scholarly journals Plasma flows and sound-speed perturbations in the average supergranule

2021 ◽  
Vol 646 ◽  
pp. A184
Author(s):  
David Korda ◽  
Michal Švanda
Keyword(s):  
Travel Time ◽  
Sound Speed ◽  
Deep Structure ◽  
Solar Rotation ◽  
Vertical Component ◽  
Inversion Method ◽  
Time Averaging ◽  
Vertical Flow ◽  
Near Surface ◽  
Time Distance

Context. Supergranules create a peak in the spatial spectrum of photospheric velocity features. Even though they have some properties of convection cells, their origin is still being debated in the literature. The time–distance helioseismology constitutes a method that is suitable for investigating the deep structure of supergranules. Aims. Our aim is to construct the model of the flows in the average supergranular cell using fully consistent time–distance inverse methodology. Methods. We used the Multi-Channel Subtractive Optimally Localised Averaging inversion method with regularisation of the cross-talk. We combined the difference and the mean travel-time averaging geometries. We applied this methodology to travel-time maps averaged over more than 104 individual supergranular cells. These cells were detected automatically in travel-time maps computed for 64 quiet days around the disc centre. The ensemble averaging method allows us to significantly improve the signal-to-noise ratio and to obtain a clear picture of the flows in the average supergranule. Results. We found near-surface divergent horizontal flows which quickly and monotonously weakened with depth; they became particularly weak at the depth of about 7 Mm, where they even apparently switched sign. The amplitude of the ‘reversed’ flow was comparable to the background flows. The inverted vertical flows and sound-speed perturbations were spoiled by unknown systematic errors. To learn about the vertical component, we integrated the continuity equation from the surface. The derived estimates of the vertical flow depicted a sub-surface increase from about 5 m s−1 at the surface to about 35 m s−1 at the depth of about 3 Mm followed by a monotonous decrease to greater depths. The vertical flow remained positive (an upflow) and became indistinguishable from the background at the depth of about 15 Mm. We further detected a systematic flow in the longitudinal direction. The course of this systematic flow with depth agrees well with the model of the solar rotation in the sub-surface layers.

scholarly journals Combined helioseismic inversions for 3D vector flows and sound-speed perturbations

2019 ◽  
Vol 622 ◽  
pp. A163 ◽  
Author(s):  
David Korda ◽  
Michal Švanda
Keyword(s):  
Cross Talk ◽  
Sound Speed ◽  
Vertical Component ◽  
Solar Interior ◽  
Systematic Bias ◽  
Travel Times ◽  
Plasma Flows ◽  
Near Surface ◽  
Time Distance ◽  
The Cross

Context. Time–distance helioseismology is the method of the study of the propagation of waves through the solar interior via the travel times of those waves. The travel times of wave packets contain information about the conditions in the interior integrated along the propagation path of the wave. The travel times are sensitive to perturbations of a variety of quantities. The usual task is to invert for the vector of plasma flows or the sound–speed perturbations separately. The separate inversions may be polluted by systematic bias, for instance, originating in the leakage of vector flows into the sound–speed perturbations and vice versa (called a cross-talk). Information about the cross-talk is necessary for a proper interpretation of results. Aims. We introduce an improved methodology of the time-distance helioseismology which allows us to invert for a full 3D vector of plasma flows and the sound–speed perturbations at once. Using this methodology one can also derive the mean value of the vertical component of plasma flows and the cross-talk between the plasma flows and the sound–speed perturbations. Methods. We used the Subtractive Optimally Localised Averaging method with a minimisation of the cross-talk as a tool for inverse modelling. In the forward model, we use Born approximation travel-time sensitivity kernels with the Model S as a background. The methodology was validated using forward-modelled travel times with both mean and difference point-to-annulus averaging geometries applied to a snapshot of fully self-consistent simulation of the convection. Results. We tested the methodology on synthetic data. We demonstrate that we are able to recover flows and sound–speed perturbations in the near-surface layers. We have taken the advantage of the sensitivity of our methodology to entire vertical velocity, and not only to its variations as in other available methodologies. The cross-talk from both the vertical flow component and the sound–speed perturbation has only a negligible effect for inversions for the horizontal flow components. Furthermore, this cross-talk can be minimised if needed. The inversions for the vertical component of the vector flows or for the sound–speed perturbations are affected by the cross-talk from the horizontal components, which needs to be minimised in order to provide valid results. It seems that there is a nearly constant cross-talk between the vertical component of the vector flows and the sound–speed perturbations.

