scholarly journals Annular Variability and Eddy–Zonal Flow Interactions in a Simplified Atmospheric GCM. Part I: Characterization of High- and Low-Frequency Behavior

2009 ◽  
Vol 66 (10) ◽  
pp. 3075-3094 ◽  
Author(s):  
Sarah Sparrow ◽  
Michael Blackburn ◽  
Joanna D. Haigh
Keyword(s):  
Low Frequency ◽  
Circulation Model ◽  
Zonal Flow ◽  
Life Cycles ◽  
Quasi Equilibrium ◽  
Global Circulation Model ◽  
Low Frequencies ◽  
Flow Interactions ◽  
Slow Evolution ◽  
Frequency Behavior

Abstract Experiments have been performed using a simplified, Newtonian forced, global circulation model to investigate how variability of the tropospheric jet can be characterized by examining the combined fluctuations of the two leading modes of annular variability. Eddy forcing of this variability is analyzed in the phase space of the leading modes using the vertically integrated momentum budget. The nature of the annular variability and eddy forcing depends on the time scale. 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 this evolution strongly: eddy location and amplitude reflect the past baroclinicity, while eddy feedback on the zonal flow may be interpreted in terms of wave breaking associated with baroclinic life cycles in lateral shear.

Multiple Timescales of the Southern Annular Mode

2021 ◽  
Author(s):  
Qiuyan Zhang ◽  
Yang Zhang ◽  
Zhaohua Wu
Keyword(s):  
Seasonal Variability ◽  
Low Frequency ◽  
Austral Summer ◽  
Zonal Flow ◽  
Southern Annular Mode ◽  
Multiple Timescales ◽  
Annular Mode ◽  
Flow Interactions ◽  
The Cross ◽  
Sst Anomalies

<p>Using the ensemble empirical mode decomposition (EEMD) method, this study systematically investigates the multiple timescales of the Southern Annular Mode (SAM) and identifies their relative contributions to the low-frequency persistence of SAM. Analyses show that the subseasonal sustaining of SAM mainly depends on the contribution of longer-timescale variabilities, especially the cross-seasonal variability. When subtracting the cross-seasonal variability from the SAM, the positive covariance between the eddy and zonal flow, which is suggested the positive eddy feedback in SAM, disappears. Composite analysis shows that only with strong cross-seasonal variability, the meridional shift of zonal wind, eddy momentum forcing and baroclinicity anomalies can be maintained for more than 20 days, mainly resulting from the longer-timescale (especially the cross-seasonal timescale) eddy-zonal flow interactions. This study further suggests that the dipolar sea surface temperature (SST) anomalies in the mid latitude of Southern Hemisphere (SH) is a possible cause for the cross-seasonal variability. Analysis shows that about half of the strong cross-seasonal timescale events are accompanied by evident dipolar SST anomalies, which mostly occur in austral summer. The cross-seasonal dependence of the eddy-zonal flow interactions suggests the longer-timescale (especially the cross-seasonal timescale) contribution cannot be neglected in subseasonal prediction of SAM.</p>

Control-Oriented Modeling of Lithium-Ion Batteries

2020 ◽  
Author(s):  
Brody Riemann ◽  
Jie Li ◽  
Kasim Adewuyi ◽  
Robert Landers ◽  
Jonghyun Park
Keyword(s):  
Low Frequency ◽  
Lithium Ion ◽  
Battery Management ◽  
Computationally Efficient ◽  
Low Frequencies ◽  
Battery Modeling ◽  
Capacitance Effect ◽  
Frequency Domains ◽  
Frequency Behavior ◽  
Time And Frequency Domains

Abstract Battery Management Systems (BMSs) require control-oriented models. Physics-based electrochemical models describe detailed battery phenomena, but are too computationally intensive for use in BMSs. Single Particle Models (SPMs) are often used for control-oriented battery modeling since they are physics-based and computationally efficient; however, they are only valid over very low frequency ranges and C-rates. Empirical Equivalent Circuit Models (ECMs) are also used in BMSs since they are computationally efficient and describe battery behavior over wide frequency ranges; however, they provide no physical understanding of the battery and often employ fractional order terms. This work provides a control-oriented battery model that combines the benefits of SPM and ECM models, while overcoming their limitations. The proposed model incorporates some of the battery physics found in electrochemical models, can easily be used in both the time and frequency domains, and describes battery behavior over its entire frequency range. A linearized SPM models battery physics at very low frequencies. For low frequencies, integer-order linear systems are used to approximate diffusion physics, and high frequency behavior is modeled by the double layer capacitance effect. The model is validated in the time and frequency domains via a comparison to Pseudo 2-Dimensional (P2D) model simulations and experimental data.

