NASA: il primo film della massa espulsa dal sole

Oggi la NASA ha tenuto una conferenza stampa per presentare i risultati di un lungo lavoro di analisi dei dati trasmessi dalla coppia di sonde orbitanti della missione STEREO, incaricata di studiare fenomeni dalla complessa dinamica come le eiezioni di massa coronale dal sole. Alcuni giornali importanti (per esempio il Daily Mail), forse riprendendo le agenzie, non hanno capito nulla e hanno pubblicato titoli allarmistici sull'arrivo di una devastante tempesta solare sul nostro pianeta. Il quotidiano britannico arriva a dire che la conferenza stampa della NASA è stata organizzata proprio per contribuire a fare fronto contro questa emergenza. In realtà i fenomeni descritti in questo filmato:

risalgono al 2008 e hanno appunto richiesto un lungo studio.

Sul sito di SpaceWeather.com è disponibile un filmato Quicktime ancora più dettagliato. Secondo gli scienziati è la prima volta che, grazie alla particolare prospettiva dovuta alla posizione delle sonde STEREO nella loro orbita, è possibile correlare anche visivamente il momento dell'espulsione della massa solare con l'arrivo del plasma qui a terra. Finora ci siamo dovuti accontentare di una visuale per così dire "frontale" che non consente di capire come il plasma evolve e cambia forma mentre viene catapultato fuori dalla fornace del sole. Quando arriva ai limiti del sistema solare il volume di questa massa può essere aumentato di dieci milioni di volte. Informazioni come queste possono aiutarci a prevenire gli effetti più devastanti di eventi che possono influire pesantemente, qui sulla terra, sulle linee dell'alta tensione, i satelliti e le radiocomunicazioni.

Spacecraft Sees Solar Storm Engulf Earth

August 18, 2011: For the first time, a spacecraft far from Earth has turned and watched a solar storm engulf our planet. The movie, released today during a NASA press conference, has galvanized solar physicists, who say it could lead to important advances in space weather forecasting.

“The movie sent chills down my spine,” says Craig DeForest of the Southwest Research Institute in Boulder, Colorado. "It shows a CME swelling into an enormous wall of plasma and then washing over the tiny blue speck of Earth where we live. I felt very small.”

CMEs are billion-ton clouds of solar plasma launched by the same explosions that spark solar flares. When they sweep past our planet, they can cause auroras, radiation storms, and in extreme cases power outages. Tracking these clouds and predicting their arrival is an important part of space weather forecasting.

“We have seen CMEs before, but never quite like this,” says Lika Guhathakurta, program scientist for the STEREO mission at NASA headquarters. “STEREO-A has given us a new view of solar storms.”

STEREO-A is one of two spacecraft launched in 2006 to observe solar activity from widely-spaced locations. At the time of the storm, STEREO-A was more than 65 million miles from Earth, giving it the “big picture” view other spacecraft in Earth orbit have been missing.

When CMEs first leave the sun, they are bright and easy to see. Visibility is quickly reduced, however, as the clouds expand into the void. By the time a typical CME crosses the orbit of Venus, it is a billion times fainter than the surface of the full Moon, and more than a thousand times fainter than the Milky Way. CMEs that reach Earth are almost as gossamer as vacuum itself and correspondingly transparent.

“Pulling these faint clouds out of the confusion of starlight and interplanetary dust has been an enormous challenge,” says DeForest.

Indeed, it took almost three years for his team to learn how to do it. Footage of the storm released today was recorded back in December 2008, and they have been working on it ever since. Now that the technique has been perfected, it can be applied on a regular basis without such a long delay.

Alysha Reinard of NOAA’s Space Weather Prediction Center explains the benefits for space weather forecasting:

“Until quite recently, spacecraft could see CMEs only when they were still quite close to the sun. By calculating a CME's speed during this brief period, we were able to estimate when it would reach Earth. After the first few hours, however, the CME would leave this field of view and after that we were 'in the dark' about its progress.”

