01
Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100-300 kHz, Δf/f≈0.5, and kθ≈1.3 cm-1) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.
Fluctuating zonal flows in the I-mode regime in Alcator C-Mod
Cziegler, I.; Diamond, P. H.; Fedorczak, N.; Manz, P.; Tynan, G. R.; Xu, M.; Churchill, R. M.; Hubbard, A. E.; Lipschultz, B.; Sierchio, J. M.; Terry, J. L.; Theiler, C.
2013-05-15
Velocity fields and density fluctuations of edge turbulence are studied in I-mode [F. Ryter et al., Plasma Phys. Controlled Fusion 40, 725 (1998)] plasmas of the Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] tokamak, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging based time-delay-estimate velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges examined to date, with the time histories of the GAM and the I-mode specific [D. Whyte et al., Nucl. Fusion 50, 105005 (2010)] Weakly Coherent Mode (WCM, f = 100–300 kHz, Δf/f≈0.5, and k{sub θ}≈1.3 cm{sup −1}) closely following each other through the entire duration of the regime. Thus, the I-mode presents an example of a plasma state in which zero frequency zonal flows and GAM continuously coexist. Using two-field (density-velocity and radial-poloidal velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. The effective nonlinear growth rate of the GAM is estimated, and its comparison to the collisional damping rate seems to suggest a new view on I-mode threshold physics.
NASA Astrophysics Data System (ADS)
Lau, E. M.; Palo, S. E.; Avery, S. K.; Avery, J. P.; Makarov, N. A.
2006-12-01
Early observations of the dynamical features of the mesosphere and lower thermosphere (MLT) over the geographic South Pole revealed the existence of a nonmigrating component of the semidiurnal tide with zonal wavenumber one. Further observational studies have documented the seasonal and interannual behavior of this semidiurnal tide component. These observations have determined that this tide maximizes during the austral summer reaching amplitudes around 20~m/s and disappears during the winter. Moreover, significant amplitude variations have been measured during the summer months. Several hypotheses have been formulated to explain the source of this semidiurnal tide component but recent studies favor the nonlinear interaction of a stationary planetary wave with zonal wavenumber one and the migrating semidiurnal tide as the source of the observed oscillation. Continuous observations of the MLT dynamics over the South Pole have been possible since the installation of a meteor radar at the Amundsen-Scott South Pole station in 2001. The seasonal, interannual, and spatial behavior of the semidiurnal tide with zonal wavenumber one has been and continues to be observed using this meteor radar. In this paper we explore the relationship between our meteor radar measurements of the aforementioned semidiurnal tide component and observations of the stationary planetary wave with zonal wavenumber one obtained from other sources.
Zonal management of arsenic contaminated ground water in Northwestern Bangladesh.
Hill, Jason; Hossain, Faisal; Bagtzoglou, Amvrossios C
2009-09-01
This paper used ordinary kriging to spatially map arsenic contamination in shallow aquifers of Northwestern Bangladesh (total area approximately 35,000 km(2)). The Northwestern region was selected because it represents a relatively safer source of large-scale and affordable water supply for the rest of Bangladesh currently faced with extensive arsenic contamination in drinking water (such as the Southern regions). Hence, the work appropriately explored sustainability issues by building upon a previously published study (Hossain et al., 2007; Water Resources Management, vol. 21: 1245-1261) where a more general nation-wide assessment afforded by kriging was identified. The arsenic database for reference comprised the nation-wide survey (of 3534 drinking wells) completed in 1999 by the British Geological Survey (BGS) in collaboration with the Department of Public Health Engineering (DPHE) of Bangladesh. Randomly sampled networks of zones from this reference database were used to develop an empirical variogram and develop maps of zonal arsenic concentration for the Northwestern region. The remaining non-sampled zones from the reference database were used to assess the accuracy of the kriged maps. Two additional criteria were explored: (1) the ability of geostatistical interpolators such as kriging to extrapolate information on spatial structure of arsenic contamination beyond small-scale exploratory domains; (2) the impact of a priori knowledge of anisotropic variability on the effectiveness of geostatistically based management. On the average, the kriging method was found to have a 90% probability of successful prediction of safe zones according to the WHO safe limit of 10ppb while for the Bangladesh safe limit of 50ppb, the safe zone prediction probability was 97%. Compared to the previous study by Hossain et al. (2007) over the rest of the contaminated country side, the probability of successful detection of safe zones in the Northwest is observed to be about 25
Dispersion in Neptune's zonal wind velocities from NIR Keck AO observations in July 2009
NASA Astrophysics Data System (ADS)
Fitzpatrick, Patrick J.; de Pater, Imke; Luszcz-Cook, Statia; Wong, Michael H.; Hammel, Heidi B.
2014-03-01
We report observations of Neptune made in H-(1.4-1.8 μm) and K'-(2.0-2.4 μm) bands on 14 and 16 July 2009 from the 10-m W.M. Keck II Telescope using the near-infrared camera NIRC2 coupled to the Adaptive Optics (AO) system. We track the positions of 54 bright atmospheric features over a few hours to derive their zonal and latitudinal velocities, and perform radiative transfer modeling to measure the cloud-top pressures of 50 features seen simultaneously in both bands. We observe one South Polar Feature (SPF) on 14 July and three SPFs on 16 July at ˜65 °S. The SPFs observed on both nights are different features, consistent with the high variability of Neptune's storms. There is significant dispersion in Neptune's zonal wind velocities about the smooth Voyager wind profile fit of Sromovsky et al. (Icarus, 105:140, 1993), much greater than the upper limit we expect from vertical wind shear, with the largest dispersion seen at equatorial and southern mid-latitudes. Comparison of feature pressures vs. residuals in zonal velocity from the smooth Voyager wind profile also directly reveals the dominance of mechanisms over vertical wind shear in causing dispersion in the zonal winds. Vertical wind shear is not the primary cause of the difference in dispersion and deviation in zonal velocities between features tracked in H-band on 14 July and those tracked in K'-band on 16 July. Dispersion in the zonal velocities of features tracked over these short time periods is dominated by one or more mechanisms, other than vertical wind shear, that can cause changes in the dispersion and deviation in the zonal velocities on timescales of hours to days.
Zonal Flow Magnetic Field Interaction in the Semi-Conducting Region of Giant Planets
NASA Astrophysics Data System (ADS)
Cao, Hao; Stevenson, David J.
2016-10-01
All four giant planets in the Solar System feature zonal flows on the order of 100 m/s in the cloud deck, and large-scale intrinsic magnetic fields on the order of 1 Gauss near the surface. The vertical structure of the zonal flows remains obscure. The end-member scenarios are shallow flows confined in the radiative atmosphere and deep flows throughout the planet with constant velocity along the direction of the spin-axis. The electrical conductivity increases smoothly as a function of depth inside Jupiter and Saturn, while a discontinuity of electrical conductivity inside Uranus and Neptune cannot be ruled out. Deep zonal flows will inevitably interact with the magnetic field, at depth with even modest electrical conductivity. Here we investigate the interaction between zonal flows and magnetic fields in the semi-conducting region of giant planets. Employing mean-field electrodynamics, we show that the interaction will generate detectable poloidal magnetic field perturbations spatially correlated with the deep zonal flows. Assuming the peak amplitude of the dynamo α-effect to be 0.1 mm/s, deep zonal flows on the order of 0.1 - 1 m/s in the semi-conducting region of Jupiter and Saturn would generate poloidal magnetic perturbations on the order of 0.01 % - 1 % of the background dipole field. These poloidal perturbations should be detectable with the in-situ magnetic field measurements from the upcoming Juno mission and the Cassini Grand Finale. This implies that magnetic field measurements can be employed to constrain the properties of deep zonal flows in the semi-conducting region of giant planets.
Turbulent Transport Regulation by Zonal Fows in Helical Systems with Radial Electric Fields
NASA Astrophysics Data System (ADS)
Sugama, Hideo
2008-11-01
Zonal flows are now well known to play a critical role in regulation of turbulent transport in plasmas. Therefore, for the purpose of improving plasma confinement, it is very important to investigate effects of magnetic configuration on zonal flows generated by turbulence [1-3]. Furthermore, in helical systems such as heliotrons and stellarators, the neoclassically-driven ExB rotaion, which is distinguished from the microscopic sheared ExB zonal flows, is expected to strongly influence not only neoclassical transport but also turbulent transport through enhancing zonal-flow generation [4,5]. In this work, gyrokinetic theory and simulation results are presented to show how the helical geometry and the ExB rotaion affect zonal flows and ion temperature gradient (ITG) turbulent transport. Larger zonal-flow generation and turbulent transport reduction are found by the gyrokinetic ITG turbulence simulation for the neoclassically optimized helical configuration, in which radial drift velocities of ripple-trapped particles decrease [6]. Further zonal-flow enhancement by the ExB rotaion can occur effectively with neoclassical optimization due to the reduction of radial displacements of ripple-trapped particles. These findings are consistent with the confinement improvement observed in the inward-shifted configuration of the Large Helical Device. Also, it is expected that this ExB effect on zonal flows causes the ion mass dependence of the ITG turbulent transport to differ from the conventional gyro-Bohm scaling in a favorable way because the zonal-flow generation increases with increasing the ratio of the ExB velocity to the ion thermal velocity. [1] H. Sugama and T.-H.Watanabe, Phys. Rev. Lett. 94, 115001 (2005). [2] H. Sugama and T.-H. Watanabe, Phys. Plasmas 13, 012501 (2006). [3] T.-H. Watanabe, H. Sugama, and S. Ferrando-Margalet, Nucl. Fusion 47, 1383 (2007). [4] H. Sugama, T.-H. Watanabe, and S. Ferrando-Margalet, Joint Conference of 17th International Toki
Muñoz, Gonzalo; Albarrán-Diego, César; Ferrer-Blasco, Teresa; Sakla, Hani F; García-Lázaro, Santiago
2011-11-01
To evaluate visual function after bilateral implantation of a zonal refractive aspheric multifocal intraocular lens (IOL). Private practice surgery center, Valencia, Spain. Cohort study. Consecutive eyes with cataract had bilateral implantation of Lentis Mplus LS-312 multifocal IOLs. Distance, intermediate, and near visual acuities; contrast sensitivity; defocus curves; and a quality-of-vision questionnaire, including presence of halos or dysphotopsia, were evaluated 6 months postoperatively. A control group of age-matched monofocal pseudophakic patients was included to compare contrast sensitivity function. In the multifocal group, the mean binocular corrected distance visual acuity (logMAR) was -0.04 ± 0.07 at 6 m, 0.11 ± 0.10 at 1 m, and 0.06 ± 0.07 at 40 cm. The defocus curve showed little intermediate vision drop off. Photopic contrast sensitivity for distance was similar to the monofocal IOL contrast sensitivity function, while photopic contrast sensitivity for near and mesopic contrast sensitivity for distance with or without glare was reduced at high frequencies. The mean patient satisfaction was 8.09 ± 1.30 (scale 0 to 10); 84.4% of patients were completely independent of spectacles. Moderate halos, glare, and night-vision problems were reported by 6.2%, 12.5%, and 15.6% of patients, respectively. The new-generation multifocal IOL provided adequate distance, intermediate, and, to a lesser extent, near vision with high rates of spectacle freedom. Halos occurred, and other photic phenomena should be expected in a small percentage of patients. No author has a financial or proprietary interest in any material or method mentioned. Copyright © 2011 ASCRS and ESCRS. Published by Elsevier Inc. All rights reserved.
Zonal shear and super-rotation in a magnetized spherical Couette-flow experiment.
