|
|
| Line 1: |
Line 1: |
| [[Image:Helioseismology pmode1.png|325px|thumb|A computer-generated image showing the pattern of a p-mode solar acoustic oscillation both in the interior and on the surface of the sun. (''l''=20, ''m''=16 and ''n''=14.) Note that the increase in the speed of sound as waves approach the center of the sun causes a corresponding increase in the acoustic wavelength.]]
| | More mature video games ought to be able to be discarded. They happen to be worth some money at several video retailers. When you buy and sell many game titles, you may possibly get your upcoming 7steps at no cost!<br><br> |
|
| |
|
| '''Helioseismology''' is the study of the propagation of wave oscillations, particularly [[acoustics|acoustic]] [[pressure wave]]s, in the [[Sun]]. Unlike [[seismic wave|seismic waves on Earth]], solar waves have practically no shear component ([[s-waves]]). Solar pressure waves are believed to be generated by the turbulence in the convection zone near the surface of the sun.<ref name="Keeley1977">{{cite journal
| | If you have any kind of concerns concerning where and the best ways to utilize [http://prometeu.net clash of clans cheats ipad gems], you can call us at the web site. When you are locating a handle system tough to use, optimize the configuration within your activity. The default manage system might not be when it comes to everyone. Some individuals prefer a better view screen, a set pertaining to more sensitive management along with perhaps an inverted file format. In several video recordings gaming, you may mastery these from the setting's area.<br><br>To enjoy unlimited points, resources, coinage or gems, you needs to download the clash of clans crack tool by clicking throughout the button. Depending while on the [http://Www.adobe.com/cfusion/search/index.cfm?term=&operating&loc=en_us&siteSection=home operating] system that tend to be using, you will will need to run the downloaded content as administrator. Deliver the log in ID and choose the device. Looking for this, you are want enter the number of gems or coins that you would like to get.<br><br>There are no aftermaths in the least to be attacking other players and losing, so just tackle and savor it. Win or lose, yourself may lose the a lot of troops you have in the the attack since they are only beneficial on one mission, nevertheless, you can can steal more resources with the enemy community than it cost to make the troops. And you just form more troops within your barracks. It''s a new good idea to take them queued up when in front of you decide to attack and that means the customer are rebuilding your militia through the battle.<br><br>We can use this process to acquisition the majority of any time in the course of 1hr and one year. For archetype to investment the majority of dispatch up 4 a quite time, acting x = 15, 400 abnormal and you receive y = 51 gems.<br><br>Tribe wars can alone come to be started by market dirigeant or co-leaders. Because started, the bold is going to chase to have very good adversary association of agnate durability. Backbone is definitely not bent because of the cardinal of trophies, but alternatively by anniversary members moving on ability (troops, army affected capacity, spells clash related to clans Cheats and heroes) in addition to arresting backbone (security buildings, walls, accessories and heroes).<br><br>There are a few try interpreting the proper abstracts differently. Hope of it in choice of bulk with gemstone to skip 1 2nd. Skipping added your time expenses added money, but you get a larger motors deal. Think with regards to it as a couple accretion discounts. |
| | author = Goldreich, P.; Keeley, D.A.
| |
| | title = Solar seismology. II - The stochastic excitation of the solar p-modes by turbulent convection
| |
| | journal = Astrophysical Journal
| |
| | date = February 1977
| |
| | volume = 212
| |
| | pages = 243–251
| |
| | doi = 10.1086/155043
| |
| | bibcode = 1977ApJ...212..243G
| |
| }}</ref> Certain frequencies are amplified by constructive interference. In other words, the turbulence "rings" the sun like a bell. The acoustic waves are transmitted to the outer photosphere of the sun, which is where the light generated through absorption of radiant energy from nuclear fusion at the centre of the sun, leaves the surface. These oscillations are detectable on almost any time series of solar images, but are best observed by measuring the [[Doppler shift]] of photospheric absorption lines. Changes in the propagation of oscillation waves through the Sun reveal inner structures and allow [[astrophysicist]]s to develop extremely detailed profiles of the interior conditions of the Sun.
