Il ciclo solare numero 24 vicinissimo al massimo. Mai così debole nell'ultimo secolo.

Da un po' di tempo la stampa generalista di tutto il mondo si occupa molto di attività solare. Un interesse che dal punto di vista giornalistico non trovo del tutto giustificato, ma che non può che farmi piacere. Un recente articolo del Wall Street Journal, "Strange doings on the sun" ha ispirato moltissime altre testate a occuparsi del massimo del ciclo solare in corso - il 24esimo nella numerazione degli scienziati solari. Un massimo molto "minimo", addirittura il meno intenso registrato dai primi del novecento a oggi. Il segno distintivo di un massimo solare non è solo rappresentato dal numero di macchie che appaiono sulla superficie della stella, ma da un fenomeno magnetico massivo che investe la polarità del campo magnetico del sole. Ogni undici anni circa questa polarità si inverte e i poli geografici cambiano il segno magnetico. La prima notizia dell'imminenza di questo "rivoltamento" è arrivata alla fine di agosto dalla NASA, che ha prodotto anche un filmato illustrativo:

Il sole è talmente esteso rispetto a noi, che il meccanismo di inversione della polarità, la cosiddetta dinamo solare, non procede in modo repentino e uniforme. Ai due poli magnetici del sole il cambio avviene fuori sincrono e in un arco di tempo che può durare più di un anno. In questo momento, per esempio, il polo nord ha già cambiato la sua polarità magnetica e il sole si trova a essere una strana combinazione di due monopoli fusi insieme (la compensazione avviene sommando tutti i fenomeni su scala locale). Ma secondo la NASA ci sono tutti i segni di un possibile completamento del processo da qui alle prossime settimane. Nel periodo di inversione si verificano turbolenti cambiamenti anche nel "lenzuolo" di corrente elettrica generata dal movimento del sole immerso nel suo campo e questa corrente a sua volta può interagire con il sistema terrestre. Alcuni ipotizzano anche possibili influssi sul nostro clima, che in questo caso potrebbero anche compensare, in parte (anche se non arrestare), il surriscaldamento globale.

Per chi ascolta la radio l'attività solare e il suo influsso sulla ionosfera è molto importante anche su scale temporali molto brevi, la regola generale è che la propagazione sulle frequenze più alte delle onde corte può trarre molti benefici dalla forte attività, mentre viceversa un sole tranquillo è più amico dei segnali che si propagano nelle frequenze basse e nelle onde medie.

Un volo ai raggi X. L'importanza degli strumenti predittivi solari per la salute dei piloti.

È un fatto poco apprezzato ma il mestiere del pilota di linea non è più rischioso degli altri solo perché l'aereo non tocca terra. Un fattore di rischio assolutamente non trascurabile è quello dovuto alla radiazione cosmica e solare che i passeggeri di un'areo possono assorbire a più di diecimila metri di quota. I piloti sono più esposti, ovviamente, ed è per questo che la loro professione viene classificata tra quelle soggette a "radiation hazard", esattamente come avviene per i lavoratori delle centrali nucleari, o negli ambulatori radiologici degli ospedali. Si calcola che nell'arco di un solo volo transpolare come il Washington-Pechino, i piloti assorbono l'equivalente di un paio di schermografie al petto. Un passeggero frequent-flyer da centomila miglia di diario di viaggio, equivale a un paziente con 20, sì venti, schermografie ai raggi X.

Come spiega la NASA in questo articolo, diventano fondamentali i modelli che consentano di valutare quali sono i livelli di intensità della componente più variabile di questa radiazione, cioè quella solare, in modo da fornire a piloti e compagnie aeree uno strumento per modificare le loro rotte in funzione dei percorsi meno esposti, soprattutto in caso di forti brillamenti e di episodi di eiezione di massa coronale dal sole. Uno strumento di questo tipo è il NAIRAS o "Nowcast of Atmosphere Ionizing Radiation for Aviation Safety", che pubblica regolarmente sul proprio sito le mappe dei livelli di radiazione alle diverse quote e in proiezione intorno al polo nord.

The FAA classifies pilots as "occupational radiation workers."  Flying high above Earth with little atmosphere to protect them, they can absorb significant doses of cosmic rays and solar radiation. During a typical polar flight from Chicago to Beijing, for instance, a pilot is exposed to the equivalent of two chest x-rays.  Multiplied over the course of a career, this can cause problems such as increased risk of cancer and possibly cataracts.

Passengers have reason to be concerned, too.

"A 100,000 mile frequent flyer gets about 20 chest x-rays," points out Chris Mertens, a senior research scientist at NASA Langley Research Center. "This is true regardless of the latitude of the flights."

It’s worth noting that even people on the ground absorb some radiation.  Cosmic rays and their by-products are so powerful, they can reach all the way down to Earth’s surface, giving a person at sea level the equivalent of one chest x-ray every 10 days or so.

On a plane, however, dose rates increase 10-fold or more.  The exposure depends on factors ranging from the altitude and latitude of the flight path (polar routes are irradiated most) to sunspot counts and solar activity (a powerful solar storm can boost radiation levels a hundredfold).  To help airline companies safeguard passengers and personnel, NASA is developing an experimental tool to predict exposures in real time.  Mertens is the PI of the system, called NAIRAS--short for "Nowcast of Atmosphere Ionizing Radiation for Aviation Safety."

(continua)

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.

Tempeste solari: tutta la meteorologia in una app

Ora che l'attività solare è tornata a fare notizia con i brillamenti e le eiezioni di massa coronale che caratterizzano la rampa in salita del ciclo 24, è decisamente il tempo di attrezzarsi al meglio per usufruire di tutte le informazioni che Internet riserva all'appassionato di "meteorologia spaziale". Parecchi siti istituzionali e hobbystici contengono una marea di dati generati dalle osservazioni al suolo e soprattutto da quelle orbitali. I lettori di questo blog cononsceranno le risorse messe per esempio a disposizione dalla NASA, dalla NOAA americana, dal belga Solar Influences Data Analysis Center, dall'australiano IPS Ionospheric Prediction Service, dai radioamatori di SolarHam, il progetto congiunto ESA/NASA, Helioviewer e anche dagli italiani del CNR con il sito di previsione ionosferica GIFINT. Ma in epoca di smartphone queste stesse informazioni cominciano a essere accessibili anche sottoforma di app.