Brito, D; Alboussière, T; Cardin, P; Gagnière, N; Jault, D; La Rizza, P; Masson, J-P; Nataf, H-C; Schmitt, D
2011-06-01
We present measurements performed in a spherical shell filled with liquid sodium, where a 74-mm-radius inner sphere is rotated while a 210-mm-radius outer sphere is at rest. The inner sphere holds a dipolar magnetic field and acts as a magnetic propeller when rotated. In this experimental setup called "Derviche Tourneur Sodium" (DTS), direct measurements of the velocity are performed by ultrasonic Doppler velocimetry. Differences in electric potential and the induced magnetic field are also measured to characterize the magnetohydrodynamic flow. Rotation frequencies of the inner sphere are varied between -30 Hz and +30 Hz, the magnetic Reynolds number based on measured sodium velocities and on the shell radius reaching to about 33. We have investigated the mean axisymmetric part of the flow, which consists of differential rotation. Strong super-rotation of the fluid with respect to the rotating inner sphere is directly measured. It is found that the organization of the mean flow does not change much throughout the entire range of parameters covered by our experiment. The direct measurements of zonal velocity give a nice illustration of Ferraro's law of isorotation in the vicinity of the inner sphere, where magnetic forces dominate inertial ones. The transition from a Ferraro regime in the interior to a geostrophic regime, where inertial forces predominate, in the outer regions has been well documented. It takes place where the local Elsasser number is about 1. A quantitative agreement with nonlinear numerical simulations is obtained when keeping the same Elsasser number. The experiments also reveal a region that violates Ferraro's law just above the inner sphere.
Self-regulating Drift wave -- Zonal Flow turbulence in a linear plasma device
NASA Astrophysics Data System (ADS)
Xie, Jinlin; Chen, Ran; Hu, Guanghai; Jin, Xiaoli; Li, Hong; Liu, Wandong; Yu, Changxuan
2012-10-01
Here we report new and interesting results about the DW-ZF system in a linear plasma device with much better control environments to illustrate important Zonal flow physics: (1) The three-dimensional spectral features of the LFZF have been provided. In particular, it is identified that the LFZF damping is dominated by ion-neutral collision in our case. Also experimental evidence of the shearing effect of ZF on DW has been given. (2) A zonal flow dominated state of the DW-ZF system has been achieved. Theoretically, it has been predicted that a significant portion of the turbulence energy can be stored in the Zonal Flows for the case of low collisionality plasmas. In our experiments we achieve a zonal flow dominated state, in which the maximum ratio of the ZF energy to the total turbulence energy is about 80%, which seems to support the hypothesis of zonostropic state in geostrophic turbulence. (3) The self-regulating dynamics in the DW-ZF system is clearly elucidated. The evolution of the energy partition ratio of drift-wave turbulence and zonal flow is investigated with varying magnetic field strength, which is found consistent with the general prey-predator model.
Buoyancy storms in a zonal stream on the polar beta-plane: Experiments with altimetry
NASA Astrophysics Data System (ADS)
Sui, Y.; Afanasyev, Y. D.
2013-06-01
Results from a new series of experiments on flows generated by localized heating in the presence of a background zonal current on the polar β-plane are presented. The flow induced by a heater without the background zonal flow is in the form of a β-plume. Zonal jets of alternating directions are formed within the plume. The westward transport velocity in the plume is proportional to the upwelling velocity above the heater in agreement with linear theory. When the background flow in the form of the eastward zonal current is present, the β-plume can be overwhelmed by the eastward current. The main control parameters of the experiment are the strength of the heater and strength of the sink which is used to create the background flow. The regime diagram shows the area where a β-plume can exist in the parameter space. The critical value of the velocity of the zonal flow below which the β-plume can exist is obtained by considering barotropic Rossby waves emitted by the baroclinic eddies in the heated area.
The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence
Staebler, Gary M.; Candy, John; Howard, Nathan T.; ...
2016-06-29
The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the thresholdmore » for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. Finally, the zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ionscale gyrokinetic simulations.« less
The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence
Staebler, Gary M.; Candy, John; Howard, Nathan T.; Holland, Christopher
2016-06-29
The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. Finally, the zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ionscale gyrokinetic simulations.
The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence
Staebler, G. M.; Candy, J.; Howard, N. T.; Holland, C.
2016-06-15
The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. The zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ion-scale gyrokinetic simulations.
An implicit, conservative, zonal-boundary scheme for Euler equation calculations
NASA Technical Reports Server (NTRS)
Rai, M. M.
1985-01-01
A zonal, or patched, grid approach is one in which the flow region of interest is divided into subregions which are then discretized independently, using existing grid generators. The equations of motion are integrated in each subregion in conjunction with zonal boundary schemes which allow proper information transfer across interfaces that separate subregions. The zonal approach greatly simplifies the treatment of complex geometries and also the addition of grid points to selected regions of the flow. A conservative, zonal boundary condition that could be used with explicit schemes was extended so that it can be used with existing second order accurate implicit integration schemes such as the Beam-Warming and Osher schemes. In the test case considered, the implicit schemes increased the rate of convergence considerably (by a factor of about 30 over that of the explicit scheme). Results demonstrating the time accuracy of the zonal scheme and the feasibility of performing calculations on zones that move relative to each other are also presented.
The role of monsoon-like zonally asymmetric heating in interhemispheric transport
NASA Astrophysics Data System (ADS)
Chen, Gang; Orbe, Clara; Waugh, Darryn
2017-03-01
While the importance of the seasonal migration of the zonally averaged Hadley circulation on interhemispheric transport of trace gases has been recognized, few studies have examined the role of the zonally asymmetric monsoonal circulation. This study investigates the role of monsoon-like zonally asymmetric heating on interhemispheric transport using a dry atmospheric model that is forced by idealized Newtonian relaxation to a prescribed radiative equilibrium temperature. When only the seasonal cycle of zonally symmetric heating is considered, the mean age of air in the Southern Hemisphere since last contact with the Northern Hemisphere midlatitude boundary layer is much larger than the observations. The introduction of monsoon-like zonally asymmetric heating not only reduces the mean age of tropospheric air to more realistic values but also produces an upper tropospheric cross-equatorial transport pathway in boreal summer that resembles the transport pathway simulated in the NASA Global Modeling Initiative Chemistry Transport Model driven with Modern-Era Retrospective Analysis for Research and Applications meteorological fields. These results highlight that the monsoon-induced eddy circulation plays an important role in the interhemispheric transport of long-lived chemical constituents.
Zonally averaged model of dynamics, chemistry and radiation for the atmosphere
NASA Technical Reports Server (NTRS)
Tung, K. K.
1985-01-01
A nongeostrophic theory of zonally averaged circulation is formulated using the nonlinear primitive equations on a sphere, taking advantage of the more direct relationship between the mean meridional circulation and diabatic heating rate which is available in isentropic coordinates. Possible differences between results of nongeostrophic theory and the commonly used geostrophic formulation are discussed concerning: (1) the role of eddy forcing of the diabatic circulation, and (2) the nonlinear nearly inviscid limit vs the geostrophic limit. Problems associated with the traditional Rossby number scaling in quasi-geostrophic formulations are pointed out and an alternate, more general scaling based on the smallness of mean meridional to zonal velocities for a rotating planet is suggested. Such a scaling recovers the geostrophic balanced wind relationship for the mean zonal flow but reveals that the mean meridional velocity is in general ageostrophic.
Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma
NASA Astrophysics Data System (ADS)
Arakawa, H.; Inagaki, S.; Sasaki, M.; Kosuga, Y.; Kobayashi, T.; Kasuya, N.; Nagashima, Y.; Yamada, T.; Lesur, M.; Fujisawa, A.; Itoh, K.; Itoh, S.-I.
2016-09-01
Turbulence and its structure formation are universal in neutral fluids and in plasmas. Turbulence annihilates global structures but can organize flows and eddies. The mutual-interactions between flow and the eddy give basic insights into the understanding of non-equilibrium and nonlinear interaction by turbulence. In fusion plasma, clarifying structure formation by Drift-wave turbulence, driven by density gradients in magnetized plasma, is an important issue. Here, a new mutual-interaction among eddy, drift wave and flow in magnetized plasma is discovered. A two-dimensional solitary eddy, which is a perturbation with circumnavigating motion localized radially and azimuthally, is transiently organized in a drift wave – zonal flow (azimuthally symmetric band-like shear flows) system. The excitation of the eddy is synchronized with zonal perturbation. The organization of the eddy has substantial impact on the acceleration of zonal flow.
Collisional Scaling of the Energy Transfer in Drift-Wave Zonal Flow Turbulence
NASA Astrophysics Data System (ADS)
Schmid, B.; Manz, P.; Ramisch, M.; Stroth, U.
2017-02-01
The collisionality scaling of density and potential coupling together with zonal flow energy transfer and spectral power is investigated at the stellarator experiment TJ-K. With a poloidal probe array, consisting of 128 Langmuir probes, density and potential fluctuations are measured on four neighboring flux surfaces simultaneously over the complete poloidal circumference. By analyzing Reynolds stress and pseudo-Reynolds stress, it is found that, for increasing collisionality, the coupling between density and potential decreases which hinders the zonal flow drive. Also, as a consequence, the nonlinear energy transfer, as well as the zonal flow contribution to the complete turbulent spectrum, decreases the same way. This is in line with theoretical expectations and is a first experimental verification of the importance of collisionality for large-scale structure formation in magnetically confined toroidal plasmas.
Collisional Scaling of the Energy Transfer in Drift-Wave Zonal Flow Turbulence.
Schmid, B; Manz, P; Ramisch, M; Stroth, U
2017-02-03
The collisionality scaling of density and potential coupling together with zonal flow energy transfer and spectral power is investigated at the stellarator experiment TJ-K. With a poloidal probe array, consisting of 128 Langmuir probes, density and potential fluctuations are measured on four neighboring flux surfaces simultaneously over the complete poloidal circumference. By analyzing Reynolds stress and pseudo-Reynolds stress, it is found that, for increasing collisionality, the coupling between density and potential decreases which hinders the zonal flow drive. Also, as a consequence, the nonlinear energy transfer, as well as the zonal flow contribution to the complete turbulent spectrum, decreases the same way. This is in line with theoretical expectations and is a first experimental verification of the importance of collisionality for large-scale structure formation in magnetically confined toroidal plasmas.
Daytime vertical and zonal velocities from 150-km echoes: Their relevance to F-region dynamics
NASA Astrophysics Data System (ADS)
Chau, Jorge L.; Woodman, Ronald F.
2004-09-01
As it was suggested by Kudeki and Fawcett [1993], and later shown by Woodman and Villanueva [1995], vertical Doppler velocities of daytime 150-km echoes represent the vertical E × B drift velocities at F region altitudes. Recently a special experiment was conducted to compare not only the vertical but also the zonal velocities from 150-km echoes with those from an incoherent scatter radar (ISR) mode perpendicular to the magnetic field. The vertical velocity comparisons show that (1) there is a very good agreement between 150-km velocity and the mean F-region E × B drift, and (2) much better agreement is found with the extrapolated values from the ISR altitudinal profiles. On the other hand poor-to-good agreement is found between their zonal components. Our preliminary zonal velocity results, indicate that there is a poor agreement before noontime, while better agreement is found in the afternoon.
