L'evento di Carrington, nel 1859 la prima tempesta geomagnetica registrata dalla scienza

Su Ars Technica è apparsa una dettagliatissima ricostruzione storica, firmata da Matthew Lasar del cosiddetto "evento di Carrington" la prima tempesta magnetica di eccezionale intensità registrata strumentalmente e con osservazioni astronomiche e atmosferiche. L'evento si verificò il 1 settembre 1859 quando l'astronomo Richard Carrington, nella sua consueta attività di osservazione e descrizione grafica delle macchie solari, osservò in diretta, otticamente, quello che gli astrofisici suoi discendenti avrebbero facilmente identificato come un brillamento solare "earth bound". >L'articolo riporta alcuni magnetogrammi registrati in contemporanea all'Osservatorio di Greenwich, che rappresentano la prima testimonianza scientifica di un episodio di cui ancora oggi non riusciamo a descrivere con precisione assoluta i meccanismi.

Le aurore boreali e australi che seguirono l'osservazione di Carrington, destò un tale scalpore che la gente si riversò nelle strade di città come New York o sulle navi in navigazione anche in acque tropicali. Nel 2006 gli scienziati della NASA pubblicarono su Advanced Space Research una selezione delle cronache apparse sulla stampa e sulla diaristica dell'epoca. Oltre alle spettacolari aurore, che illuminarono quasi a giorno l'oscurità della sera (già verso l'ora del tramonto), le cronache rivelano gli effetti sulle reti telegrafiche, che in alcuni casi continuarono a funzionare, anche a batterie staccate, con quella che venne chiamata "corrente aurorale". Nel 1865, forse con ancora in testa il ricordo di quella incredibile notte, il paesaggista americano Frederic Edwin Church dipinse un quadro intitolato "Aurora Borealis".

Una lettura davvero molto interessante.

Proiettili di plasma dal sole

La macchia solare 1105 ha prodotto uno spettacolare brillamento ripreso dal Solar Dynamics Observatory ieri, 8 settembre. Il filmato è davvero impressionante. Per fortuna l'eruzione di plasma non era diretta verso la terra, altrimenti avremmo subito un bel colpo di frusta. Sono comunque apparse intense aurore boreali al nord. Il sole sta gradualmente riprendendo la sua attività, anche se ultimamente il periodo ha continuato a essere caratterizzato dall'assenza di macchie che è stato il segno distintivo dell'ultimo, prolungatissimo minimo.

Missione THEMIS, ecco come funziona lo "spaziomoto"

I satelliti della missione THEMIS aiutano gli scienziati a spiegare i meccanismi di un nuovo tipo di evento "magneto-sismico" all'interfaccia tra plasma solare e campo magnetico terrestre. L'analogia con i terremoti induce i geofisici a parlare di spaziomoto, con onde di shock che si propagano dalla coda della magnetosfera rimbalzano tra linee di campo, come una palla o la crosta terrestre in caso di terremoti. Il fenomeno secondo gli scienziati potrebbe scatenare aurore boreali e tempeste di ionizzazione che a loro volta andrebbero a interferire con le comunicazioni e sistemi GPS.

Spacequakes Rumble Near Earth

Rumbles without sound

Auroras rain down

Magnetic fields shake

Beware the spacequake

July 27, 2010: Researchers using NASA's fleet of five THEMIS spacecraft have discovered a form of space weather that packs the punch of an earthquake and plays a key role in sparking bright Northern Lights. They call it "the spacequake."

A spacequake in action. Click to launch a computer-simulated movie created by Walt Feimer of Goddard's Scientific Visualization Lab.

A spacequake is a temblor in Earth's magnetic field. It is felt most strongly in Earth orbit, but is not exclusive to space. The effects can reach all the way down to the surface of Earth itself.

"Magnetic reverberations have been detected at ground stations all around the globe, much like seismic detectors measure a large earthquake," says THEMIS principal investigator Vassilis Angelopoulos of UCLA.

It's an apt analogy because "the total energy in a spacequake can rival that of a magnitude 5 or 6 earthquake," according to Evgeny Panov of the Space Research Institute in Austria. Panov is first author of a paper reporting the results in the April 2010 issue of Geophysical Research Letters (GRL).