Io per esempio conoscevo Sun Viewer (oggi "NASA Space Weather Media Viewer") e 3D Sun, che visualizza in tempo reale i dati provenienti dalle sonde in orbita eliocentrica STEREO. Francesco Clemente, che ringrazio, mi ha segnalato la recente uscita NASA SWx, una potente applicazione iPhone che permette di accedere a una vasta quantità di grafici osservativi e predittivi riferiti a sole, eliosfera, magnetosfera, ionosfera e superficie planetaria. Il programma viene descritto in dettaglio in questa recensione apparsa sul sito dell'Istituto di astrofisica di Trieste, l'INAF. L'applicazione è disponibile per iPhone e per Android. Girellando per l'iTunes Store ho trovato anche una app, SWx Monitor, del coreano Space Environment Lab, più condensata nelle sue informazioni ma altrettanto utile. Il difetto di tutte queste app, che hanno il grosso vantaggio di essere tutte gratuite, è quello di dare praticamente per scontato tutta la teoria che c'è dietro la meteorologia spaziale, la fisica delle macchie, del magnetismo e del vento solari, l'interazione tra il vento solare e la magnetosfera terrestre, le dinamiche della ionosfera. Una teoria che da sola non potremmo condensare nemmeno in tre corsi di laurea, ma merita di essere divulgata. Fa eccezione 3D Sun, che visualizza anche qualche notizia e qualche spiegazione. Per fortuna su Web si trovano parecchie risorse, come lo Space Weather Primer preparato dalla NOAA, lo Space Weather Center della NASA, l'eccellente sezione Education dell'IPS australiano. Restano i collegamenti tra la meteorologia spaziale e la propagazione delle onde radio, materia studiata dai radioamatori e dai DXer. Ma il discorso sarebbe molto lungo e per nulla conclusivo.

Solar Orbiter, nel 2017 mai così vicino al sole

Il Solar Terrestrial Center of Excellence belga, una delle mie fonti informative sull'attività solare misurata da osservatori europei, ha portato a termine un restyling della sua periodica newsletter a periodicità circa settimanale. Oggi la pubblicazione si presenta come una piccola rivista con articoli e fotografie. La neswletter è accessibile dal sito dove è possibile anche consultare l'archivio e si può visualizzare nel browser o in formato PDF. Uno dei primi articoli riguarda la missione Solar Orbiter, scelta recentemente dall'ESA insieme a Euclid (la missione che studierà la materia oscura) per caratterizzare i piani esplorativi dell'Ente spaziale europeo nel decennio 2015-2025. Il Solar Orbiter dovrebbe essere lanciato da un vettore Atlas della NASA nel 2017 con l'obiettivo di inserire in una orbita solare mai tanto ravvicinata (0,22 UA al perielio) una sonda in grado di visualizzare i poli del nostro astro e soprattutto di studiarne l'atmosfera e le emissioni di vento solare. Un piano molto ambizioso che utilizzerà strumenti di assoluta avanguardia come l'Extreme Ultraviolet Imager, una suite di tre telescopi EUV trasportati a bordo della sonda, insieme a tanti altri laboratori di misura. Sempre a proposito di dati solari, un'altra risorsa europea è il portale continentale di meteorologia spaziale.

Sole e clima, le possibili conseguenze di Maunder

Archiviato il ciclo solare numero 23, siamo ormai entrati ufficialmente nel numero 24, ma il sole è ben lontano dall'essere pirotecnico. Anzi, i modelli che cercano di prevedere l'andamento del ciclo producono risultati rivisti costantemente al ribasso. All'inizio di gennaio il Marshall Space Flight Center della NASA ha pubblicato le ultime stime e se i fatti le confermeranno ci troviamo indiscutibilmente in un "minimo di Maunder", una condizione solare caratterizzata da un numero di macchie estremamente basso. Secondo la NASA il picco del ciclo 24 si raggiungerà nel giugno del 2013 e avrà un numero massimo "normalizzato" di sole 59 macchie, contro al valore superiore a 110 calcolato per il massimo del ciclo 23.

Ho trovato a questo proposito un commento sul blog americano di geopolitica Fabius Maximus, in cui queste stime vengono prese in esame alla luce dei potenziali effetti di raffreddamento del clima e di conseguente impatto sui prezzi agricoli:

Summary: Yesterday we asked if food prices will continue to rise, destabilizing the third world? Today we ask the same question, with the Sun as the suspect. This takes us to the frontier of science, beyond the cartoon certainties fed to us by the news media. This is un-news, hidden from the public as these uncertainties challenge the story of human-emitted CO2 as the driver of Earth’s climate. If the sun continues to slow, and if that cools our world, then the resulting cool phase will send food prices on a one-way trip to the moon, which will rock the world. But despite the confident assertions on many sceptic website, this remains just speculation. One of the many shockwaves (low probability, high inpact) scenarios for which we should prepare — but not panic.

Naturalmente la questione della correlazione tra ciclo solare e clima è lungi dall'essere risolta, ma gli scienziati ne discutono da tempo (il post di Fabius Maximus è ricco di riferimenti ad articoli, alcuni dei quali da me già citati in passato). Qui su RP interessano soprattutto le correlazioni, decisamente più strette, ampiamente dimostrate, ma mai del tutto spiegate e forse inspiegabili, tra attività solare, attività geomagnetica e propagazione dei segnali radio. Ma tutto quello che riguarda lo "space weather" esercita un enorme fascino.

Un posto (software) a due passi dal sole

Un incredibile strumento software (open source, multipiattaforma e disponibile anche in versione Web based) per accedere ai dati di imaging e astrofici sul nostro sole è stato rilasciato oggi dall'ESA. JHelioviewer è una spettacolare finestra aperta sul disco nel nostro astro, sia in tempo reale sia per quanto concerne i dati di un archivio alimentato da due missioni spaziali: l'ESA/NASA Solar and Heliospheric Observatory (SOHO) e il Solar Dynamics Observatory (SDO). Per molti si tratterà di immagini e informazioni assolutamente inedite, inserite in una interfaccia divulgativa che aiuterà a far luce sui misteri della meteorologia spaziale e di tanti fenomeni della fisica planetaria e della propagazione delle onde radio.

Il software (Windows, Mac e LInux/Java) può essere prelevato dal sito www.jhelioviewer.org o consultato nella versione Web all'indirizzo www.helioviewer.org

ESA offers a new way of looking at the Sun

14 Dec 2010

ESA has released interactive, open-source software that gives both scientists and the public an unprecedented insight into the ever-changing face of the Sun. JHelioviewer allows easy access to over 14 years worth of data from the ESA/NASA Solar and Heliospheric Observatory (SOHO) along with the latest information beaming back from NASA's Solar Dynamics Observatory (SDO).