Calculation of Zonal Winds using Accelerometer and Rate Data from Mars Global Surveyor
NASA Technical Reports Server (NTRS)
Baird, Darren T.; Tolson, Robert; Bougher, Stephen; Steers, Brian
2006-01-01
The Mars Global Surveyor spacecraft was initially placed into a high eccentricity, nearly polar orbit about Mars with a 45-hour period. To accomplish the science objectives of the mission, a 2-hour, circular orbit was required. Using a method known as aerobraking, numerous passes through the upper atmosphere slowed the spacecraft, thereby reducing the orbital period and eccentricity. To successfully perform aerobraking, the spacecraft was designed to be longitudinally, aerodynamically stable in pitch and yaw. Since the orbit is nearly polar, the yaw orientation of the spacecraft was sensitive to disturbances caused by the zonal components of wind (east-to-west or west-to-east) acting on the spacecraft at aerobraking altitudes. Zonal wind velocities were computed by equating the aerodynamic and inertia-related torques acting on the spacecraft. Comparisons of calculated zonal winds with those computed from the Mars Thermospheric Global Circulation Model are discussed.
Comparison of ejection fraction and zonal mean velocity of myocardial fiber shortening.
Nakhjavan, F K; Natarajan, G; Goldberg, H
1975-08-01
To determine the extent of cardiac involvement until a diminished ejection fraction (EF) is present, zonal mean velocity of circumferential fiber shortening (Vcf) was measured from the left ventriculogram in 36 patients. The longitudinal axis (apex to mid-point of the aortic valve plane) in right anterior oblique view was divided into four equal parts by three perpeendicular chords. Zonal Vct and percent shortening along the proximal, middle and distal chords were measured. The results of this study indicate that a normal EF is frequently associated with a reduced Vct in one or even two zones. A reduced EF is generally accompanied by a diminished Vct in all three zones of the heart. In addition, a close correlation was found between zonal Vct and percent shortening. Hence the latter, which is much simpler to measure, can be instead of Vct Ejection fraction as a measure of myocardial performance is not as sensitive as Vct, especially in hearts with asynchrony of contraction.
An analysis of the strong zonal circulation within the stratosphere of Venus
NASA Technical Reports Server (NTRS)
Ramanathan, V.; Cess, R. D.
1975-01-01
A dynamic model is presented for the strong zonal circulation within the stratosphere of Venus which was observed by Mariner 10 and Venera. Rotational effects are neglected, a compressible and radiating atmosphere is considered, and diurnal radiative heating is shown to be negligible in the lower stratosphere (below 85 km). Analysis of the model indicates that propagating internal gravity waves generated by solar heating of the upper stratosphere may induce mean zonal velocities within the upper and lower stratosphere which would have a retrograde direction. The nonlinear equations of motion and energy are solved by an approximate analytical method to determine the magnitude of the zonal velocity, which is found to increase from zero at the tropopause to about 200 m/sec at the 85-km level. The calculated velocity near the UV cloud level compares favorably with the observed value of 100 m/sec.
Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma
Arakawa, H.; Inagaki, S.; Sasaki, M.; Kosuga, Y.; Kobayashi, T.; Kasuya, N.; Nagashima, Y.; Yamada, T.; Lesur, M.; Fujisawa, A.; Itoh, K.; Itoh, S.-I.
2016-01-01
Turbulence and its structure formation are universal in neutral fluids and in plasmas. Turbulence annihilates global structures but can organize flows and eddies. The mutual-interactions between flow and the eddy give basic insights into the understanding of non-equilibrium and nonlinear interaction by turbulence. In fusion plasma, clarifying structure formation by Drift-wave turbulence, driven by density gradients in magnetized plasma, is an important issue. Here, a new mutual-interaction among eddy, drift wave and flow in magnetized plasma is discovered. A two-dimensional solitary eddy, which is a perturbation with circumnavigating motion localized radially and azimuthally, is transiently organized in a drift wave – zonal flow (azimuthally symmetric band-like shear flows) system. The excitation of the eddy is synchronized with zonal perturbation. The organization of the eddy has substantial impact on the acceleration of zonal flow. PMID:27628894
NASA Astrophysics Data System (ADS)
Li, Mengyang; Li, Dahai; Zhang, Chen; E, Kewei; Hong, Zhihan; Li, Chengxu
2015-08-01
Zonal wavefront reconstruction by use of the well known Southwell algorithm with rectangular grid patterns has been considered in the literature. However, when the grid patterns are nonrectangular, modal wavefront reconstruction has been extensively used. We propose an improved zonal wavefront reconstruction algorithm for Hartmann type test with arbitrary grid patterns. We develop the mathematical expressions to show that the wavefront over arbitrary grid patterns, such as misaligned, partly obscured, and non-square mesh grids, can be estimated well. Both iterative solution and least-square solution for the proposed algorithm are described and compared. Numerical calculation shows that the zonal wavefront reconstruction over nonrectangular profile with the proposed algorithm results in a significant improvement in comparison with the Southwell algorithm.
Convergence acceleration for a three-dimensional Euler/Navier-Stokes zonal approach
NASA Technical Reports Server (NTRS)
Flores, J.
1985-01-01
A fast diagonal algorithm is coupled with a zonal approach to solve the three-dimensional Euler/Navier-Stokes equations. Transonic viscous solutions are obtained on a 150,000 point mesh for a NACA 0012 wing. The new computational approach yields a speedup by as much as a factor of 40 over the standard Beam-Warming algorithm/zonal method originally coded. A three-order-of-magnitude drop in the L2-norm of the residual requires approximately 500 iterations, which takes about 45 min of CPU time on a Cray-XMP. The numerically computed solutions are in good agreement with experimental results. Effects on convergence rate owing to increasing the zonal boundary overlap regions, different stretching distributions in the viscous regions, and different CFL values are also explored.
Jupiter: New estimates of mean zonal flow at the cloud level
NASA Technical Reports Server (NTRS)
Limaye, Sanjay S.
1986-01-01
In order to reexamine the magnitude differences of the Jovian atmosphere's jets, as determined by Voyager 1 and 2 images, a novel approach is used to ascertain the zonal mean east-west component of motion. This technique is based on digital pattern matching, and is applied on pairs of mapped images to yield a profile of the mean zonal component that reproduces the exact locations of the easterly and westerly jets between + and 60 deg latitude. Results were obtained for all of the Voyager 1 and 2 cylindrical mosaics; the correlation coefficient between Voyagers 1 and 2 in mean zonal flow between + and - 60 deg latitude, determined from violet filter mosaics, is 0.998.
Conservative zonal schemes for patched grids in 2 and 3 dimensions
NASA Technical Reports Server (NTRS)
Hessenius, Kristin A.
1987-01-01
The computation of flow over complex geometries, such as realistic aircraft configurations, poses difficult grid generation problems for computational aerodynamicists. The creation of a traditional, single-module grid of acceptable quality about an entire configuration may be impossible even with the most sophisticated of grid generation techniques. A zonal approach, wherein the flow field is partitioned into several regions within which grids are independently generated, is a practical alternative for treating complicated geometries. This technique not only alleviates the problems of discretizing a complex region, but also facilitates a block processing approach to computation thereby circumventing computer memory limitations. The use of such a zonal scheme, however, requires the development of an interfacing procedure that ensures a stable, accurate, and conservative calculation for the transfer of information across the zonal borders.
NASA Astrophysics Data System (ADS)
Galperin, Boris; Hoemann, Jesse; Espa, Stefania; Di Nitto, Gabriella; Lacorata, Guglielmo
2016-12-01
Turbulence with inverse energy cascade and its transport properties are investigated experimentally in a flow associated with a westward propagating jet. Turbulence and the jet were produced by an electromagnetic force in a rotating tank filled with an electrolytic saline solution. The parabolic free surface emulated the topographic β effect which evoked the zonation. The spectral and transport flow characteristics were highly anisotropic. Turbulence is diagnosed by exploring the analogy between vertical and horizontal turbulent overturns in, respectively, stably stratified and quasigeostrophic flows which gives rise to a method of potential vorticity (PV) monotonizing. The anisotropization of transport properties of the flow is investigated using the finite scale Lyapunov exponent technique. After initial exponential particle separation, radial (meridional in geophysical and planetary applications) diffusion attains a short-ranged Richardson regime which transitions to the Taylor (scale-independent diffusivity) one. The azimuthal (zonal) diffusion exhibits a double-plateau structure which attains a superdiffusive regime on large scales. The transition to the Taylor regime for the radial diffusion takes place at a scale of turbulence anisotropization. The radial eddy diffusivity in both regimes as well as the transition scale are all determined by the rate of the inverse energy cascade, ɛ , that can be diagnosed by the PV monotonizing. Conversely, ɛ can be deduced from the scale of the Richardson-Taylor regime transition in the radial eddy diffusivity which, thus, provides an additional tool of diagnosing anisotropic macroturbulence with inverse energy cascade.
Galperin, Boris; Hoemann, Jesse; Espa, Stefania; Di Nitto, Gabriella; Lacorata, Guglielmo
2016-12-01
Turbulence with inverse energy cascade and its transport properties are investigated experimentally in a flow associated with a westward propagating jet. Turbulence and the jet were produced by an electromagnetic force in a rotating tank filled with an electrolytic saline solution. The parabolic free surface emulated the topographic β effect which evoked the zonation. The spectral and transport flow characteristics were highly anisotropic. Turbulence is diagnosed by exploring the analogy between vertical and horizontal turbulent overturns in, respectively, stably stratified and quasigeostrophic flows which gives rise to a method of potential vorticity (PV) monotonizing. The anisotropization of transport properties of the flow is investigated using the finite scale Lyapunov exponent technique. After initial exponential particle separation, radial (meridional in geophysical and planetary applications) diffusion attains a short-ranged Richardson regime which transitions to the Taylor (scale-independent diffusivity) one. The azimuthal (zonal) diffusion exhibits a double-plateau structure which attains a superdiffusive regime on large scales. The transition to the Taylor regime for the radial diffusion takes place at a scale of turbulence anisotropization. The radial eddy diffusivity in both regimes as well as the transition scale are all determined by the rate of the inverse energy cascade, ε, that can be diagnosed by the PV monotonizing. Conversely, ε can be deduced from the scale of the Richardson-Taylor regime transition in the radial eddy diffusivity which, thus, provides an additional tool of diagnosing anisotropic macroturbulence with inverse energy cascade.
A zonal method for modeling powered-lift aircraft flow fields
NASA Technical Reports Server (NTRS)
Roberts, D. W.
1989-01-01
A zonal method for modeling powered-lift aircraft flow fields is based on the coupling of a three-dimensional Navier-Stokes code to a potential flow code. By minimizing the extent of the viscous Navier-Stokes zones the zonal method can be a cost effective flow analysis tool. The successful coupling of the zonal solutions provides the viscous/inviscid interations that are necessary to achieve convergent and unique overall solutions. The feasibility of coupling the two vastly different codes is demonstrated. The interzone boundaries were overlapped to facilitate the passing of boundary condition information between the codes. Routines were developed to extract the normal velocity boundary conditions for the potential flow zone from the viscous zone solution. Similarly, the velocity vector direction along with the total conditions were obtained from the potential flow solution to provide boundary conditions for the Navier-Stokes solution. Studies were conducted to determine the influence of the overlap of the interzone boundaries and the convergence of the zonal solutions on the convergence of the overall solution. The zonal method was applied to a jet impingement problem to model the suckdown effect that results from the entrainment of the inviscid zone flow by the viscous zone jet. The resultant potential flow solution created a lower pressure on the base of the vehicle which produces the suckdown load. The feasibility of the zonal method was demonstrated. By enhancing the Navier-Stokes code for powered-lift flow fields and optimizing the convergence of the coupled analysis a practical flow analysis tool will result.
