scholarly journals Dynamics of Sunspot Series on Time Scales From Days to Years: Correlation of Sunspot Births, Variable Lifetimes, and Evolution of the High-Frequency Spectral Component

2017 ◽  
Vol 122 (12) ◽  
pp. 11,874-11,887 ◽  
Author(s):  
A. Shapoval ◽  
J.-L. Le Mouël ◽  
M. Shnirman ◽  
V. Courtillot
Keyword(s):  
Time Scales ◽  
High Frequency ◽  
Spectral Component ◽  
Sunspot Series

scholarly journals Interannual modulation of extratropical high frequency variability

1997 ◽  
Vol 40 (4) ◽  
Author(s):  
R. Caballero
Keyword(s):  
Normal Mode ◽  
Time Scales ◽  
High Frequency ◽  
Spherical Geometry ◽  
Simple Explanation ◽  
Space And Time ◽  
High Frequency Variability ◽  
Hemisphere Winter ◽  
Selection Of

A simple explanation is presented for the observed interannual changes in the dominant space and time scales of Northem Hemisphere winter extratropical high frequency variability. It is found that such changes can suc- cessfully be predicted by linearizing a 2-level quasi-geostrophic mode] in spherical geometry around the ob- served zona] mean states. The mechanisms responsible for the selection of the most unstable normal mode are investigated.

scholarly journals THE PROBABILITY CHARACTERISTICS OP WAVES AND WAVE PRESSURES AT A VERTICAL BREAKWATER

1984 ◽  
Vol 1 (19) ◽  
pp. 50
Author(s):  
Huang Peiji ◽  
Zhao Binglai
Keyword(s):  
Probability Distribution ◽  
High Frequency ◽  
Pressure Field ◽  
Spectral Component ◽  
High Frequency Band ◽  
Wave Pressure ◽  
Spectral Components ◽  
Wave Heights ◽  
Vertical Breakwater ◽  
Equilibrium Range

In this paper, under the condition of waves in front of a breakwater being not broken, studies were made on the characterises of probability distribution of waves and wave pressures, the regularity of the spectral component attenuation with depth and the constitution of the high frequency band of wave pressure spectrum. The distributions of wave heights in front of a vertical breakwater, the range of wave pressure fluctuation at different subsurface levels, and the wave periods have shown that they are practically invariable with depth and can be determined theoretically. The spectral constitution of wave pressure field and the regularity of attenuation of spectral components were analyzed at the vertical breakwater, and a new expression describing the equilibrium range of wave pressure spectrum was obtained.

scholarly journals Time scales of arsenic variability and the role of high-frequency monitoring at three water-supply wells in New Hampshire, USA

2020 ◽  
Vol 709 ◽  
pp. 135946 ◽  
Author(s):  
James R. Degnan ◽  
Joseph P. Levitt ◽  
Melinda L. Erickson ◽  
Bryant C. Jurgens ◽  
Bruce D. Lindsey ◽  
...  
Keyword(s):  
Water Supply ◽  
Time Scales ◽  
New Hampshire ◽  
High Frequency ◽  
Frequency Monitoring

scholarly journals Stochastic Subgrid-Scale Ocean Mixing: Impacts on Low-Frequency Variability

2017 ◽  
Vol 30 (13) ◽  
pp. 4997-5019 ◽  
Author(s):  
Stephan Juricke ◽  
Tim N. Palmer ◽  
Laure Zanna
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
High Frequency ◽  
Low Frequency ◽  
Global Ocean ◽  
Small Scale ◽  
Subgrid Scale ◽  
Low Frequency Variability ◽  
Ocean Models