“The ability to track a cloud continuously from the Sun to Earth is a big improvement,” she continues. “In the past, our very best predictions of CME arrival times had uncertainties of plus or minus 4 hours,” she continues. “The kind of movies we’ve seen today could significantly reduce the error bars.”

The movies pinpoint not only the arrival time of the CME, but also its mass. From the brightness of the cloud, researchers can calculate the gas density with impressive precision. Their results for the Dec. 2008 event agreed with actual in situ measurements at the few percent level. When this technique is applied to future storms, forecasters will be able to estimate its impact with greater confidence.

At the press conference, DeForest pointed out some of the movie’s highlights: When the CME first left the sun, it was cavernous, with walls of magnetism encircling a cloud of low-density gas. As the CME crossed the Sun-Earth divide, however, its shape changed. The CME “snow-plowed” through the solar wind, scooping up material to form a towering wall of plasma. By the time the CME reached Earth, its forward wall was sagging inward under the weight of accumulated gas.

The kind of magnetic transformations revealed by the movie deeply impressed Guhathakurta: “I have always thought that in heliophysics understanding the magnetic field is equivalent to the ‘dark energy’ problem of astrophysics. Often, we cannot see the magnetic field, yet it orchestrates almost everything. These images from STEREO give us a real sense of what the underlying magnetic field is doing.”

All of the speakers at today’s press event stressed that the images go beyond the understanding of a single event. The inner physics of CMEs have been laid bare for the first time—a development that will profoundly shape theoretical models and computer-generated forecasts of CMEs for many years to come.

“This is what the STEREO mission was launched to do,” concludes Guhathakurta, “and it is terrific to see it live up to that promise.

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."

Aurore boreali ed elettroni killer, il sole si risveglia

Oggi Repubblica riportava la notizia della "scoperta" delle particelle che scatenano le aurore boreali. Ho ricostruito la fonte: era un'Ansa relativa al meeting della Royal Astronomical Society, dove è stato presentato uno studio di Colin Forsyth sui dati raccolti con i satelliti della missione Cluster, in particolare l'esperimento Plasma Electron And Currents Experiment (PEACE). Secondo Forsyth le aurore boreali e australi vengono "accese" dall'interazione tra gli strati più alti della nostra atmosfera e gli elettroni delle fasce esterne che vengono tenute insieme dal campo magnetico planetario.

Cluster takes first look at acceleration processes driving aurora

12-Apr-2010

Scientists from University College London (UCL) have made the first direct observations of charged particles that lead to some of the brightest aurora using the Cluster spacecraft. Dr Colin Forsyth will present the results at the RAS National Astronomy Meeting (NAM2010) in Glasgow on Monday 12th April.

The aurora, or northern and southern lights, are caused by highly energetic charged particles, normally held in space by Earth’s magnetic field, colliding with Earth’s upper atmosphere. As these high-energy particles collide with molecules in the atmosphere they lose energy, causing the atmospheric molecules to glow and heating the atmosphere. The result of is spectacular displays of shimmering curtains of red, green and blue light normally seen above the polar regions, but occasionally seen as far south as northern England.

Despite their frequent occurrence, there are still many questions regarding the physical processes behind the aurora. The particles that excite the aurora are accelerated up to high energies in a region extending to around 50 000 km (31 000 miles) above the atmosphere. By understanding the accelerating processes in this region, scientists hope to further understand the aurora.

Launched in 2000, the joint European Space Agency (ESA) and NASA Cluster mission consists of four identical spacecraft flying in a close formation around the Earth. Each spacecraft carries a suite of instruments to study the charged particles and electromagnetic fields in the space environment around the Earth known as the magnetosphere. The multi-point perspective of the Cluster spacecraft allows scientists build up a 3D picture of the magnetosphere.

Dr. Colin Forsyth has been leading an international team hoping to directly measure the acceleration of charged particles above the aurora. At NAM2010, Dr. Forsyth will present data from the Plasma Electron And Currents Experiment (PEACE), built by UCL’s Mullard Space Science Laboratory, showing this acceleration in action.