Shear in the zonal drifts of 3 m irregularities inside spread F plumes observed over Sanya
NASA Astrophysics Data System (ADS)
Li, Guozhu; Ning, Baiqi; Liu, Libo; Abdu, M. A.; Wan, Weixing; Hu, Lianhuan
2015-09-01
Incoherent scatter radars near magnetic equator regularly measured a vertical shear in zonal drifts of the evening background plasma, with westward drifts below the equatorial F region peak and eastward drifts above. We report here observations of a clear shear structure in the zonal drifts of 3 m irregularities inside spread F (SF) backscatter plumes measured with a 47.5 MHz coherent scatter radar operated at a low-latitude site Sanya (18.4°N, 109.6°E; dip latitude 12.8°N). The radar interferometry analysis on the zonal drifts of the 3 m irregularities yields results consistent with that estimated from the irregularity echo Doppler velocity measurements with multiple beams. It is shown that the SF 3 m irregularities move westward at the lowest altitudes, while at higher altitudes in the same SF plume structure, the 3 m irregularities drift eastward. One interesting point is that the vertical shear of zonal drifts was centered at ~300 km altitude over Sanya, which maps to an apex altitude of ~650 km at magnetic equator and is thus apparently higher than the apex altitudes 250-450 km where the zonal velocity shear has usually been observed. Analysis of the observations suggests that while the possibility of local generation of the shear flow of the irregularities can exist, the possibility of a plasma vortex appearing at relative high altitudes causing the zonal drift shear of F region 3 m irregularities measured over Sanya cannot be totally ruled out.
Subsurface Zonal and Meridional Flow Derived from GONG and SDO/HMI: A Comparison of Systematics
NASA Astrophysics Data System (ADS)
Komm, R.; González Hernández, I.; Howe, R.; Hill, F.
2015-04-01
We study the subsurface flows in the near-surface layers of the solar convection zone from the surface to a depth of 16 Mm derived from Global Oscillation Network Group (GONG) and Helioseismic and Magnetic Imager (HMI) Dopplergrams using a ring-diagram analysis. We characterize the systematic east-west and north-south variations present in the zonal and meridional flows and compare flows derived from GONG and HMI data before and after the correction. The average east-west variation with depth of one flow component resembles the average north-south variation with depth of the other component. The east-west variation of the zonal flow together with the north-south variation of the meridional flow can be modeled as a systematic radial velocity. This indicates a solar center-to-limb variation as the underlying cause. The north-south variation of the zonal flow and the east-west variation of the meridional flow require two separate functions. The east-west variation of the meridional flow consists mainly of an annual variation with the B 0 angle, while the north-south trend of the zonal flow consists of a constant non-zero component in addition to an annual variation. This indicates a geometric projection artifact. After compensating for these systematic effects, the meridional and zonal flows derived from HMI data agree well with those derived from GONG data. An offset remains between the zonal flow derived from GONG and HMI data. The equatorward meridional flows at high latitude that appear episodically depending on the B 0 angle are absent from the corrected flows.
NASA Astrophysics Data System (ADS)
Preusse, Peter; Eckermann, Stephen D.; Offermann, Dirk
2000-12-01
Gravity wave temperature fluctuations acquired by the CRISTA instrument are compared to previous estimates of zonal-mean gravity wave temperature variance inferred from the LIMS, MLS and GPS/MET satellite instruments during northern winter. Careful attention is paid to the range of vertical wavelengths resolved by each instrument. Good agreement between CRISTA data and previously published results from LIMS, MLS and GPS/MET are found. Key latitudinal features in these variances are consistent with previous findings from ground-based measurements and some simple models. We conclude that all four satellite instruments provide reliable global data on zonal-mean gravity wave temperature fluctuations throughout the middle atmosphere.
Electromagnetic interchange-like mode and zonal flow in electron-magnetohydrodynamic plasma
Chakrabarti, Nikhil; Horiuchi, Ritoku
2006-10-15
A numerical simulation of the nonlinear state of interchange instability associated with electron inertia in an unmagnetized plasma is studied. It is shown that a self-consistent sheared transverse electron current flow is generated due to nonlinear mechanisms. This zonal flow can reduce the growth rate of the magnetic interchange-like instability and reach a steady state. The zonal flow generation mechanisms are discussed by truncated Fourier mode representation. In the truncated model, three mode equations are considered that have an exact analytic solution that matches well with the numerical solution. The effect of different boundary conditions in such investigations is also discussed.
Constraints on the Observed Zonal Flows from the Magnetic Fields in Giant Planets
NASA Astrophysics Data System (ADS)
Liu, J. J.; Stevenson, D. J.
2003-05-01
The zonal winds on the surface of the giant planets are very strong ( 100m/s ) and stable (on a decadal time scale). Observations by the Galileo probe suggest that the zonal flow might be deep seated. However, the magnitude of the zonal flow must be reduced to a small value in the interior of the giant planets because the flow is defined relative to the magnetic field frame of reference (System III) and very large zonal flows can not be tolerated in a high conductivity region. The mechanisms for reducing the magnitude of the zonal flow and the coupling between the zonal flow and magnetic field are unclear. Here we use a coupled Navier-Stokes equation and the magnetic induction equation in steady state to study this. From Navier-Stokes, we find that the zonal flow vth can be expressed in three parts: vth(s,z) = a(s) + Bth2/4μ0ρ Ω s + F(grad(ρ ),Bth)/4μ0ρ Ω s, where a(s) is an arbitrary function of cylindrical radius (s) only, z is the coordinate parallel to the rotation axis, Bth is the toroidal field, μ 0 is the permeability of free space, ρ (s,z) is the density, Ω is the planetary rotation and F is a function of the density gradient (grad(ρ )) and the toroidal magnetic field. The first part is the geostrophic flow consistent with the Taylor-Proudman theorem. The second part is due to the tensile force that arises from the curvature of the toroidal field, and always leads a prograde flow. The third part comes from the density variation and meridional gradient of the toroidal field, and may lead to the prograde flow or the retrograde flow. Whether the flow observed on the surface could be reduced to small values in the interior will depend on the direction of the flow, the density gradient and also the structure of the toroidal magnetic field. It can also be shown that the magnitude of the generated toroidal magnetic field in the interior of the giant planets is very large and around 10 Tesla for consistency with the observed zonal flow on the surface of
Computational analysis of rotor-stator interaction in turbomachinery using zonal techniques
NASA Technical Reports Server (NTRS)
Madavan, Nateri K.; Rai, Man Mohan
1990-01-01
The development of CFD zonal techniques which allow more intensive computational treatment in some regions than in others, in conjunction with robust, high-accuracy algorithms for the numerical solution of the Navier-Stokes equations, is presently shown to have facilitated the investigation of rotor-stator interactions in turbomachinery. Attention is given to integration schemes with two and three spatial dimensions, the conservative 'patched' and the nonconservative zonal boundary schemes, and such natural boundary conditions as those of the endwall, the stator inlet, the airfoil surface, and the rotor exit. Illustrative three-dimensional rotor-stator interaction calculations are presented.
Exploring the connections between dark spot dynamics and zonal wind structure on Uranus
NASA Astrophysics Data System (ADS)
Le Beau, Raymond P.; Palotai, Csaba
2015-11-01
The past several years have witnessed new observations revealing more clouds and long-lived features in the atmosphere of Uranus. Each new set of images provides new cloud-tracking data and the opportunity to assess the structure of the zonal winds on Uranus. This has led to a sequence of fits for the Uranian zonal winds with the latest entries being those proposed in Sromovsky et al. (2015). Karkoschka (2015) also provides a new view of the zonal winds, but in this case through reanalyzing the Voyager II observations. While all these profiles have in common features like a retrograde equatorial jet, the details of these profiles differ significantly. These differences can be further accentuated when considering the vorticity profiles derived from these zonal winds. As shown in LeBeau and Dowling (1998) and Hammel et al. (2009), atmospheric simulations using different zonal vorticity profiles suggest that the vorticity gradient can affect the dynamics of dark spot vortices in the atmosphere. Later work (Deng et al. 2009) has indicated that these dynamics may be further complicated by the presence of cloud companion features.To further investigate these interactions, some of the most recent zonal profiles are used in simulations of Uranus with the Explicit Planetary Isentropic Coordinate (EPIC) atmospheric model. By inducing vortices at different latitudes, the effects of different zonal wind profiles on these features can be investigated. A methane microphysics model is used to generate representative companion clouds. The subsequent vortex and companion cloud motions can then be compared to observations, providing another tool in the effort to understand possible changes in the zonal wind structure of Uranus.References:L.A. Sromovsky et al. Icarus 258:192-223, 2015E. Karkoschka. Icarus 250:294-307, 2015H.B. Hammel et al. Icarus 201:257-271, 2009R.P. LeBeau and T.E. Dowling. Icarus 132:239-265, 1998X. Deng et al. 1st AIAA Atmospheric and Space Environments
Fluctuating Zonal Flows in I-mode in Alcator C-Mod
NASA Astrophysics Data System (ADS)
Cziegler, Istvan
2012-10-01
Velocity fields and density fluctuations of edge turbulence have been studied in I-mode [1] plasmas of Alcator C-Mod, which are characterized by a strong thermal transport barrier in the edge while providing little or no barrier to the transport of both bulk and impurity particles. This allows access to steady state, high performance discharges without explosive edge relaxations or impurity accumulation. The key feature in the I-mode edge seems to be a weakly coherent mode (WCM) at 100-300 kHz, with δf 150 kHz and a poloidal wavenumber k 1.5,-1. Although previous work showed no clear geodesic-acoustic modes (GAM) on C-Mod, using a newly implemented, gas-puff-imaging (GPI) based time-delay-estimate (TDE) velocity inference algorithm, GAM are now shown to be ubiquitous in all I-mode discharges, with the time histories of the GAM and the WCM closely following each other through the entire duration of the regime. The central frequency of the WCM is shown to scale with HITER,98, which itself scales with the depth of the radial electric field well in the edge [2]. Thus, the I-mode presents an example of a plasma state in which quasi-static zonal flows (ZF) and GAM continuously coexist. Using both single- (density) and two-field (density-velocity) bispectral methods, the GAM are shown to be coupled to the WCM and to be responsible for its broad frequency structure. Since the WCM activity is strongly correlated to the I-mode behavior [3], and due to the known dependence of the GAM damping on collisionality [4], the decrease in GAM amplitude, and with it WCM activity, at higher densities offers an explanation for the density limit for I-mode access [3].[4pt] [1] F. Ryter et al, Plasma Phys. Control. Fusion 40 725 (1998)[0pt] [2] R. McDermott et al, Phys. Plasmas 16 056103 (2009)[0pt] [3] D. Whyte et al, Nucl. Fus. 50 105005 (2010)[0pt] [4] S. Novakovskii et al, Phys. Plasmas 4 4272 (1997)
NASA Astrophysics Data System (ADS)
Haigh, J. D.; Sparrow, S. N.; Blackburn, M.; Simpson, I. R.
