Interazione tra vento solare e geomagnetismo: gli effetti sulla propagazione

Tempo fa mi è capitato sott'occhio un bell'articolo scritto nel 2005 da Paul Harden, NA5N in cui vengono spiegati molto bene i meccanismi di interazione tra il campo magnetico terrestre e il vento solare. Quando il secondo si anima a causa del verificarsi di grossi eventi come i brillamenti o i buchi coronali, i livelli di ionizzazione della ionosfera e le condizioni geomagnetiche subiscono pesanti condizionamenti, che a loro volta incidono sulla propagazione delle onde medie e corte. Come suggerisce Harden, non tutte le tempeste solari vengono però per nuocere: il periodo di tempo di 24-48 tra l'esplosione di un brillamento e l'arrivo a terra della relativa onda d'urto, può essere molto positivo per chi sta dando la caccia a un segnale radio molto lontano. Dal 2005 a oggi sono stati ulteriormente analizzati gli effetti della componente verticale (Bz) del campo magnetico interplanetario. Quando questo vettore punta molto a sud, il ricongiungimento delle linee del campo magnetico solare con quello terrestre provoca forti flussi di corrente e condizioni geomagnetiche particcolarmente instabili, con cattiva propagazione. Proprio per questo motivo l'andamento di Bz oggi viene sorvegliato dagli appassionati che cercano di improvvisarsi "meteorologi spaziali".

Potete scaricare qui l'articolo di Harden, mentre qui (tra le varie fonti disponibili) troverete i dati sul vento solare e l'orientamento del vettore Bz. I momenti più favorevoli sono quelli immediatamente successivi a un brillamento e in presenza di angoli positivi per Bz.

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.

Tempeste solari, la termosfera diventa una centrale elettrica

Nel corso del forte periodo di attività solare dell'inizio del mese, caratterizzato da episodi di eiezione di massa coronale, la nostra termosfera, lo strato più elevato dell'atmosfera, avrebbe assorbito una energia pari a quella necessaria per alimentare l'intera rete elettrica di New York per un paio d'anni (peccato non poterla sfruttare). La NASA ha realizzato un breve ma istruttivo filmato su fenomeni destinati sicuramente ad aumentare da qui al 2013-14, periodo per cui è previsto il massimo del ciclo solare attualmente in corso.

Qui l'originale dell'articolo appena pubblicato, con i rimandi ai dati misurati dal programma SABER (radiometria all'infrarosso), uno dei quattro strumenti del satellite TIMED che studia la dinamica di termosfera, mesosfera e ionosfera.

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."

Ciclo solare 24, un massimo sotto quota 90

Nuove previsioni per sull'andamento del ciclo solare numero 24. Il picco dovrebbe arrivare nel 2013 e sarà molto basso (numero di macchie intorno al 90, poco sopra il 78 raggiunto nel massimo del 1928). Questo non deve far sembrare che il sole attuale non possa essere "pericoloso", perché eventi come tempeste solari, brillamenti, eiezioni e relative conseguenze geomagnetiche sono spesso non correlati all'intensità del ciclo. I danni che le infrastrutture elettriche e di telecomunicazioni subiscono in caso di perturbazioni geomagnetiche molto intense posso costare un sacco di soldi.