The Sun has been under almost constant human surveillance from space since the SOHO mission was launched in December 1995. Since then, the space telescope has delivered a daily stream of 250MB of solar data back to researchers on Earth. With 12 instruments on board, probing every area of our star - from its interior out to the corona and the solar wind - SOHO has compiled a vast library of solar data. This solar opus is beginning to be complemented by SDO, which is returning 1.5TB of data per day. At 6000 times the data rate of SOHO, and containing a constant stream of high-resolution images of the Sun over 10 spectral channels, the volume of data from SDO has made it necessary to develop new ways of visualizing the data. This will be key in achieving SDO's goal of helping scientists understand how the Sun's magnetic field is generated and structured and how this stored magnetic energy is converted and released into the heliosphere.

The challenge is that with this vast and ever-growing forest of data it is hard to see the wood from the trees. "If you wanted to study a phenomenon in a specific region on the Sun on a certain day then you needed to download a large volume of data and calibrate it with the appropriate software. As part of a lengthy process you'd turn it into an animated sequence, that may or may not turn out to be useful," Daniel Müller, SOHO Deputy Project Scientist, explained. "JHelioviewer is a novel way of visually browsing the archive; you can quickly identify interesting stuff and then go and get the scientific data. It greatly speeds up the process," he added.

Developed as part of the ESA/NASA Helioviewer Project, JHelioviewer is an interactive, simple to use index of the data gleaned from fifteen years of watching the Sun from space. However, the true power of the tool lies in its ability to allow cross-referencing of different aspects of the large data sets; many events observed on the Sun are interconnected and occur over vastly different temporal and spatial scales. For the first time, JHelioviewer allows users to overlay series of images from the Sun, from different instruments, and compile an animated sequence, which they can then manipulate as they watch, in order to follow a solar event from start to finish.

"All solar scales are coupled: you have small scale phenomena tying into large scale events. We now have a unique tool to tackle this hierarchy of scales," said Müller. He went on to say: "Before, you could either see the large-scale corona, or small patches on the solar surface. But you've never had the option to overlay the two and zoom in and out as you watch the Sun's activity evolve."

In this marriage of scales lies fresh potential for scientists to tackle some of the most pressing issues in modern solar physics. With more than 14 years worth of SOHO data now easy to access, users can follow the Sun's changing activity over an entire 11-year solar cycle. Alternatively, the differential rotation of the Sun can be compensated for, allowing sunspots - indicators of solar activity cycles - to be tracked as they rotate across the solar surface. Researchers can also juxtapose images of the Sun's corona, from SOHO's LASCO coronagraph, with concurrent ultraviolet data of the lower corona, provided by the EIT instrument, and MDI measurements of the magnetic field on the solar surface. This can be done with the minimum of fuss, allowing more time for the links between coronal mass ejections (CMEs) and activity on the solar surface to be explored.

This leads on to the phenomenon of 'space weather': a term brought into everyday language through the pioneering work of SOHO over the last decade and a half. "JHelioviewer will help the search for the triggers or proxies that then translate into geomagnetic phenomena such as storms in Earth's magnetosphere," Müller suggested. Knowledge of such trigger mechanisms could allow Sun-watching scientists to give prior warning of such events, which have the potential to damage satellites and power grids.

And as well as opening up the Sun to solar researchers, JHelioviewer has already caught the eye of the wider scientific community. "We've already had discussions with the Mars Reconnaissance Orbiter team, as well as with the medical world, about how they might use the open-source software to analyse massive data sets in their own respective fields," Müller revealed.

However, the potential impact of JHelioviewer reaches out beyond the scientific community; the software has been specifically designed to be used by the non-expert as well. Interested members of the public have access to just the same data as the scientists and can use it to explore the Sun for themselves. "It puts millions of SOHO images at your fingertips. Anyone with a computer and internet access can use it to make a movie of how the Sun evolved over the last decade," pointed out Müller. "You could even see how the Sun looked on your birthday or Christmas; you can pick and choose whatever you like," he added.

JHelioviewer has been developed as part of the ESA/NASA Helioviewer Project (Principal Investigators: Daniel Müller (ESA), Jack Ireland (ADNET Systems, Inc. / NASA Goddard Space Flight Center)) by an interdisciplinary team of solar physicists and software developers. It is based on the JPEG 2000 image compression standard and written in Java and OpenGL. The server hosting the software and related JPEG 2000 files is located at the Solar Data Analysis Center (SDAC) at NASA's Goddard Space Flight Center.

The JHelioviewer software is available to download for several operating systems. It is complemented by the website Helioviewer.org, a web-based image browser.

Sole, l'eruzione magnetica è globale

Il primo di agosto di quest'anno si è verificata una eruzione solare che con l'aiuto dei dati raccolti dalla missione Solar Dynamics Observatory e dalle sonde gemelle della missione STEREO, è stata classificata tra le più peculiari finora registrate dall'uomo. Diversamente dalle teorie che volevano questi fenomeni abbastanza confinati a vaste ma limitate aree di attività della corona solare, l'eruzione agostana ha coinvolto l'intero emisfero visibile del sole. Una globalità del fenomeno che ha suggerito agli scienziati nuove modalità di analisi "olistica", che dovrebbe portare a migliori chances predittive e quindi a un maggior livello di preparazione in diversi ambiti della vita terrestre, come le centrali elettriche o il volo civile ad alte quote.

Global Eruption Rocks the Sun

12.13.10

Dr. Tony Phillips

NASA's Goddard Space Flight Center

On August 1, 2010, an entire hemisphere of the sun erupted. Filaments of magnetism snapped and exploded, shock waves raced across the stellar surface, billion-ton clouds of hot gas billowed into space. Astronomers knew they had witnessed something big. It was so big, it may have shattered old ideas about solar activity. "The August 1st event really opened our eyes," says Karel Schrijver of Lockheed Martin’s Solar and Astrophysics Lab in Palo Alto, CA. "We see that solar storms can be global events, playing out on scales we scarcely imagined before."

For the past three months, Schrijver has been working with fellow Lockheed-Martin solar physicist Alan Title to understand what happened during the "Great Eruption." They had plenty of data: The event was recorded in unprecedented detail by NASA's Solar Dynamics Observatory and twin STEREO spacecraft. With several colleagues present to offer commentary, they outlined their findings at a press conference today at the American Geophysical Union meeting in San Francisco.

