scholarly journals Probing Surface Flows and Magnetic Activity with Time-Distance Helioseismology

2001 ◽  
Vol 203 ◽  
pp. 189-191 ◽  
Author(s):  
L. Gizon ◽  
T. L. Duvall ◽  
R. M. Larsen
Keyword(s):  
Large Scale ◽  
Active Regions ◽  
Magnetic Activity ◽  
Near Surface ◽  
Surface Flows ◽  
Time Sensitivity ◽  
Horizontal Flows ◽  
Time Distance ◽  
Radial Outflow ◽  
Sunspot Penumbra

We estimate near-surface flows using the techniques of f-mode time-distance helioseismology together with MDI/SOHO data. (1) Synoptic maps of horizontal flows are obtained for 1996, 1998 and 1999. Rotation, torsional oscillations and meridional circulation are measured. We detect weak large-scale flows converging toward active regions. Travel times are found to be shorter at locations of high magnetic activity. In addition, we measure the motion of the supergranulation pattern. (2) Realistic travel-time sensitivity kernels are used in an iterative deconvolution to infer horizontal flows at a high spatial resolution. The radial outflow outside a sunspot penumbra, called the moat, is measured.

scholarly journals Average surface flows before the formation of solar active regions and their relationship to the supergranulation pattern

2019 ◽  
Vol 628 ◽  
pp. A37 ◽  
Author(s):  
A. C. Birch ◽  
H. Schunker ◽  
D. C. Braun ◽  
L. Gizon
Keyword(s):  
Simple Model ◽  
Active Region ◽  
Active Regions ◽  
Convergence Region ◽  
Near Surface ◽  
Surface Flows ◽  
Quiet Sun ◽  
Horizontal Flows ◽  
Solar Active Regions ◽  
Region Emergence

Context. The emergence of solar active regions is an important but poorly understood aspect of the solar dynamo. Aims. Knowledge of the flows associated with the rise of active-region-forming magnetic concentrations through the near-surface layers will help determine the mechanisms of active region formation. Methods. We used helioseismic holography and granulation tracking to measure the horizontal flows at the surface that precede the emergence of active regions. We then averaged these flows over about sixty emerging active regions to reduce the noise, selecting active regions that emerge into relatively quiet Sun. To help interpret the results, we constructed a simple model flow field by generating synthetic “emergence locations” that are probabilistically related to the locations of supergranulation-scale convergence regions in the quiet Sun. Results. The flow maps obtained from helioseismology and granulation tracking are very similar (correlation coefficients for single maps around 0.96). We find that active region emergence is, on average, preceded by converging horizontal flows of amplitude about 40 m s−1. The convergence region extends over about 40 Mm in the east-west direction and about 20 Mm in the north-south direction and is centered in the retrograde direction relative to the emergence location. This flow pattern is largely reproduced by a model in which active region emergence occurs preferentially in the prograde direction relative to supergranulation inflows. Conclusions. Averaging over many active regions reveals a statistically significant pattern of near-surface flows prior to emergence. The qualitative success of our simple model suggests that rising flux concentrations and supergranule-scale flows interact during the emergence process.

scholarly journals The Chief Joseph dike swarm of the Columbia River flood basalts, and the legacy data set of William H. Taubeneck

Geosphere ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 1082-1106
Author(s):  
Matthew C. Morriss ◽  
Leif Karlstrom ◽  
Morgan W.M. Nasholds ◽  
John A. Wolff
Keyword(s):  
Large Scale ◽  
Columbia River ◽  
Flood Basalt ◽  
Continental Flood Basalt ◽  
Data Set ◽  
Average Width ◽  
Near Surface ◽  
Surface Flows ◽  
Dike Swarm ◽  
Stress Changes

Abstract The Miocene Columbia River Basalt Group (CRBG) is the youngest and best studied continental flood basalt province on Earth. The 210,000 km3 of basaltic lava flows in this province were fed by a series of dike swarms, the largest of which is the Chief Joseph dike swarm (CJDS) exposed in northeastern Oregon and southwestern Washington. We present and augment an extensive data set of field observations, collected by Dr. William H. Taubeneck (1923–2016; Oregon State University, 1955–1983); this data set elucidates the structure of the CJDS in new detail. The large-scale structure of the CJDS, represented by 4279 mapped segments mostly cropping out over an area of 100 × 350 km2, is defined by regions of high dike density, up to ∼5 segments/km−2 with an average width of 8 m and lengths of ∼100–1000 m. The dikes in the CJDS are exposed across a range of paleodepths, from visibly feeding surface flows to ∼2 km in depth at the time of intrusion. Based on extrapolation of outcrops, we estimate the volume of the CJDS dikes to be 2.5 × 102–6 × 104 km3, or between 0.1% and 34% of the known volume of the magma represented by the surface flows fed by these dikes. A dominant NNW dike segment orientation characterizes the swarm. However, prominent sub-trends often crosscut NNW-oriented dikes, suggesting a change in dike orientations that may correspond to magmatically driven stress changes over the duration of swarm emplacement. Near-surface crustal dilation across the swarm is ∼0.5–2.7 km to the E-W and ∼0.2–1.3 km to the N-S across the 100 × 350 km region, resulting in strain across this region of 0.4%–13.0% E-W and 0.04%–0.3% N-S. Host-rock partial melt is rare in the CJDS, suggesting that only a small fraction of dikes were long-lived.