New Solar Cycle Prediction
05.29.2009


May 29, 2009: An international panel of experts led by NOAA and sponsored by NASA has released a new prediction for the next solar cycle. Solar Cycle 24 will peak, they say, in May 2013 with a below-average number of sunspots. "If our prediction is correct, Solar Cycle 24 will have a peak sunspot number of 90, the lowest of any cycle since 1928 when Solar Cycle 16 peaked at 78," says panel chairman Doug Biesecker of the NOAA Space Weather Prediction Center.
It is tempting to describe such a cycle as "weak" or "mild," but that could give the wrong impression.
"Even a below-average cycle is capable of producing severe space weather," points out Biesecker. "The great geomagnetic storm of 1859, for instance, occurred during a solar cycle of about the same size we’re predicting for 2013."
The 1859 storm--known as the "Carrington Event" after astronomer Richard Carrington who witnessed the instigating solar flare--electrified transmission cables, set fires in telegraph offices, and produced Northern Lights so bright that people could read newspapers by their red and green glow. A recent report by the National Academy of Sciences found that if a similar storm occurred today, it could cause $1 to 2 trillion in damages to society's high-tech infrastructure and require four to ten years for complete recovery. For comparison, Hurricane Katrina caused "only" $80 to 125 billion in damage.
The latest forecast revises an earlier prediction issued in 2007. At that time, a sharply divided panel believed solar minimum would come in March 2008 followed by either a strong solar maximum in 2011 or a weak solar maximum in 2012. Competing models gave different answers, and researchers were eager for the sun to reveal which was correct. "It turns out that none of our models were totally correct," says Dean Pesnell of the Goddard Space Flight Center, NASA's lead representative on the panel. "The sun is behaving in an unexpected and very interesting way."
Researchers have known about the solar cycle since the mid-1800s. Graphs of sunspot numbers resemble a roller coaster, going up and down with an approximately 11-year period. At first glance, it looks like a regular pattern, but predicting the peaks and valleys has proven troublesome. Cycles vary in length from about 9 to 14 years. Some peaks are high, others low. The valleys are usually brief, lasting only a couple of years, but sometimes they stretch out much longer. In the 17th century the sun plunged into a 70-year period of spotlessness known as the Maunder Minimum that still baffles scientists.
Right now, the solar cycle is in a valley--the deepest of the past century. In 2008 and 2009, the sun set Space Age records for low sunspot counts, weak solar wind, and low solar irradiance. The sun has gone more than two years without a significant solar flare. "In our professional careers, we've never seen anything quite like it," says Pesnell. "Solar minimum has lasted far beyond the date we predicted in 2007."
In recent months, however, the sun has begun to show timorous signs of life. Small sunspots and "proto-sunspots" are popping up with increasing frequency. Enormous currents of plasma on the sun’s surface ("zonal flows") are gaining strength and slowly drifting toward the sun’s equator. Radio astronomers have detected a tiny but significant uptick in solar radio emissions. All these things are precursors of an awakening Solar Cycle 24 and form the basis for the panel's new, almost unanimous forecast.
According to the forecast, the sun should remain generally calm for at least another year. From a research point of view, that's good news because solar minimum has proven to be more interesting than anyone imagined. Low solar activity has a profound effect on Earth’s atmosphere, allowing it to cool and contract. Space junk accumulates in Earth orbit because there is less aerodynamic drag. The becalmed solar wind whips up fewer magnetic storms around Earth's poles. Cosmic rays that are normally pushed back by solar wind instead intrude on the near-Earth environment. There are other side-effects, too, that can be studied only so long as the sun remains quiet.
Meanwhile, the sun pays little heed to human committees. There could be more surprises, panelists acknowledge, and more revisions to the forecast. "Go ahead and mark your calendar for May 2013," says Pesnell. "But use a pencil."

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

I rischi delle tempeste solari in uno studio della NASA

La NASA ha finanziato uno studio che analizza il possibile impatto delle avverse condizioni della "meteorologia spaziale" (le tempeste solari e le relative turbolenze ionosferiche) sulle infastrutture e altre tecnologie sulla terra (in particolare le reti di comunicazione e distribuzione dell'energia). L'impatto può avere serie conseguenze economiche e sulla qualità della vita di chi da quelle infrastrutture dipende. Lo studio è stato effettuato dalla National Academy of Science.

NASA-FUNDED STUDY REVEALS HAZARDS OF SEVERE SPACE WEATHER

WASHINGTON -- A NASA-funded study describes how extreme solar eruptions could have severe consequences for communications, power grids and other technology on Earth. The National Academy of Sciences in Washington conducted the study.