Explosions on the sun are not localized or isolated events, they announced. Instead, solar activity is interconnected by magnetism over breathtaking distances. Solar flares, tsunamis, coronal mass ejections--they can go off all at once, hundreds of thousands of miles apart, in a dizzyingly-complex concert of violence. "To predict eruptions we can no longer focus on the magnetic fields of isolated active regions," says Title, "we have to know the surface magnetic field of practically the entire sun." This revelation increases the work load for space weather forecasters, but it also increases the potential accuracy of their forecasts.

"The whole-sun approach could lead to breakthroughs in predicting solar activity," commented Rodney Viereck of NOAA's Space Weather Prediction Center in Boulder, CO. "This in turn would provide improved forecasts to our customers such as electric power grid operators and commercial airlines, who could take action to protect their systems and ensure the safety of passengers and crew."

In a paper they prepared for the Journal of Geophysical Research (JGR), Schrijver and Title broke down the Great Eruption into more than a dozen significant shock waves, flares, filament eruptions, and CMEs spanning 180 degrees of solar longitude and 28 hours of time. At first it seemed to be a cacophony of disorder until they plotted the events on a map of the sun's magnetic field.

Title describes the Eureka! moment: "We saw that all the events of substantial coronal activity were connected by a wide-ranging system of separatrices, separators, and quasi-separatrix layers." A "separatrix" is a magnetic fault zone where small changes in surrounding plasma currents can set off big electromagnetic storms.

Researchers have long suspected this kind of magnetic connection was possible. "The notion of 'sympathetic' flares goes back at least three quarters of a century," they wrote in their JGR paper. Sometimes observers would see flares going off one after another--like popcorn--but it was impossible to prove a link between them. Arguments in favor of cause and effect were statistical and often full of doubt. "For this kind of work, SDO and STEREO are game-changers," says Lika Guhathakurta, NASA's Living with a Star Program Scientist. "Together, the three spacecraft monitor 97% of the sun, allowing researchers to see connections that they could only guess at in the past."

To wit, barely two-thirds of the August event was visible from Earth, yet all of it could be seen by the SDO-STEREO fleet. Moreover, SDO's measurements of the sun's magnetic field revealed direct connections between the various components of the Great Eruption—no statistics required.

Much remains to be done. "We're still sorting out cause and effect," says Schrijver. "Was the event one big chain reaction, in which one eruption triggered another--bang, bang, bang!--in sequence? Or did everything go off together as a consequence of some greater change in the sun's global magnetic field?"

Further analysis may yet reveal the underlying trigger; for now, the team is still wrapping their minds around the global character of solar activity. One commentator recalled the old adage of three blind men describing an elephant--one by feeling the trunk, one by holding the tail, and another by sniffing a toenail. Studying the sun one sunspot at a time may be just as limiting. "Not all eruptions are going to be global," notes Guhathakurta. "But the global character of solar activity can no longer be ignored."

As if the sun wasn't big enough already….

Vele di massa coronale in uno studio NASA

In una spettacolare ricostruzione tridimensionale, gli scienziati della NASA hanno pubblicato su Nature Communications (pdf disponibile, ma affrettatevi) uno studio sulla propagazione nello spazio delle eiezioni di massa coronale. Queste masse di materiale particellare solare percorrono sulla traiettoria sole-terra un tracciato non lineare e iniscono per abbattersi come un colpo di frusta sul nostro sistema geomagnetico. La materia coronale si stende come una vela spaziale, si gonfia, accelera e colpisce con violenza.

I dati utilizzati per questo studio provengono dalla missione STEREO e sono stati rielaborati dal supercomputer del Trinity College di Dublino. L'articolo che segue è stato pubblicato su Science News.

Solar Storms can Change Directions, Surprising Forecasters

Sept. 21, 2010: Solar storms don't always travel in a straight line. But once they start heading in our direction, they can accelerate rapidly, gathering steam for a harder hit on Earth's magnetic field.

So say researchers who have been using data from NASA's twin STEREO spacecraft to unravel the 3D structure of solar storms. Their findings are presented in today's issue of Nature Communications.

"This really surprised us," says co-author Peter Gallagher of Trinity College in Dublin, Ireland. "Solar coronal mass ejections (CMEs) can start out going one way—and then turn in a different direction."

The result was so strange, at first they thought they'd done something wrong. After double- and triple-checking their work on dozens of eruptions, however, the team knew they were onto something.

"Our 3D visualizations clearly show that solar storms can be deflected from high solar latitudes and end up hitting planets they might otherwise have missed," says lead author Jason Byrne, a graduate student at the Trinity Center for High Performance Computing.

The key to their analysis was an innovative computing technique called "multiscale image processing." Gallagher explains:

"'Multiscale processing' means taking an image and sorting the things in it according to size. Suppose you're interested in race cars. If you have a photo that contains a bowl of fruit, a person, and a dragster, you could use multiscale processing to single out the race car and study its characteristics."

In medical research, multiscale processing has been used to identify individual nuclei in crowded pictures of cells. In astronomy, it comes in handy for picking galaxies out of a busy star field. Gallagher and colleagues are the first to refine and use it in the realm of solar physics.

"We applied the multiscale technique to coronagraph data from NASA's twin STEREO spacecraft," Gallagher continues. "Our computer was able to look at starry images cluttered with streamers and bright knots of solar wind and zero in on the CMEs."

(continua)

Nuove previsioni per un sole "senza macchia"

C'è un supplemento di indagine allo studio che i due ricercatori del National Solar Observatory Matthew Penn e William Livingston avevano pubblicato lo scorso anno a proposito del progressivo calo di intensità del campo magnetico associato alle macchie solari. Le macchie sul sole, sostengono i due scienziati, stanno attraversando una fase di calo quantitativo e qualitativo. Le conclusioni della nuova ricerca pubblicata in occasione dell'ultimo simposio IAU, segnalato su Science parlano di un futuro "immacolato" per il nostro sole. L'attuale ciclo 24 potrebbe avere un numero complessivo di macchie pari alla metà del valore registrato nel ciclo appena trascorso. Il ciclo 25, tra una decina d'anni, potrebbe essere "spotless". In pratica un nuovo minimo di Maunder che potrebbe verificarsi tra il 2015 e il 2020.