scholarly journals Investigation of a sunspot complex by time-distance helioseismology

2010 ◽  
Vol 6 (S273) ◽  
pp. 320-324 ◽  
Author(s):  
A. G. Kosovichev ◽  
T. L. Duvall
Keyword(s):  
Acoustic Waves ◽  
Sound Speed ◽  
Active Regions ◽  
Magnetic Activity ◽  
Depth Range ◽  
Travel Times ◽  
Magnetic Structures ◽  
Flow Maps ◽  
Time Distance ◽  
Deep Focus

AbstractSunspot regions often form complexes of activity that may live for several solar rotations, and represent a major component of the Sun's magnetic activity. It had been suggested that the close appearance of active regions in space and time might be related to common subsurface roots, or “nests” of activity. EUV images show that the active regions are magnetically connected in the corona, but subsurface connections have not been established. We investigate the subsurface structure and dynamics of a large complex of activity, NOAA 10987-10989, observed during the SOHO/MDI Dynamics run in March-April 2008, which was a part of the Whole Heliospheric Interval (WHI) campaign. The active regions in this complex appeared in a narrow latitudinal range, probably representing a subsurface toroidal flux tube. We use the MDI full-disk Dopplergrams to measure perturbations of travel times of acoustic waves traveling to various depths by using time-distance helioseismology, and obtain sound-speed and flow maps by inversion of the travel times. The subsurface flow maps show an interesting dynamics of decaying active regions with persistent shearing flows, which may be important for driving the flaring and CME activity, observed during the WHI campaign. Our analyses, including the seismic sound-speed inversion results and the distribution of deep-focus travel-time anomalies, gave indications of diverging roots of the magnetic structures, as could be expected from Ω-loop structures. However, no clear connection in the depth range of 0-48 Mm among the three active regions in this complex of activity was detected.

scholarly journals Global Evolution of Photospheric Magnetic Fields

1990 ◽  
Vol 138 ◽  
pp. 281-295
Author(s):  
V. I. Makarov ◽  
K. R. Sivaraman
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Magnetic Activity ◽  
Field Pattern ◽  
The Sun ◽  
Coronal Emission ◽  
Global Magnetic Field ◽  
Global Modes

The main features concerning the evolution of the large scale photospheric magnetic fields derived from synoptic maps as well as from H-alpha synoptic charts are reviewed. The significance of a variety of observations that indicate the presence of a high latitude component as a counterpart to the sunspot phenomenon at lower latitudes is reviewed. It is argued that these two components describe the global magnetic field on the sun. It is demonstrated that this scenario is able to link many phenomena observed on the sun (coronal emission, ephemeral active regions, geomagnetic activity, torsional oscillations, polar faculae and global modes in the magnetic field pattern) with the global magnetic activity.

scholarly journals Solar east-west flow correlations that persist for months at low latitudes are dominated by active region inflows

2020 ◽  
Vol 644 ◽  
pp. A103
Author(s):  
Chris S. Hanson ◽  
Thomas L. Duvall ◽  
Aaron C. Birch ◽  
Laurent Gizon ◽  
Katepalli R. Sreenivasan
Keyword(s):  
Active Regions ◽  
Magnetic Activity ◽  
Near Surface ◽  
Rotation Periods ◽  
Flow Maps ◽  
Low Latitudes ◽  
Flow Features ◽  
Solar Dynamics ◽  
Convective Cells ◽  
East West