The resulting report provides some of the first clear economic data that effectively quantifies today's risk of extreme conditions in space driven by magnetic activity on the sun and disturbances in the near-Earth environment. Instances of extreme space weather are rare and are categorized with other natural hazards that have a low frequency but high consequences. "Obviously, the sun is Earth's life blood," said Richard Fisher, director of the Heliophysics division at NASA Headquarters in Washington. "To mitigate possible public safety issues, it is vital that we better understand extreme space weather events caused by the sun's activity."
Besides emitting a continuous stream of plasma called the solar wind, the sun periodically releases billions of tons of matter called coronal mass ejections. These immense clouds of material, when directed toward Earth, can cause large magnetic storms in the magnetosphere and upper atmosphere. Such space weather can affect the performance and reliability of space-borne and ground-based technological systems.
Space weather can produce solar storm electromagnetic fields that induce extreme currents in wires, disrupting power lines, causing wide-spread blackouts and affecting communication cables that support the Internet. Severe space weather also produces solar energetic particles and the dislocation of the Earth's radiation belts, which can damage satellites used for commercial communications, global
positioning and weather forecasting. Space weather has been recognized as causing problems with new technology since the invention of the telegraph in the 19th century.
A catastrophic failure of commercial and government infrastructure in space and on the ground can be mitigated through raising public awareness, improving vulnerable infrastructure and developing advanced forecasting capabilities. Without preventive actions or plans, the trend of increased dependency on modern space-weather sensitive assets could make society more vulnerable in the future.
NASA requested the study to assess the potential damage from significant space weather during the next 20 years. National and international experts from industry, government and academia participated in the study. The report documents the possibility of a space weather event that has societal effects and causes damage
similar to natural disasters on Earth. "From a public policy perspective, it is quite significant that we have begun the extremely challenging task of assessing space weather impacts in a quantitative way," said Daniel Baker, professor and director of the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. Baker chaired the panel that prepared the report.
"Whether it is terrestrial catastrophes or extreme space weather incidents, the results can be devastating to modern societies that depend in a myriad of ways on advanced technological systems," said Baker. "We were delighted that NASA helped support bringing together dozens of world experts from industry and government to share their experiences and begin planning of improved public policy strategies."
The sun is currently near the minimum of its 11-year activity cycle. It is expected that solar storms will increase in frequency and intensity toward the next solar maximum, expected to occur around 2012.
The Heliophysics Division of NASA's Science Mission Directorate in Washington provided funding for the study. The division seeks to understand the sun, its solar processes and the interaction of solar plasma and radiation with Earth, other planets and the universe. Understanding the connections between the sun and its planets will allow better prediction on the impacts of solar activity on humans,
technological systems and even the presence of life itself in the universe.
The National Academies are chartered by Congress to provide independent technical and scientific advice to the federal government. For images related to the study and more information about the Heliophysics Division, visit:
http://nasascience.nasa.gov/heliophysics
To view the National Academy of Sciences' complete report, visit:
http://www.nap.edu/catalog/12507.html

Una strana smagliatura nella magnetosfera terrestre

Lo scorso anno le sonde della missione THEMIS con le loro misure hanno fatto una scoperta eccezionale proprio mentre stavano attraversando la linea di confine dove il vento solare interagisce con la magnetosfera terrestre. La missione THEMIS è stata concepita dalla NASA proprio per studiare questo tipo di interazioni, mettendo in evidenza i meccanismi che finiscono per generare fenomeni come la aurore boreali.
La scoperta consiste in una estesa smagliatura nel campo magnetico che avvolge la terra, un evento che ha stupito gli scienziati non tanto per il fatto in sé (queste smagliature sono all'ordine del giorno), ma per le modalità di comparsa. Finora si credeva che la magnetosfera si "allentasse" quando si trovava a interagire, nell'emisfero settentrionale, con un vento solare il cui campo puntasse verso sud. Questa regola, finora, era stata ferrea, ma le sonde THEMIS hanno misurato la smagliatura in una situzione del tutto opposta: con il campo sul fronte del vento solare che puntava a nord (la teoria voleva che un campo così orientato avrebbe dovuto rinforzare, non indebolire, il campo terrestre).
Quali conseguenze potrebbe avere questa scoperta? Quando nella magnetosfera si aprono questi squarci, il vento solare la carica come una pila. Una pila pronta a scatenare gli eventi aurorali quando il vento solare subisce le sue improvvise accelerazioni o in presenza di eventi coronali eiettivi. E' come se un forte colpo di frusta rompesse il vaso riempito di vento solare. Ora i fisici cominciano ad associare questa nuova osservazione con un'altra circostanza: durante i cicli solari di numero pari, come questo ciclo 24, il fronte del vento solare è orientato comunemente verso nord. Se un vento di questo tipo può "sfondare" facilmente la magnetosfera, dicono gli scienziati, ci si può aspettare eventi molto intensi nel corso delle tempeste che caratterizzeranno questo ciclo.