Queste osservazioni sono molto specifiche e non dicono quali potrebbero gli effetti complessivi su fenomeni come i brillamenti e eiezioni di massa coronale, che hanno un impatto diretto sulla ionosfera e sul campo magnetico della terra. Certo è che l'ultima parte del ciclo 23 è stata caratterizzata da un minimo prolungato e un lungo periodo a macchie zero.

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.

Termosfera e minimo solare: una contrazione di troppo

La termosfera, il livello superiore della nostra atmosfera, oltre i 90 km di quota, all'interfaccia tra terra e spazio e primo punto di contatto con la radiazione solare del nostro sistema planetario, è sempre stata sensibile alle variazioni del ciclo solare. La sua densità aumenta e diminuisce in funzione della radiazione ultravioletta del sole e durante i minimi la termosfera si contrae per tornare a espandersi man mano che la attività solare ritorna a essere intensa. Secondo uno studio di John Emmert del Naval Research Lab, nel corso del minimo solare raggiunto nel 2010, la contrazione della termosfera è stata inspiegabilmente superiore al normale. Gli scienziati hanno proposto un modello di interazione in cui hanno un ruolo anche le molecole di CO2, il gas serra per eccellenza. Ma anche l'aumento della presenza di questo gas non spiegherebbe del tutto l'anomalo comportamento della termosfera (un comportamento che Emmert e colleghi misurano con precisione andando a verificare il "drag" l'attrito che la densità di questo strato esercita sui satelliti a orbita bassa). Secondo lo studio pubblicato sulle Geophysical Research Letters, l'effetto combinato del minimo solare+aumento di CO2 sarebbe sufficiente a spiegare solo il 40% del volume di contrazione effettivamente riscontrato (qui la CO2, diversamente da quanto accade negli strati più bassi dell'atmosfera, esercita un effetto refrigerante, raffreddando la termosfera che in condizioni di massimo solare può raggiungere temperature di 1400K a causa della radiazione assorbita dalle sue molecole).

C'è un fattore che sfugge e gli scienziati pensano a una possibile conseguenza delle variazioni climatiche recenti. Gli sforzi di misurazione proseguono alla ricerca di questo fattore misterioso. Lo stato di salute della termosfera è molto importante proprio per proteggerci da un eccesso di radiazione solare incidente.

A Puzzling Collapse of Earth's Upper Atmosphere

July 15, 2010: NASA-funded researchers are monitoring a big event in our planet's atmosphere. High above Earth's surface where the atmosphere meets space, a rarefied layer of gas called "the thermosphere" recently collapsed and now is rebounding again.

"This is the biggest contraction of the thermosphere in at least 43 years," says John Emmert of the Naval Research Lab, lead author of a paper announcing the finding in the June 19th issue of the Geophysical Research Letters (GRL). "It's a Space Age record."

The collapse happened during the deep solar minimum of 2008-2009—a fact which comes as little surprise to researchers. The thermosphere always cools and contracts when solar activity is low. In this case, however, the magnitude of the collapse was two to three times greater than low solar activity could explain.

"Something is going on that we do not understand," says Emmert.

The thermosphere ranges in altitude from 90 km to 600+ km. It is a realm of meteors, auroras and satellites, which skim through the thermosphere as they circle Earth. It is also where solar radiation makes first contact with our planet. The thermosphere intercepts extreme ultraviolet (EUV) photons from the sun before they can reach the ground. When solar activity is high, solar EUV warms the thermosphere, causing it to puff up like a marshmallow held over a camp fire. (This heating can raise temperatures as high as 1400 K—hence the name thermosphere.) When solar activity is low, the opposite happens.

Lately, solar activity has been very low. In 2008 and 2009, the sun plunged into a century-class solar minimum. Sunspots were scarce, solar flares almost non-existent, and solar EUV radiation was at a low ebb. Researchers immediately turned their attention to the thermosphere to see what would happen.

How do you know what's happening all the way up in the thermosphere?

Emmert uses a clever technique: Because satellites feel aerodynamic drag when they move through the thermosphere, it is possible to monitor conditions there by watching satellites decay. He analyzed the decay rates of more than 5000 satellites ranging in altitude between 200 and 600 km and ranging in time between 1967 and 2010. This provided a unique space-time sampling of thermospheric density, temperature, and pressure covering almost the entire Space Age. In this way he discovered that the thermospheric collapse of 2008-2009 was not only bigger than any previous collapse, but also bigger than the sun alone could explain.

One possible explanation is carbon dioxide (CO2).

When carbon dioxide gets into the thermosphere, it acts as a coolant, shedding heat via infrared radiation. It is widely-known that CO2 levels have been increasing in Earth's atmosphere. Extra CO2 in the thermosphere could have magnified the cooling action of solar minimum.

"But the numbers don't quite add up," says Emmert. "Even when we take CO2 into account using our best understanding of how it operates as a coolant, we cannot fully explain the thermosphere's collapse."

According to Emmert and colleagues, low solar EUV accounts for about 30% of the collapse. Extra CO2 accounts for at least another 10%. That leaves as much as 60% unaccounted for.

In their GRL paper, the authors acknowledge that the situation is complicated. There's more to it than just solar EUV and terrestrial CO2. For instance, trends in global climate could alter the composition of the thermosphere, changing its thermal properties and the way it responds to external stimuli. The overall sensitivity of the thermosphere to solar radiation could actually be increasing.

"The density anomalies," they wrote, "may signify that an as-yet-unidentified climatological tipping point involving energy balance and chemistry feedbacks has been reached."

Or not.

Important clues may be found in the way the thermosphere rebounds. Solar minimum is now coming to an end, EUV radiation is on the rise, and the thermosphere is puffing up again. Exactly how the recovery proceeds could unravel the contributions of solar vs. terrestrial sources.

"We will continue to monitor the situation," says Emmert.

For more information see Emmert, J. T., J. L. Lean, and J. M. Picone (2010), Record-low thermospheric density during the 2008 solar minimum, Geophys. Res. Lett., 37, L12102.

Tsunami e suoni della corona solare

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

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

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

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

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

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3 March 2010

Mega-tsunami hits House of Commons

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

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

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

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

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

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

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

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

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

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

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

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

Dinamica solare in HD: piccole variazioni, grandi effetti

Continuano ad arrivare copiosi i risultati delle osservazioni del Solar Dynamics Observatory. Questa volta il protagonista è l'Atmospheric Imaging Assembly, uno dei tre strumenti a bordo del satellite SDO. Consente una visuale ad alta risoluzione e su un amplissima gamma di temperature della corona solare.

