helioseismology

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helioseismology

(heel-ee-oh-sÿz-mol -ŏ-jee) The study of the Sun's interior by the observation of solar oscillations. First detected in 1960 by measuring the Doppler shifts of Fraunhofer lines at several points on the Sun's disk away from active regions, the oscillations are a rhythmic rise and fall of regions of the solar photosphere (and lower chromosphere) several thousand kilometers in diameter. They have periods of about 5 minutes, persist at any one point for less than half an hour, and attain a maximum velocity of about 0.5 km s–1. The oscillations are thought to be produced by the outward propagation of low-frequency sound waves, generated by turbulence in the convective zone, and by analyzing their global occurrence over an extended period of time it is possible to build up a picture of the Sun's interior.

Instruments used in the observation of solar oscillations include grating spectrographs, narrow-band interference filter (Lyot filter, magneto-optical filter, or Fabry–Perot interferometer) imagers, and Michelson interferometers – notably the Fourier tachometer, which has been in operation since 1985 and simultaneously monitors more than 60 000 points on the Sun's disk. A number of collaborative programs have been established, for example the Global Oscillations Network Group (GONG). These are complemented by continuous monitoring by the helioseismology instrument on ESA's spacecraft, the Solar Heliospheric Observatory (SOHO).

helioseismology

[‚hē·lē·ō‚sīz′mäl·ə·jē]
(astronomy)
The analysis of wave motions of the solar surface to determine the structure of the sun's interior.
References in periodicals archive ?
At present, helioseismic measurements (see [section]6) indicate that the degree of solar oblateness may be slightly smaller [288, 289], but the general feature remains.
This labeled image taken by SDO's Helioseismic and Magnetic Imager shows the location of two active regions on the sun, labeled AR1944 and AR1943, which straddle a giant sunspot complex.
Supply of thermal and structural models, engineering, qualification, flight reservation system for image stabilization and Helioseismic Polarimetric Imager instrument on the Solar Orbiter mission.
Along with many of the structural ([section]) and helioseismic ([section]) lines of evidence, they are amongst the simplest to visualize.
Helioseismic and Magnetic Imager (HMI) Like swarms of needles poking up through a swath of fabric, magnetic field lines poke through the visible solar surface.
The immense amount of data collected during our research requires a powerful HPC solution capable of ingesting and analyzing data quickly and with precision," said Phil Scherrer, principal investigator, Helioseismic and Magnetic Imager, Stanford University.
The solar scientists used the Stanford-operated Helioseismic and Magnetic Imager (HMI) - an instrument onboard NASA's Solar Dynamics Observatory satellite - to track solar waves in much the way seismologists would study seismic movements beneath the surface of the Earth.
Second, solar helium levels are inherently linked to the gaseous models of the Sun [16-18] and the application of theoretical findings to the interpretation of helioseismic results [19-23].
The Helioseismic and Magnetic Imager (HMI) will look inside the Sun and map the plasma flows that generate the Sun's magnetic fields.
Numerical Simulation of Scattering of Helioseismic MHD Waves by Sunspots
Helioseismic analysis of the Sun has revealed that sound waves travel faster within sunspots relative to the photosphere [42,43].
Washington, August 17 ( ANI ): Researchers have used the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory satellite to obtain what they believe is the definitive and baffling answer about the slightly flattened surface of the sun.