A Giant Breach in Earth's Magnetic Field

12.16.2008

Dec. 16, 2008: NASA's five THEMIS spacecraft have discovered a breach in Earth's magnetic field ten times larger than anything previously thought to exist. Solar wind can flow in through the opening to "load up" the magnetosphere for powerful geomagnetic storms. But the breach itself is not the biggest surprise. Researchers are even more amazed at the strange and unexpected way it forms, overturning long-held ideas of space physics.
"At first I didn't believe it," says THEMIS project scientist David Sibeck of the Goddard Space Flight Center. "This finding fundamentally alters our understanding of the solar wind-magnetosphere interaction."
The magnetosphere is a bubble of magnetism that surrounds Earth and protects us from solar wind. Exploring the bubble is a key goal of the THEMIS mission, launched in February 2007. The big discovery came on June 3, 2007, when the five probes serendipitously flew through the breach just as it was opening. Onboard sensors recorded a torrent of solar wind particles streaming into the magnetosphere, signaling an event of unexpected size and importance.
"The opening was huge—four times wider than Earth itself," says Wenhui Li, a space physicist at the University of New Hampshire who has been analyzing the data. Li's colleague Jimmy Raeder, also of New Hampshire, says "1027 particles per second were flowing into the magnetosphere—that's a 1 followed by 27 zeros. This kind of influx is an order of magnitude greater than what we thought was possible."
The event began with little warning when a gentle gust of solar wind delivered a bundle of magnetic fields from the Sun to Earth. Like an octopus wrapping its tentacles around a big clam, solar magnetic fields draped themselves around the magnetosphere and cracked it open. The cracking was accomplished by means of a process called "magnetic reconnection." High above Earth's poles, solar and terrestrial magnetic fields linked up (reconnected) to form conduits for solar wind. Conduits over the Arctic and Antarctic quickly expanded; within minutes they overlapped over Earth's equator to create the biggest magnetic breach ever recorded by Earth-orbiting spacecraft.

(a sinistra) A computer model of solar wind flowing around Earth's magnetic field on June 3, 2007; white arrows trace the extent of the breach. The model is based on actual measurements made by the THEMIS probes. Background colors represent solar wind density; red is high density, blue is low. Note the layer of relatively dense material beneath the tips of the white arrows; that is solar wind entering Earth's magnetic field through the breach.