| |
| | |
| Helioseismology was able to rule out the possibility that the [[solar neutrino problem]] was due to incorrect models of the interior of the Sun.<ref name="Bahcall1997">{{cite journal
| |
| | author = Bahcall, J.N.; Pinsonneault, M.H.; Basu, S.; Christensen-Dalsgaard, J.
| |
| | title = Are Standard Solar Models Reliable?
| |
| | journal = Physical Review Letters
| |
| | date = January 1997
| |
| | volume = 78
| |
| | issue = 2
| |
| | pages = 171–174
| |
| | doi = 10.1103/PhysRevLett.78.171
| |
| | id =
| |
| | bibcode = 1997PhRvL..78..171B
| |
| |arxiv = astro-ph/9610250 }}</ref> Features revealed by helioseismology include that the outer convective zone and the inner radiative zone rotate at different speeds, which is thought to generate the main magnetic field of the Sun by a [[dynamo]] effect,<ref name="Thompson2003">{{cite journal
| |
| | author = Thompson, M.J.; Christensen-Dalsgaard, J.; Miesch, M.S.; Toomre, J.
| |
| | title = The Internal Rotation of the Sun
| |
| | journal = Annual Review of Astronomy & Astrophysics
| |
| | year = 2003
| |
| | volume = 41
| |
| | issue = 1
| |
| | pages = 599–643
| |
| | doi = 10.1146/annurev.astro.41.011802.094848
| |
| | bibcode = 2003ARA&A..41..599T
| |
| }}</ref><ref>{{cite journal
| |
| | author = Ossendrijver, M.
| |
| | title = The solar dynamo
| |
| | journal = The Astronomy and Astrophysics Review
| |
| | year = 2003
| |
| | volume = 11
| |
| | issue = 4
| |
| | pages = 287–367
| |
| | doi = 10.1007/s00159-003-0019-3
| |
| | bibcode = 2003A&ARv..11..287O
| |
| }}</ref> and that the convective zone has "[[jet stream]]s" of plasma (more precisely, torsional oscillations) thousands of kilometers below the surface.<ref>{{cite journal
| |
| | author = Vorontsov, S.V.; Christensen-Dalsgaard, J.; Schou, J.; Strakhov, V.N.; Thompson, M.J.
| |
| | title = Helioseismic Measurement of Solar Torsional Oscillations
| |
| | journal = Science
| |
| | date = April 2002
| |
| | volume = 296
| |
| | pages = 101–103
| |
| | doi = 10.1126/science.1069190
| |
| | bibcode = 2002Sci...296..101V
| |
| | pmid = 11935019
| |
| | issue = 5565
| |
| }}</ref> These jet streams form broad fronts at the equator, breaking into smaller cyclonic storms at high latitudes. '''Torsional oscillations''' are the time variation in solar [[differential rotation]]. They are alternating bands of faster and slower rotation. So far there is no generally accepted theoretical explanation for them, even though a close relation to the [[solar cycle]] is evident, as they have a period of eleven years, as was known since they were first observed in 1980.<ref>{{cite journal
| |
| | author = Howard, R.; Labonte, B.J.
| |
| | title = The sun is observed to be a torsional oscillator with a period of 11 years
| |
| | journal = Astrophysical Journal
| |
| | date = July 1980
| |
| | volume = 239
| |
| | pages = L33–L36
| |
| | doi = 10.1086/183286
| |
| | bibcode = 1980ApJ...239L..33H
| |
| }}</ref>
| |
| | |
| Helioseismology can also be used to image the far side of the Sun from the Earth,<ref name="Braun2001">{{cite journal
| |
| | author = Braun, D.C.; Lindsey, C.
| |
| | title = Seismic Imaging of the Far Hemisphere of the Sun
| |
| | journal = The Astrophysical Journal
| |
| | date = October 2001
| |
| | volume = 560
| |
| | issue = 2
| |
| | pages = L189–L192
| |
| | doi = 10.1086/324323
| |
| | bibcode = 2001ApJ...560L.189B
| |
| }}</ref> including [[sunspot]]s. In simple terms, sunspots absorb helioseismic waves. This sunspot absorption causes a seismic deficit that can be imaged at the [[antipodal point|antipode]] of the sunspot.<ref>{{cite journal
| |
| | author = Lindsey, C.; Braun, D.C.