In 2007, THEMIS discovered the precursors of spacequakes. The action begins in Earth's magnetic tail, which is stretched out like a windsock by the million mph solar wind. Sometimes the tail can become so stretched and tension-filled, it snaps back like an over-torqued rubber band. Solar wind plasma trapped in the tail hurtles toward Earth. On more than one occasion, the five THEMIS spacecraft were in the line of fire when these "plasma jets" swept by. Clearly, the jets were going to hit Earth. But what would happen then? The fleet moved closer to the planet to find out.

"Now we know," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "Plasma jets trigger spacequakes."

According to THEMIS, the jets crash into the geomagnetic field some 30,000 km above Earth's equator. The impact sets off a rebounding process, in which the incoming plasma actually bounces up and down on the reverberating magnetic field. Researchers call it "repetitive flow rebuffing." It's akin to a tennis ball bouncing up and down on a carpeted floor. The first bounce is a big one, followed by bounces of decreasing amplitude as energy is dissipated in the carpet.

"We've long suspected that something like this was happening," says Sibeck. "By observing the process in situ, however, THEMIS has discovered something new and surprising."

The surprise is plasma vortices, huge whirls of magnetized gas as wide as Earth itself, spinning on the verge of the quaking magnetic field. "When plasma jets hit the inner magnetosphere, vortices with opposite sense of rotation appear and reappear on either side of the plasma jet," explains Rumi Nakamura of the Space Research Institute in Austria, a co-author of the study. "We believe the vortices can generate substantial electrical currents in the near-Earth environment."

Acting together, vortices and spacequakes could have a noticeable effect on Earth. The tails of vortices may funnel particles into Earth's atmosphere, sparking auroras and making waves of ionization that disturb radio communications and GPS. By tugging on surface magnetic fields, spacequakes generate currents in the very ground we walk on. Ground current surges can have profound consequences, in extreme cases bringing down power grids over a wide area.

After THEMIS discovered the jets and quakes, Joachim Birn of the Los Alamos National Lab in New Mexico conducted a computer simulation of the rebounding process. Lo and behold, vortices appeared in good accord with THEMIS measurements. Moreover, the simulations suggest that the rebounding process can be seen from Earth's surface in the form of ripples and whirls in auroral displays. Ground stations report just such a phenomenon.

"It's a complicated process, but it all fits together," says Sibeck.

The work isn't finished. "We still have a lot to learn," he adds. "How big can spacequakes become? How many vortices can swirl around Earth at once--and how do they interact with one another?"

Stay tuned for answers from THEMIS.

Vortices swirl

plasma a'twirl

Richter predicts

a magnitude six

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".

L'incredibile duplice aurora di saturno

Proprio come succede qui sulla terra, anche sul pianeta saturno le particelle solari interagiscono con il campo magnetico generando lo spettacolare fenomeno delle aurore alle latitudini polari. Il telescopio spaziale Hubble, approfittando della rara occasione dell'equinozio saturniano (un fenomeno che si verifica solo una volta ogni quindici anni) ha catturato le spettacolari immagini di una duplice aurora. I filmati conservati sul sito dello Space Telescope sono davvero incredibili.
Accludo qui l'eccellente articolo esplicativo appena pubblicato dall'ESA. La leggera asimmetria che caratterizza i due anelli aurorali che potete vedere intorno ai poli del pianeta denunciano le differenze di forma del suo campo magnetico.