2009-05-01
Idealised-forcing experiments have been performed previously using a simplified, Newtonian forced, global circulation model. In each of these experiments, changes to the stratospheric equilibrium temperature distribution lead to changes in the strength and position of the tropospheric mid-latitude jets and storm-tracks and to the extent of the Hadley cells and mean meridional circulation. The work presented here investigates how such shifts in the tropospheric jet can be understood by examining combined fluctuations of the first two modes of annular variability. Attention is paid to the evolution of the flow on different timescales as defined by empirical mode decomposition and related to the autocorrelation timescale for the mode of variability. At low frequencies the zonal flow and baroclinic eddies are in quasi-equilibrium and anomalies propagate poleward. The eddies are shown primarily to reinforce the anomalous state and are closely balanced by the linear damping, leaving slow evolution as a residual. At high frequencies the flow is strongly evolving and anomalies are initiated on the poleward side of the tropospheric jet and propagate equatorward. The eddies are shown to drive the evolution more strongly. Eddy amplitudes reflect the past baroclinicity and their feedback on the mean flow can be understood in accordance with traditional ideas of baroclinic lifecycle events. The state of the stratosphere determines the background position and strength of the jet upon which the variability is superimposed, and also the timescale at which the behaviour switches from low-frequency to high-frequency (as defined above). When the temperature structure of the stratosphere is such that the jet is positioned more equatorward then high frequency behaviour is dominant to much longer timescales.
A Model of the Saturation of Multi-scale Turbulence by Zonal Flow Mixing
NASA Astrophysics Data System (ADS)
Staebler, G. M.; Candy, J.; Holland, C.; Howard, N.
2016-10-01
Analysis of the spectrum of the saturated electric potential fluctuations from multi-scale (both ion and electron scales) gyrokinetic turbulence simulations, in tokamak geometry, reveals that fluctuating zonal (axisymmetric) ExB flows couple the ion and electron scales. The zonal flows are driven by the ion-scale instabilities but strongly regulate the amplitude of the electron-scale turbulence. The electron-scale turbulence can grow to large amplitude when the linear growth rate of the ETG modes exceeds the zonal flow mixing rate due to advection of the ETG modes. The model of the zonal flow mixing is shown to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron-scale turbulence when the ion-scale turbulence is reduced. The nonlinear upshift of the effective critical ion temperature gradient (Dimits shift) is also captured by the new model. Prediction of the core plasma fusion performance of ITER with TGLF using the new saturation model yields a 19% increase in fusion power for hybrid regime operation. This work was supported by the US Department of Energy contracts: DE-FG02-95ER54309, DE-FC02-04ER54698, DE-FC02-08ER54963, DE-AC02-05CH11231, DE-FC02-04ER54698, and DE-SC0006957.
Self-Organization of Zonal Jets in Outer Planet Atmospheres: Uranus and Neptune
NASA Technical Reports Server (NTRS)
Friedson, A. James
1997-01-01
The statistical mechnical theory of a two-dimensional Euler fluid is appleid for the first time to explore the spontaneous self-oganization of zonal jets in outer planet atmospheres. Globally conserved integralls of motion are found to play a central role in defining jet structure.
On the influence of zonal gravity wave distributions on the Southern Hemisphere winter circulation
NASA Astrophysics Data System (ADS)
Lilienthal, Friederike; Jacobi, Christoph; Schmidt, Torsten; de la Torre, Alejandro; Alexander, Peter
2017-07-01
A mechanistic global circulation model is used to simulate the Southern Hemisphere stratospheric, mesospheric, and lower thermospheric circulation during austral winter. The model includes a gravity wave (GW) parameterization that is initiated by prescribed 2-D fields of GW parameters in the troposphere. These are based on observations of GW potential energy calculated using GPS radio occultations and show enhanced GW activity east of the Andes and around the Antarctic. In order to detect the influence of an observation-based and thus realistic 2-D GW distribution on the middle atmosphere circulation, we perform model experiments with zonal mean and 2-D GW initialization, and additionally with and without forcing of stationary planetary waves (SPWs) at the lower boundary of the model. As a result, we find additional forcing of SPWs in the stratosphere, a weaker zonal wind jet in the mesosphere, cooling of the mesosphere and warming near the mesopause above the jet. SPW wavenumber 1 (SPW1) amplitudes are generally increased by about 10 % when GWs are introduced being longitudinally dependent. However, at the upper part of the zonal wind jet, SPW1 in zonal wind and GW acceleration are out of phase, which reduces the amplitudes there.
USDA-ARS?s Scientific Manuscript database
e Japanese beetle (Popillia japonica) exhibits rapid paralysis after consuming flowers from zonal geranium (Pelargonium × hortorum). Activity-guided fractionations were conducted with polar flower petal extracts from Pelargonium × hortorum cv. Nittany Lion Red, which led to the isolation of a paraly...
The Effect of Zonally Asymmetric Ozone Heating on the Northern Hemisphere Winter Polar Stratosphere
2010-12-09
winds). Differences in the ensemble mean winds are negligible throughout much of December. In Jan - uary, the 3DO3 mean westerly winds are ∼5 m s−1...wave propagation versus wave damping in modulating the planetary wave drag and thus the zonal-mean circulation. Acknowledgments. We thank John Albers
A Model Study of Zonal Forcing in the Equatorial Stratosphere by Convectively Induced Gravity Waves
NASA Technical Reports Server (NTRS)
Alexander, M. J.; Holton, James R.
1997-01-01
A two-dimensional cloud-resolving model is used to examine the possible role of gravity waves generated by a simulated tropical squall line in forcing the quasi-biennial oscillation (QBO) of the zonal winds in the equatorial stratosphere. A simulation with constant background stratospheric winds is compared to simulations with background winds characteristic of the westerly and easterly QBO phases, respectively. In all three cases a broad spectrum of both eastward and westward propagating gravity waves is excited. In the constant background wind case the vertical momentum flux is nearly constant with height in the stratosphere, after correction for waves leaving the model domain. In the easterly and westerly shear cases, however, westward and eastward propagating waves, respectively, are strongly damped as they approach their critical levels, owing to the strongly scale-dependent vertical diffusion in the model. The profiles of zonal forcing induced by this wave damping are similar to profiles given by critical level absorption, but displaced slightly downward. The magnitude of the zonal forcing is of order 5 m/s/day. It is estimated that if 2% of the area of the Tropics were occupied by storms of similar magnitude, mesoscale gravity waves could provide nearly 1/4 of the zonal forcing required for the QBO.
Stimulated zonal flow generation in the case of TEM and TIM microturbulence
NASA Astrophysics Data System (ADS)
Gravier, E.; Lesur, M.; Reveille, T.; Drouot, T.
2016-09-01
In this paper, we show that in some parameter range in gyrokinetic simulations, it is possible to apply a control method to stimulate the appearance of zonal flows while minimizing the duration of the control process and the impact on plasma parameters. For this purpose, a gyrokinetic code considering only trapped particles is used. The starting point of our work is a situation where zonal flows transiently appear after the nonlinear phase of saturation of trapped electron modes or trapped ion modes' micro-instabilities. These are observed to be strongly reduced in a later phase, permitting streamers to govern the plasma behavior in the steady-state. By intervening during this latter state (after this transient growth and decay of zonal flow), i.e., by increasing the ion/electron temperature ratio for a short time, it is found to be possible to bifurcate to a new steady-state, in which zonal flows are strongly present and are maintained indefinitely, thereby allowing a significant reduction in radial heat fluxes.
NASA Astrophysics Data System (ADS)
Sobral, J. H. A.; Abdu, M. A.; Takahashi, H.; Sawant, H.; Zamlutti, C. J.; Borba, G. L.
1999-01-01
The understanding of postsunset zonal drifts of ionospheric plasma depletions in the equatorial and subequatorial regions are of importance to the knowledge of the electrodynamics of the nocturnal ionosphere. Drifts occurring over the low latitude station Cachoeira Paulista-CP during the October and March time frames are analyzed for the period 1980 - 1992. That analysis is based upon about 650 days of zonal scanning photometer measurements of the nocturnal O I 630 nm airglow. The zonal motions of valleys of the O I 630 nm intensity are used to infer the eastward plasma velocity variations with local time. In this way, the velocity variations with solar activity and magnetic activity are studied. The mean trend in the velocity local time variation is a decrease from early evening to postmidnight hours, as expected in view of the F-region vertical electric fields, naturally decreasing magnitudes after sunset due to recombination. The zonal velocity decay between 21 LT and 02 LT is faster during the period of maximum solar activity than during the solar minimum period.
Levison, Ashleigh L; Baynes, Kimberly; Lowder, Careen Y; Srivastava, Sunil K
2016-01-01
A 74-year-old female with acute zonal occult outer retinopathy presented with a new lesion suspicious for choroidal neovascularization (CNV) in her right eye. Optical coherence tomography angiography (OCTA) confirmed the presence of CNV. OCTA is a new imaging technique that may help guide diagnosis and management of choroidal neovascular membranes in uveitic diseases.
Time-varying zonal asymmetries in stratospheric nitrous oxide and methane
NASA Technical Reports Server (NTRS)
Gao, H.; Stanford, J. L.
1993-01-01
Previously analyses of Stratospheric And Mesospheric Sounder (SAMS) data of atmospheric constituent gases have dealt almost exclusively with zonal means (and mostly monthly means), owing perhaps to concern over data quality. The purpose of this note is to show that, with care, time-dependent zonally-asymmetric features may be recovered from the SAMS nitrous oxide and methane data. As an example, we demonstrate the existence of zonal wave-1 constituent perturbations with periods of a few weeks in the middle and upper stratosphere. When the perturbations are normalized by the constituent zonal-mean mixing ratio to compensate for the slowly varying (in both space and time) background concentration of constituents, wavepacket-like features are found over all latitudes and seasons in the three-year SAMS record. One specific low-latitude case discussed had features which appear to be consistent with constituent oscillations induced by episodic equatorial Kelvin waves. Further studies are needed to better identify the nature of the plethora of observed wave-like phenomena.
Daytime zonal drifts in the ionospheric E and 150 km regions estimated using EAR observations
NASA Astrophysics Data System (ADS)
Peddapati, PavanChaitanya; Otsuka, Yuichi; Yamamoto, Mamoru; Yokoyama, Tatsuhiro; Patra, Amit
2016-07-01
The Equatorial Atmosphere Radar (EAR), located at Kototabang (0.2o S, 100.32o E, mag. lat. 10.36o S), Indonesia, is capable of detecting both E region and 150 km echoes during daytime. We have conducted multi-beam observations using the EAR during daytime covering all seasons to study seasonal variations of these echoes and their dynamics. Given the facts that drifts at the 150 km region are governed primarily by electric field, drifts at the E region are governed by both electric field and neutral wind, simultaneous observations of drifts in both E and 150 km regions would help understand their variations. In this paper we present local time and seasonal variations of zonal drifts in the E and 150 km regions estimated using multi-beam observations. Zonal drifts (positive eastward) in the E and 150 km regions are found to be in the range of -10 to -60 m/s and -40 to 80 m/s, respectively. In the E region, zonal drifts show height reversal and temporal variations having tidal signature and noticeable seasonal variations. Zonal drifts in the 150 km region also show noticeable height and seasonal variations. These results are compared with model drifts and evaluated in terms of electric field and neutral wind.
NASA Technical Reports Server (NTRS)
Lieberman, R. S.; Burrage, M. D.; Gell, D. A.; Hays, P. B.; Marshall, A. R.; Orthland, D. A.; Skinner, W. R.; Wu, D. L.; Vincent, R. A.; Franke, S. J.
1993-01-01
This paper presents analyses of mesospheric and lower thermospheric zonal mean winds observed by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS). Monthly averages of the equatorial zonal mean zonal winds are presented for January 1992 through June 1993. Equatorial zonal winds in the 70-90 km region are dominated by a semiannual oscillation (SAO), ranging from 30 m/s (westerly) to -100 m/s (easterly). At high latitudes the zonal wind variations are predominantly annual. Above 90 km, the low-latitude flow is easterly at all times, punctuated by a small semiannual variation. This behavior may be related to the deposition of momentum by the diurnal tides.