Kinematics of Eddy–Mean Flow Interaction in an Idealized Atmospheric Model

2013 ◽  
Vol 70 (8) ◽  
pp. 2574-2595 ◽  
Author(s):  
Sergey Kravtsov ◽  
Sergey K. Gulev
Keyword(s):  
Time Series ◽  
Storm Track ◽  
Low Frequency ◽  
Atmospheric Model ◽  
Life Cycles ◽  
Mean Flow ◽  
Atmospheric Variability ◽  
Low Frequencies ◽  
The North ◽  
Position Time Series

Abstract The authors analyze atmospheric variability simulated in a two-layer baroclinic β-channel quasigeostrophic model by combining Eulerian and feature-tracking analysis approaches. The leading mode of the model's low-frequency variability (LFV) is associated with the irregular shifts of the zonal-mean jet to the north and south of its climatological position accompanied by simultaneous intensification of the jet, while the deviations from the zonal-mean fields are dominated by propagating anomalies with wavenumbers 3–5. The model's variability is shown to stem from the life cycles of cyclones and anticyclones. In particular, synthetic streamfunction fields constructed by launching idealized composite-mean eddies along the actual full-model-simulated cyclone/anticyclone tracks reproduce nearly perfectly not only the dominant propagating waves, but also the jet-shifting LFV. The composite eddy tracks conditioned on the phase of the jet-shifting variability migrate north or south along with the zonal-mean jet. The synoptic-eddy life cycles in the states with poleward (equatorward) zonal-jet shift exhibit longer-than-climatological lifetimes; this is caused, arguably, by a barotropic feedback associated with preferred anticyclonic (cyclonic) wave breaking in these respective states. Lagged correlation and cross-spectrum analyses of zonal-mean jet position time series and the time series representing mean latitudinal location of the eddies at a given time demonstrate that jet latitude leads the storm-track latitude at low frequencies. This indicates that the LFV associated with the jet-shifting mode here is more dynamically involved than being a mere consequence of the random variations in the distribution of the synoptic systems.

Low Frequency Noise Behavior in Semiconductors

1997 ◽  
Vol 11 (20) ◽  
pp. 899-907
Author(s):  
S. V. Melkonyan ◽  
F. V. Gasparyan ◽  
V. M. Aroutiunyan
Keyword(s):  
Spectral Density ◽  
Characteristic Frequency ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Frequency Behavior

The low frequency behavior of the generation-recombination noise in the homogeneous semiconductors is investigated. The form of Lorentz law for spectral density of noise at low frequencies is made more precise. It is shown that at superlow frequencies the spectrum of generation-recombination noise changes into the 1/f-law. The characteristic frequency of this change depends on the temperature and dimensions of the sample.

scholarly journals Geostrophic Turbulence in the Frequency–Wavenumber Domain: Eddy-Driven Low-Frequency Variability*

2014 ◽  
Vol 44 (8) ◽  
pp. 2050-2069 ◽  
Author(s):  
Brian K. Arbic ◽  
Malte Müller ◽  
James G. Richman ◽  
Jay F. Shriver ◽  
Andrew J. Morten ◽  
...  
Keyword(s):  
High Resolution ◽  
Kinetic Energy ◽  
General Circulation Model ◽  
General Circulation ◽  
Low Frequency ◽  
Circulation Model ◽  
Satellite Altimeter ◽  
Low Frequencies ◽  
Low Frequency Variability ◽  
Geostrophic Turbulence