“The Cluster spacecraft have been manoeuvred such that one of them was at a higher altitude than the others when they passed over the auroral regions” said Dr. Forsyth. “We were then able to simultaneously measure the particle energies at different heights and thus their acceleration. These exciting new results will give us new insight into the accelerating processes and the transfer of energy from the magnetosphere into the atmosphere”.

These new observations are the first step in understanding the processes behind the aurora and its impact on the atmosphere. Dr. Forsyth and his team aim to link these and similar observations to observations of large-scale processes in the magnetosphere and detected on the ground in the auroral regions. This could be a key factor in understanding how energy from the magnetosphere affects Earth’s atmosphere.

In realtà Forsyth aveva presentato i suoi studi anche in occasione della conferenza PEACE nel marzo scorso e sul sito della missione Cluster si trova anche, per quel periodo, un interessante comunicato relativo a uno studio molto simile volto a identificare i meccanismi di accelerazione dei cosiddetti "elettroni killer": elettroni altamente energetici prodotti nella cintura esterna, la fascia di Van Allen (tenuta insieme dal campo magnetico del nostro pianeta). Questi elettroni sono detti killer perché riescono a perforare le schermature dei satelliti e a provocare minuscole scariche, veri e propri fulmini in scala ridotta, che possono danneggiare l'elettronica di bordo. I dati raccolti da Cluster e analoghe sonde orbitali hanno permettono di identificare il fenomeno delle "scosse" interplanetarie provocate dalle eiezioni di massa coronale come quella che si è verificata domenica 11 aprile. La massa percuote l'involucro rappresentato dalle linee del campo magnetico terrestre generando onde magnetiche a frequenze VLF e ULF. I ritmici colpi di frusta, specie quelli a frequenze ULF, finiscono per indurre negli elettroni della Fascia di Van Allen una forte e rapida - su scale di soli 15 minuti - accelerazione.

Conoscere questi dettagli potrà aiutarci in futuro a prendere le contromisure necessarie per proteggere sonde e astronauti in orbita, ma chissà che non ci serva anche per affinare la nostra capacità di prevedere le condizioni radiopropagative.

Shocking recipe for 'killer electrons'

11 Mar 2010

Interplanetary shocks can create "killer electrons" in the near-Earth space environment within 15 minutes of the shock reaching the Earth's protective magnetic bubble. The underlying mechanism for this process has now been revealed as a result of a rare configuration of satellites, including Cluster, SOHO and Double Star.

For decades we have known that our near-Earth space environment is intimately linked to the Sun's activity. However, models of this relationship are still not accurate enough to predict - in detail - the impact on Earth of violent explosions (known as coronal mass ejections) on the Sun. In particular, it is not yet possible to determine where and to which extent a specific region of near-Earth space might be harmful for a spacecraft or perturb sat-nav signals.

This situation is rapidly improving. Thanks to an armada of scientific spacecraft, we live in a period of unprecedented opportunity for remote and in situ observations of the Sun and the near-Earth space environment. A recent study, led by Qiugang Zong from Peking University (China) and University of Massachusetts Lowell (USA), has investigated the relationship between interplanetary shocks, triggered by coronal mass ejections (CME), and so-called "killer-electrons", and uncovered the underlying mechanism.

"Killer electrons" are highly energetic particles trapped in the Earth's outer radiation belt. Their name derives from the fact that, due to their energy, they can penetrate the thick shielding of satellites and cause microscopic lightning strikes which damage and sometimes destroy vital onboard electronic components.

Theories show that several physical processes can accelerate electrons to these harmful energies; the predominant processes are interaction with waves either in the Very Low Frequency (3 to 30 kHz) domain or in the Ultra Low Frequency (between 0.001 to 1 Hz) domain. Up until recently it has been unclear which process is predominantly at work in the Earth's radiation belts after the impact of an interplanetary shock.