NASA Technical Reports Server (NTRS)
North, G. R.; Bell, T. L.; Cahalan, R. F.; Moeng, F. J.
1982-01-01
Geometric characteristics of the spherical earth are shown to be responsible for the increase of variance with latitude of zonally averaged meteorological statistics. An analytic model is constructed to display the effect of a spherical geometry on zonal averages, employing a sphere labeled with radial unit vectors in a real, stochastic field expanded in complex spherical harmonics. The variance of a zonally averaged field is found to be expressible in terms of the spectrum of the vector field of the spherical harmonics. A maximum variance is then located at the poles, and the ratio of the variance to the zonally averaged grid-point variance, weighted by the cosine of the latitude, yields the zonal correlation typical of the latitude. An example is provided for the 500 mb level in the Northern Hemisphere compared to 15 years of data. Variance is determined to increase north of 60 deg latitude.
NASA Technical Reports Server (NTRS)
North, G. R.; Bell, T. L.; Cahalan, R. F.; Moeng, F. J.
1982-01-01
Geometric characteristics of the spherical earth are shown to be responsible for the increase of variance with latitude of zonally averaged meteorological statistics. An analytic model is constructed to display the effect of a spherical geometry on zonal averages, employing a sphere labeled with radial unit vectors in a real, stochastic field expanded in complex spherical harmonics. The variance of a zonally averaged field is found to be expressible in terms of the spectrum of the vector field of the spherical harmonics. A maximum variance is then located at the poles, and the ratio of the variance to the zonally averaged grid-point variance, weighted by the cosine of the latitude, yields the zonal correlation typical of the latitude. An example is provided for the 500 mb level in the Northern Hemisphere compared to 15 years of data. Variance is determined to increase north of 60 deg latitude.
NASA Technical Reports Server (NTRS)
Vancleef, Garrett Warren; Shaw, John H.
1989-01-01
Atmospheric winds at heights between 25 and 120 km have been retrieved with precisions of 5/ms from the Doppler shifts of atmospheric absorption lines measured from a satellite-borne instrument. Lines of the upsilon 3 CO2 and upsilon 2 H2O rotation-vibration bands caused by gases in the instrument allowed the instrumental frequency scale to be absolutely calibrated so that accurate relative speeds could be obtained. By comparing the positions of both sets of instrumental lines the calibration of the frequency scale was determined to be stable to a precision of less than 2 x 10(-5) cm during the course of each occultation. It was found that the instrumental resolution of 0.015 cm after apodization, the signal to noise ratio of about 100 and stable calibration allowed relative speeds to be determined to a precision of 5 ms or better by using small numbers of absorption lines between 1600 and 3200 cm. Absolute absorption line positions were simultaneously recovered to precisions of 5 x 10(-5) cm or better. The wind speed profiles determined from four sunset occultations and one sunrise occultation show remarkable similarities in the magnitudes and directions of the zonal wind velocities as functions of height. These wind profiles appear to be manifestations of atmospheric tides.
NASA Astrophysics Data System (ADS)
Ernst, Darin
2008-11-01
#1#23pt1.5pt 1.5pt#1###2˜ > > Trapped electron mode (TEM) turbulence exhibits rich zonal flow dynamics, which depends strongly on plasma parameters. The role zonal flows in TEM turbulence is explored through a series of linear and nonlinear gyrokinetic simulations using both PIC (the GEM code) and continuum (the GS2 code) methods. A new nonlinear upshift [1,2] in the TEM critical density gradient (associated with zonal flow dominated states near threshold) increases strongly with collisionality, for density gradient driven cases. In contrast, zonal flows have little effect on TEM turbulence with strong electron temperature gradients and Te= 3Ti [3]. This apparent contradiction has been resolved in parameteric studies showing that zonal flows are weaker as the electron temperature gradient and Te/Ti increase [4]. The parametric variation of zonal flows is consistent with linear stability properties and nonlinear instability theory. A new stability diagram based on 2,000 GS2 simulations clarifies the roles of resonant and non-resonant TEM, ``ubiquitous,'' and electron temperature gradient (ETG) driven modes. Larger electron temperature gradients couple TEM and ETG modes, resulting in short wavelengths kαρs>1. Accordingly, a sudden onset of nonlinear fine scale structure is seen for ηe≡dTe/dne> 1. For short wavelengths, the ions are more adiabatic, the zonal flow potential <φ>˜
Effects of density stratification in driving zonal flow in gas giants
NASA Astrophysics Data System (ADS)
Gastine, T.; Wicht, J.
2011-12-01
The banded structures at the surfaces of Jupiter and Saturn are associated with prograde and retrograde zonal flows. The depth of these jets remains however poorly known. Theoretical scenarios range from ``shallow models'', that assume that zonal flows are restricted to a very thin layer close to the surface; to ``deep models'' that suppose that the jets involve the whole molecular shell (typically 104 kms). The latter idea was supported by fully 3-D numerical simulations (e.g. Heimpel, 2005) using the Boussinesq approximation, meaning that the background properties (temperature, density, ...) are constant with radius (Christensen, 2002). While this approximation is suitable for liquid iron cores of planets, it is more questionable in the envelopes of gas giants, where density increases by several orders of magnitude (Guillot, 1999). The anelastic approximation provides a more realistic framework to simulate the dynamics of zonal flows as it allows compressibility effects, while filtering out fast acoustic waves (Lantz & Fan, 1999). Recent anelastic simulations suggest that including compressibility effects yields interesting differences to Boussinesq approaches (Jones, 2009; Showman et al., 2011). Here, we therefore adopt an anelastic formulation to simulate 3-D compressible flows in rapidly rotating shells. We have conducted a systematic parametric study on the effects of background density stratification and analysed the influences on both convective flows and zonal jets. Despite the strong dependence of convection on the density stratification (i.e. the typical lengthscale of convective flows decreases when compressibility increases), the comparison between Boussinesq and anelastic simulations reveals striking common features: the latitudinal extent, the amplitude and the number of zonal jets is found to be nearly independent of the density stratification, provided convection is strongly driven. Mass-weighted properties of the flow (and notably a mass
NASA Astrophysics Data System (ADS)
Carrano, C. S.; Groves, K. M.; Valladares, C. E.; Delay, S. H.
2014-12-01
A complete characterization of field-aligned ionospheric irregularities responsible for the scintillation of satellite signals includes not only their spectral properties (power spectral strength, spectral index, anisotropy ratio, and outer-scale) but also their horizontal drift velocity. From a system impacts perspective, the horizontal drift velocity is important in that it dictates the rate of signal fading and also, to an extent, the level of phase fluctuations encountered by the receiver. From a physics perspective, studying the longitudinal morphology of zonal irregularity may lead to an improved understanding of the F region dynamo and regional electrodynamics at low latitudes. The irregularity drift at low latitudes is predominantly zonal and is most commonly measured by cross-correlating observations of satellite signals made by a pair of closely-spaced antennas. The AFRL-SCINDA network operates a small number of VHF spaced-antenna systems at low latitude stations for this purpose. A far greater number of GPS scintillation monitors are operated by AFRL-SCINDA (25-30) and the Low Latitude Ionospheric Sensor Network (35-50), but the receivers are situated too far apart to monitor the drift using cross-correlation techniques. In this paper, we present an alternative approach that leverages the weak scatter scintillation theory (Rino, Radio Sci., 1979) to infer the zonal irregularity drift from single-station GPS measurements of S4, sigma-phi, and the propagation geometry alone. Unlike the spaced-receiver technique, this technique requires assumptions for the height of the scattering layer (which introduces a bias in the drift estimates) and the spectral index of the irregularities (which affects the spread of the drift estimates about the mean). Nevertheless, theory and experiment show that the ratio of sigma-phi to S4 is less sensitive to these parameters than it is to the zonal drift, and hence the zonal drift can be estimated with reasonable accuracy. In
Development of an upwind, finite-volume code with finite-rate chemistry
NASA Technical Reports Server (NTRS)
Molvik, Gregory A.
1994-01-01
Under this grant, two numerical algorithms were developed to predict the flow of viscous, hypersonic, chemically reacting gases over three-dimensional bodies. Both algorithms take advantage of the benefits of upwind differencing, total variation diminishing techniques, and a finite-volume framework, but obtain their solution in two separate manners. The first algorithm is a zonal, time-marching scheme, and is generally used to obtain solutions in the subsonic portions of the flow field. The second algorithm is a much less expensive, space-marching scheme and can be used for the computation of the larger, supersonic portion of the flow field. Both codes compute their interface fluxes with a temporal Riemann solver and the resulting schemes are made fully implicit including the chemical source terms and boundary conditions. Strong coupling is used between the fluid dynamic, chemical, and turbulence equations. These codes have been validated on numerous hypersonic test cases and have provided excellent comparison with existing data.
Zonal jets and QBO-like oscillations on Jupiter and Saturn
NASA Astrophysics Data System (ADS)
Showman, Adam P.; Zhang, Xi; Tan, Xianyu
2016-10-01
At the levels of their visible cloud decks, the giant planets Jupiter and Saturn exhibit numerous east-west (zonal) jet streams with speeds ranging up to 150 m/sec on Jupiter and 400 m/sec on Saturn. Moreover, both planets exhibit long-term stratospheric oscillations involving perturbations of zonal wind and temperature that propagate downward over time on timescales of ~4 years (Jupiter) and ~15 years (Saturn). These oscillations, dubbed the Quasi Quadrennial Oscillation (QQO) for Jupiter and the Semi-Annual Oscillation (SAO) on Saturn, are thought to be analogous to the Quasi-Biennial Oscillation (QBO) on Earth, which is driven by upward propagation of equatorial waves from the troposphere. Here, we test the hypothesis that the zonal jets on Jupiter and Saturn, as well as QBO-like oscillations, can result from interaction of the stably stratified atmosphere with an underlying convective interior. We performed global, three-dimensional, high-resolution numerical simulations of the flow in the stratosphere and upper troposphere of Jupiter-like planets. The effect of convection is parameterized by introducing thermal perturbations that randomly perturb the radiative convective boundary with some characteristic timescale, horizontal wavenumber, and amplitude. Radiative damping is represented using a Newtonian cooling scheme with a characteristic radiative time constant. In the simulations, the convective perturbations generate atmospheric waves and turbulence that interact with the rotation to produce numerous zonal jets. Moreover, the equatorial stratosphere exhibits stacked eastward and westward jets that migrate downward over time, exactly as occurs in the terrestrial QBO, Jovian QQO, and Saturnian SAO. This is the first demonstration of a QBO-like phenomenon in 3D numerical simulations of a giant planet. We will describe how the properties of the zonal jets and equatorial oscillation depend on the details of the forcing and damping. These simulations have
Comparison of CHAMP and TIME-GCM nonmigrating tidal signals in the thermospheric zonal wind
NASA Astrophysics Data System (ADS)
Häusler, K.; Lühr, H.; Hagan, M. E.; Maute, A.; Roble, R. G.