Context. Giant-cell convection is believed to be an important component of solar dynamics. For example, it is expected to play a crucial role in maintaining the Sun’s differential rotation. Aims. We reexamine early reports of giant convective cells detected using a correlation analysis of Dopplergrams. We extend this analysis using 19 years of space- and ground-based observations of near-surface horizontal flows. Methods. Flow maps are derived through the local correlation tracking of granules and helioseismic ring-diagram analysis. We compute temporal auto-correlation functions of the east-west flows at fixed latitude. Results. Correlations in the east-west velocity can be clearly seen up to five rotation periods. The signal consists of features with longitudinal wavenumbers up to m = 9 at low latitudes. Comparison with magnetic images indicates that these flow features are associated with magnetic activity. The signal is not seen above the noise level during solar minimum. Conclusions. Our results show that the long-term correlations in east-west flows at low latitudes are predominantly due to inflows into active regions and not to giant convective cells.

scholarly journals CSI 2264: Simultaneous optical and X-ray variability in the pre-main sequence stars of NGC 2264

2019 ◽  
Vol 628 ◽  
pp. A74 ◽  
Author(s):  
M. G. Guarcello ◽  
E. Flaccomio ◽  
G. Micela ◽  
C. Argiroffi ◽  
S. Sciortino ◽  
...  
Keyword(s):  
Large Scale ◽  
Main Sequence ◽  
Active Regions ◽  
Magnetic Activity ◽  
X Rays ◽  
Class Iii ◽  
Main Sequence Stars ◽  
X Ray ◽  
Rotational Modulation ◽  
Stellar Properties

Context. Pre-main sequence stars are variable sources. In diskless stars this variability is mainly due to the rotational modulation of dark photospheric spots and active regions, as in main sequence stars even if associated with a stronger magnetic activity. Aims. We aim at analyzing the simultaneous optical and X-ray variability in these stars to unveil how the activity in the photosphere is connected with that in the corona, to identify the dominant surface magnetic activity, and to correlate our results with stellar properties, such as rotation and mass. Methods. We analyzed the simultaneous optical and X-ray variability in stars without inner disks (e.g., class III objects and stars with transition disks) in NGC 2264 from observations obtained with Chandra/ACIS-I and CoRoT as part of the Coordinated Synoptic Investigation of NGC 2264. We searched for those stars whose optical and X-ray variability is correlated, anti-correlated, or not correlated by sampling their optical and X-ray light curves in suitable time intervals and studying the correlation between the flux observed in optical and in X-rays. We then studied how this classification is related with stellar properties. Results. Starting from a sample of 74 class III/transition disk (TD) stars observed with CoRoT and detected with Chandra with more than 60 counts, we selected 16 stars whose optical and X-ray variability is anti-correlated, 11 correlated, and 17 where there is no correlation. The remaining stars did not fall in any of these groups. We interpreted the anti-correlated optical and X-ray variability as typical of spot-dominated sources, due to the rotational modulation of photospheric spots spatially coincident to coronal active regions, and correlated variability typical of faculae-dominated sources, where the brightening due to faculae is dominant over the darkening due to spots. Conclusions. Stars with “anti-correlated” variability rotate slower and are less massive than those with “correlated” variability. Furthermore, cool stars in our sample have larger u − r variability than hot stars. This suggests that there is a connection between stellar rotation, mass, and the dominant surface magnetic activity, which may be related with the topology of the large-scale magnetic field. We thus discuss this scenario in the framework of the complex magnetic properties of weak-line T Tauri stars observed as part of recent projects.

scholarly journals What Seismic Minimum Reveals about Solar Magnetism below the Surface

2022 ◽  
Vol 924 (1) ◽  
pp. L20
Author(s):  
Kiran Jain ◽  
Niket Jain ◽  
Sushanta C. Tripathy ◽  
Mausumi Dikpati
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Active Regions ◽  
Magnetic Activity ◽  
Solar Interior ◽  
Solar Cycles ◽  
Surface Shear ◽  
Near Surface ◽  
Global Oscillation Network Group ◽  
Primary Driver

Abstract The Sun’s magnetic field varies on multiple timescales. Observations show that the minimum between cycles 24 and 25 was the second consecutive minimum that was deeper and wider than several earlier minima. Since the active regions observed at the Sun’s surface are manifestations of the magnetic field generated in the interior, it is crucial to investigate/understand the dynamics below the surface. In this context, we report by probing the solar interior with helioseismic techniques applied to long-term oscillations data from the Global Oscillation Network Group, that the seismic minima in deeper layers have been occurring about a year earlier than that at the surface for the last two consecutive solar cycles. Our findings also demonstrate a decrease in strong magnetic fields at the base of the convection zone, the primary driver of the surface magnetic activity. We conclude that the magnetic fields located in the core and near-surface shear layers, in addition to the tachocline fields, play an important role in modifying the oscillation frequencies. This further strengthens the existence of a relic magnetic field in the Sun’s core.

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