Saturn's aurorae offer stunning double show

11 Feb 2010
Researchers using the NASA/ESA Hubble Space Telescope recently took advantage of a rare opportunity to record Saturn when its rings are edge-on, resulting in a unique movie featuring both of the giant planet's poles. Saturn is only in this position every 15 years and this favourable orientation has allowed a sustained study of Saturn's almost symmetric northern and southern lights.
An enormous and grand ringed planet, Saturn is certainly one of the most intriguing bodies orbiting the Sun. Hubble has now taken a fresh look at the fluttering aurorae that light up both of Saturn's poles.
It takes Saturn almost thirty years to orbit the Sun, with the opportunity to image both of its poles occurring only twice in that period. Hubble has been snapping pictures of the planet at different angles since the beginning of the mission in 1990, but 2009 brought a unique chance for Hubble to image Saturn with the rings edge-on and both poles in view. At the same time Saturn was approaching its equinox so both poles were equally illuminated by the Sun's rays.
These recent observations go well beyond just a still image and have allowed researchers to monitor the behaviour of both Saturn's poles in the same shot over a sustained period of time. The movie they created from the data, collected over several days during January and March 2009, has aided astronomers studying both Saturn's northern and southern aurorae. Given the rarity of such an event, this new footage will likely be the last and best equinox movie that Hubble captures of our planetary neighbour.
Despite its remoteness, the Sun's influence is still felt by Saturn. The Sun constantly emits particles that reach all the planets of the Solar System as the solar wind. When this electrically charged stream gets close to a planet with a magnetic field, like Saturn or the Earth, the field traps the particles, bouncing them back and forth between its two poles. A natural consequence of the shape of the planet's magnetic field, a series of invisible "traffic lanes" exist between the two poles along which the electrically charged particles are confined as they oscillate between the poles. The magnetic field is stronger at the poles and the particles tend to concentrate there, where they interact with atoms in the upper layers of the atmosphere, creating aurorae, the familiar glow that the inhabitants of the Earth's polar regions know as the northern and southern lights.
At first glance the light show of Saturn's aurorae appears symmetric at the two poles. However, analysing the new data in greater detail, astronomers have discovered some subtle differences between the northern and southern aurorae, which reveal important information about Saturn's magnetic field. The northern auroral oval is slightly smaller and more intense than the southern one, implying that Saturn's magnetic field is not equally distributed across the planet; it is slightly uneven and stronger in the north than the south. As a result, the electrically charged particles in the north are accelerated to higher energies as they are fired toward the atmosphere than those in the south. This confirms a previous result obtained by the space probe Cassini, in orbit around the ringed planet since 2004.

E se le macchie solari sparissero?

Il sito Spaceweather ha appena pubblicato un approfondimento della notizia relativa a uno studio sulla variabilità magnetica delle macchie solari, le quali, secondo due astrofisici del National Solar Observatory di Tucson, stanno perdendo visibilmente intensità. Il sito è andato a chiedere direttamente il parere dei due studiosi, che ammettono che a fronte di una simile perdita di intensità non è del tutto da escludere l'ipotesi che le macchie solari, che sono appunto legate all'intensità dei campi magnetici, spariscano quasi completamente. Ci sono insomma condizioni solari compatibili con il celebre minimo di Maunder, che iniziò nel 1645 e si prolungò per oltre 70 anni. Altri esperti ritengono che il sole si è semplicemente addormentato un po', che entro un anno tutto ripartirà.
Un paio di giorni prima il sito aveva pubblicato un altro articolo che fa riflettere sulle possibile conseguenze di questo profondo minimo solare sul sistema geomagnetico. Il 2 settembre 1859 durante un massimo a bassa intensità come quello che si prevede nei prossimi 3 o 4 anni, fu registrata a terra una tempesta geomagnetica di proporzioni colossali, con l'aurora boreale visibile addirittura a Cuba. Il giorno prima l'astronomo dilettante Richard Carrington aveva avvistato e descritto un potentissimo brillamento sulla superficie del sole, in corrispondenza di un esteso gruppo di macchie. A terra, i fili dei telegrafi si caricarono al punto da provocare scintille, danneggiando gli apparecchi riceventi e addirittura infiammando le strisce di carta degli inchiostratori. La morale? Che anche un minimo solare o un ciclo a bassa intensità possono fare da sfondo a tempeste geomagnetiche di grandi proporzioni. Anche dal punto di vista propagative, la mia esperienza di cicli solari e correlazioni con la ricezione di segnali lontani mi induce a credere che non si debba temere un blackout delle onde corte o delle aperture in E sporadico in FM. In questo fine settimana sentivo cose molto interessanti, incluso il servizio per le forze armate americane ripetuto dalla base nel Pacifico alle isole Hawaii, e molti segnali interessanti nelle bande alte radioamatoriali. La stagione dell'E sporadico non è stata eccezionale, ma sembra ormai chiaro che il fenomeno non è fortemente correlato all'andamento del ciclo.