Dalle prime immagini gli scienziati riescono a capire meglio perché una variazione su minuscola scala sul Sole finisca per avere enormi ripercussioni anche sul nostro pianeta, dove le perturbazioni solari si fanno sentire sui cavi dell'alta tensione e sui sistemi di comunicazione satellitare. A corredo dell'articolo che segue, trovate una quantita di immagini, filmati e presentazioni a questo indirizzo.

La presentazione sull'AIA la potete trovare qui, in Pdf, mentre qui trovate un incredibile database di eventi solari, l'interfaccia di ricerca SolSearch che estrae i dati dalla Heliophysics Events Knowledgebase (HEK), uno dei servizi del Solar and Astrophysics Laboratory della Lockheed Martin.

Spacecraft Reveals Small Solar Events Have Large Scale Effects

05.25.10

NASA's Solar Dynamics Observatory, or SDO, has allowed scientists for the first time to comprehensively view the dynamic nature of storms on the sun. Solar storms have been recognized as a cause of technological problems on Earth since the invention of the telegraph in the 19th century.

The Atmospheric Imaging Assembly (AIA), one of three instruments aboard SDO, allowed scientists to discover that even minor solar events are never truly small scale. Shortly after AIA opened its doors on March 30, scientists observed a large eruptive prominence on the sun's edge, followed by a filament eruption a third of the way across the star's disk from the eruption.

"Even small events restructure large regions of the solar surface," said Alan Title, AIA principal investigator at Lockheed Martin Advanced Technology Center in Palo Alto, Calif. "It's been possible to recognize the size of these regions because of the combination of spatial, temporal and area coverage provided by AIA."

The AIA instrument also has observed a number of very small flares that have generated magnetic instabilities and waves with clearly-observed effects over a substantial fraction of the solar surface. The instrument is capturing full-disk images in eight different temperature bands that span 10,000 to 36-million degrees Fahrenheit. This allows scientists to observe entire events that are very difficult to discern by looking in a single temperature band, at a slower rate, or over a more limited field of view.

The data from SDO is providing a torrent of new information and spectacular images to be studied and interpreted. Using AIA's high-resolution and nearly continuous full-disk images of the sun, scientists have a better understanding of how even small events on our nearest star can significantly impact technological infrastructure on Earth.

Solar storms produce disturbances in electromagnetic fields that can induce large currents in wires, disrupting power lines and causing widespread blackouts. The storms can interfere with global positioning systems, cable television, and communications between ground controllers and satellites and airplane pilots flying near Earth's poles. Radio noise from solar storms also can disrupt cell phone service.

Launched in Feb. 2010, the spacecraft's commissioning May 14 confirmed all three of its instruments successfully passed an on-orbit checkout, were calibrated and are collecting science data.

"We're already at five million images and counting," said Dean Pesnell, the SDO project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "With data and images pouring in from SDO, solar scientists are poised to make discoveries that will rewrite the books on how changes in solar activity have a direct effect on Earth. The observatory is working great, and it's just going to get better."

Goddard built, operates and manages the SDO spacecraft for NASA's Science Mission Directorate in Washington. SDO is the first mission of NASA's Living with a Star Program. The program's goal is to develop the scientific understanding necessary to address those aspects of the sun-Earth system that directly affect our lives and society.

SDO, il sole fa spettacolo in HD

Gli scienziati della NASA osservano con stupore immagini e filmati ad alta risoluzione che il Solar Dynamics Observatory ci restituiscono del nostro sole, spiegando misteri finori irrisolti come la "pioggia coronale", la ricaduta di materiale plasmatico dopo le eruzioni nell'atmosfera solare.

SDO Observes Massive Eruption, Scorching Rain

April 27, 2010: Just last week, scientists working with NASA's new Solar Dynamics

Observatory (SDO) released the most astonishing movies of the sun anyone had ever seen. Now, they're doing it again.

"SDO has just observed a massive eruption on the sun—one of the biggest in years," says Lika Guhathakurta of NASA headquarters in Washington DC. "The footage is not only dramatic, but also could solve a longstanding mystery of solar physics."

Karel Schrijver of Lockheed Martin's Solar and Astrophysics Lab is leading the analysis. "We can see a billion tons of magnetized plasma blasting into space while debris from the explosion falls back onto the sun surface. These may be our best data yet."

Astronomers have seen eruptions like this before, but rarely so large and never in such fluid detail. As science team member Alan Title of Lockheed Martin pointed out at last week's press conference, "no other telescope comes close to the combined spatial, temporal and spectral resolution of SDO."

Schrijver says his favorite part of the movie is the coronal rain. "Blobs of plasma are falling back to the surface of the sun, making bright splashes where they hit," he explains. "This is a phenomenon I've been studying for years."

Coronal rain has long been a mystery. It's not surprising that plasma should fall back to the sun. After all, the sun's gravity is powerful. The puzzle of coronal rain is how slowly it seems to fall. "The sun's gravity should be pulling the material down much faster than it actually moves. What's slowing the descent?" he wonders.

For the first time, SDO provides an answer. "The rain appears to be buoyed by a 'cushion' of hot gas," says Schrijver. "Previous observatories couldn't see it, but it is there."

One of SDO's game-changing capabilities is temperature sensing. Using an array of ultraviolet telescopes called the Atmospheric Imaging Assembly (AIA), the observatory can remotely measure the temperature of gas in the sun's atmosphere. Coronal rain turns out to be relatively cool—"only" 60,000 K. When the rains falls, it is supported, in part, by an underlying cushion of much hotter material, between 1,000,000 and 2,200,000 K. "You can see the hot gas in the color-coded temperature movie," says Schrijver. "Cool material is red, hotter material is blue-green. The hot gas effectively slows the descent of the coronal rain."

Dick Fisher, the head of NASA's Heliophysics Division in Washington DC, has been working in solar physics for nearly forty years. "In all that time," he says, "I've never seen images like this."

"I wonder, what will next week bring?"