The size of the breach took researchers by surprise. "We've seen things like this before," says Raeder, "but never on such a large scale. The entire day-side of the magnetosphere was open to the solar wind."
The circumstances were even more surprising. Space physicists have long believed that holes in Earth's magnetosphere open only in response to solar magnetic fields that point south. The great breach of June 2007, however, opened in response to a solar magnetic field that pointed north.
"To the lay person, this may sound like a quibble, but to a space physicist, it is almost seismic," says Sibeck. "When I tell my colleagues, most react with skepticism, as if I'm trying to convince them that the sun rises in the west."
Here is why they can't believe their ears: The solar wind presses against Earth's magnetosphere almost directly above the equator where our planet's magnetic field points north. Suppose a bundle of solar magnetism comes along, and it points north, too. The two fields should reinforce one another, strengthening Earth's magnetic defenses and slamming the door shut on the solar wind. In the language of space physics, a north-pointing solar magnetic field is called a "northern IMF" and it is synonymous with shields up!
"So, you can imagine our surprise when a northern IMF came along and shields went down instead," says Sibeck. "This completely overturns our understanding of things."
Northern IMF events don't actually trigger geomagnetic storms, notes Raeder, but they do set the stage for storms by loading the magnetosphere with plasma. A loaded magnetosphere is primed for auroras, power outages, and other disturbances that can result when, say, a CME (coronal mass ejection) hits.
The years ahead could be especially lively. Raeder explains: "We're entering Solar Cycle 24. For reasons not fully understood, CMEs in even-numbered solar cycles (like 24) tend to hit Earth with a leading edge that is magnetized north. Such a CME should open a breach and load the magnetosphere with plasma just before the storm gets underway. It's the perfect sequence for a really big event."
Sibeck agrees. "This could result in stronger geomagnetic storms than we have seen in many years."

Elettrone staffetta, protoni solari in arrivo

Un semplice ma efficace metodo statistico per anticipare, non foss'altro che per qualche decina di minuti, l'arrivo delle tempeste solari particellari, quelle che in caso di fenomeni particolarmente intensi come le eiezioni coronali vedono il sole trasformarsi in una mitragliatrice di elettroni, protoni e interi atomi ionizzati, i più temuti. Per gli astronauti al lavoro fuori dalla copertura protettiva del campo magnetico terrestre, essere investiti da queste particelle può rappresentare un serio rischio per la salute. Ora sembra che grazie ai dati raccolti dagli analizzatori di particelle del satellite del progetto SOHO, Arik Posner, un ricercatore che lavora per la NASA, sia appunto riuscito a sviluppare una tecnica predittiva che partendo dalla prima avanguardia degli elettroni (che essendo più leggeri possono precedere di parecchio l'arrivo degli ioni), riesce a valutare le possibilità di tempeste più intense, lanciando un allarme che darebbe agli astronauti il tempo di mettersi al riparo e agli operatori dei satelliti, la possibilità di mettere in standby gli strumenti più sensibili. Posner ha verificato la validità delle sue matrici predittive analizzando i dati degli ultimi anni e ogni volta le sue simulazioni riuscivano ad anticipare di diversi minuti (fino a 74) i temibili "proton event". Considerando gli effetti di queste particelle pesanti sulla ionosfera, forse sarebbe possibile trarre qualche indicazione utile anche per l'ascolto, al suolo, di stazioni particolarmente difficili.