FLUCTUATIONS OF THE MODAL ARRIVAL TIMES DUE TO LINEAR INTERNAL WAVES: APPLICATION TO INVERSION

2006 ◽  
Vol 14 (04) ◽  
pp. 469-487 ◽  
Author(s):  
GERALDINE BOUCHAGE ◽  
MICHAEL I. TAROUDAKIS
Keyword(s):  
Travel Time ◽  
Internal Waves ◽  
Acoustic Field ◽  
Sound Speed ◽  
Inversion Method ◽  
Perturbation Approach ◽  
Arrival Times ◽  
Inversion Procedure ◽  
Time Information ◽  
A Current

It is well known that internal waves in the ocean are an important source of environmental variability which has serious effects in the structure of an acoustic field due to a known source. When measurements of the acoustic field form the input data for an inversion procedure aiming at the recovery of the environmental parameters, the information they carry on includes the internal wave effects. It is therefore natural to assume that neglecting the effects of the internal waves in an inversion procedure based on acoustic field measurements, errors are induced in the inversion. The paper deals with this problem and addresses the case of inversion schemes using travel time information of an acoustic signal. Using a statistical 2D model of the internal waves, based on the Garrett and Munk spectrum, the spatial and temporal evolution of the internal waves field as well as the fluctuations of the sound speed profile is estimated for a characteristic shallow-water environment. Considering a sound speed anomaly in the water column as the oceanographic feature to be recovered, the paper studies the influence of the internal waves field on the modal travel time information obtained through the propagation of a tomographic signal through this environment. The sound speed anomaly denoted as "current" is described by a suitable Gaussian function. Using an analytical expression based on a perturbation approach, the difference in the modal arrival times calculated for a background environment and a perturbed one (considering that the sound speed perturbations are due either to a current or to the summation of a current and of the internal waves field) was calculated for each propagating mode of the waveguide. These calculations led to the conclusion that the internal waves have a non-negligible impact on the arrival times and that the maximum amplitude of a current can be under- or overestimated of several meters per second when these waves are not taken into account in the inversion method, whereas they are present in the oceanic medium.

STACKING OF REFLECTIONS FROM COMPLEX STRUCTURES

Geophysics ◽  
1974 ◽  
Vol 39 (4) ◽  
pp. 427-440 ◽  
Author(s):  
Max K. Miller
Keyword(s):  
Deep Structure ◽  
Control Model ◽  
Layer Model ◽  
Low Velocity ◽  
Seismic Reflection Data ◽  
Near Surface ◽  
Static Correction ◽  
Reflection Data ◽  
Actual Field ◽  
Interval Velocities

Common‐depth‐point seismic reflection data were generated on a computer using simple ray tracing and analyzed with processing techniques currently used on actual field recordings. Constant velocity layers with curved interfaces were used to simulate complex geologic shapes. Two models were chosen to illustrate problems caused by curved geologic interfaces, i.e., interfaces at depths which vary laterally in a nonlinear fashion and produce large spatial variations in the apparent stacking velocity. A three‐layer model with a deep structure and no weathering was used as a control model. For comparison, a low velocity weathering layer also of variable thickness was inserted near the surface of the control model. The low velocity layer was thicker than the ordinary thin weathering layers where state‐of‐the‐art static correction methods work well. Traveltime, moveout, apparent rms velocities, and interval velocities were calculated for both models. The weathering introduces errors into the rms velocities and traveltimes. A method is described to compensate for these errors. A static correction applied to the traveltimes reduced the fluctuation of apparent rms velocities. Values for the thick weathering layer model were “over corrected” so that synclines (anticlines) replaced false anticlines (synclines) for both near‐surface and deep zones. It is concluded that computer modeling is a useful tool for analyzing specific problems of processing CDP seismic data such as errors in velocity estimates produced by large lateral variations in overburden.