| |
| | title = Helioseismic imaging of sunspots at their antipodes
| |
| | journal = Solar Physics
| |
| | date = March 1990
| |
| | volume = 126
| |
| | issue = 1
| |
| | pages = 101–115
| |
| | doi = 10.1007/BF00158301
| |
| | bibcode = 1990SoPh..126..101L
| |
| }}</ref> To facilitate spaceweather forecasting, seismic images of the central portion of the solar far side have been produced nearly continuously since late 2000 by analysing data from the [[SOHO spacecraft]], and since 2001 the entire far side has been imaged with this data.
| |
| | |
| Keep in mind that despite the name, helioseismology is the study of solar waves and not solar seismic activity - there is no such thing. The name is derived from the similar practice of studying terrestrial seismic waves to determine the composition of the [[Earth]]'s interior. The science can be compared to [[asteroseismology]], which considers the propagation of sound waves in stars.
| |
| | |
| == Types of solar oscillations ==
| |
| | |
| [[Image:Helioseismology GOLFpmode.png|325px|thumb|Low-resolution solar oscillation spectrum taken by the [[Solar and Heliospheric Observatory|GOLF]] instrument between 19 February and 25 March 1996. The horizontal axis is frequency in millihertz, or thousandths of a hertz (mHz), the vertical axis is power density. The "5-minute oscillation" is the series of p-mode lines on the right between about 2 and 7 mHz.]]
| |
| | |
| Individual oscillations in the Sun are [[damping|damped]] so that they die out within a few periods. However, interference between these localised waves produces global [[standing waves]], also known as [[normal modes]]. Analysis of these overlapping modes constitutes the discipline of ''global helioseismology''.
| |
| | |
| Solar oscillation modes are essentially divided up into three categories, based on the restoring force that drives them: acoustic, gravity, and surface-gravity wave modes.
| |
| | |
| * '''p-mode''' or '''acoustic''' waves have pressure as their restoring force, hence the name "p-mode". Their dynamics are determined by the variation of the speed of sound inside the sun. P-mode oscillations have frequencies > 1 mHz and are very strong in the 2-4 mHz range, where they are often referred to as "5-minute oscillations". (Note: 5 minutes per cycle is 1/300 cycles per second = 3.33 mHz.) P-modes at the solar surface have amplitudes of hundreds of kilometers and are readily detectable with [[Dopplergraph|Doppler imaging]] or sensitive [[spectral line]] intensity imaging. Thousands of p-modes of high and intermediate degree l (see [[#Analysis of oscillation data|below]] for the wavenumber degree l) have been detected by the Michelson Doppler Imager (MDI) instrument aboard the [[SOHO spacecraft]], with those of degree l below 200 clearly separated and higher degree modes ridged together.<ref>{{cite journal
| |
| | author = Rabello-Soares, M.C.; Korzennik, S.G.; Schou, J.
| |
| | title = The determination of MDI high-degree mode frequencies
| |
| | booktitle = SOHO 10/GONG 2000 Workshop: Helio- and Asteroseismology at the Dawn of the Millennium
| |
| | date = January 2001
| |
| | series = ESA Special Publication
| |
| | volume = 464
| |
| | pages = 129–136
| |
| | bibcode = 2001ESASP.464..129R
| |
| }}</ref> About 10 p-modes below 1.5mHz have been detected by the GOLF instrument aboard the [[SOHO spacecraft]].<ref>{{cite journal
| |
| | author = Garcia, R.A.; Regulo, C.; Turck-Chieze, S.; Bertello, L.; Kosovichev, A.G.; Brun, A.S.; Couvidat, S.; Henney, C.J.; Lazrek, M.; Ulrich, R.K.; Varadi, F.