Are Sunspots Disappearing?
09.03.2009

September 3, 2009: The sun is in the pits of the deepest solar minimum in nearly a century. Weeks and sometimes whole months go by without even a single tiny sunspot. The quiet has dragged out for more than two years, prompting some observers to wonder, are sunspots disappearing?
"Personally, I'm betting that sunspots are coming back," says researcher Matt Penn of the National Solar Observatory (NSO) in Tucson, Arizona. But, he allows, "there is some evidence that they won't."
Penn's colleague Bill Livingston of the NSO has been measuring the magnetic fields of sunspots for the past 17 years, and he has found a remarkable trend. Sunspot magnetism is on the decline: "Sunspot magnetic fields are dropping by about 50 gauss per year," says Penn. "If we extrapolate this trend into the future, sunspots could completely vanish around the year 2015."
This disappearing act is possible because sunspots are made of magnetism. The "firmament" of a sunspot is not matter but rather a strong magnetic field that appears dark because it blocks the upflow of heat from the sun's interior. If Earth lost its magnetic field, the solid planet would remain intact, but if a sunspot loses its magnetism, it ceases to exist.
"According to our measurements, sunspots seem to form only if the magnetic field is stronger than about 1500 gauss," says Livingston. "If the current trend continues, we'll hit that threshold in the near future, and solar magnetic fields would become too weak to form sunspots."
"This work has caused a sensation in the field of solar physics," comments NASA sunspot expert David Hathaway, who is not directly involved in the research. "It's controversial stuff."
The controversy is not about the data. "We know Livingston and Penn are excellent observers," says Hathaway. "The trend that they have discovered appears to be real." The part colleagues have trouble believing is the extrapolation. Hathaway notes that most of their data were taken after the maximum of Solar Cycle 23 (2000-2002) when sunspot activity naturally began to decline. "The drop in magnetic fields could be a normal aspect of the solar cycle and not a sign that sunspots are permanently vanishing."
Penn himself wonders about these points. "Our technique is relatively new and the data stretches back in time only 17 years. We could be observing a temporary downturn that will reverse itself."
The technique they're using was pioneered by Livingston at the McMath-Pierce solar telescope near Tucson. He looks at a spectral line emitted by iron atoms in the sun's atmosphere. Sunspot magnetic fields cause the line to split in two—an effect called "Zeeman splitting" after Dutch physicist Pieter Zeeman who discovered the phenomenon in the 19th century. The size of the split reveals the intensity of the magnetism.
Astronomers have been measuring sunspot magnetic fields in this general way for nearly a century, but Livingston added a twist. While most researchers measure the splitting of spectral lines in the visible part of the sun's spectrum, Livingston decided to try an infra-red spectral line. Infrared lines are much more sensitive to the Zeeman effect and provide more accurate answers. Also, he dedicated himself to measuring a large number of sunspots—more than 900 between 1998 and 2005 alone. The combination of accuracy and numbers revealed the downturn.
If sunspots do go away, it wouldn't be the first time. In the 17th century, the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists. The sunspot drought began in 1645 and lasted until 1715; during that time, some of the best astronomers in history (e.g., Cassini) monitored the sun and failed to count more than a few dozen sunspots per year, compared to the usual thousands.
"Whether [the current downturn] is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen," Livingston and Penn caution in a recent issue of EOS. "Other indications of solar activity suggest that sunspots must return in earnest within the next year."
Whatever happens, notes Hathaway, "the sun is behaving in an interesting way and I believe we're about to learn something new."