Two-dimensional elastic pseudo-spectral modeling of wide-aperture seismic array data with application to the Wichita Uplift-Anadarko Basin region of southwestern Oklahoma

1990 ◽  
Vol 80 (6A) ◽  
pp. 1677-1695 ◽  
Author(s):  
Ik Bum Kang ◽  
George A. McMechan
Keyword(s):  
Large Scale ◽  
Deep Structure ◽  
Sedimentary Basins ◽  
P Wave ◽  
Two Dimensional ◽  
Anadarko Basin ◽  
Near Surface ◽  
University Of Texas ◽  
Wide Aperture ◽  
The University

Abstract Full wave field modeling of wide-aperture data is performed with a pseudospectral implementation of the elastic wave equation. This approach naturally produces three-component stress and two-component particle displacement, velocity, and acceleration seismograms for compressional, shear, and Rayleigh waves. It also has distinct advantages in terms of computational requirements over finite-differencing when data from large-scale structures are to be modeled at high frequencies. The algorithm is applied to iterative two-dimensional modeling of seismograms from a survey performed in 1985 by The University of Texas at El Paso and The University of Texas at Dallas across the Anadarko basin and the Wichita Mountains in southwestern Oklahoma. The results provide an independent look at details of near-surface structure and reflector configurations. Near-surface (<3 km deep) structure and scattering effects account for a large percentage (>70 per cent) of the energy in the observed seismograms. The interpretation of the data is consistent with the results of previous studies of these data, but provides considerably more detail. Overall, the P-wave velocities in the Wichita Uplift are more typical of the middle crust than the upper crust (5.3 to 7.1 km/sec). At the surface, the uplift is either exposed as weathered outcrop (5.0 to 5.3 km/sec) or is overlain with sediments of up to 0.4 km in thickness, ranging in velocity from 2.7 to 3.4 km/sec, generally increasing with depth. The core of the uplift is relatively seismically transparent. A very clear, coherent reflection is observed from the Mountain View fault, which dips at ≈40° to the southwest, to at least 12 km depth. Velocities in the Anadarko Basin are typical of sedimentary basins; there is a general increase from ≈2.7 km/sec at the surface to ≈5.9 km/sec at ≈16 km depth, with discontinuous reflections at depths of ≈8, 10, 12, and 16 km.

Multi-itinerary optimization as cloud service

2021 ◽  
Vol 64 (11) ◽  
pp. 121-129
Author(s):  
Alexandru Cristian ◽  
Luke Marshall ◽  
Mihai Negrea ◽  
Flavius Stoichescu ◽  
Peiwei Cao ◽  
...  
Keyword(s):  
Travel Time ◽  
Time Windows ◽  
Algorithm Design ◽  
Cloud Service ◽  
Multiple Agents ◽  
Solution Quality ◽  
Traffic Conditions ◽  
Time Distance ◽  
And Performance ◽  
Vehicle Capacity

In this paper, we describe multi-itinerary optimization (MIO)---a novel Bing Maps service that automates the process of building itineraries for multiple agents while optimizing their routes to minimize travel time or distance. MIO can be used by organizations with a fleet of vehicles and drivers, mobile salesforce, or a team of personnel in the field, to maximize workforce efficiency. It supports a variety of constraints, such as service time windows, duration, priority, pickup and delivery dependencies, and vehicle capacity. MIO also considers traffic conditions between locations, resulting in algorithmic challenges at multiple levels (e.g., calculating time-dependent travel-time distance matrices at scale and scheduling services for multiple agents). To support an end-to-end cloud service with turnaround times of a few seconds, our algorithm design targets a sweet spot between accuracy and performance. Toward that end, we build a scalable approach based on the ALNS metaheuristic. Our experiments show that accounting for traffic significantly improves solution quality: MIO finds efficient routes that avoid late arrivals, whereas traffic-agnostic approaches result in a 15% increase in the combined travel time and the lateness of an arrival. Furthermore, our approach generates itineraries with substantially higher quality than a cutting-edge heuristic (LKH), with faster running times for large instances.