2010-02-01
Four years (2002-2005) of continuous accelerometer measurements taken onboard the CHAMP satellite (orbit altitude ˜400 km) offer a unique opportunity to investigate the thermospheric zonal wind on a global scale. Recently, we were able to relate the longitudinal wave-4 structure in the zonal wind at equatorial latitudes to the influence of nonmigrating tides and in particular to the eastward propagating diurnal tide with zonal wave number 3 (DE3). The DE3 tide is primarily excited by latent heat release in the tropical troposphere in deep convective clouds. In order to investigate the mechanisms that couple the tidal signals to the upper thermosphere, we undertook a comparison with the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) developed at the National Center for Atmospheric Research (NCAR). We ran the model for a day in March, June, September, and December and applied the same processing steps to the model output as was done for the CHAMP tidal analysis. The main results of the comparison can be summarized as follows: (1) TIME-GCM simulations do not correctly reproduce the observed intra-annual variations of DE3 and the eastward propagating diurnal tide with zonal wave number 2 (DE2). (2) Simulations of DE3 for June are more successful. Both TIME-GCM and CHAMP show an increase in DE3 amplitudes with decreasing solar flux level. (3) The amplitudes of the simulated westward propagating diurnal tide with zonal wave number 2 (DW2) and the standing diurnal tide (D0) increase with increasing solar flux in June. The predicted dependence of DW2 and DO on solar flux is also observed by CHAMP.
The zonal harmonic model of polarity transitions: A test using successive reversals
NASA Astrophysics Data System (ADS)
Theyer, F.; Herrero-Bervera, E.; Hsu, V.; Hammond, S. R.
1985-02-01
A recently developed zonal model for the last geomagnetic field reversal, which describes time- and latitude-dependent transitional behavior of intensity and inclination in terms of dominance of low-order field harmonics, was tested using a latitudinal and chronological succession of transition records. The primary data were derived from a high-resolution study of five Matuyama to Brunhes deep-sea cores collected along a 40° meridional band in the north-central Pacific. The transitions analyzed were the onsets and terminations of the Olduvai and Jaramaillo events and the Matuyama-Brunhes boundary. Supplementary data, published by previous workers, included a Jaramillo onset record from the southern Indian Ocean and a transition recorded in the Triassic Chugwater Formation of North America. In a general sense, the measured inclination and intensity records indicate the Jaramillo transitions and the last reversal to be remarkably similar to each other and to differ from the Olduvais. Crosscorrelation of the measured data sets with synthetic zonal harmonic records for the core latitudes indicates that the zonal harmonic model does predict the behavior of Matuyama-Brunhes reversal in the northern hemisphere. For the older reversals, however, the present model requires substantial modification. This is particularly so in the case of the Jaramillo onset: although two inclination and intensity records of this transition from northern and southern hemisphere sediments strongly resemble each other, the current model produces a synthetic record for one hemisphere that is incompatible with that hemisphere's measured data. Further, to model zonally the Olduvai reversals (for which a wide latitudinal northern hemisphere sampling was available), a substantially different ratio of low-order multipole components from that of the standard model is required, and the modeled solution was unsatisfactory at very low latitude. A modified zonal harmonic approach, which introduces a
Comparative analysis of zonal systems for macro-level crash modeling.
Cai, Qing; Abdel-Aty, Mohamed; Lee, Jaeyoung; Eluru, Naveen
2017-06-01
Macro-level traffic safety analysis has been undertaken at different spatial configurations. However, clear guidelines for the appropriate zonal system selection for safety analysis are unavailable. In this study, a comparative analysis was conducted to determine the optimal zonal system for macroscopic crash modeling considering census tracts (CTs), state-wide traffic analysis zones (STAZs), and a newly developed traffic-related zone system labeled traffic analysis districts (TADs). Poisson lognormal models for three crash types (i.e., total, severe, and non-motorized mode crashes) are developed based on the three zonal systems without and with consideration of spatial autocorrelation. The study proposes a method to compare the modeling performance of the three types of geographic units at different spatial configurations through a grid based framework. Specifically, the study region is partitioned to grids of various sizes and the model prediction accuracy of the various macro models is considered within these grids of various sizes. These model comparison results for all crash types indicated that the models based on TADs consistently offer a better performance compared to the others. Besides, the models considering spatial autocorrelation outperform the ones that do not consider it. Based on the modeling results and motivation for developing the different zonal systems, it is recommended using CTs for socio-demographic data collection, employing TAZs for transportation demand forecasting, and adopting TADs for transportation safety planning. The findings from this study can help practitioners select appropriate zonal systems for traffic crash modeling, which leads to develop more efficient policies to enhance transportation safety. Copyright © 2017 Elsevier Ltd and National Safety Council. All rights reserved.
Aburjania, G. D.; Chargazia, Kh. Z.
2011-02-15
A study is made of the generation and subsequent linear and nonlinear evolution of ultralow-frequency planetary electromagnetic waves in the E region of a dissipative ionosphere in the presence of a nonuniform zonal wind (a sheared flow). Hall currents flowing in the E region and such permanent global factors as the spatial nonuniformity of the geomagnetic field and of the normal component of the Earth's angular velocity give rise to fast and slow planetary-scale electromagnetic waves. The efficiency of the linear amplification of planetary electromagnetic waves in their interaction with a nonuniform zonal wind is analyzed. When there are sheared flows, the operators of linear problems are non-self-conjugate and the corresponding eigenfunctions are nonorthogonal, so the canonical modal approach is poorly suited for studying such motions and it is necessary to utilize the so-called nonmodal mathematical analysis. It is shown that, in the linear evolutionary stage, planetary electromagnetic waves efficiently extract energy from the sheared flow, thereby substantially increasing their amplitude and, accordingly, energy. The criterion for instability of a sheared flow in an ionospheric medium is derived. As the shear instability develops and the perturbation amplitude grows, a nonlinear self-localization mechanism comes into play and the process ends with the self-organization of nonlinear, highly localized, solitary vortex structures. The system thus acquires a new degree of freedom, thereby providing a new way for the perturbation to evolve in a medium with a sheared flow. Depending on the shape of the sheared flow velocity profile, nonlinear structures can be either purely monopole vortices or vortex streets against the background of the zonal wind. The accumulation of such vortices can lead to a strongly turbulent state in an ionospheric medium.
Time-variant zonal jet-like structures (striations) in the ocean circulation
NASA Astrophysics Data System (ADS)
Melnichenko, Oleg; Maximenko, Nikolai; Sasaki, Hideharu
2010-05-01
Recently, prominent jet-like features of the ocean circulation, called hereafter striations, with a meridional scale of O(300-500 km) and extending for thousands of kilometers in length, have been detected in satellite and in situ observations and in high-resolution numerical models. There are at least two distinct types of oceanic striations. The first one is quasi-stationary striations, which are best seen in multi-year time-averaged velocity fields. The second type is migrating or time-variant striations, which have been detected in velocity anomaly fields and which exhibit systematic and coherent meridional phase propagation. In this study we focus on time-variant striations and examine their spatial and temporal properties using fourteen years of satellite sea level anomaly observations and output of the Ocean general circulation model For the Earth Simulator (OFES). Time-variant striations are found to populate low and mid-latitudes. Rare exceptions are observed in the eastern parts of sub-polar regions. We put forward interpretation of the time-variant striations as low-frequency waves with nearly meridional orientation of the wave number vector. They have larger amplitudes in areas where the overall eddy kinetic energy level is higher. The wavelengths are, in general, decreasing with latitude and appear to be related to the first-mode deformation wavelength, with the averaged ratio of the former to the latter of about 2. Geographically, however, this ratio tends to be smaller in low latitudes and increases poleward. Zonal phase speeds are westward and decreasing with latitude, qualitatively in agreement with the Rossby wave dynamics. The fact that meridional scale of the striations closely follow the scale of the most energetic mesoscale variability, commonly associated with large oceanic eddies, makes separation of these two phenomena difficult and suggests that their dynamics are coupled. In a regional example in the eastern North Pacific we show that
Electromagnetic gyrokinetic turbulence in finite-beta helical plasmas
Ishizawa, A.; Watanabe, T.-H.; Sugama, H.; Nakajima, N.; Maeyama, S.
2014-05-15
A saturation mechanism for microturbulence in a regime of weak zonal flow generation is investigated by means of electromagnetic gyrokinetic simulations. The study identifies a new saturation process of the kinetic ballooning mode (KBM) turbulence originating from the spatial structure of the KBM instabilities in a finite-beta Large Helical Device (LHD) plasma. Specifically, the most unstable KBM in LHD has an inclined mode structure with respect to the mid-plane of a torus, i.e., it has a finite radial wave-number in flux tube coordinates, in contrast to KBMs in tokamaks as well as ion-temperature gradient modes in tokamaks and helical systems. The simulations reveal that the growth of KBMs in LHD is saturated by nonlinear interactions of oppositely inclined convection cells through mutual shearing as well as by the zonal flow. The saturation mechanism is quantitatively investigated by analysis of the nonlinear entropy transfer that shows not only the mutual shearing but also a self-interaction with an elongated mode structure along the magnetic field line.
High Temperature, High Pressure Devices for Zonal Isolation in Geothermal Wells
Fabian, Paul
2012-03-31
The U.S. Department of Energy is leading the development of alternative energy sources that will ensure the long-term energy independence of our nation. One key renewable resource being advanced is geothermal energy which offers an environmentally benign, reliable source of energy for the nation. To utilize this resource, water will be introduced into wells 3 to 10 km deep to create a geothermal reservoir. This approach is known as an Enhanced Geothermal System (EGS). The high temperatures and pressures at these depths have become a limiting factor in the development of this energy source. For example, reliable zonal isolation for high-temperature applications at high differential pressures is needed to conduct mini-fracs and other stress state diagnostics. Zonal isolation is essential for many EGS reservoir development activities. To date, the capability has not been sufficiently demonstrated to isolate sections of the wellbore to: 1) enable stimulation; and 2) seal off unwanted flow regions in unknown EGS completion schemes and high-temperature (>200°C) environments. In addition, packers and other zonal isolation tools are required to eliminate fluid loss, to help identify and mitigate short circuiting of flow from injectors to producers, and to target individual fractures or fracture networks for testing and validating reservoir models. General-purpose open-hole packers do not exist for geothermal environments, with the primary barrier being the poor stability of elastomeric seals at high temperature above 175°C. Experimental packer systems have been developed for geothermal environments but they currently only operate at low pressure, they are not retrievable, and they are not commercially available. The development of the high-temperature, high-pressure (HTHP) zonal isolation device would provide the geothermal community with the capability to conduct mini-fracs, eliminate fluid loss, to help identify and mitigate short circuiting of flow from injectors to
Zonal variations in K+ currents in vestibular crista calyx terminals
Meredith, Frances L.
2014-01-01
We developed a rodent crista slice to investigate regional variations in electrophysiological properties of vestibular afferent terminals. Thin transverse slices of the gerbil crista ampullaris were made and electrical properties of calyx terminals in central zones (CZ) and peripheral zones (PZ) compared with whole cell patch clamp. Spontaneous action potential firing was observed in 25% of current-clamp recordings and was either regular or irregular in both zones. Firing was abolished when extracellular choline replaced Na+ but persisted when hair cell mechanotransduction channels or calyx AMPA receptors were blocked. This suggests that ion channels intrinsic to the calyx can generate spontaneous firing. In response to depolarizing voltage steps, outward K+ currents were observed at potentials above −60 mV. K+ currents in PZ calyces showed significantly more inactivation than currents in CZ calyces. Underlying K+ channel populations contributing to these differences were investigated. The KCNQ channel blocker XE991 dihydrochloride blocked a slowly activating, sustained outward current in both PZ and CZ calyces, indicating the presence of KCNQ channels. Mean reduction was greatest in PZ calyces. XE991 also reduced action potential firing frequency in CZ and PZ calyces and broadened mean action potential width. The K+ channel blocker 4-aminopyridine (10–50 μM) blocked rapidly activating, moderately inactivating currents that were more prevalent in PZ calyces. α-Dendrotoxin, a selective blocker of KV1 channels, reduced outward currents in CZ calyces but not in PZ calyces. Regional variations in K+ conductances may contribute to different firing responses in calyx afferents. PMID:25343781
Results of a zonally truncated three-dimensional model of the Venus middle atmosphere
NASA Technical Reports Server (NTRS)
Newman, M.