Abstract Motivated by the potential of oceanic mesoscale eddies to drive intrinsic low-frequency variability, this paper examines geostrophic turbulence in the frequency–wavenumber domain. Frequency–wavenumber spectra, spectral fluxes, and spectral transfers are computed from an idealized two-layer quasigeostrophic (QG) turbulence model, a realistic high-resolution global ocean general circulation model, and gridded satellite altimeter products. In the idealized QG model, energy in low wavenumbers, arising from nonlinear interactions via the well-known inverse cascade, is associated with energy in low frequencies and vice versa, although not in a simple way. The range of frequencies that are highly energized and engaged in nonlinear transfer is much greater than the range of highly energized and engaged wavenumbers. Low-frequency, low-wavenumber energy is maintained primarily by nonlinearities in the QG model, with forcing and friction playing important but secondary roles. In the high-resolution ocean model, nonlinearities also generally drive kinetic energy to low frequencies as well as to low wavenumbers. Implications for the maintenance of low-frequency oceanic variability are discussed. The cascade of surface kinetic energy to low frequencies that predominates in idealized and realistic models is seen in some regions of the gridded altimeter product, but not in others. Exercises conducted with the general circulation model suggest that the spatial and temporal filtering inherent in the construction of gridded satellite altimeter maps may contribute to the discrepancies between the direction of the frequency cascade in models versus gridded altimeter maps seen in some regions. Of course, another potential reason for the discrepancy is missing physics in the models utilized here.

scholarly journals Practical Applications of Diffusive Realization of Fractional Integrator with SoftFrac

Electronics ◽  
2021 ◽  
Vol 10 (15) ◽  
pp. 1767
Author(s):  
Jerzy Baranowski ◽  
Waldemar Bauer ◽  
Rafał Mularczyk
Keyword(s):  
Fractional Calculus ◽  
Fractional Integral ◽  
Low Frequency ◽  
Phase Lag ◽  
Low Frequencies ◽  
Practical Applications ◽  
Fractional Integrator ◽  
The World ◽  
Frequency Behavior ◽  
Domain Integration

Fractional calculus has found multiple applications around the world. It is especially prevalent in the domains of control and electronics. One of the key elements of fractional applications is the fractional integral (or integrator) which is a backbone of famous PIλD controller. It gives advantages of traditional PID with a limited phase lag. The are, however, issues with implementation, which will allow good low-frequency behavior. In this paper, we consider a diffusive realization of a fractional integrator with the use of quadratures. We implemented this method in numerical package SoftFrac, and we illustrate how different quadratures work for this purpose. We show superiority of bounded domain integration with logarithmic transformation and explain issues with behavior for extremely low frequencies.

Low-Frequency Variability in a Turbulent Baroclinic Jet: Eddy–Mean Flow Interactions in a Two-Level Model

2010 ◽  
Vol 67 (2) ◽  
pp. 452-467 ◽  
Author(s):  
Joseph Bernstein ◽  
Brian Farrell
Keyword(s):  
Time Scale ◽  
General Circulation ◽  
Channel Model ◽  
Low Frequency ◽  
Circulation Model ◽  
Coupled System ◽  
Mean Flow ◽  
Low Frequency Variability ◽  
Flow Interactions ◽  
The Waves

Abstract The origin of low-frequency variability in the midlatitude jet is investigated using a two-level baroclinic channel model. The model state fields are separated into slow and fast components using intermediate time- scale averaging. In the equation for the fast variables the nonlinear wave–wave interactions are parameterized as a stochastic excitation. The slowly varying ensemble mean eddy fluxes obtained from the resulting stochastic turbulence model are coupled with the slowly varying mean flow dynamics. This forms a coupled set of deterministic equations on the slow time scale that governs the dynamics of the eddy–mean flow interaction. The equilibria of this coupled system are found as a function of the excitation strength, which controls the level of turbulence. At low levels of turbulence the equilibrated flow with zonally symmetric mean forcing remains zonally symmetric, but as excitation increases it undergoes zonal symmetry-breaking bifurcations. Time-dependent flows arising from these bifurcations take the form of westward-propagating wavelike structures resembling blocking patterns. Features of these waves are characteristic of blocking in both observations and atmospheric general circulation model simulations including retrogression, eddy variance concentrated upstream of the waves, and eddy momentum flux forcing the waves.

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