Skip to content | Change text size
 

Sunquakes explored by Monash team

22 August 2007

(Above)Sound waves refract in the solar interior to repeatedly bounce off the surface. Waves which visit different depths can reveal information on where they have been.

(Below)The ringing of the Sun, like a complex bell, extends deep into the core.

A recent international conference hosted by Monash University, SOHO 19 / GONG 2007 Seismology of Magnetic Activity, has been hailed a significant success.

Monash was awarded the major international conference, SOHO 19/GONG 2007 Seismology of Magnetic Activity, from July 9 to 13 at the Monash Conference Centre, Collins Street, Melbourne.

The meeting was co-sponsored by two of the most important solar observing programs in the world, SOHO and GONG. SOHO is a joint European/US spacecraft, and GONG a global terrestrial network of six telescopes. SOHO 19/GONG 2007 was the first SOHO meeting ever held outside Europe or North America.

SOHO, the Solar & Heliospheric Observatory, is a project of international collaboration between the European Space Agency (ESA) and US National Aeronautics and Space Administration (NASA) to study the sun from its deep core to the outer corona and the solar wind, and has proved to be the most important solar observatory in modern times.

The Global Oscillation Network Group (GONG) is a solar community-based program to conduct a detailed study of solar internal structure and dynamics using helioseismology.

In order to exploit this new technique, GONG has developed a six-station network of extremely sensitive, and stable velocity imagers located around the Earth to obtain nearly continuous observations of the Sun's "five-minute" oscillations, or pulsations. One of it's six stations is in Learmonth, Western Australia.

The Monash team, lead by Professor of Solar Physics Paul Cally, was congratulated by the leaders of both the SOHO and GONG teams, who hailed it as one of the most successful and valuable meetings in the long SOHO sequence.

"It was also the conference where the "mode conversion and transmission" mechanism championed by the Monash team for several years finally gained widespread acceptance. Many of the new results shown at the meeting verified the Monash theory," Professor Cally said.

"Mode conversion" is a process by which sound waves are converted into "magneto-acoustic" waves in surface magnetic regions, such as sunspots, with profound consequences for their subsequent propagation.

The Monash team also presented amazing new results on sunquakes. Solar flares high in the corona are the most explosive events in the solar system, releasing the equivalent of millions of hydrogen bombs’ energy over only a few minutes. Occasionally, this causes a massive quake on the surface thousands of kilometres below.

Magnetic fields in the Sun's outer atmosphere, the corona, are revealed by the Transition Region and Coronal Explorer (TRACE) spacecraft.

Until recently, only one example of sunquakes was known, and this was found by direct imaging of the surface ripples. However, a Monash project lead by Dr Alina Donea has applied the novel technique of helioseismic holography to actually image the source of the quake -- the initial "punch" the flare imparts to the photosphere -- rather than the effect, the ripples.

Using this technique, applied to a careful search through the SOHO records, they have discovered a further 15 examples of sunquakes, which allows for a better understanding of how they are produced and why only some flares excite quakes.

"Monash hosts Australia's only helioseismology research team, but one that has become highly regarded internationally. The awarding of SOHO 19/GONG 2007 to Monash, and its successful staging, bodes well for the future of this amazing science in this country," Professor Cally said.