The Ions are Coming!
05.25.2007

A scientist using the Solar and Heliospheric Observatory (SOHO) has found a way to forecast solar radiation storms. The new method offers as much as one hour advance warning, giving astronauts time to seek shelter and ground controllers time to safeguard their satellites when a storm is approaching.
"Solar radiation storms are notoriously difficult to predict—they often take us by surprise," says physicist Arik Posner who developed the technique. "But now we've found a way to anticipate these events." Posner is a member of the research staff of the Southwest Research Institute in San Antonio, Texas; he also works at NASA Headquarters in Washington, DC. His study, Up to one-Hour Forecasting of Radiation Hazards from Solar Energetic Ion Events, appears in the journal Space Weather.
Solar radiation storms are swarms of electrons, protons and heavy ions accelerated to high speed by explosions on the sun. Here on Earth we are protected from these particles by our planet's atmosphere and magnetic field. Astronauts in Earth orbit are fairly safe, too; Earth's magnetic field extends out far enough to shield them. The danger begins when astronauts leave this protective cocoon. The Moon and Mars, for instance, have no global magnetic fields, and "astronauts working on the surface of those worlds could be at risk," says Posner.
"A one hour warning would reduce the odds of an astronaut being caught in a solar storm outside of a lunar habitat, where astronauts are most vulnerable," notes Francis Cucinotta, chief scientist for NASA's Space Radiation Program.
Spacecraft and satellites would also benefit. Subatomic particles striking CPUs and other electronics can cause onboard computers to suddenly reboot or issue nonsense commands. If, say, a satellite operator knows that a storm is coming, he can put his craft in a protective "safe mode" until the storm passes.
The type of particle most feared by astronaut safety experts is the ion, that is, an atom which has lost one or more of its charge-balancing electrons. "Energetic ions can damage tissue and break strands of DNA, causing health problems ranging from nausea to cataracts to cancer," says Cucinotta.
So the goal is to predict when the ions will arrive. The key to that, it turns out, is electrons. "Electrons are always detected ahead of the more dangerous ions," says Posner. This has been known for years, but only recently has Posner's research turned the "electrons first" aspect of radiation storms into a tool for forecasting.
Every radiation storm is a mix of electrons, protons and heavier ions. The electrons, being lighter and faster than the others, race out ahead. They are like heralds proclaiming the ions are coming! Posner realized that by measuring the "rise time and intensity of the initial electron surge" he could tell how many ions were following and when they would arrive.
The key to the breakthrough was the COSTEP instrument onboard SOHO. COSTEP is short for "Comprehensive Suprathermal and Energetic Particle Analyzer." Essentially, the device counts particles coming from the sun and measures their energies.
Posner looked at hundreds of radiation storms recorded by COSTEP between 1996 and 2002, and he was able to construct an empirical, predictive matrix: "Plug electron data into the matrix, and an ion forecast pops out."
The next step was to test his results. He decided to try out the matrix on COSTEP data gathered in 2003, a year he hadn't yet analyzed and which formed no part of the matrix itself. "I applied the matrix to the electron data; it successfully predicted all four major ion storms of 2003 with advance warnings ranging from 7 to 74 minutes."
Posner says the method is not yet perfect. He points out, for instance, the brief seven minute warning for one storm in 2003. "I'd like to improve that," he says. "The matrix also generated three false alarms for 2003—that is, storm alerts followed by weak storms or no storms at all." In those few cases, astronauts would have dashed to safety unnecessarily.
Improvements will come as Posner works his way through even more of COSTEP's rich dataset: "Launched with SOHO in 1995, COSTEP has been operating through an entire solar cycle including the solar maximum in 2001—and it is still going strong," says Prof. Bernd Heber, COSTEP's principle investigator at the University of Kiel in Germany.
The method is currently being considered by planners at the Johnson Space Center in their design of future lunar missions. "Posner's technique reduces the odds of exposure by more than 20 percent compared to current methods, allowing astronauts to venture farther from their outpost," says Cucinotta. "That's good news for both science and exploration."
(http://science.nasa.gov/headlines/y2007/25may_costep.htm?list863652)

Pochi consensi sul ciclo solare numero 24

Mentre la macchia solare 953 continua il suo percorso apparente (è il sole che sta girando sul proprio asse) verso il centro del disco, portando con sé un potenziale di brillamenti e tempeste geomagnetiche per i prossimi giorni, gli scienziati si sono riuniti a Boulder, in Colorado, per discutere delle previsioni relative al prossimo ciclo solare, il numero 24, che dovrebbe iniziare il prossimo marzo per raggiungere il suo picco verso il 2011 (quando probabilmente non ci saranno più molte stazioni in onde corte locali da ascoltare). C'è chi pensa che sarà molto intenso, ma come sempre le proiezioni sono alquanto variabili.

This week in Boulder, Colorado, a group of leading solar physicists met to compare and discuss their predictions for the next solar maximum. On April 25th they held a press conference and announced ... a split decision. One camp holds that Solar Cycle 24 will be intense and peak in 2011; a second group predicts a much weaker maximum in 2012. As a community, solar physicists are still undecided on the best way to predict solar activity. The plot is a summary of 40 different forecasts, none of which agree in detail. The confusion won't last forever. As Cycle 24 unfolds, the sun itself will tell us which is correct.
Researchers were able to agree on one thing: Solar activity is entering a period of deep minimum. Based on declining sunspot numbers and other factors, the cycle should hit rock bottom in March 2008 plus or minus six months.