On 7 November 2004, a strong interplanetary shock impacted upon the magnetosphere, the Earth's magnetic bubble. The speed and the orientation of the wave front induced by this shock were determined using measurements obtained by instruments on the Cluster and Double Star satellites, along with other satellites widely spread across the magnetosphere. At geostationary altitude, the magnetosphere extends over roughly 84,000 km. Thus, having nine scientific satellites (four Cluster spacecraft, two Double Star spacecraft, NOAA GOES-10 and GOES-12, and the NASA Polar spacecraft) distributed over this large area of space during the impact of an interplanetary shock makes it a rare event to study.

"While the constant flow of solar wind particles propagates at an average speed of 500 km/s, the wave front propagation speed was more than 1200 km/s at geostationary orbit (36,000 km altitude) compared to 660 km/s in the plasmasphere", says Qiugang Zong lead author of the paper describing this result.

For this event, the amount of energetic electrons in the outer radiation belt started to increase almost immediately after the shock arrival. This substantial rise of "killer electrons" is found to be caused by a two-step process: The initial acceleration is due to the strong shock-related magnetic field compression. Immediately after the impact of the interplanetary shock, its passage across the magnetosphere triggered the Earth's magnetic lines to wobble at Ultra Low Frequencies (ULF). In turn, these ULF waves were found to effectively accelerate seed electrons, provided by the first step, to become "killer electrons".

"Both VLF and ULF waves accelerate electrons in the Earth’s radiation belts, but with different time scales. The ULF waves are much faster to do that than the VLF, due to their much larger amplitudes. They can explain the short time interval between shock impact and electrons being accelerated up to harmful energies", says Zong. "Data from the four Cluster satellites allowed the identification of ULF waves able to accelerate electrons", says Malcolm Dunlop, Rutherford Appleton Laboratory, Didcot (UK), and co-author of this study. "The Cluster constellation was also key to estimate the time needed for seed electrons to become ‘killer electrons’, after only 15 minutes!" added Zong.

"These new findings can help us to improve the models predicting the radiation environment in which satellites and astronauts operate. With solar activity now ramping up, we expect more of these shocks to impact our magnetosphere over the months and years to come", says Philippe Escoubet, Cluster project scientist at the European Space Agency. "Fortunately", he added, "even after almost 10 years in operation, the Cluster satellites are in excellent condition and can continue to quantify these effects".

La missione STEREO rivela lo "tsunami" solare

Le immagini del sole raccolte dai satelliti della missione STEREO durante un massivo evento di "eiezione di massa coronale" causato dall'attività magnetica del nostro astro sono davvero impressionanti. Permettono di osservare per la prima volta un meccanismo che finora era stato solo ipotizzato: gli tsunami solari. Nei filmati diffusi in questi giorni dalla NASA si vede chiaramente la massa che viene espulsa dalla corona solare e il poderoso effetto di rinculo che come un'onda sismica perrcorre a ritroso la superficie della stella, per milioni di chilometri. Un'esplosione che viene calcolata equivalente a 2.400 megatoni. L'altezza dell'eiezione in sé è strabiliante. Quella raggiunta dalla massa coronale "filmata" da STEREO è di centomila chilometri.
La missione STEREO ha collocato una coppia di satelliti in posizione ortoganale rispetto al sole e consente di effettuare osservazioni in prospettiva, con lo stesso effetto di profondità e tridimensionalità che possiamo ottenere puntando due occhi invece di uno. Lo tsunami solare non dovrebbe avere alcun effetto qui sulla terra (diversamente dalle eiezioni di massa coronale, che influiscono sulla ionosfera e lo spazio esterno), ma lo studio di fenomeni di questo tipo può essere molto rivelatore.

Monster Waves on the Sun are Real

November 24, 2009: Sometimes you really can believe your eyes. That's what NASA's STEREO (Solar Terrestrial Relations Observatory) spacecraft are telling researchers about a controversial phenomenon on the sun known as the "solar tsunami."

