scholarly journals Stochastic Low-frequency Variability in Three-dimensional Radiation Hydrodynamical Models of Massive Star Envelopes

2022 ◽  
Vol 924 (1) ◽  
pp. L11
Author(s):  
William C. Schultz ◽  
Lars Bildsten ◽  
Yan-Fei Jiang
Keyword(s):  
Main Sequence ◽  
Three Dimensional ◽  
Power Spectra ◽  
Low Frequency ◽  
Surface Region ◽  
Stellar Envelope ◽  
Near Surface ◽  
Ab Initio Simulations ◽  
Low Frequency Variability ◽  
Hydrostatic Balance

Abstract Increasing main-sequence stellar luminosity with stellar mass leads to the eventual dominance of radiation pressure in stellar-envelope hydrostatic balance. As the luminosity approaches the Eddington limit, additional instabilities (beyond conventional convection) can occur. These instabilities readily manifest in the outer envelopes of OB stars, where the opacity increase associated with iron yields density and gas-pressure inversions in 1D models. Additionally, recent photometric surveys (e.g., TESS) have detected excess broadband low-frequency variability in power spectra of OB star lightcurves, called stochastic low-frequency variability (SLFV). This motivates our novel 3D Athena++ radiation hydrodynamical (RHD) simulations of two 35 M ⊙ star envelopes (the outer ≈15% of the stellar radial extent), one on the zero-age main sequence and the other in the middle of the main sequence. Both models exhibit turbulent motion far above and below the conventional iron-opacity peak convection zone (FeCZ), obliterating any “quiet” part of the near-surface region and leading to velocities at the photosphere of 10–100 km s−1, directly agreeing with spectroscopic data. Surface turbulence also produces SLFV in model lightcurves with amplitudes and power-law slopes that are strikingly similar to those of observed stars. The characteristic frequencies associated with SLFV in our models are comparable to the thermal time in the FeCZ (≈3–7 day−1). These ab initio simulations are directly validated by observations and, though more models are needed, we remain optimistic that 3D RHD models of main-sequence O-star envelopes exhibit SLFV originating from the FeCZ.

scholarly journals Site Specific Three-dimensional Structural Analysis in Tissues and Cells Using Automated DualBeam Slice &View

2007 ◽  
Vol 15 (2) ◽  
pp. 26-31 ◽  
Author(s):  
Ben Lich
Keyword(s):  
Electron Microscopy ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
Three Dimensional ◽  
Surface Region ◽  
Dimensional Structure ◽  
Near Surface ◽  
Imaging Capability ◽  
Fluorescent Markers ◽  
Confocal And Electron Microscopy

DualBeam instruments that combine the imaging capability of scanning electron microscopy (SEM) with the cutting and deposition capability of a focused ion beam (FIB) provide biologists with a powerful tool for investigating three-dimensional structure with nanoscale (1 nm-100 nm) resolution. Ever since Van Leeuwenhoek used the first microscope to describe bacteria more than 300 years ago, microscopy has played a central role in scientists' efforts to understand biological systems. Light microscopy is generally limited to a useful resolution of about a micrometer. More recently the use of confocal and electron microscopy has enabled investigations at higher resolution. Used with fluorescent markers, confocal microscopy can detect and localize molecular scale features, but its imaging resolution is still limited. SEM is capable of nanometer resolution, but is limited to the near surface region of the sample.

3D Numerical Simulation of Electromagnetic Field during Low Frequency Electromagnetic Casting Process

2010 ◽  
Vol 154-155 ◽  
pp. 1472-1475
Author(s):  
Xiang Jie Wang ◽  
Jian Zhong Cui ◽  
Hai Tao Zhang
Keyword(s):  
Magnetic Field ◽  
Numerical Simulation ◽  
Three Dimensional ◽  
Low Frequency ◽  
Fem Analysis ◽  
Casting Process ◽  
Surface Region ◽  
Element Model ◽  
Current Intensity ◽  
Three Dimensional Finite Element

The rules of the distribution of magnetic field were carried out by numerical simulation. The distribution of magnetic field was got, and the effects of current intensity and frequency on the distribution of magnetic field were analyzed by constructing three-dimensional finite element model and using ANSYS software which is a kind of commercial FEM analysis software. The results show that the intensity of magnetic field is proportional to current intensity, magnetic field is mainly localized in the surface region of liquid melt and there is a notable edge effect in the corner.

scholarly journals 6-Hour to 1-Year Variance of Five Global Precipitation Sets

2007 ◽  
Vol 11 (11) ◽  
pp. 1-29 ◽  
Author(s):  
Alex C. Ruane ◽  
John O. Roads
Keyword(s):  
High Frequency ◽  
Spectral Characteristics ◽  
Power Spectra ◽  
Low Frequency ◽  
Tropical Rainfall Measuring Mission ◽  
Seasonal Migration ◽  
Low Frequency Variability ◽  
Precipitation Estimation ◽  
The Indian Ocean ◽  
Global Precipitation