GEOMAGNETIC MEGA-STORM: On Sept. 2nd, a billion-ton coronal mass ejection (CME) slammed into Earth's magnetic field. Campers in the Rocky Mountains woke up in the middle of the night, thinking that the glow they saw was sunrise. No, it was the Northern Lights. People in Cuba read their morning paper by the red illumination of aurora borealis. Earth was peppered by particles so energetic, they altered the chemistry of polar ice.
Hard to believe? It really happened--exactly 150 years ago. This map shows where auroras were sighted in the early hours of Sept. 2, 1859:
As the day unfolded, the gathering storm electrified telegraph lines, shocking technicians and setting their telegraph papers on fire. The "Victorian Internet" was knocked offline. Magnetometers around the world recorded strong disturbances in the planetary magnetic field for more than a week.
The cause of all this was an extraordinary solar flare witnessed the day before by British astronomer Richard Carrington. His sighting marked the discovery of solar flares and foreshadowed a new field of study: space weather. According to the National Academy of Sciences, if a similar flare occurred today, it would cause $1 to 2 trillion in damage to society's high-tech infrastructure and require four to ten years for complete recovery.
A repeat of the Carrington Event seems unlikely from our low vantage in a deep solar minimum--but don't let the quiet fool you. Strong flares can occur even during weak solar cycles. Indeed, the Carrington flare itself occured during a relatively weak cycle similar to the one expected to peak in 2012-2013. Could it happen again? Let's hope not.

Macchie solari e foto aurorali per il ciclo 24

Oggi alle 15.44 UT il sole ha attraversato la linea dell'equatore celeste. Buon equinozio e buon autunno a tutti! La stagione degli ascolti asiatici ha inizio e Giampaolo Galassi mi segnalava l'altra sera le prime giapponesi in onde medie verso le 20.30 UTC. Ma la notizia del giorno, dopo un mese di agosto con il sole senza macchie, è la comparsa sul disco solare di un gruppo di macchie (piccole, sono grandi "solo" quanto la terra) chiaramente appartenenti al ciclo 24, quello nuovo. La polarità inversa rispetto alle macchie del 23esimo è un sintomo inequivocabile.
Molto è stato detto sui possibili effetti, anche climatologici, di un ciclo solare a bassa intensità. Io continuo ad avere la sensazione che dovremmo prendere con un po' di scetticismo in più la mole di misurazioni strumentali che stiamo accumulando, senza mai dimenticare che lo stiamo facendo da pochi decenni con tale dovizia di cifre dopo la virgola. Vedrete che il ciclo, che dopotutto ne dura undici, di anni, avrà modo di recuperare. A dispetto di una attività molto bassa il 9 agosto scorso è stata segnalata un'aurora boreale. Auguriamoci che sia possibile tornare a vederne qualcuna anche alle nostre latitudini, come è avvenuto qualche anno fa in fase di massimo discendente. E' uno degli spettacoli naturali più indescrivibili e mi piace celebrare la prima macchia importante del nuovo ciclo con un link al sito di Tony Prower, fotografo di aurore. Tony my ha scritto una ventina di giorni fa chiedendomi di scambiarci i collegamenti ai rispettivi siti. Abita in Islanda, il nostro fortunato amico, e pubblica regolarmente le sue fotografie di paesaggi, tramonti e northern lights sul suo spazio Iceland Aurora. Non potete immaginare quanto lo invidio. Tony, a few notes in your language - and please forgive the delay - just to say how I appreciated your message and how I feel flattered by your link exchange proposal. Your photo album is the most impressive I've ever seen as far as aurora and twilight landscapes are concerned, and I'm happy to contribute, albeit minimally, to its promotion. Thanks and let's keep in touch.

NEW SUNSPOT: For the first time in months, a significant sunspot is emerging on the sun. It is a fast-growing active region with two dark cores, each larger than Earth. The magnetic polarity of the sunspot identifies it as a member of new Sunspot Cycle 24. Because the year 2008 has brought so many blank suns, some observers have wondered if we are ever going to climb out of the ongoing deep solar minimum. Today's new sunspot is an encouraging sign that the 11-year solar cycle is indeed progressing, albeit slowly.

Una pallottola al plasma per far ballare l'aurora

Testing, testing. Sono finalmente arrivato a Favignana, dove la connettività 3G sembra funzionare molto bene rispetto a due anni fa. La vista è immutata e continua a mozzare il fiato. Specie quando uno ce l'ha corto come me in questo periodo.