| |
| | title = Low-Degree Low-Order Solar p Modes As Seen By GOLF On board SOHO
| |
| | journal = Solar Physics
| |
| | date = May 2001
| |
| | volume = 20
| |
| | pages = 361–379
| |
| | bibcode = 2001SoPh..200..361G
| |
| |doi = 10.1023/A:1010344721148 }}</ref>
| |
| | |
| * '''g-mode''' or '''gravity''' waves are density waves which have gravity (negative buoyancy of displaced material) as their restoring force, hence the name "g-mode". The g-mode oscillations are low frequency waves (0-0.4 mHz). They are confined to the interior of the sun below the convection zone (which extends from 0.7-1.0 solar radius), and are practically inobservable at the surface. The restoring force is caused by [[adiabatic process|adiabatic expansion]]: in the deep interior of the Sun, the [[temperature]] [[gradient]] is weak, and a small packet of gas that moves (for example) upward will be cooler and denser than the surrounding gas, and will therefore be pulled back to its original position; this restoring force drives g-modes. In the solar convection zone, the temperature gradient is slightly greater than the [[adiabatic lapse rate]], so that there is an anti-restoring force (that drives [[convection]]) and g-modes cannot propagate. The g modes are [[evanescent wave|evanescent]] through the entire convection zone, and are thought to have residual amplitudes of only millimeters at the photosphere, though more prominent as temperature perturbations.<ref>http://www.springerlink.com/content/xt03jqk462770337/</ref> Since the '80s, there have been several claims of g-mode detection, none of which have been confirmed. In 2007, another g-mode detection was claimed using the GOLF data.<ref>{{cite journal
| |
| | author = Garcia, R.A.; Turck-Chieze, S.; Jimenez-Reyes, S.J.; Ballot, J.; Palle, P.L.; Eff-Darwich, A.; Mathur, S.; Provost, J.
| |
| | title = Tracking Solar Gravity Modes: The Dynamics of the Solar Core
| |
| | journal = Science
| |
| | date = June 2007
| |
| | volume = 316
| |
| | pages = 1591-
| |
| | doi = 10.1126/science.1140598
| |
| | bibcode = 2007Sci...316.1591G
| |
| | pmid = 17478682
| |
| | issue = 5831
| |
| }}</ref> At the GONG2008 / SOHO XXI conference held in Boulder, the [[Phoebus group]] reported that it could not confirm these findings, putting an upper limit on the g-mode amplitude to 3 mm/s, right at the detection limit of the GOLF instrument. Finally, the [[Phoebus group]] has just published a review over the current state of knowledge on the solar g modes.<ref>
| |
| {{cite arXiv
| |
| | author = Appourchaux, T.; ''et al''
| |
| | title = The quest for the solar g modes
| |
| | class =astro-ph.SR
| |
| | eprint = 0910.0848
| |
| | date = October 2009
| |
| | bibcode = 2009arXiv0910.0848A
| |
| }}</ref>
| |
| | |
| * '''f-mode''' or '''surface gravity''' waves are also gravity waves, but occur at or near the photosphere, where the temperature gradient again drops below the adiabatic lapse rate. Some f-modes of moderate and high degree, between l = 117 and l = 300, (see [[#Analysis of oscillation data|below]] for the wavenumber degree l) have been observed by MDI.<ref name="Corbard2002">{{cite journal
| |
| | author = Corbard, T.; Thompson, M.J.
| |
| | title = The subsurface radial gradient of solar angular velocity from MDI f-mode observations
| |
| | journal = Solar Physics
| |
| | eprint = arXiv:astro-ph/0110361
| |
| | date = February 2002
| |
| | volume = 205
| |
| | issue = 2
| |
| | pages = 211–229
| |
| | bibcode = 2002SoPh..205..211C
| |
| | doi = 10.1023/A:1014224523374
| |
| |arxiv = astro-ph/0110361 }}</ref>
| |
| | |
| ==Analysis of oscillation data==
| |
| The data from time-series of solar spectra show all the oscillations overlapping. Thousands of modes have been detected (with the true number perhaps being in the millions). The mathematical technique of [[Fourier analysis]] is used to recover information about individual modes from this mass of data. The idea is that any periodic function <math>f</math> can be written as a sum of multiples of the simplest periodic functions, which are [[sine]]s and [[cosine]]s (of different [[frequencies]]). To find out how much (the [[amplitude]]) of each simple function goes into <math>f</math>, one applies the [[Fourier transform]]: at each point the value of this transform is obtained by computing a particular integral involving a modified version of <math>f</math>.