A method of obtaining P and S travel-time curves within a “Stripped Earth”*

1952 ◽  
Vol 42 (4) ◽  
pp. 313-314
Author(s):  
V. C. Stechschulte
Keyword(s):  
Travel Time ◽  
Depth Distribution ◽  
Epicentral Distance ◽  
Travel Times ◽  
Depth Of Focus ◽  
Distance Curve ◽  
Simple Method ◽  
Time Distance ◽  
Deep Focus

Abstract A simple method is outlined for obtaining from a time-distance curve of a deep-focus earthquake a table of travel times within an earth “stripped” to the depth h, the depth of focus. The method depends on the fact that such a curve for a deep-focus earthquake has a point of inflection and therefore has the same slope at two different values of epicentral distance. The Herglotz-Wiechert method may then be applied to these travel times to obtain a velocity-depth distribution.

scholarly journals Seismic investigations of the Martian near-surface at the InSight landing site

2020 ◽  
Author(s):  
Cedric Schmelzbach ◽  
Nienke Brinkman ◽  
David Sollberger ◽  
Sharon Kedar ◽  
Matthias Grott ◽  
...  
Keyword(s):  
Deep Structure ◽  
Landing Site ◽  
P Wave ◽  
Mission Design ◽  
Normal Operation ◽  
Seismic Signals ◽  
Martian Surface ◽  
Broadband Seismometer ◽  
Near Surface ◽  
Martian Regolith

<p>The InSight ultra-sensitive broadband seismometer package (SEIS) was installed on the Martian surface with the goal to study the seismicity on Mars and the deep interior of the Planet. A second surface-based instrument, the heat flow and physical properties package HP<sup>3</sup>, was placed on the Martian ground about 1.1 m away from SEIS. HP<sup>3</sup> includes a self-hammering probe called the ‘mole’ to measure the heat coming from Mars' interior at shallow depth to reveal the planet's thermal history. While SEIS was designed to study the deep structure of Mars, seismic signals such as the hammering ‘noise’ as well as ambient and other instrument-generated vibrations allow us to investigate the shallow subsurface. The resultant near-surface elastic property models provide additional information to interpret the SEIS data and allow extracting unique geotechnical information on the Martian regolith.</p><p>The seismic signals recorded during HP<sup>3</sup> mole operations provide information about the mole attitude and health as well as shed light on the near-surface, despite the fact that the HP<sup>3 </sup>mole continues to have difficulty penetrating below 40 cm (one mole length). The seismic investigation of the HP<sup>3</sup> hammering signals, however, was not originally planned during mission design and hence faced several technical challenges. For example, the anti-aliasing filters of the seismic-data acquisition chain were adapted when recording the mole hammering to allow recovering information above the nominal Nyquist frequency. In addition, the independently operating SEIS, HP<sup>3</sup> and lander clocks had to be correlated more frequently than in normal operation to enable high-precision timing.</p><p>To date, the analysis of the hammering signals allowed us to constrain the bulk P-wave velocity of the volume between the mole tip and SEIS (top 30 cm) to around 120 m/s. This low velocity value is compatible with laboratory tests performed on Martian regolith analogs with a density of around 1500 kg/m<sup>3</sup>. Furthermore, the SEIS leveling system resonances, seismic recordings of atmospheric pressure signals, HP<sup>3</sup> housekeeping data, and imagery provide additional constraints to establish a first seismic model of the shallow (topmost meters) subsurface at the landing site.</p>

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