Solar Dynamics Observatory, il sole in hi-res

Pubblico da quasi cinque anni le notizie - e le immagini - relative alle ricerche nel campo della fisica solare e della sua interazione con il sistema terrestre (una interazione che abbraccia anche aspetti profondamente sociali), ma quello che comincia ad arrivare dal Solar Dynamics Observatory lanciato a febbraio dalla NASA è davvero stupefacente. Le immagini viste sono solo una frazione minima degli 1,5 terabyte di informazione giornaliera che SDO rimanda a terra. Oggi l'apertura di Repubblica.it contiene un link a una "foto navigabile" di una atmosefera solare restituita a una risoluzione mai vista, ma altre immagini e filmati raccontano episodi recenti come il brillamento del 30 marzo scorso e tanti altri. Persino l'Huffington Post ha dedicato spazio all'eruzione del 13 aprile, facendo vedere un filmato HD a dir poco spettacolare (immagini riprese in quel caso dalla missione STEREO. Nel frattempo, anche il telescopio spaziale Hubble festeggia in questi giorni il suo ventesimo compleanno.

NASA's New Eye on the Sun Delivers Stunning First Images

04.21.10

NASA's recently launched Solar Dynamics Observatory, or SDO, is returning early images that confirm an unprecedented new capability for scientists to better understand our sun’s dynamic processes. These solar activities affect everything on Earth.

Some of the images from the spacecraft show never-before-seen detail of material streaming outward and away from sunspots. Others show extreme close-ups of activity on the sun’s surface. The spacecraft also has made the first high-resolution measurements of solar flares in a broad range of extreme ultraviolet wavelengths.

"These initial images show a dynamic sun that I had never seen in more than 40 years of solar research,” said Richard Fisher, director of the Heliophysics Division at NASA Headquarters in Washington. "SDO will change our understanding of the sun and its processes, which affect our lives and society. This mission will have a huge impact on science, similar to the impact of the Hubble Space Telescope on modern astrophysics.”

Launched on Feb. 11, 2010, SDO is the most advanced spacecraft ever designed to study the sun. During its five-year mission, it will examine the sun's magnetic field and also provide a better understanding of the role the sun plays in Earth's atmospheric chemistry and climate. Since launch, engineers have been conducting testing and verification of the spacecraft’s components. Now fully operational, SDO will provide images with clarity 10 times better than high-definition television and will return more comprehensive science data faster than any other solar observing spacecraft.

SDO will determine how the sun's magnetic field is generated, structured and converted into violent solar events such as turbulent solar wind, solar flares and coronal mass ejections. These immense clouds of material, when directed toward Earth, can cause large magnetic storms in our planet’s magnetosphere and upper atmosphere.

SDO will provide critical data that will improve the ability to predict these space weather events. NASA's Goddard Space Flight Center in Greenbelt, Md., built, operates and manages the SDO spacecraft for the agency’s Science Mission Directorate in Washington.

“I’m so proud of our brilliant work force at Goddard, which is rewriting science textbooks once again.” said Sen. Barbara Mikulski, D-Md., chairwoman of the Commerce, Justice and Science Appropriations Subcommittee that funds NASA. “This time Goddard is shedding new light on our closest star, the sun, discovering new information about powerful solar flares that affect us here on Earth by damaging communication satellites and temporarily knocking out power grids. Better data means more accurate solar storm warnings.”

Space weather has been recognized as a cause of technological problems since the invention of the telegraph in the 19th century. These events produce disturbances in electromagnetic fields on Earth that can induce extreme currents in wires, disrupting power lines and causing widespread blackouts. These solar storms can interfere with communications between ground controllers, satellites and airplane pilots flying near Earth's poles. Radio noise from the storm also can disrupt cell phone service.

SDO will send 1.5 terabytes of data back to Earth each day, which is equivalent to a daily download of half a million songs onto an MP3 player. The observatory carries three state-of the-art instruments for conducting solar research.

The Helioseismic and Magnetic Imager maps solar magnetic fields and looks beneath the sun’s opaque surface. The experiment will decipher the physics of the sun’s activity, taking pictures in several very narrow bands of visible light. Scientists will be able to make ultrasound images of the sun and study active regions in a way similar to watching sand shift in a desert dune. The instrument’s principal investigator is Phil Scherrer of Stanford University. HMI was built by a collaboration of Stanford University and the Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif.

The Atmospheric Imaging Assembly is a group of four telescopes designed to photograph the sun’s surface and atmosphere. The instrument covers 10 different wavelength bands, or colors, selected to reveal key aspects of solar activity. These types of images will show details never seen before by scientists. The principal investigator is Alan Title of the Lockheed Martin Solar and Astrophysics Laboratory, which built the instrument.

The Extreme Ultraviolet Variability Experiment measures fluctuations in the sun’s radiant emissions. These emissions have a direct and powerful effect on Earth’s upper atmosphere -- heating it, puffing it up, and breaking apart atoms and molecules. Researchers don’t know how fast the sun can vary at many of these wavelengths, so they expect to make discoveries about flare events. The principal investigator is Tom Woods of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. LASP built the instrument.

"These amazing images, which show our dynamic sun in a new level of detail, are only the beginning of SDO's contribution to our understanding of the sun," said SDO Project Scientist Dean Pesnell of Goddard.

SDO is the first mission of NASA's Living with a Star Program, or LWS, and the crown jewel in a fleet of NASA missions that study our sun and space environment. The goal of LWS is to develop the scientific understanding necessary to address those aspects of the connected sun-Earth system that directly affect our lives and society.

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".

Un telescopio spaziale per il nostro sole mutevole

Non ce ne accorgiamo, dicono gli scienziati della NASA, ma il nostro sole è una stella variabile, una continua fabbrica di fenomeni misteriosi, un vero e proprio laboratorio di astrofisica. Per studiarla, per cercare di capire tutte le conseguenze della sua dinamicità sulla nostra atmosfera e probabilmente il nostro clima, sta per essere lanciata, il 9 febbraio l'ambiziosa missione del Solar Dynamics Observatory. Che ha anche aperto un fantastico canale su You Tube.