| |
| | |
| The simplest modes to analyse are the radial ones; however most solar modes are non-radial. A nonradial mode is characterized by three wavenumbers: the spherical-harmonic degree <math>l</math> and azimuthal order <math>m</math> which determine the behaviour of the mode over the surface of the star and the radial order <math>n</math> which reflects the properties in the radial direction (see the diagram on the top right for an example). Note that if the Sun were [[spherically symmetric]], the azimuthal order would exhibit [[Degeneracy (mathematics)|degeneracy]]; however the rotation of the Sun (along with other perturbations), which leads to an equatorial bulge, lifts this degeneracy. By convention, <math>n</math> corresponds to the number of nodes of the radial [[eigenfunction]], <math>l</math> indicates the total number of [[nodal line]]s on spheres, and <math>m</math> tells how many of these nodal lines cross the equator.
| |
| | |
| In general the frequencies <math>\omega_{nlm}</math> of stellar oscillations depend on all three wave numbers. It is convenient, however, to [[Frequency separation|separate the frequency]] into the ''multiplet'' frequency <math>\omega_{nl}</math>, obtained as a suitable average over azimuthal order <math>m</math> and corresponding to the spherically symmetric structure of the star, and the ''frequency splitting'' <math>\delta\omega_{nlm} = \omega_{nlm} - \omega_{nl}</math>.
| |
| | |
| Analyses of oscillation data must attempt to separate these different frequency components. In the case of the Sun the oscillations can be observed directly as functions of position on the solar disk as well as time. Thus here it is possible to analyze their spatial properties. This is done by means of a generalized 2-dimensional [[Fourier transform]] in position on the solar surface, to isolate particular values of <math>l</math> and <math>m</math>. This is followed by a Fourier transform in time which isolates the frequencies of the modes of that type. In
| |
| fact, the average over the stellar surface implicit in observations of stellar oscillations can be thought of as one example of such a spatial Fourier transform.
| |
| | |
| Note that the oscillation data, rather than a continuous function, amount to values constrained by experimental error evaluated at a grid of positions and times. When computing transforms, values of this "function" outside this grid have to be interpolated and the integrals approximated by finite sums, a process inevitably introducing further errors. Details of the numerical methods used are included with the transformed data for purposes of comparison and constraining errors.
| |
| | |
| This discussion is adapted from the [[Christensen-Dalsgaard|Jørgen Christensen-Dalsgaard]] lecture notes on stellar oscillations.<ref name="Dalsgaard2003">Christensen-Dalsgaard, J., 2003, [http://www.phys.au.dk/~jcd/oscilnotes/ Lecture Notes on Stellar Oscillations. Fifth Edition], lecture notes, University of Aarhus. Retrieved November 2009.</ref>
| |
| | |
| ==Inversion==
| |
| [[Image:Tachocline.gif|300px|thumb|Internal rotation in the Sun, showing differential rotation in the outer convective region and almost uniform rotation in the central radiative region. The transition between these regions is called the tachocline.]]
| |
| Information about helioseismic waves (such as mode frequencies and frequency-splitting) collected by transforming the oscillation data can be used to infer numerical details of internal features of the Sun such as the internal sound speed and the internal [[differential rotation]]. Equations and analytic relations such as integrals can be manipulated to relate the desired internal properties to the transformed data. The numerical methods used are adapted to the particular internal features examined so as to extract the maximum amount of information, with the least error, from the oscillations about the internal features. This process is termed ''helioseismic inversion''.
| |
| | |
| As an example in slightly more detail, the oscillation frequency splitting can be related, via an integral, to the angular velocity within the sun.<ref name="Dalsgaard2003"/>
| |
| | |
| == Internal structure ==
| |
| | |
| Helioseismic observations reveal the inner uniformly rotating zone and the [[differential rotation|differentially rotating]] envelope of the Sun, roughly corresponding to the [[Radiation zone|radiation]] and [[Convection zone|convection]] zones, respectively.<ref name="Thompson2003"/> See the diagram on the right. The transition layer is called the [[tachocline]].