Years ago, when solar physicists first witnessed a towering wave of hot plasma racing along the sun's surface, they doubted their senses. The scale of the thing was staggering. It rose up higher than Earth itself and rippled out from a central point in a circular pattern millions of kilometers in circumference. Skeptical observers suggested it might be a shadow of some kind—a trick of the eye—but surely not a real wave. "Now we know," says Joe Gurman of the Solar Physics Lab at the Goddard Space Flight Center. "Solar tsunamis are real."
The twin STEREO spacecraft confirmed their reality in February 2009 when sunspot 11012 unexpectedly erupted. The blast hurled a billion-ton cloud of gas (a "CME") into space and sent a tsunami racing along the sun's surface. STEREO recorded the wave from two positions separated by 90o, giving researchers an unprecedented view of the event.
"It was definitely a wave," says Spiros Patsourakos of George Mason University, lead author of a paper reporting the finding in the Astrophysical Journal Letters. "Not a wave of water," he adds, "but a giant wave of hot plasma and magnetism."
The technical name is "fast-mode magnetohydrodynamical wave"—or "MHD wave" for short. The one STEREO saw reared up about 100,000 km high, and raced outward at 250 km/s (560,000 mph) packing as much energy as 2400 megatons of TNT (1029 ergs).
Solar tsunamis were discovered back in 1997 by the Solar and Heliospheric Observatory (SOHO). In May of that year, a CME came blasting up from an active region on the sun's surface, and SOHO recorded a tsunami rippling away from the blast site. "We wondered," recalls Gurman, "is that a wave—or just a shadow of the CME overhead?"
SOHO's single point of view was not enough to answer the question—neither for that first wave nor for many similar events recorded by SOHO in years that followed. The question remained open until after the launch of STEREO in 2006. At the time of the February 2009 eruption, STEREO-B was directly over the blast site while STEREO-A was stationed at right angles —"perfect geometry for cracking the mystery," says co-author Angelos Vourlidas of the Naval Research Lab in Washington DC.
The physical reality of the waves has been further confirmed by movies of the waves crashing into things. "We've seen the waves reflected by coronal holes (magnetic holes in the sun's atmosphere)," says Vourlidas. "And there is a wonderful movie of a solar prominence oscillating after it gets hit by a wave. We call it the 'dancing prominence.'"
Solar tsunamis pose no direct threat to Earth. Nevertheless, they are important to study. "We can use them to diagnose conditions on the sun," notes Gurman. "By watching how the waves propagate and bounce off things, we can gather information about the sun's lower atmosphere available in no other way."
"Tsunami waves can also improve our forecasting of space weather," adds Vourlidas, "Like a bull-eye, they 'mark the spot' where an eruption takes place. Pinpointing the blast site can help us anticipate when a CME or radiation storm will reach Earth."
And they're pretty entertaining, too. "The movies," he says, "are out of this world."

Croissant energetici dal sole

L'altro giorno la NASA ha presentato i primi risultati della missione STEREO, costituita da due satelliti collocati in orbita nei punti lagrangiani L4 e L5 per osservare il sole in modalità stereoscopica. I due occhi satellitari hanno generato immagini e prospettive tridimensionali che hanno finalmente dato una forma a eventi dirompenti come le eiezioni di massa coronale, grosse bolle di plasma solare che colpiscono il campo magnetico terrestre e provocano forti perturbazioni (anche alla propagazione dei segnali radio). Ed è saltato fuori che queste eiezioni assomigliano... a un croissant. Inteso come cornetto del bar. Sembra un risultato banale ma non lo è del tutto perché la forma a mezza luna si spiega con l'effetto distorcente provocato dai campi magnetici solari e sarebbe supportato dalle attuali teorie. Potete visualizzare una ricostruzione animata dell'esplosione legata a un CME in questo filmato QuickTime. A questo altro indirizzo trovate invece la trascrizione di una intervista a uno degli scienziati della missione STEREO e all'audio registrato.

