Tsunami e suoni della corona solare

Giorni fa su Repubblica.it è stato pubblicato un pezzo sugli esperimenti condotti dal gruppo di fisica solare della Sheffield University, che tra l'altro ha "trasposto" l'effetto acustico - quello di una corda di chitarra pizzicata - collegato alle osservazioni di fenomeni quali le Eziezioni di massa coronale (CME). Una registrazione audio di questo effetto è presente su SoundCloud:

Sound of the Sun (courtesy Richard Morton) by University of Sheffield

Questa pagina sul sito dell'ufficio stampa della università contiene altre spiegazioni e filmati su questo esperimento di "astrofisica acustica".

Sono andato a guardarmi la fonte originale di queste storie sul sito del Media Center dell'ateneo britannico. Il gruppo di scienziati è lo stesso che nel marzo scorso ha addirittura partecipato a una udienza parlamentare a Londra per spiegare le sue teorie sulla enorme differenza di temperatura che nelle stelle come il Sole sussiste tra superficie e atmosfera (corona). Gli astrofisici della Sheffield ritengono che questo gradiente sia correlato alla presenza di una gran quantità di scosse di tipo sismico, dei veri e propri tsunami, che agitano gli strati della coronosfera.

Ecco un comunicato che spiega a grandi linee queste teorie, che secondo il team guidato da Robertus von Fay-Siebenburgen potrebbero essere alla base di nuovi approcci interdisciplinare allo studio della fisica solare, anche ai fini di un diverso modo di sfruttarne qui a terra l'energia, prevenendo al tempo stesso gli effetti negativi dei dirompenti fenomeni che si verificano sul Sole e all'interfaccia tra questo e il campo magnetico del nostro pianeta.

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3 March 2010

Mega-tsunami hits House of Commons

A breakthrough discovery by experts at the University of Sheffield, which sheds light on mega-tsunamis on the Sun, is set to be revealed at the House of Commons next week (Monday 8 March 2010).

Solar physicists from the University will discuss their discovery of solar Transition Region Quakes to an audience of MPs both from the House of Commons and the House of Lords at the House of Commons Marquee, after being selected by the Parliamentary and Scientific Committee. It is hoped their findings hold the key to understanding the long-standing secret of solar coronal heating.

The solar transition region is located about 2000km above the Sun´s visible surface. It is the narrow layer of sharp transition in density and temperature between the relatively cool solar chromosphere, which reaches temperatures of about 10-20,000 Kelvin, and the very hot upper corona, which sees temperature hit 1-10 Megakelvin.

The way in which the solar corona is heated to temperatures of over a million degrees has so far remained a long-standing puzzle of solar and space physics, especially as this region of the Sun is even further away from the centre of energy production than the underlying solar surface.

But the team of experts at the University, including Professor Robertus von Fay-Siebenburgen, postdoctoral research associate Dr Victor Fedun and postgraduate student Eamon Scullion, all from the University´s Department of Applied Mathematics and members of the Solar Wave Theory Group and the Solar Physics and Space Plasma Research Centre, (SWAT/SP2RC), have addressed this enigma by discovering that Transition Region Quakes power the lower base of the solar corona.

The quakes take the form of mega-tsunamis generated by narrow (a few 100 km radius), long (10-40,000 km) rapidly rising (10-100 km/s) plasma jets. When these jets hit the transition region, they excite a wealth of Transition Region Quakes that have now been observed and modelled for the first time.

The breakthrough has allowed the experts to estimate that at any moment of time there are about 60,000 of these mega-tsunamis splashing and crashing around the Transition Region.

Colleagues at SP2RC, and in SWAT, devoted many years of research to understand this energy balance and wave processes of the solar atmosphere, using a combined approach of analytical theory, numerical modelling using a supercomputer Iceberg in Sheffield and the UKMHD Cluster in St Andrews, as well as joint satellite observations involving more than one spacecraft simultaneously.

The next step for the team will be to investigate the properties of this torrential sea and focus on the details of transferring the tsunami energy into plasma heat.

The news comes as the University of Sheffield launches a unique venture entitled Project Sunshine, led by the Faculty of Science. The Project aims to unite scientists across the traditional boundaries in both the pure and applied sciences to harness the power of the sun and tackle the biggest challenge facing the world today: meeting the increasing food and energy needs of the world´s population in the context of an uncertain climate and global environment change. It is hoped that Project Sunshine will change the way scientists think and work and become the inspiration for a new generation of scientists focused on solving the world´s problems.

Professor Robertus von Fay-Siebenburgen from the University of Sheffield´s Department of Applied Mathematics and Head of SP2RC, said: "This is indeed a very promising and fantastic result. We may now get a step closer to resolve one of the greatest puzzles of astrophysics - why the atmosphere of stars, like the Sun, is so much hotter than its surface.

"A number of international space missions are devoted to studying the heating of the solar atmosphere. With the Japanese-lead Hinode satellite on board the high-resolution UK-built EIS camera that we have used in this research, we were very lucky to observe these massive and energetic waves. This leap forward will certainly help us reveal the secrets of the Sun."