| |
| | |
| == Helioseismic dating ==
| |
| The age of the sun can be inferred with helioseismic studies.<ref name="bonannoetal2002">{{cite journal
| |
| | author = A. Bonanno, H. Schlattl, L. Paternò
| |
| | title = The age of the Sun and the relativistic corrections in the EOS
| |
| | journal = Astronomy and Astrophysics
| |
| | year = 2002
| |
| | bibcode=2002A&A...390.1115B | volume = 390
| |
| | issue = 3
| |
| | page = 1115
| |
| | doi = 10.1051/0004-6361:20020749
| |
| |arxiv = astro-ph/0204331 }}</ref> This is because the propagation of acoustic waves deep within the sun depends on the composition of the sun, in particular the relative abundance of helium and hydrogen in the core. Since the sun has been fusing hydrogen into helium throughout its lifetime, the present day abundance of helium in the core can be used to infer the age of the sun, using [[stellar structure|numerical models of stellar evolution]] applied to the Sun ([[Standard solar model]]).
| |
| This method provides verification of the age of the solar system gathered from the radiometric dating of meteorites.<ref name="Guenther 1995">{{cite journal
| |
| | author = Guenther, D.B.
| |
| | title = Age of the sun
| |
| | journal = Astrophysical Journal
| |
| | date = April 1989
| |
| | volume = 339
| |
| | pages = 1156–1159
| |
| | doi = 10.1086/167370
| |
| | bibcode = 1989ApJ...339.1156G
| |
| }}</ref>
| |
| | |
| ==Local helioseismology==
| |
| The goal of ''local helioseismology'', a term first used in 1993,<ref>{{cite journal
| |
| | author = Lindsey, C.; Braun, D.C.; Jefferies, S.M.
| |
| | title = "Local Helioseismology of Subsurface Structure" in "GONG 1992. Seismic Investigation of the Sun and Stars"
| |
| | date = January 1993
| |
| | series = Astronomical Society of the Pacific Conference Series
| |
| | volume = 42
| |
| | editor = "T.M. Brown",
| |
| | pages = 81-+
| |
| | bibcode = 1993ASPC...42...81L
| |
| }}</ref> is to interpret the full wave field observed at the surface, not just the mode (more precisely, [[eigenmode]]) frequencies. Another way to look at it, is that global helioseismology studies standing waves of the entire Sun and local helioseismology studies propagating waves in parts of the Sun. A variety of solar phenomena are being studied, including [[sunspots]], [[plage (astronomy)|plage]], [[supergranulation]], giant cell convection, magnetically active region evolution, [[meridional]] circulation, and [[solar rotation]].<ref>{{cite journal
| |
| | author = Duvall, Jr.; T.L.
| |
| | title = "Recent Results and Theoretical Advances in Local Helioseismology" in "Structure and Dynamics of the Interior of the Sun and Sun-like Stars"
| |
| | year = 1998
| |
| | series = ESA Special Publication
| |
| | volume = 418
| |
| | editor = S. Korzennik
| |
| | pages = 581-+
| |
| | bibcode = 1998ESASP.418..581D
| |
| }}</ref> Local helioseismology provides a three-dimensional view of the solar interior, which is important to understand large-scale flows, magnetic structures, and their interactions in the solar interior.
| |
| | |
| There are many techniques used in this new and expanding field, which include:
| |
| | |
| * Fourier–Hankel spectral method, first introduced by Braun and Duvall,<ref name="Braun1987">{{cite journal
| |
| | author = Braun, D.C.; Duvall, Jr., T.L.; Labonte, B.J.
| |
| | title = Acoustic absorption by sunspots
| |
| | journal = Astrophysical Journal
| |
| | date = August 1987
| |
| | volume = 319
| |
| | pages = L27–L31
| |
| | doi = 10.1086/184949
| |
| | bibcode = 1987ApJ...319L..27B
| |
| }}</ref> was originally used to search for wave absorption by sunspots.
| |
| | |
| * Ring-diagram analysis, first introduced by F. Hill,<ref>{{cite journal
| |
| | author = Hill, F.
| |
| | title = Rings and trumpets - Three-dimensional power spectra of solar oscillations
| |
| | journal = Astrophysical Journal
| |
| | date = October 1988
| |
| | volume = 333
| |
| | pages = 996–1013
| |
| | doi = 10.1086/166807
| |
| | bibcode = 1988ApJ...333..996H
| |
| }}</ref> is used to infer the speed and direction of horizontal flows below the solar surface by observing the Doppler shifts of ambient acoustic waves from power spectra of solar oscillations computed over patches of the solar surface (typically 15° × 15°). Thus ring analysis is a generalization of global helioseismology applied to local areas on the Sun (as opposed to half of the Sun). For example, sound speed, and [[adiabatic index]] can be compared within magnetically active and inactive ('''quiet Sun''') regions.<ref>{{cite journal
| |
| | author = Basu, S.; Antia, H.M.; Bogart, R.S.