NASA SPACECRAFT SHOW THREE DIMENSIONAL ANATOMY OF A SOLAR STORM

WASHINGTON -- Twin NASA spacecraft have provided scientists with their first view of the speed, trajectory, and three-dimensional shape of powerful explosions from the sun known as coronal mass ejections, or CMEs. This new capability will dramatically enhance scientists' ability to predict if and how these solar tsunamis could affect Earth.
When directed toward our planet, these ejections can be breathtakingly beautiful and yet potentially cause damaging effects worldwide. The brightly colored phenomena known as auroras -- more commonly called Northern or Southern Lights -- are examples of Earth's upper atmosphere harmlessly being disturbed by a CME. However, ejections can produce a form of solar cosmic rays that can be hazardous to spacecraft, astronauts and technology on Earth.
Space weather produces disturbances in electromagnetic fields on Earth that can induce extreme currents in wires, disrupting power lines and causing wide-spread blackouts. These sun storms can interfere with communications between ground controllers and satellites and with airplane pilots flying near Earth's poles. Radio noise from the storm also can disrupt cell phone service. Space weather has been recognized as causing problems with new technology since the invention of the telegraph in the 19th century.
NASA's twin Solar Terrestrial Relations Observatory, or STEREO, spacecraft are providing the unique scientific tool to study these ejections as never before. Launched in October 2006, STEREO's nearly identical observatories can make simultaneous observations of these ejections of plasma and magnetic energy that originate from the sun's outer atmosphere, or corona. The spacecraft are stationed at different vantage points. One leads Earth in its orbit around the sun, while the other trails the planet.
Using three-dimensional observations, solar physicists can examine a CME's structure, velocity, mass, and direction in the corona while tracking it through interplanetary space. These measurements can help determine when a CME will reach Earth and predict how much energy it will deliver to our magnetosphere, which is Earth's protective magnetic shield.
"Before this unique mission, measurements and the subsequent data of a CME observed near the sun had to wait until the ejections arrived at Earth three to seven days later," said Angelos Vourlidas, a solar physicist at the Naval Research Laboratory in Washington. Vourlidas is a project scientist for the Sun Earth Connection Coronal and Heliospheric Investigation, STEREO's key science instrument suite. "Now we can see a CME from the time it leaves the solar surface until it reaches Earth, and we can reconstruct the event in 3D directly from the images."
These ejections carry billions of tons of plasma into space at thousands of miles per hour. This plasma, which carries with it some of the magnetic field from the corona, can create a large, moving disturbance in space that produces a shock wave. The wave can accelerate some of the surrounding particles to high energies that can produce a form of solar cosmic rays. This process also can create disruptive space weather during and following the CME's interaction with Earth's magnetosphere and upper atmosphere.
"The new vantage point of these spacecraft has revolutionized the study of solar physics," said Madhulika Guhathakurta, STEREO program scientist at NASA Headquarters in Washington. "We can better determine the impact of CME effects on Earth because of our new ability to observe in 3D."
STEREO is part of NASA's Solar Terrestrial Probes Program in NASA's Science Mission Directorate in Washington. The program seeks to understand the fundamental physical processes of the space environment from the sun to Earth and other planets.
The Solar Terrestrial Probes Program also seeks to understand how society, technological systems and the habitability of planets are affected by solar processes. This information may lead to a better ability to predict extreme and dynamic conditions in space, and the development of new technologies to increase safety and productivity of human and robotic space exploration.
For more information about NASA's STEREO mission, visit: http://www.nasa.gov/stereo

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The Surprising Shape of Solar Storms
04.14.2009

April 14, 2009: This just in: The Sun is blasting the solar system with croissants.