In global ocean models, the representation of small-scale, high-frequency processes considerably influences the large-scale oceanic circulation and its low-frequency variability. This study investigates the impact of stochastic perturbation schemes based on three different subgrid-scale parameterizations in multidecadal ocean-only simulations with the ocean model NEMO at 1° resolution. The three parameterizations are an enhanced vertical diffusion scheme for unstable stratification, the Gent–McWilliams (GM) scheme, and a turbulent kinetic energy mixing scheme, all commonly used in state-of-the-art ocean models. The focus here is on changes in interannual variability caused by the comparatively high-frequency stochastic perturbations with subseasonal decorrelation time scales. These perturbations lead to significant improvements in the representation of low-frequency variability in the ocean, with the stochastic GM scheme showing the strongest impact. Interannual variability of the Southern Ocean eddy and Eulerian streamfunctions is increased by an order of magnitude and by 20%, respectively. Interannual sea surface height variability is increased by about 20%–25% as well, especially in the Southern Ocean and in the Kuroshio region, consistent with a strong underestimation of interannual variability in the model when compared to reanalysis and altimetry observations. These results suggest that enhancing subgrid-scale variability in ocean models can improve model variability and potentially its response to forcing on much longer time scales, while also providing an estimate of model uncertainty.

scholarly journals Time Scales of Southern Ocean Eddy Equilibration

2016 ◽  
Vol 46 (9) ◽  
pp. 2785-2805 ◽  
Author(s):  
Anirban Sinha ◽  
Ryan P. Abernathey
Keyword(s):  
Southern Ocean ◽  
Time Scales ◽  
Wind Stress ◽  
Time Scale ◽  
High Frequency ◽  
Channel Model ◽  
Large Fraction ◽  
Low Frequency ◽  
Amplitude Response ◽  
Relative Conversion

AbstractStratification in the Southern Ocean is determined primarily by a competition between westerly wind-driven upwelling and baroclinic eddy transport. This study investigates the time scales of equilibration of the Southern Ocean in response to changing winds through an idealized channel model. An analytical framework describing the energetic pathways between wind input, available potential energy (APE), eddy kinetic energy (EKE), and dissipation provides a simple theory of the phase and amplitude response to oscillating wind stress. The transient ocean response to variable winds lies between the two limits of Ekman response (high frequency), characterized by the isopycnal slope responding directly to wind stress, and “eddy saturation” (low frequency), wherein a large fraction of the anomalous wind work goes into mesoscale eddies. The crossover time scale is the time scale of meridional eddy diffusive transport across the Antarctic Circumpolar Current (ACC) front. For wind variability with a period of 3 months (high-frequency forcing), the relative conversion of wind work to APE/EKE is 11, while for a period of 16 years (low-frequency forcing), the relative conversion to APE/EKE reduces to 3. The system’s frequency response is characterized by a complex transfer function. Both the phase and amplitude response of EKE and APE predicted by the linear analytic framework are verified using multiple ensemble experiments in an eddy-resolving (4-km horizontal resolution) isopycnal coordinate model. The results from the numerical experiments show agreement with the linear theory and can be used to explain certain features observed in previous modeling studies and observations.

scholarly journals Time scales of mixing in an imperforate scleractinian coelenteron

2020 ◽  
Author(s):  
Sara D. Williams ◽  
Mark R. Patterson
Keyword(s):  
Oxygen Concentration ◽  
Time Scales ◽  
High Frequency ◽  
Oxygen Flux ◽  
Electrical Network ◽  
Small Magnitude ◽  
Network Time ◽  
Power Spectral ◽  
Oxygen Dynamics ◽  
Gastrovascular System

AbstractCoelentera are the largest components by volume in the gastrovascular system connecting polyps in a scleractinian colony. Thus to understand colony connectivity which is predicted to affect corals’ response to environmental change, we must first describe the dynamics inside these gastric cavities of individual polyps. We determined key time scales of mixing in coelentera by using microelectrodes to measure oxygen concentration after a light-to-dark transition in three polyps each of three colonies of Montastraea cavernosa in the laboratory. The gastrovascular system was modeled as an electrical network where voltage represents oxygen concentration, current represents oxygen flux, capacitors represent volume compartments, and resistors represent impedance to oxygen flux. The time constant of mixing, defined as the time needed for the system to disperse 63.2% of the fluid in the coelenteron, was determined from the oxygen dynamics in the coelenteron as modeled by a resistor-capacitor network. Time constants were on the order of three minutes and oxygen dynamics were well fit by the model prediction. However, as polyps depleted oxygen, we observed small magnitude (~ 0.1 ppm), high-frequency fluctuations in oxygen concentration. A power spectral density analysis identified two time scales of high-frequency mixing in the coelenteron. The greatest variance occurred at a period of 48.3 ± 2.8 seconds, with a secondary peak seen at 35.9 ± 2.3 seconds. The microenvironment within polyps of M. cavernosa can respond as fast or faster than their external environment can fluctuate, thus scleractinian polyps have the capacity to mediate their response to changing environmental conditions.