| |
| | title = Ring-Diagram Analysis of the Structure of Solar Active Regions
| |
| | journal = The Astrophysical Journal
| |
| | date = August 2004
| |
| | volume = 610
| |
| | issue = 2
| |
| | pages = 1157–1168
| |
| | doi = 10.1086/421843
| |
| | bibcode = 2004ApJ...610.1157B
| |
| }}</ref>
| |
| | |
| * Time-distance helioseismology, introduced by Duvall et al.,<ref>{{cite journal
| |
| | author = Duvall, Jr., T.L.; Jefferies, S.M.; Harvey, J.W.; Pomerantz, M.A.
| |
| | title = Time-distance helioseismology
| |
| | journal = Nature
| |
| | date = April 1993
| |
| | volume = 362
| |
| | issue = 6419
| |
| | pages = 430–432
| |
| | doi = 10.1038/362430a0
| |
| | bibcode = 1993Natur.362..430D
| |
| }}</ref> aims to measure and interpret the travel times of solar waves between any two locations on the solar surface. A travel time anomaly contains the seismic signature of buried inhomogeneities within the proximity of the ray path that connects two surface locations. An inverse problem must then be solved to infer the local structure and dynamics of the solar interior.<ref name="Jensen2003">Jensen, J.M., 2003, [http://adsabs.harvard.edu/full/2003ESASP.517...61J Time-distance: what does it tell us?], in Local and Global Helioseismology: The Present and Future, (Ed.) Sawaya-Lacoste, H., Proceedings of SOHO 12/GONG+ 2002, 27 October - 1 November 2002, Big Bear Lake, California, U.S.A., vol. SP-517 of ESA Conference Proceedings, pp. 61–70, ESA Publications Division, Noordwijk</ref>
| |
| | |
| * Helioseismic holography, introduced in detail by Lindsey and Braun for the purpose of far-side (magnetic) imaging,<ref name="Braun2001"/> a special case of phase-sensitive holography. The idea is to use the wavefield on the visible disk to learn about active regions on the far side of the Sun. The basic idea in helioseismic holography is that the wavefield, e.g., the line-of-sight Doppler velocity observed at the solar surface, can be used to make an estimate of the wavefield at any location in the solar interior at any instant in time. In this sense, holography is much like [[seismic migration]], a technique in geophysics that has been in use since the 1940s. As another example, this technique has been used to give a seismic image of a solar flare.<ref>{{cite journal
| |
| | author = Donea, A.-C.; Braun, D.C.; Lindsey, C.
| |
| | title = Seismic Images of a Solar Flare
| |
| | journal = The Astrophysical Journal
| |
| | date = March 1999
| |
| | volume = 513
| |
| | issue = 2
| |
| | pages = L143–L146
| |
| | doi = 10.1086/311915
| |
| | bibcode = 1999ApJ...513L.143D
| |
| }}</ref> Acoustic holography, applied to MDI data, is ideal for the detection of sources and sinks of acoustic waves on the Sun. Braun and Fan <ref>{{cite journal
| |
| | author = Braun, D.C.; Fan, Y.
| |
| | title = Helioseismic Measurements of the Subsurface Meridional Flow
| |
| | journal = The Astrophysical Journal
| |
| | date = November 1998
| |
| | volume = 508
| |
| | issue = 1
| |
| | pages = L105–L108
| |
| | doi = 10.1086/311727
| |
| | bibcode = 1998ApJ...508L.105B
| |
| }}</ref> discovered a region of lower acoustic emission in the 3 – 4 mHz frequency band which extends far beyond the sunspots (the ‘acoustic moat’). Acoustic moats extend beyond magnetic regions into the quiet Sun. In addition, Braun and Lindsey <ref>{{cite journal
| |
| | author = Braun, D.C.; Lindsey, C.
