Archive Trawl Gives BISON Three Decades Of Solar Music

SOLAR SCIENCE

Solar modes of oscillation are standing sound waves, and are specified by three parameters, l, m and n. l gives the total number of surface node circles, m the number of surface node circles intersecting at the north (or south) pole, and n the number of nodes from the Sun's surface to its core. The velocity distribution at any one time is a combination of millions of these modes, with l values ranging from zero to over one thousand. They are detected from the tiny variations of the surface velocity field over the Sun's disk. BiSON specifically observes low-l modes, i.e. l<=4. Our instruments use integrated sunlight, and so they measure the average surface velocity over the solar disk. The higher l modes have nearly equal areas of the disk which are receding and approaching, effectively cancelling out any velocity signal. This can be seen by comparing the images above which show how the surface velocity varies over the solar disk for a pair of modes. The left image shows the l=36 m=24 mode, and the right image the l=1 m=1 mode. The redder a region, the faster it is receding, and the bluer, the faster it is approaching the observer. Node lines, where there is no net velocity, show up purple. Over the course of a period of about five minutes, the blue areas will go through purple through to red and then back again. The red areas will likewise go through purple to blue and back again.

Birmingham, UK (SPX) Mar 31, 2005
Scientists in Birmingham have scoured the archives and put together a complete archive of helioseismic data for nearly three solar cycles.

The results from reprocessing the data will shed light on the link between helioseismology, the study of sound waves resonating within the Sun, and solar activity.

Dr Graham Verner will be presenting preliminary findings at the RAS National Astronomy Meeting at the University of Birmingham on Tuesday 5th April.

The Sun is a like a vast bell that is being struck continuously by tiny grains of sand and is ringing away.

Acoustic waves, generated in the outermost layers of the Sun's interior, bounce off the surface and then are refracted up again repeatedly and can create standing waves.

The internal waves, which typically have an oscillatory period of five minutes, can be studied by measuring the Doppler shift of ripples that they cause on the Sun 's surface.

Some of the sound waves penetrate into the deep interior of the Sun, so they give scientists an opportunity to study these core regions where the nuclear reactions occur that power the Sun and also drive its evolution.

The Birmingham Solar Oscillations Network (BiSON) group has been collecting helioseismic data since 1976. Initially the group had only one station and only operated in the summer.

As more stations were added, the quality of the data and the time-coverage improved, and in 1979 the group first observed the now familiar 5-minute oscillations.

In the early 1990s a full 6-station network, now known as BiSON, was established, providing high quality and low noise data. Other groups have collected helioseismic data for one full 1-year solar cycle but the BiSON archive is the only one that extends back through three cycles.

There are millions of oscillation modes for standing waves inside the Sun. BiSON did pioneering work in the early 1990s on identifying the relationship between mode frequencies and solar activity.

Now, with 29 years of data, they hope to look for changes between successive solar cycles and any long period trends. The results from this new analysis of old data should be published in the next few months.

SOLAR SCIENCE

April Solar Eclipse

Moffett Field CA (SPX) Apr 04, 2005
Solar eclipses are grand cosmic events that no nature-watcher wants to miss - and an opportunity to see one will occur for most of the southern United States on Friday afternoon, April 8th.

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