Missione SWARM: l'ESA scende in campo magnetico

La missione SWARM, lanciata in questi giorni dall'ESA promette di essere molto interessante. Si tratta di tre satelliti con sofisticati strumenti di misura magnetica orbitanti a circa 500 km di quota. Il loro obiettivo è misurare con estrema precisione e livello di dettaglio le variazioni del campo magnetico terrestre, un sistema molto variabile per intensità e orientamento (capace addirittura di invertire compleamente la sua polarità, come alcuni sospettano possa avvenire su scale di tempo ravvicinate) che ci protegge dalle radiazioni cosmiche e interagisce con l'elettromagnetismo solare, con meccanismi ancora in larga parte sconosciuti che influiscono sul fenomeni come la propagazione delle onde radio, ma anche sulla dinamica dell'atmosfera, così importante per la stabilità delle orbite satellitari.

L'ESA ha pubblicato una bellissima brochure che descrive SWARM, tutti i suoi strumenti e le finalità. Scaricatela qui.

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.

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.

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.

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.

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.

E se le macchie solari sparissero?

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

Are Sunspots Disappearing?
09.03.2009

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

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

Le macchie solari si stanno lentamente spegnendo?

Quarantaquattro. Gatti? No, giorni - a oggi - senza macchie solari. Il minimo magnetico del nostro astro comincia a preoccupare seriamente i ricercatori. A inizio luglio, la comparsa della macchia numero 1024 aveva fatto illudere un po' tutti segnando un pur timido inizio del ciclo 24. Passata la macchia, gabbato lo sole: da allora tutto è tornato quieto e il disco solare continua a essere immacolato, con i valori geomagnetici che in effetti si mantengono sempre molto bassi. Dal punto di vista propagativo le cose per i segnali radio deboli e lontani sembrano andare a senso alterno. Qui a L'Ago ieri e stamattina la presenza dell'Alaska nei 25 metri della banda broadcast è un buon indicatore, anche nelle bande amatoriali dei 20 metri, quindi su frequenze abbastanza alte che a rigor di logica sarebbero favorite dall'attività solare, ci sono segnali interessanti. In FM la stagione dell'E sporadico si sta chiudendo con gli ultimi fuochi delle aperture in Europa (qui in Italia con la banda così affollata, è difficile rendersene conto): non è stata una grande stagione ma si deve anche dire che l'E sporadico non sembra essere del tutto correlato all'attività solare, ci possono essere aperture molto intense anche senza macchie solari. In compenso oltreoceano segnalano già le aperture in onde medie, transatlantiche e transpacifiche. Ho provato ad ascoltare qualcosa nella mia postazione ligure, ma tra venerdì e sabato non c'era granché, mentre ieri le fortissime scariche elettriche atmosferiche mi hanno fatto desistere. Interessante la frequenza di 638 kHz (separata di un kHz dal canale europeo dei 639), dove dopo il tramonto si può ascoltare, con difficoltà, NBC Nigeria da Kaduna.
E il sole? Oggi su Space Weather c'è un articolo piuttosto allarmante di due studiosi del National Solar Observatory di Tucson, in Arizona, che hanno calcolato una netta diminuzione nell'intensità del campo magnetico associato alle macchie solari. Gli scienziati hanno lavorato misurando l'effetto Zeeman, che determina un diverso comportamento degli elettroni in presenza di campi magnetici costanti (elettroni con diverso numero quantito interagiscono in modo diverso e non passano più tra livelli energetici fissi ma "splittati") sugli atomi di ferro prossimi alle macchie solari. Dalle loro analisi emerge che la separazione Zeeman delle linee spettrali osservate è meno marcata e quindi il campo che genera le macchie è in proporzione più basso. E senza campo, le macchie possono - come si vede - scomparire del tutto.
Insomma, un minimo davvero minimo, che giustamente viene paragonato a quello della Borsa (arrivato in basso scende ancora più in basso) e comporta, oltre al crollo delle emissioni radio a 10,7 centimetri di lambda (mai così basse in 55 anni di misurazioni), anche un calo dell'irraggiamento.



Nel caso dei raggi UV estremi è addirittura del 6%, non abbastanza per invertire gli effetti del riscaldamento globale ma sufficiente per determinare, per esempio, un minor rigonfiamento degli strati alti dell'atmosfera (meno caldi) con una conseguente dimunuzione dell'attrito sui satelliti a orbita bassa, che diventano più longevi (con loro sono più longevi anche i detriti spaziali e questo è meno bello).

QUIET SUN: Today marks the 44th consecutive day without spots on the sun--one of the longest quiet spells of the current solar minimum. In early July, sunspot 1024 seemed to herald the long-awaited onset of Solar Cycle 24, but shortly after that apparition, sunspot production turned off again. Deep solar minimum continues...
ARE SUNSPOTS DISAPPEARING? Sunspots are made of magnetism. The "firmament" of a sunspot is not matter but rather a strong magnetic field that appears dark because it blocks the upflow of heat from the sun's fiery depths. Without magnetism, there would be no sunspots.

That's what makes the following graph a little troubling:


According to Bill Livingston and Matt Penn of the National Solar Observatory in Tucson, Arizona, sunspot magnetic fields are waning. The two respected solar astronomers have been measuring solar magnetism since 1992. Their technique is based on Zeeman splitting of infrared spectral lines emitted by iron atoms in the vicinity of sunspots. Extrapolating their data into the future suggests that sunspots could completely disappear within decades. That would be a bummer for Spaceweather.com.
Don't count out sunspots just yet, however. While the data of Livingston and Penn are widely thought to be correct, far-reaching extrapolations may be premature. This type of measurement is relatively new, and the data reaches back less than 17 years. "Whether this is an omen of long-term sunspot decline, analogous to the Maunder Minimum, remains to be seen," they caution in a recent EOS article.
One thing is certain. Solar Minimum is a lot more interesting than it sounds: more.