In viaggio questa notte sul treno per Palermo leggevo delle grandi scoperte della missione satellitare Themis, che ha svelato il meccanismo magnetico (veri e propri proiettili di plasma sparati, grazie al fenomeno della ricombinazione delle linee di campo, da una distanza pari a circa un terzo della distanza terra-luna) che genera l'energia necessaria per far "danzare" l'aurora boreale. Con quel risultato onirico e fatato che incanta gli spettatori a terra alle alte latitudini (vi assicuro, è davvero uno spettacolo che vale un viaggio).
Bellissmo l'articolo che trovate a questo indirizzo.

NASA SATELLITES DISCOVER WHAT POWERS NORTHERN LIGHTS

GREENBELT, Md. -- Researchers using a fleet of five NASA satellites have discovered that explosions of magnetic energy a third of the way to the moon power substorms that cause sudden brightenings and rapid movements of the aurora borealis, called the Northern Lights.
The culprit turns out to be magnetic reconnection, a common process that occurs throughout the universe when stressed magnetic field lines suddenly snap to a new shape, like a rubber band that's been stretched too far.
"We discovered what makes the Northern Lights dance," said Dr.Vassilis Angelopoulos of the University of California, Los Angeles.
Angelopoulos is the principal investigator for the Time History of Events and Macroscale Interactions during Substorms mission, or THEMIS.
Substorms produce dynamic changes in the auroral displays seen near Earth's northern and southern magnetic poles, causing a burst of light and movement in the Northern and Southern Lights.
Substorms often accompany intense space storms that can disrupt radio communications and global positioning system signals and cause power outages. Solving the mystery of where, when, and how substorms occur will allow scientists to construct more realistic substorm models and better predict a magnetic storm's intensity and effects.
"As they capture and store energy from the solar wind, the Earth's magnetic field lines stretch far out into space. Magnetic reconnection releases the energy stored within these stretched magnetic field lines, flinging charged particles back toward the Earth's atmosphere," said David Sibeck, THEMIS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "They create halos of shimmering aurora circling the northern and southern poles." Scientists directly observe the beginning of substorms using five THEMIS satellites and a network of 20 ground observatories located throughout Canada and Alaska. Launched in February 2007, the five identical satellites line up once every four days along the equator and take observations synchronized with the ground observatories.
Each ground station uses a magnetometer and a camera pointed upward to determine where and when an auroral substorm will begin.
Instruments measure the auroral light from particles flowing along Earth's magnetic field and the electrical currents these particles generate.
During each alignment, the satellites capture data that allow scientists to precisely pinpoint where, when, and how substorms measured on the ground develop in space. On Feb. 26, 2008, during one such THEMIS lineup, the satellites observed an isolated substorm begin in space, while the ground-based observatories recorded the intense auroral brightening and space currents over North America.
These observations confirm for the first time that magnetic reconnection triggers the onset of substorms. The discovery supports the reconnection model of substorms, which asserts a substorm starting to occur follows a particular pattern. This pattern consists of a period of reconnection, followed by rapid auroral brightening and rapid expansion of the aurora toward the poles. This culminates in a redistribution of the electrical currents flowing in space around Earth.
THEMIS is the fifth medium-class mission under NASA's Explorer Program. The program, managed by the Explorers Program Office at Goddard provides frequent flight opportunities for world-class space investigations in heliophysics and astrophysics. The University of California, Berkeley's Space Sciences Laboratory in Berkeley, Calif., managed the project development and is currently operating the THEMIS mission. ATK Space (formerly Swales Aerospace) of Beltsville, Md., built the THEMIS satellites.
The THEMIS team's findings will appear online July 24 in Science Express and Aug. 14 in the journal science. For more information about the THEMIS mission, visit: http://www.nasa.gov./themis

Un tuffo nell'aurora

Mercoledì prossimo, 17 gennaio, sarà possibile seguire in diretta telefonica o Web la conferenza stampa della missione Themis, che la NASA lancerà a metà febbraio. La missione studierà i meccanismi alla base delle aurore boreali ad alta dinamicità, quelle che avvengono in condizioni di "sub-tempesta" magnetica. C'è in gioco un evento che non è solo spettacolare da vedere, ma è normalmente associato a grosse perturbazioni propagative e veri e propri danni alle strumentazioni dei satelliti.