1992-01-01
Although the equatorial rotational speed of the solid surface of Venus is only 4 m s(exp-1), the atmospheric rotational speed reaches a maximum of approximately 100 m s(exp-1) near the equatorial cloud top level (65 to 70 km). This phenomenon, known as superrotation, is the central dynamical problem of the Venus atmosphere. We report here the results of numerical simulations aimed at clarifying the mechanism for maintaining the equatorial cloud top rotation. Maintenance of an equatorial rotational speed maximum above the surface requires waves or eddies that systematically transport angular momentum against its zonal mean gradient. The zonally symmetric Hadley circulation is driven thermally and acts to reduce the rotational speed at the equatorial cloud top level; thus wave or eddy transport must counter this tendency as well as friction. Planetary waves arising from horizontal shear instability of the zonal flow (barotropic instability) could maintain the equatorial rotation by transporting angular momentum horizontally from midlatitudes toward the equator. Alternatively, vertically propagating waves could provide the required momentum source. The relative motion between the rotating atmosphere and the pattern of solar heating, which as a maximum where solar radiation is absorbed near the cloud tops, drives diurnal and semidiurnal thermal tides that propagate vertically away from the cloud top level. The effect of this wave propagation is to transport momentum toward the cloud top level at low latitudes and accelerate the mean zonal flow there. We employ a semispectral primitive equation model with a zonal mean flow and zonal wavenumbers 1 and 2. These waves correspond to the diurnal and semidiurnal tides, but they can also be excited by barotropic or baroclinic instability. Waves of higher wavenumbers and interactions between the waves are neglected. Symmetry about the equator is assumed, so the model applies to one hemisphere and covers the altitude range 30 to
NASA Astrophysics Data System (ADS)
Santos, Angela; Sobral, J. H. A.; Batista, Inez S.; Abdu, Mangalathayil; Souza, Jonas
2016-07-01
In this work, we investigate the equatorial F region zonal plasma drifts over Jicamarca, Peru, under magnetically disturbed conditions during two solar minimum epochs, one of them being the recent prolonged solar activity minimum. The study utilizes the plasma drifts measured by the Jicamarca (11.95° S; 76.87° W) incoherent scatter radar during two events that occurred on 10 April 1997 and 24 June 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the SUPIM-INPE. Two main points are focused: (1) the connection between prompt penetration electric fields and zonal and vertical plasma drifts and (2) anomalous behavior of daytime zonal drift in the absence of any magnetic storm. A perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm. Based on a detailed quantitative analysis we will show that this anticorrelation is driven mainly by a vertical Hall electric field induced by the primary zonal penetration electric field in the presence of enhanced nighttime E region conductivity. An increase in the field line integrated Hall-to-Pedersen conductivity ratio, arising from energetic particle precipitation in the South American Magnetic Anomaly (SAMA) region is found to be capable of explaining the observed anti correlation between the vertical and zonal plasma drifts. Evidence for the particle ionization is provided from the occurrence of anomalous sporadic E layers over the SAMA region. It will also be shown that the zonal plasma drift reversal to eastward in the afternoon can occur earlier due to the weakening of the zonal wind system during the prolonged solar minimum period.
NASA Astrophysics Data System (ADS)
Olwendo, O. J.; Baluku, T.; Baki, P.; Cilliers, P. J.; Mito, C.; Doherty, P.
2013-05-01
In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip -24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00 LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March-April than in September-October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30-160 m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east-west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives
Zonal wavefront sensing using a grating array printed on a polyester film
Pathak, Biswajit; Boruah, Bosanta R.; Kumar, Suraj
2015-12-15
In this paper, we describe the development of a zonal wavefront sensor that comprises an array of binary diffraction gratings realized on a transparent sheet (i.e., polyester film) followed by a focusing lens and a camera. The sensor works in a manner similar to that of a Shack-Hartmann wavefront sensor. The fabrication of the array of gratings is immune to certain issues associated with the fabrication of the lenslet array which is commonly used in zonal wavefront sensing. Besides the sensing method offers several important advantages such as flexible dynamic range, easy configurability, and option to enhance the sensing frame rate. Here, we have demonstrated the working of the proposed sensor using a proof-of-principle experimental arrangement.
Ranger, Christopher M; Winter, Rudolph E; Singh, Ajay P; Reding, Michael E; Frantz, Jonathan M; Locke, James C; Krause, Charles R
2011-01-25
The Japanese beetle (JB), Popillia japonica, exhibits rapid paralysis after consuming flower petals of zonal geranium, Pelargonium x hortorum. Activity-guided fractionations were conducted with polar flower petal extracts from P. x hortorum cv. Nittany Lion Red, which led to the isolation of a paralysis-inducing compound. High-resolution-MS and NMR ((1)H, (13)C, COSY, heteronuclear sequential quantum correlation, heteronuclear multiple bond correlation) analysis identified the paralytic compound as quisqualic acid (C(5)H(7)N(3)O(5)), a known but rare agonist of excitatory amino acid receptors. Optical rotation measurements and chiral HPLC analysis determined an L-configuration. Geranium-derived and synthetic L-quisqualic acid demonstrated the same positive paralytic dose-response. Isolation of a neurotoxic, excitatory amino acid from zonal geranium establishes the phytochemical basis for induced paralysis of the JB, which had remained uncharacterized since the phenomenon was first described in 1920.
Measurement of osmotic second virial coefficients by zonal size-exclusion chromatography.
Winzor, Donald J
2016-07-01
Numerical simulation of protein migration reflecting linear concentration dependence of the partition isotherm has been used to invalidate a published procedure for measuring osmotic second virial coefficients (B22) by zonal exclusion chromatography. Failure of the zonal procedure to emulate its frontal chromatographic counterpart reflects ambiguity about the solute concentration that should be used to replace the applied concentration in the rigorous quantitative expression for frontal migration; the recommended use of the peak concentration in the eluted zone is incorrect on theoretical grounds. Furthermore, the claim for its validation on empirical grounds has been traced to the use of inappropriate B22 magnitudes as the standards against which the experimentally derived values were being tested. Copyright © 2016 Elsevier Inc. All rights reserved.
Interaction of moist convection with zonal jets on Jupiter and Saturn
NASA Astrophysics Data System (ADS)
Li, Liming; Ingersoll, Andrew P.; Huang, Xianglei
2006-01-01
Observations suggest that moist convection plays an important role in the large-scale dynamics of Jupiter's and Saturn's atmospheres. Here we use a reduced-gravity quasigeostrophic model, with a parameterization of moist convection that is based on observations, to study the interaction between moist convection and zonal jets on Jupiter and Saturn. Stable jets with approximately the same width and strength as observations are generated in the model. The observed zonal jets violate the barotropic stability criterion but the modeled jets do so only if the flow in the deep underlying layer is westward. The model results suggest that a length scale and a velocity scale associated with moist convection control the width and strength of the jets. The length scale and velocity scale offer a possible explanation of why the jets of Saturn are stronger and wider than those of Jupiter.
Linkage between the northeast Mongolian precipitation and the Northern Hemisphere Zonal Circulation
NASA Astrophysics Data System (ADS)
Wang, Huijun
2006-10-01
The long-term relationship between the tree-ring-reconstructed annual precipitation in northeastern Mongolia (PRM) and the Northern Hemisphere Zonal Circulation (NHZC), defined as the normalized zonal mean sea-level pressure at 60°N in May June July, is examined in this study. A significant correlation coefficient (0.31) was found between the NHZC indices and PRM based on the dataset for the period of 1872 1995. The mechanisms responsible for the relationship are discussed through analyses of the atmospheric general circulation variability associated with NHZC. It follows that NHZC-related atmospheric circulation variability provides an anomalous southeast flow from the ocean to Northeast Mongolia (northwest flow from Northeast Mongolia to the ocean) in the middle and low troposphere in positive (negative) phase of NHZC, resulting in more (less) water vapor transport to the target region and more (less) precipitation in Northeast Mongolia.
Instability of non-zonal baroclinic flows - Multiple-scale analysis
NASA Technical Reports Server (NTRS)
Niehaus, M. C. W.
1981-01-01
The linear instability of a non-zonal flow can be reduced to an eigenvalue-eigenfunction problem, governed by a nonseparable partial differential equation (Niehaus, 1980). Approximate solutions, found by the method of multiple scales, are derived here and compared with earlier results found using a spectral method. The amplitude maxima are correctly located. The zonal variations of local wavenumber and of amplitude are qualitatively correct, but not sufficiently extreme. Because the method is oversensitive to local conditions, and less sensitive to global constraints, this comparison provides theoretical limits to the possibility of parameterizing transient eddies in terms of the local time mean state of the atmosphere. The method can be extended easily to flows with more realistic vertical structure.
Earth zonal harmonics from rapid numerical analysis of long satellite arcs
NASA Technical Reports Server (NTRS)
Wagner, C. A.
1972-01-01
A zonal geopotential is presented to degree 21 from evaluation of mean elements for 21 satellites including 2 of low inclination. Each satellite is represented by an arc of at least one apsidal rotation. The lengths range from 200 to 800 days. Differential correction of the initial elements in all of the arcs, together with radiation pressure and atmospheric drag coefficients, was accomplished simultaneously with the correction for the zonal harmonics. The satellite orbits and their variations are generated by numerical integration of the Lagrange equations for mean elements. Disturbances due to precession and nutation of the earth's pole, atmospheric drag, radiation pressure and luni-solar gravity are added at from 1- to 8-day intervals in the integrated orbits. The results agree well with recent solutions from other authors using different methods and different satellite sets.
CFD zonal modeling of leading-edge ice effects for a complete aircraft
NASA Technical Reports Server (NTRS)
Summa, J. M.; Strash, D. J.; Lednicer, D. A.
1993-01-01
A simplified, uncoupled zonal procedure was utilized to assess the capability of numerically simulating icing effects on a Boeing 727-200 aircraft. The computational approach combines potential flow, plus boundary layer simulations by VSAERO for the un-iced aircraft forces and moments, with Navier-Stokes simulations by ARC3D for the incremental forces and moments due to iced components. These are compared with wind tunnel longitudinal force and moment data. Although the computational results compared favorably with the test data in the linear angle of attack range, it is clear that for general aircraft icing calculations, a multiblock Navier-Stokes code will be required for the viscous component of this zonal method.
Zonal and tesseral harmonic coefficients for the geopotential function, from zero to 18th order
NASA Technical Reports Server (NTRS)
Kirkpatrick, J. C.
1976-01-01
Zonal and tesseral harmonic coefficients for the geopotential function are usually tabulated in normalized form to provide immediate information as to the relative significance of the coefficients in the gravity model. The normalized form of the geopotential coefficients cannot be used for computational purposes unless the gravity model has been modified to receive them. This modification is usually not done because the absolute or unnormalized form of the coefficients can be obtained from the simple mathematical relationship that relates the two forms. This computation can be quite tedious for hand calculation, especially for the higher order terms, and can be costly in terms of storage and execution time for machine computation. In this report, zonal and tesseral harmonic coefficients for the geopotential function are tabulated in absolute or unnormalized form. The report is designed to be used as a ready reference for both hand and machine calculation to save the user time and effort.
Calculation of a residual mean meridional circulation for a zonal-mean tracer transport model
Choi, W.K.; Rotman, D.A.; Wuebbles, D.J.
1995-04-01
Because of