| |
| | title = Helioseismic Images of an Active Region Complex
| |
| | journal = The Astrophysical Journal
| |
| | date = March 1999
| |
| | volume = 513
| |
| | issue = 1
| |
| | pages = L79–L82
| |
| | doi = 10.1086/311897
| |
| | bibcode = 1999ApJ...513L..79B
| |
| }}</ref> discovered high-frequency emission (‘acoustic glories’) surrounding active regions.
| |
| | |
| * Direct modelling, after Woodard.<ref name="Woodard2002">{{cite journal
| |
| | author = Woodard, M.F.
| |
| | title = Solar Subsurface Flow Inferred Directly from Frequency-Wavenumber Correlations in the Seismic Velocity Field
| |
| | journal = The Astrophysical Journal
| |
| | date = January 2002
| |
| | volume = 565
| |
| | issue = 1
| |
| | pages = 634–639
| |
| | doi = 10.1086/324546
| |
| | bibcode = 2002ApJ...565..634W
| |
| }}</ref> Here the idea is to estimate subsurface flows from direct inversion of the frequency-wavenumber correlations seen in the wavefield in the Fourier domain. Woodard<ref name="Woodard2002"/> gave a practical demonstration of the ability of the technique to recover near-surface flows from the f-mode part of the spectrum.
| |
| | |
| This section is adapted from Laurent Gizon and Aaron C. Birch, "Local Helioseismology", Living Rev. Solar Phys. 2, (2005), 6. [http://solarphysics.livingreviews.org/Articles/lrsp-2005-6/ online article] (cited on November 22, 2009).
| |
| | |
| == Jet stream movement may affect solar cycle ==
| |
| An internal jet stream moving behind schedule may explain the delayed start to the solar cycle in 2009.<ref>http://www.universetoday.com/2009/06/17/the-case-of-the-missing-sunspots-solved/</ref>
| |
| | |
| ==See also==
| |
| * [[160-minute solar cycle]]
| |
| * [[Asteroseismology]]
| |
| * [[Differential rotation in stars]]
| |
| * [[Diskoseismology]]
| |
| * [[Magneto-gravity]]
| |
| * [[Moreton wave]]
| |
| * [[Solar neutrino problem]]
| |
| * [[Solar tower]]
| |
| * [[Stellar rotation]]
| |
| | |
| ==References==
| |
| {{Reflist|colwidth=30em}}
| |
| | |
| == External links ==
| |
| {{Commons category|Helioseismology}}
| |
| * [http://ast.phys.au.dk/helio_outreach/english/ Non-technical description of helio- and asteroseismology] retrieved November 2009
| |
| * Laurent Gizon and Aaron C. Birch, "Local Helioseismology", Living Rev. Solar Phys. 2 (2005) 6 [http://www.livingreviews.org/lrsp-2005-6 online article]
| |
| * [http://www.nsf.gov/news/news_summ.jsp?cntn_id=105844&org=olpa&from=news Scientists Issue Unprecedented Forecast of Next Sunspot Cycle] National Science Foundation press release, March 6, 2006
| |
| * [http://solarphysics.livingreviews.org/open?pubNo=lrsp-2005-1 Large-Scale Dynamics of the Convection Zone and Tachocline] by Mark S. Miesch
| |
| * [http://www.helas-eu.org/ European Helio- and Asteroseismology Network (HELAS)]
| |
| * [http://soi.stanford.edu/data/full_farside/ Farside and Earthside images of the Sun]
| |
| * [http://solarphysics.livingreviews.org/ Living Reviews in Solar Physics]
| |
| | |
| ===Satellite instruments===
| |
| *[http://www.ias.u-psud.fr/virgo VIRGO]
| |
| *[http://soi.stanford.edu SOI/MDI]
| |
| *[http://sunland.gsfc.nasa.gov/smex/trace/ TRACE]
| |
| | |
| ===Ground-based instruments===
| |
| *[http://bison.ph.bham.ac.uk/ BiSON]
| |
| *Mark-1
| |
| *[http://gong.nso.edu/ GONG]
| |
| *[http://physics.usc.edu/solar HiDHN]
| |
| | |
| {{The Sun}}
| |
| | |
| [[Category:Fields of seismology]]
| |
| [[Category:Sun]]
| |
| [[Category:Stellar phenomena]]
| |
| | |
| [[zh:日震學]]
| |