Ecco il testo di presentazione dal sito ufficiale dei satelliti Themis:

On a clear night over the far northern areas of the world, you may witness a hauntingly beautiful light display in the sky that can disrupt your satellite TV and leave you in the dark.
The eerie glow of the northern lights seems exquisite and quite harmless. Most times, it is harmless. The display, resembling a slow-moving ribbon silently undulating in the sky, is called the aurora. It is also visible in far southern regions around the South Pole.
Occasionally, however, the aurora becomes much more dynamic. The single auroral ribbon may split into several ribbons or even break into clusters that race north and south. This dynamic light show in the polar skies is associated with what scientists call a magnetospheric substorm. Substorms are very closely related to full-blown space storms that can disable spacecraft, radio communication, GPS navigation, and power systems while supplying killer electrons to the radiation belts surrounding Earth. The purpose of NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is to understand the physical instability (trigger mechanism) for magnetospheric substorms.

Ci si può collegare a questo indirizzo per ascoltare la presentazione, guidata dal capo progetto Peter Harvey, di Berkeley. Il materiale stampa verrà reso disponibile su questa pagina.

Le aurore, battito cardiaco della magnetosfera

Un nuovo importante studio, effettuato da Applied Physics Lab della Johns Hopkins University e da Aeronautica Militare USA su una mole di dati raccolti da satelliti NASA e da altre agenzie, conferma che fenomeni come l'aurora boreale e altre turbolenze magnetiche non sono, come si credeva, correlati ai forti campi elettrici del vento solare e quindi ai brillamenti nell'atmosfera del sole. La correlazione più certa sembra essere quella, magnetica, ai confini tra i campi magnetici solare e terrestre. E' ciò che i ricercatori chiamano "battito cardiaco della magnetosfera": il tasso di "connessione" tra le linee di campo magnetico del sole e della terra (Radiopassioni aveva trattato questo stesso argomento qualche tempo fa parlando di uno studio molto simile).

Il testo del comunicato stampa rilasciato per l'occasione è interessante, ma ancora più dettagliato è il materiale diffuso per la presentazione della ricerca davanti alla American Geophysical Union a San Francisco, lo scorso 11 dicembre. Gli autori dello studio sottolineano di aver ricavato una singola formula che sulla base delle osservazioni magnetiche a circa 40 mila chilometri di quota (all'interfaccia tra i due campi magnetici) fornisce accurate previsioni sull'intensità delle aurore e altri dieci parametri significativi.

New findings indicate that the aurora and other near-Earth space weather are driven by the rate at which the Earth’s and Sun’s magnetic fields connect, or merge, and not by the solar wind’s electric field as was previously assumed. The merging occurs at a spot between the Earth and Sun, roughly 40,000 miles above the planet’s surface, and appears fundamental to the circulation of particles and magnetic fields throughout near-Earth space.
Researchers at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and the Air Force Research Laboratory at Hanscom Air Force Base (Massachusetts) will announce the results of their study at the Fall American Geophysical Union Meeting in San Francisco on Dec. 11. The researchers, led by Patrick Newell of APL, have developed a formula that describes the merging rate of the magnetic field lines and predicts 10 different types of near-Earth space weather activity, such as the aurora and magnetic disturbances.
“Having this formula is a big step forward for understanding how the Sun and Earth interact,” says Newell. And that understanding could help predict the space weather that affects communications, navigation, and the health of humans in space.
The space between the Earth and Sun is not empty, but filled with energetic particles, most of which are generated in the solar atmosphere. Temperatures of a few million degrees accelerate a stream of these particles, called the solar wind, to roughly one million miles per hour. Space weather scientists had long assumed that near-Earth space weather phenomena could best be predicted by the behavior of the solar wind electric field. However, Newell and his colleagues were the first to put this theory to a rigorous test with many data sets from a number of years.

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