Solar Dynamics Observatory: The 'Variable Sun' Mission
02.05.2010

February 5, 2010: For some years now, an unorthodox idea has been gaining favor among astronomers. It contradicts old teachings and unsettles thoughtful observers, especially climatologists. "The sun," explains Lika Guhathakurta of NASA headquarters in Washington DC, "is a variable star." But it looks so constant... That's only a limitation of the human eye. Modern telescopes and spacecraft have penetrated the sun's blinding glare and found a maelstrom of unpredictable turmoil. Solar flares explode with the power of a billion atomic bombs. Clouds of magnetized gas (CMEs) big enough to swallow planets break away from the stellar surface. Holes in the sun's atmosphere spew million mile-per-hour gusts of solar wind. And those are the things that can happen in just one day.
Over longer periods of decades to centuries, solar activity waxes and wanes with a complex rhythm that researchers are still sorting out. The most famous "beat" is the 11-year sunspot cycle, described in many texts as a regular, clockwork process. In fact, it seems to have a mind of its own.
"It's not even 11 years," says Guhathakurtha. "The cycle ranges in length from 9 to 12 years. Some cycles are intense, with many sunspots and solar flares; others are mild, with relatively little solar activity. In the 17th century, during a period called the 'Maunder Minimum,' the cycle appeared to stop altogether for about 70 years and no one knows why."
There is no need to go so far back in time, however, to find an example of the cycle's unpredictability. Right now the sun is climbing out of a century-class solar minimum that almost no one anticipated.
"The depth of the solar minimum in 2008-2009 really took us by surprise," says sunspot expert David Hathaway of the Marshall Space Flight Center in Huntsville, Alabama. "It highlights how far we still have to go to successfully forecast solar activity."
That's a problem, because human society is increasingly vulnerable to solar flare ups. Modern people depend on a network of interconnected high-tech systems for the basics of daily life. Smart power grids, GPS navigation, air travel, financial services, emergency radio communications—they can all be knocked out by intense solar activity. According to a 2008 study by the National Academy of Sciences, a century-class solar storm could cause twenty times more economic damage than Hurricane Katrina.
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NASA SDO, dall'orbita tutti i segreti del Sole

Stavo seguendo in diretta su Nasa TV la conferenza stampa della missione Solar Dynamics Observatory, un telescopio spaziale che verrà lanciato il 9 febbraio prossimo con lo scopo di studiare in condizioni orbitali i vari fenomeni che caratterizzano la variabilità del Sole e i suoi effetti sulla Terra. Una missione senza precedenti, che durerà 15 anni e ci fornirà, si spera molte risposte sugli attuali misteri della fisica solare. C'è una grande attesa per l'avvio della missione proprio nelle settimane in cui il nostro astro dà chiari segni di ripresa del suo ciclo di attività dopo una prolungatissima fase di minimo.

Ecco un articolo di Space Daily, dove si parla anche del ruolo degli astrofisici dell'università del New Mexico.

Studying The Secrets Of The Sun by Staff Writers Las Cruces NM (SPX) Jan 18, 2010

All life on planet Earth owes its existence to the sun. The sun's rays are where we derive our vitamin D and where most plants get their energy to go through photosynthesis. It was worshipped as a deity by ancient cultures and its power is now harnessed as a source of renewable energy.
The sun is a star at the center of our solar system. Its mass makes up more than 99 percent of the mass of our solar system and is 109 times the size of the planet we call home. More than 1.3 million Earths could comfortably fit inside the sun. Its core can reach temperatures of 27 million degrees Fahrenheit. With all that we now know about this bright star, there are still many areas of the sun that are an enigma to us.
New Mexico's climate and clear skies make it an ideal location for stellar and solar observations, and scientists around the globe are taking advantage and employing the expertise of local researchers in finding out everything they can about the sun - from the inside out. "I think New Mexico is really coming of age in the field of astronomy in terms of what is happening at our individual campus and what is happening with our national and international collaborations," said Bernie McNamara, professor in New Mexico State University's Department of Astronomy. "We are actually at the stage now where New Mexico institutions are being sought out as collaborators."
NASA is about to launch a 15-year mission to study the sun continuously through satellites and telescopes and NMSU is set to play an integral part in interpreting the data collected from the instruments. From a single, ground-based telescope, the sun cannot be viewed once it sets, creating gaps in data collection. The main aspect of the soon-to-be-launched multi-billion dollar Solar Dynamic Observatory satellite is that it will allow the sun to be viewed continuously, said Jason Jackiewicz, assistant professor of astronomy at NMSU.
Researchers will use state-of-the-art instruments to study the oscillations on the surface of the sun as well as seismic data that will look inside the sun in order to find the source of solar events.
"The mission is designed to understand the magnetic sun," Jackiewicz said. "We are trying to predict when and where a sunspot will pop through the surface of the sun. If we can do that, it might give us an idea of how we can predict solar flares and other mass ejections."
Jackiewicz earned a spot on the SDO team, charged with setting up a data analysis pipeline to detect magnetic structures beneath the surface of the sun. "This satellite will provide us with the best data, by far, that we have seen in a long time," Jackiewicz said.
Astronomers at NMSU also are using grants from NASA and the National Science Foundation to help predict space weather in order to prevent damage done by solar magnetic storms to space-based and ground-based electronic facilities.
The National Solar Observatory, which has observation sites at Sacramento Peak in Sunspot, N.M., and at Kitt Peak in Tucson, Ariz., is consolidating its operations in anticipation of a new telescope based in Hawaii called the Advanced Technology Solar Telescope. When it is completed, the ATST will have the ability to study the smallest spatial features of the sun.
A second major new solar project that New Mexico may well play a role in is called the Stellar Oscillation Network Group. Led by a group of Danish institutions it aims to build eight telescopes around the world so that stars can be viewed continuously.
NMSU, in collaboration with other institutions, has applied for funding from NSF's Major Research Instrumentation Program to place one of these new telescopes at the Apache Point Observatory, in Sunspot.
SONG is fundamentally different from other kinds of solar missions because its telescopes will measure stellar oscillations through the motion of the star's surface. This will be done with a precision not before possible, McNamara said.
"The science behind this project is really unprecedented," Jackiewicz said.
The Air Force Research Laboratory is working to relocate its Space Weather Center of Excellence to New Mexico from Massachusetts. The AFRL is a major force in the state in solar and stellar research and its scientists are interested in teaming with an institution in New Mexico to continue their work.
McNamara said officials have spoken to researchers at the University of New Mexico and also plan to speak to researchers at NMSU to be a part of the partnership.
At NMSU, the 21st Century Space and Aerospace Cluster - made up of members from the astronomy, computer science, electrical and computer engineering, mechanical and aerospace engineering and physics departments and the Physical Science Laboratory - works to promote space-related education and research at the university.
The NSF has awarded several grants in New Mexico that focus on solar research, including projects at Los Alamos National Laboratory, UNM and NSO, where graduate students from NMSU and other universities work under the mentorship of renowned scientists. "Within New Mexico, we are gaining a strong national and international reputation in the field of solar physics that makes us an attractive partner," McNamara said.
As interest in the sun and its impact on Earth continues to increase, New Mexico is donning its sunshades and doing everything it can to stay at the forefront of revolutionary solar research.