Questo è il testo parziale del comunicato stampa rilasciato dopo l'incontro cui si riferiva la notizia apparsa oggi su Spaceweather.com. Un approfondimento della notizia si può leggere su Science Daily di ieri.

NEXT SOLAR STORM CYCLE WILL START LATE

Experts Split Over Intensity

The next 11-year cycle of solar storms will most likely start next March and peak in late 2011 or mid-2012 – up to a year later than expected – according to a forecast issued today by NOAA’s Space Environment Center in coordination with an international panel of solar experts.
Expected to start last fall, the delayed onset of Solar Cycle 24 stymied the panel and left them evenly split on whether a weak or strong period of solar storms lies ahead, but neither group predicts a record-breaker. The Space Environment Center led the prediction panel and issued the forecast at its annual Space Weather Workshop in Boulder. NASA sponsored the panel.
“The Space Environment Center’s space weather alerts, warnings, and forecasts are a critical component of NOAA’s seamless stewardship of the Earth’s total environment, from the Sun to the sea,” said retired Vice Adm. Conrad C. Lautenbacher, Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator.
During an active solar period, violent eruptions occur more often on the Sun. Solar flares and vast explosions, known as coronal mass ejections, shoot energetic photons and highly charged matter toward Earth, jolting the planet’s ionosphere and geomagnetic field, potentially affecting power grids, critical military and airline communications, satellites, Global Positioning System signals, and even threatening astronauts with harmful radiation. These same storms illuminate night skies with brilliant sheets of red and green known as auroras, or the northern or southern lights.
Solar cycle intensity is measured in maximum number of sunspots – dark blotches on the Sun that mark areas of heightened magnetic activity. The more sunspots there are, the more likely it is that major solar storms will occur.
In the cycle forecast issued today, half of the panel predicts a moderately strong cycle of 140 sunspots, plus or minus 20, expected to peak in October of 2011. The other half predicts a moderately weak cycle of 90 sunspots, plus or minus 10, peaking in August of 2012. An average solar cycle ranges from 75 to 155 sunspots. The late decline of Cycle 23 has helped shift the panel away from its earlier leaning toward a strong Cycle 24. Now the group is evenly split between strong and weak.
“By giving a long-term outlook, we’re advancing a new field—space climate—that’s still in its infancy,” said retired Air Force Brig. Gen. David L. Johnson, director of NOAA’s National Weather Service. “Issuing a cycle prediction of the onset this far in advance lies on the very edge of what we know about the Sun.”
Scientists have issued cycle predictions only twice before. In 1989, a panel met to predict Cycle 22, which peaked that same year. Scientists met again in September of 1996 to predict Cycle 23—six months after the cycle had begun. Both groups did better at predicting timing than intensity, according to Space Environment Center scientist Douglas Biesecker, who chairs the current panel. He describes the group’s confidence level as “high” for its estimate of a March 2008 onset and “moderate” overall for the two estimates of peak sunspot number and when those peaks would occur.
One disagreement among the current panel members centers on the importance of magnetic fields around the Sun’s poles as the previous cycle decays. End-cycle polar fields are the bedrock of the approach predicting a weak Cycle 24. The strong-cycle forecasters place more importance on other precursors extending over a several-cycle history. Another clue will be whether Cycle 24 sunspots appear by mid 2008. If not, the strong-cycle group might change their forecast.
The first year after solar minimum, marking the end of Cycle 23, will provide the information scientists need to arrive at a consensus. NOAA and the panel decided to issue their best estimate now and update the forecast as the cycle progresses, since Space Environment Center customers have been requesting a forecast for over a year.
“The panelists in each camp have clear views on why they believe in their prediction, why they might be wrong, and what it would take to change their minds,” said Biesecker. “We’re on the verge of understanding and agreeing on which precursors are most important in predicting future solar activity.”