Researchers studying data from NASA's twin STEREO probes have found that ferocious solar storms called CMEs (coronal mass ejections) are shaped like a French pastry. The elegance and simplicity of the new "croissant model" is expected to dramatically improve forecasts of severe space weather.
"We believe we can now predict when a CME will hit Earth with only 3-hours of uncertainty," says Angelos Vourlidas of the Naval Research Lab, who helped develop the model. "That's a four-fold improvement over older methods."
Coronal mass ejections are billion-ton clouds of hot magnetized gas that explode away from the sun at speeds topping a million mph. Sometimes the clouds make a beeline for Earth and when they hit they can cause geomagnetic storms, satellite outages, auroras, and power blackouts. The ability to predict the speed and trajectory of a CME is key to space weather forecasting.
"This is an important advance," says Lika Guhathakurta, STEREO program scientist at NASA headquarters in Washington DC. "From a distance, CMEs appear to be a complicated and varied population. What we have discovered is that they are not so varied after all. Almost all of the 40-plus CMEs we have studied so far with STEREO have a common shape--akin to a croissant."
Thousands of CMEs have been observed by NASA and European Space Agency spacecraft, but until now their common shape was unknown. That's because in the past observations were made from only a single point of view. The STEREO mission has the advantage of numbers. It consists of two probes that flank the sun and photograph explosions from opposite sides. STEREO's sensitive wide-field cameras can track CMEs over a wider area of sky than any other spacecraft, following the progress of the storm all the way from the sun to the orbit of Earth.
"STEREO has done what no previous mission could," notes Guhathakurta.
Vourlidas says he is not surprised that CMEs resemble French pastries. "I have suspected this all along. The croissant shape is a natural result of twisted magnetic fields on the sun and is predicted by a majority of theoretical models."
He offers the following analogy: Take a length of rope and hold one end in each hand. Start twisting the ends in opposite directions. Twist, twist and continue twisting until the middle of the rope is a fat knotted mess. "That's how CMEs get started—as twisted ropes of solar magnetism. When the energy in the twist reaches some threshold, there is an explosion which expels the CME away from the sun. It looks like a croissant because the twisted ropes are fat in the middle and thin on the ends."
The shape alone, however, does not tell the full story of a CME. The contents of the CME must be considered, too. How much plasma does it contain? What is the orientation and strength of its internal magnetic field? When a CME strikes, the havoc it causes will depend on the answers—answers the croissant model does not yet provide.
"There is more work to do. We must learn to look at a CME and not only trace its shape, but also inventory in contents," says Guhathakurta. "We are halfway there."
Eventually, the quest to learn what lies inside the croissant will be taken up by other spacecraft such as the Solar Dynamics Observatory, slated to launch in August 2009, and Solar Probe+, a daring mission (still on the drawing board) to fly close to the sun and actually enter these storms near their source.
STEREO isn't finished, though. The two probes are continuing their journeys to opposite sides of the sun for a 24/7, 360-degree view of the star. Along the way, they'll actually run into a few CMEs and have the chance to sample the 'croissants' in situ.

Le tempeste solari in 3D della missione STEREO

Martedì prossimo la NASA organizza una conferenza stampa per presentare i risultati della missione satellitare Stereo, che sta analizzando il nostro sole nello spazio tridimensionale. L'attenzione si concentra sui modelli predittivi delle "eiezioni di massa coronale" eventi particolaremente intensi che catapultano sul nostro campo magnetico e sulla ionosfera, come un vero proiettile, una quantità di plasma solare e un mix di particelle più pesanti.

E' presumibile che gli scienziati della NASA avranno a disposizione informazioni e immagini inediti, che offriranno uno spettacolare quadro di insieme della meteorologia spaziale. Le eiezioni di massa coronale (CME) possono provocare serie perturbazioni ai sistemi terrestri e orbitali di telecomunicazione e generazione di energia. Essere in grado di prevederle e spiegarle può essere ancora più vitale per gli astronauti delle varie missioni di esplorazione. Non dimentichiamo che oltre alla consolidata esperienza della Space Station la NASA si appresta a lanciare nuove iniziative che avranno per target, 40 anni dopo la missione Apollo, la luna. La conferenza stampa sulle CME verrà trasmessa da NASA Television e dovrebbe iniziare il 14 aprile alle 13 EDT, le nostre 19.

