A Comprehensive Method to Measure Solar Meridional Circulation and the Center-to-limb Effect Using Time–Distance Helioseismology

Several techniques are used to study local areas in helioseismology, including time-distance helioseismology, acoustic imaging/holography, and ring diagram analysis. These techniques can be used to study flows, magnetic fields, and temperature inhomogeneities. The “local” area studied can be as small as a supergranule, or as large as the entire convection zone in the case of meridional circulation as studied by Giles and colleagues. Active regions have been studied with some interesting results, with complicated flow patterns below sunspots and detectable sound speed inhomogeneities in the 10 Mm below the spots. Another interesting result is the detection of sunspots on the back side of the Sun by Lindsey and Braun using the holography technique. A confirmation of their result using the time-distance technique is presented.

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Time-Distance Helioseismology of Deep Meridional Circulation

Astrophysics and Space Science Proceedings - Dynamics of the Sun and Stars ◽

10.1007/978-3-030-55336-4_11 ◽

2020 ◽

pp. 107-113

Author(s):

S. P. Rajaguru ◽

H. M. Antia

Keyword(s):

Meridional Circulation ◽

Time Distance

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Large-scale photospheric motions determined from granule tracking and helioseismology from SDO/HMI data

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732014 ◽

2018 ◽

Vol 611 ◽

pp. A92 ◽

Cited By ~ 2

Author(s):

Th. Roudier ◽

M. Švanda ◽

J. Ballot ◽

J. M. Malherbe ◽

M. Rieutord

Keyword(s):

Differential Rotation ◽

Large Scale ◽

Meridional Circulation ◽

Solar Surface ◽

Solar Rotation ◽

Large Sunspot ◽

Torsional Waves ◽

Time Distance ◽

Dynamo Process ◽

Good Agreement

Context. Large-scale flows in the Sun play an important role in the dynamo process linked to the solar cycle. The important large-scale flows are the differential rotation and the meridional circulation with an amplitude of km s−1 and few m s−1, respectively. These flows also have a cycle-related components, namely the torsional oscillations.Aim. Our attempt is to determine large-scale plasma flows on the solar surface by deriving horizontal flow velocities using the techniques of solar granule tracking, dopplergrams, and time–distance helioseismology.Methods. Coherent structure tracking (CST) and time-distance helioseismology were used to investigate the solar differential rotation and meridional circulation at the solar surface on a 30-day HMI/SDO sequence. The influence of a large sunspot on these large-scale flows with a specific 7-day HMI/SDO sequence has been also studied.Results. The large-scale flows measured by the CST on the solar surface and the same flow determined from the same data with the helioseismology in the first 1 Mm below the surface are in good agreement in amplitude and direction. The torsional waves are also located at the same latitudes with amplitude of the same order. We are able to measure the meridional circulation correctly using the CST method with only 3 days of data and after averaging between ± 15° in longitude.Conclusions. We conclude that the combination of CST and Doppler velocities allows us to detect properly the differential solar rotation and also smaller amplitude flows such as the meridional circulation and torsional waves. The results of our methods are in good agreement with helioseismic measurements.

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Meridional Circulation, Turbulence, and Diffusion Processes in Stars

International Astronomical Union Colloquium ◽

10.1017/s0252921100080477 ◽

1976 ◽

Vol 32 ◽

pp. 109-116 ◽

Cited By ~ 1

Author(s):

S. Vauclair

Keyword(s):

Convection Zone ◽

Diffusion Processes ◽

Meridional Circulation ◽

Diffusion Time ◽

Work In Progress ◽

First Results ◽

Stellar Envelopes ◽

And Diffusion ◽

Turbulence And Diffusion ◽

Hr Diagram

This paper gives the first results of a work in progress, in collaboration with G. Michaud and G. Vauclair. It is a first attempt to compute the effects of meridional circulation and turbulence on diffusion processes in stellar envelopes. Computations have been made for a 2 Mʘstar, which lies in the Am - δ Scuti region of the HR diagram.Let us recall that in Am stars diffusion cannot occur between the two outer convection zones, contrary to what was assumed by Watson (1970, 1971) and Smith (1971), since they are linked by overshooting (Latour, 1972; Toomre et al., 1975). But diffusion may occur at the bottom of the second convection zone. According to Vauclair et al. (1974), the second convection zone, due to He II ionization, disappears after a time equal to the helium diffusion time, and then diffusion may happen at the bottom of the first convection zone, so that the arguments by Watson and Smith are preserved.

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Aggression replacement training: A comprehensive method for aggressive youth and "youth at risk"

PsycEXTRA Dataset ◽

10.1037/e552522012-123 ◽

2004 ◽

Author(s):

Eeva-Liisa Salmi

Keyword(s):

At Risk ◽

Aggression Replacement Training ◽

Comprehensive Method ◽

Youth At Risk ◽

Aggressive Youth

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Individual functions of subjective time distance and emotional reaction

PsycEXTRA Dataset ◽

10.1037/e573352009-001 ◽

1971 ◽

Author(s):

U. Lundberg ◽

G. Ekman

Keyword(s):

Emotional Reaction ◽

Subjective Time ◽

Time Distance

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ASSESSMENT OF STATISTICAL SIGNIFICANCE OF HISTORIC DANUBE FLOODS

Proceedings of the XXVII Conference of the Danubian Countries on Hydrological Forecasting and Hydrological Bases of Water Management ◽

10.15407/uhmi.conference.01.05 ◽

2020 ◽

Author(s):

Stevan Prohaska ◽

◽

Aleksandra Ilić ◽

Pavla Pekarova ◽

◽

...

Keyword(s):

Middle Ages ◽

Linear Trend ◽

Statistical Significance ◽

Danube River ◽

Exceedance Probability ◽

Simultaneous Occurrence ◽

Flood Wave ◽

Probability Of Occurrence ◽

Comprehensive Method ◽

Flood Hydrograph

Data on historic floods along the Danube River exist since the year 1012. In the Middle Ages, floods were estimated based on historical documents, including original handwritten notes, newspaper articles, chronicles, formal letters, books, maps and photographs. From 1500 until the beginning of organized water regime observations, floods were hydraulically reconstructed based on water marks on old buildings in cities along the Danube (Passau, Melk, Emmersdorf an der Donau, Spilz, Schonbuhen and Bratislava). The paper presents a procedure for assessing the statistical significance of registered historic floods using a comprehensive method for defining theoretical flood hydrographs at hydrological stations. The approach is based on correlation analysis of two basic flood hydrograph parameters – maximum hydrograph ordinate (peak) and flood wave volume. The PROIL model is used to define the probability of simultaneous occurrence of these parameters. It defines the exceedance probability of two random variables, in the specific case two hydrograph parameters of the form: P{Qmax more equal to qmax,p)∩(Wmax more equal to wmax,p)} = P (1) where: Qmax – maximum hydrograph ordinate (peak); qmax,p – maximum discharge of the probability of occurrence p; Wmax – maximum hydrograph volume; wmax,p – maximum flood wave volume of the probability of occurrence p; P – exceedance probability. Spatial positions of the lines of exceedance of two flood hydrograph parameters and the empirical points of the corresponding parameters of the considered historic flood in the correlation field Qmax - Wmax, allow direct assessment of the exceedance probability of a historic flood, or its statistical significance. The proposed procedure was applied in practice to assess the statistical significance of the biggest floods registered along the Danube in the sector from its mouth to the Djerdap 1 Dam. The linear trend in the time-series of maximum annual flows at a representative hydrological station and the frequency of historic floods in the considered sector of the Danube are discussed at the end of the paper.

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