scholarly journals Nucleotide variation and balancing selection at the Ckma gene in Atlantic cod: Analysis with multiple merger coalescent models

2014 ◽  
Author(s):  
Einar Árnason ◽  
Katrín Halldórsdóttir
Keyword(s):  
Natural Selection ◽  
Population Size ◽  
Time Scales ◽  
High Frequency ◽  
Atlantic Cod ◽  
Balancing Selection ◽  
Reproductive Capacity ◽  
Parameter Estimates ◽  
Nucleotide Variation ◽  
High Fecundity

A high-fecundity organisms, such as Atlantic cod, can withstand substantial natural selection and can at any time simultaneously replace alleles at a number of loci due to their excess reproductive capacity. High-fecundity organisms may reproduce by sweepstakes leading to highly skewed heavy-tailed offspring distribution. Under such reproduction the Kingman coalescent of binary mergers breaks down and models of multiple merger coalescent are more appropriate. Here we study nucleotide variation at the Ckma (Creatine Kinase Muscle type A) gene in Atlantic cod. The gene shows extreme differentiation between the North (Canada, Greenland, Iceland, Norway, Barents Sea) and the South (Faroe Islands, North-, Baltic-, Celtic-, and Irish Seas) with a between regions FST > 0.8 whereas neutral loci show no differentiation. This is evidence for natural selection. The protein sequence is conserved by purifying selection whereas silent and non-coding sites show extreme differentiation. Relative to outgroup the site-frequency spectrum has three modes, a mode at singleton sites and two high frequency modes at opposite frequencies representing divergent branches of the gene genealogy that is evidence for balancing selection. Analysis with multiple-merger coalescent models can account for the high frequency of singleton sites and indicate reproductive sweepstakes. Coalescent time scales with population size and with the inverse of variance in offspring number. Parameter estimates using multiple-merger coalescent models show fast time-scales. Time-scales of mitochondrial DNA are about square root of the effective population size and time-scales of nuclear genes are much faster.

scholarly journals Post-lockdown abatement of COVID-19 by fast periodic switching

2021 ◽  
Vol 17 (1) ◽  
pp. e1008604
Author(s):  
Michelangelo Bin ◽  
Peter Y. K. Cheung ◽  
Emanuele Crisostomi ◽  
Pietro Ferraro ◽  
Hugo Lhachemi ◽  
...  
Keyword(s):  
Time Scales ◽  
High Frequency ◽  
Software Tool ◽  
Proof Of Concept ◽  
Concept System ◽  
Fast Switching ◽  
Potential Efficacy ◽  
The Social ◽  
Wave Effects ◽  
Short Time

COVID-19 abatement strategies have risks and uncertainties which could lead to repeating waves of infection. We show—as proof of concept grounded on rigorous mathematical evidence—that periodic, high-frequency alternation of into, and out-of, lockdown effectively mitigates second-wave effects, while allowing continued, albeit reduced, economic activity. Periodicity confers (i) predictability, which is essential for economic sustainability, and (ii) robustness, since lockdown periods are not activated by uncertain measurements over short time scales. In turn—while not eliminating the virus—this fast switching policy is sustainable over time, and it mitigates the infection until a vaccine or treatment becomes available, while alleviating the social costs associated with long lockdowns. Typically, the policy might be in the form of 1-day of work followed by 6-days of lockdown every week (or perhaps 2 days working, 5 days off) and it can be modified at a slow-rate based on measurements filtered over longer time scales. Our results highlight the potential efficacy of high frequency switching interventions in post lockdown mitigation. All code is available on Github at https://github.com/V4p1d/FPSP_Covid19. A software tool has also been developed so that interested parties can explore the proof-of-concept system.

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