NASA SCIENCE UPDATE TO DISCUSS ANATOMY OF SOLAR STORMS
WASHINGTON -- NASA will hold a Science Update at 1 p.m. EDT, Tuesday, April 14, to present new findings and three-dimensional views revealing the inner workings of solar storms known as coronal mass ejections. The data will improve the ability to predict how and when these solar tsunamis impact Earth, affecting communication systems, power grids, and other technology. The briefing will take place in the James E. Webb Memorial Auditorium at NASA Headquarters, 300 E St., S.W., and will be carried live on NASA Television.

Briefing participants are:

• Michael Kaiser, project scientist, Solar Terrestrial Relations Observatory (STEREO), NASA's Goddard Space Flight Center in Greenbelt, Md.
• Angelos Vourlidas, project scientist, Sun Earth Connection Coronal and Heliospheric Investigation, Naval Research Laboratory in Washington
• Antoinette Galvin, principal investigator, Plasma and Suprathermal Ion Composition instrument, University of New Hampshire in Durham
• Madhulika Guhathakurta, STEREO program scientist, NASA Headquarters

For information about NASA TV, streaming video, downlink and schedule information, visit:

http://www.nasa.gov/ntv

For more information about the STEREO mission, visit:

http://www.nasa.gov/stereo

Buon Capodanno, sole

Stavo guardando ora su Repubblica.it la minigalleria di fotografie notturne dalla base antartica australiana di Casey, con gli spettacolari effetti di una aurora australe. E' in un certo senso il Capodanno del sole, che proprio in queste settimane chiude il ciclo 23 e inaugura il ciclo numero 24 (RP, non faccio per vantarmi, ha già dato la notizia quasi un mese fa). Verso metà dicembra era stata avvistata alle alte latitudini settentrionali del disco solare una zona di addensamento magnetico con polarità invertita, non ancora una macchia ma il segno incontrovertibile che le cose stavano cambiando. Un ciclo è sempre caratterizzato da un preciso andamento delle macchie che lo caratterizzano. Mentre il sole gira su stesso le macchie si spostano da nord verso sud, con una zona di una determinata polarità che "guida" il movimento (leading polarity) e una di polarità opposta che segue (trailing polarity). Quando raggiungono l'altro emisfero invertono questa polarità. Nell'immagine pubblicata dal centro belga SIDC, si nota il grande gruppo poco sotto l'equatore, con la leading polarity negativa (nera) e la trailing positiva (bianca). Verso i 30 di latitudine nord ecco una piccola macchia con la stessa polarità: non dovrebbe essere così se questa macchia appartenesse al ciclo 23, le cui aree di addensamento partivano dal nord con una leading polarity positiva. Questa macchietta appartiene al "nuovo" sole, che secondo gli esperti dovrebbe essere molto attivo.
E infatti, la nostra aurora australe potrebbe essere legata al primo evento "halo" CME (eiezione di materia coronale, uno sbuffo di plasma denso che approfitta di una smagliatura magnetica per proiettare le sue linee di intenso magnetismo verso lo spazio) del nuovo ciclo. Dopo poche ore, gli effetti dei CME si fanno sentire sul nostro campo geomagnetico determinando aurore ed effetti di assorbimento sui tracciati propagativi delle onde radio. Un'altra CME di classe C o possibilmente M si era verificata proprio il 31, questo "alone" dell'8 è successivo. Il Solar Influences Data Analysis Center di Bruxelles pubblica un magnetogramma della prima macchia del ciclo 24 catturato tra il 4 e 5 gennaio, con un disegno inviato dall'Osservatorio Astrofisico di Catania e altre informazioni che arrivano tra l'altro da un piccolo osservatorio del Canton Ticino, la Specola Solare Ticinese di Locarno, che nel 2007 ha celebrato il suo mezzo secolo di vita. Auguri!