Abstract Three-hourly time series of precipitation from three high-resolution precipitation products [Tropical Rainfall Measuring Mission (TRMM) algorithm 3B-42, the Climate Prediction Center’s morphing method (CMORPH), and the Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks (PERSIANN)] and two reanalyses are examined for their frequency characteristics using broad and narrow variance categories. After isolating the diurnally forced peaks (at 24, 12, 8, and 6 h), the power spectra are divided into comprehensive broad bands comprising the annual (∼80 days–1 yr), intraseasonal (20 to ∼80 days), slow (6–20 days) and fast (36 h–6 days) synoptic, and high-frequency (6–36 h) periods. Global maps accounting for 100% of precipitation’s variance are analyzed to identify unique regional behaviors. Annual variability is strongest over regions affected by the seasonal migration of the intertropical convergence zone, as well as over monsoonal regions. The intraseasonal band displays off-equatorial evidence of the Madden–Julian oscillation (MJO), particularly in the Indian Ocean, but the MJO’s rainfall is partially manifested in the slow synoptic band and at higher frequencies. The fast synoptic band is particularly strong over the oceans, while high-frequency variability is enhanced over land by more extreme surface gradients. Diurnal variance is strongest at low latitudes and is pronounced over regions with well-known diurnal circulations, including mountains and coastlines. Interproduct and intermodel differences also indicate biases of the precipitation product algorithms and convective parameterizations, including a strong bias toward low-frequency variability in the relaxed Arakawa–Schubert parameterization employed by one of the reanalyses, as well as increased white-spectral characteristics over land in the precipitation products.

scholarly journals Interannual Subtropical Indian Ocean Variability due to Long Baroclinic Planetary Waves

2020 ◽  
Vol 33 (16) ◽  
pp. 6765-6791
Author(s):  
Christopher C. Chapman ◽  
Bernadette M. Sloyan ◽  
Terence J. O’Kane ◽  
Matthew A. Chamberlain
Keyword(s):  
Indian Ocean ◽  
Feature Tracking ◽  
Model Simulation ◽  
Low Frequency ◽  
Phase Speed ◽  
Heat Fluxes ◽  
Planetary Waves ◽  
Near Surface ◽  
South Indian ◽  
Low Frequency Variability

AbstractLow-frequency variability in the south Indian Ocean is studied by analyzing 200 years of output from a fully coupled climate model simulation. At time scales of 2–10 years, the variability is dominated by westward-propagating features that form on the eastern side of the basin. Using feature tracking and clustering, the spatiotemporal characteristics and preferred pathways of the propagating features are identified and studied in detail. By comparison of the phase speed and vertical structure of the propagating anomalies identified by the feature tracking with linear theory, we conclude that these features are likely mode 1 or 2 baroclinic planetary waves. The effects of this low-frequency variability on the climate system is investigated. By analysis of the mixed-layer temperature budget, it is shown that at particular geographic locations, the propagating features can substantially modify the near-surface ocean and induce significant fluxes of heat into the atmosphere. In turn, these heat fluxes can drive a coherent atmospheric response, although this response does not appear to feed back onto the ocean. Finally, we discuss the implications for the interannual climate predictability.

Interactions between Decadal to Multidecadal Ocean Variability and Stratospheric Sudden Warmings

2021 ◽  
Author(s):  
Blanca Ayarzagüena ◽  
Elisa Manzini ◽  
Natalia Calvo ◽  
Daniela Matei
Keyword(s):  
Decadal Variability ◽  
Low Frequency ◽  
Max Planck ◽  
Near Surface ◽  
Multidecadal Variability ◽  
Pacific Decadal Variability ◽  
Surface Circulation ◽  
Low Frequency Variability ◽  
First Time ◽  
Observational Record

<p>Major sudden stratospheric warmings (SSWs) are largest instances of the boreal polar stratospheric variability. Their effects extend farther from the polar stratosphere, affecting for example near-surface circulation. According to observations, SSWs are not equally distributed along time, with decades with almost no events and decades with SSWs happening almost every winter. This suggests the existence of multidecadal variability of SSWs. Some previous studies have pointed to phenomena in the ocean surface as the main precursors of this low-frequency variability. However, the relatively short observational record and the need of long model simulations with daily output have not enabled an analysis of the influences of these oceanic phenomena on SSWs</p><p>The goal of this study is to investigate the effects of Atlantic Multidecadal Variability (AMV) and Pacific Decadal Variability (PDV) on SSWs. To do so, we use for the first time a large ensemble of historical experiments (Max Planck Grand Ensemble) that allows us to examine the modulation of the frequency, precursors and surface impact of SSWs by both types of oceanic variability. Our results reveal that PDV has an impact on the frequency of SSWs, with a significant higher rate of SSWs for its positive than the negative phase. As for AMV, the main effect of AMV is centered on the tropospheric response to SSWs, with almost no modulation in the occurrence of the event. This last finding would be useful in order to predict the tropospheric fingerprint of SSWs.</p>

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