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

La ionosfera si abbassa

Ho letto solo oggi, con qualche settimana di ritardo una notizia che riguarda i primi risultati ottenuti da un satellite lanciato lo scorso aprile per studiare la ionosfera e i suoi fenomeni. Il satellite CNOF/S, Communication/Navigation Outage Forecast System, fa parte di una missione dell'Air Force americana con la collaborazione di NASA e università il cui obiettivo è fornire dati sulle possibili alterazioni nelle comunicazioni alle alte frequenze, in virtù di fenomeni perturbativi come le "scintillazioni", che disturbano le operazioni terra-satellite anche nelle UHF e in banda L.

Secondo le ultime analisi effettuate con gli strumenti della missione CINDI, Coupled Ion-Neutral Dynamics Investigations (qui trovate delle interessanti animazioni), la ionosfera si starebbe abbassando di quota. La regione di transizione tra ionosfera e spazio, teoricamente collocata intorno a quota 950 chilometri durante il giorno è stata misurata a 800 chilometri. Nelle ore notturne il limite si dimezza, scendendo a 420 chilometri di quota contro i 640 misurati da terra.
I due articoli che seguono, ricavati dal sito Space Mart e dal sito della University of Texas Dallas (cui è affidata la direzione scientifica della missione CINDI) riassumono questo e altri risultati, tra cui per esempio il rilevamento di un livello termico ionosferico assai più basso del previsto. La ionosfera è più fredda e meno alta. In teoria, una quota più bassa implicherebbe una riduzione dei percorsi propagativi per chi ascolta in onde medie e corte. Ma in realtà sospetto che i dati raccolti in questi mesi dalla missione C/NOFS-CINDI siano piuttosto uno strumento di conoscenza aggiuntivo, più preciso di quelli, molto circoscritti e limitati, di cui disponevamo finora. Il ritratto della ionosfera che sta emergendo non è "diverso", ma "nuovo". Il che non lo rende meno interessante per noi.

Contraction Of Boundary Between The Earth's Ionosphere And Space

The C/NOFS mission gives scientists a new tool for forecasting space weather. The CINDI instrument aboard C/NOFS specifically studies the major elements that influence space weather near Earths equator.

by Staff Writers (Credit: NASA) Washington DC (SPX) Dec 19, 2008

Observations made by NASA instruments onboard an Air Force satellite have shown that the boundary between the Earth's upper atmosphere and space has moved to extraordinarily low altitudes. These observations were made by the Coupled Ion Neutral Dynamics Investigation (CINDI) instrument suite, which was launched aboard the U.S. Air Force's Communication/Navigation Outage Forecast System (C/NOFS) satellite on April 16, 2008.
The CINDI suite, which was built under the direction Principal Investigator Rod Heelis of the University of Texas at Dallas, includes both ion and neutral sensors and makes measurements of the variations in neutral and ion densities and drifts.
CINDI and C/NOFS were designed to study disturbances in Earth's ionosphere that can result in a disruption of navigation and communication signals. The ionosphere is a gaseous envelope of electrically charged particles that surrounds our planet and it is important because Radar, radio waves, and global positioning system signals can be disrupted by ionospheric disturbances.
CINDI's first discovery was, however, that the ionosphere was not where it had been expected to be. During the first months of CINDI operations the transition between the ionosphere and space was found to be at about 260 miles (420 km) altitude during the nighttime, barely rising above 500 miles (800 km) during the day.
These altitudes were extraordinarily low compared with the more typical values of 400 miles (640 km) during the nighttime and 600 miles (960 km) during the day.
The height of the ionosphere/space transition is controlled in part by the amount of extreme ultraviolet energy emitted by the Sun and a somewhat contracted ionosphere could have been expected because C/NOFS was launched during a minimum in the 11-year cycle of solar activity. However, the size of the actual contraction caught investigators by surprise.
In fact, when they looked back over records of solar activity, they found that C/NOFS had been launched during the quietest solar minimum since the space age began.
This extraordinary circumstance is providing an unparalleled opportunity to study the connection between the interior dynamics of the Sun and the response of the Earth's space environment.
CINDI is a NASA sponsored Mission of Opportunity conducted by the University of Texas at Dallas. NASA's Explorer Program at Goddard Space Flight Center, Greenbelt, Md., managed the CINDI mission. The Explorer Program provides frequent flight opportunities for world-class scientific investigations from space within heliophysics and astrophysics.
The CINDI investigation is carried out as an enhancement to the science objectives of the C/NOFS satellite undertaken by the Air Force Research Laboratory and the Space and Missile Command Test and Evaluation Directorate.

***

UT Dallas Project Helps Fill Out Picture of Earth’s Ionosphere

Researchers’ Instruments Reveal Surprises About Size and Shape of Electrically Charged Layer

Dec. 16, 2008

A space weather satellite with Coupled Ion-Neutral Dynamics Investigation (CINDI) instruments aboard have for the first time revealed the size and shape of the gaseous envelope of electrically charged particles that surrounds the globe.

Called the ionosphere, this essential border between Earth and space has now been mapped at its upper boundary and shown to occupy less height than expected.
Measurements from CINDI instrumentation have made the first map of the ionosphere’s upper surface. It expands and contracts from day to night but has much less height than expected.
A collaboration among NASA, the U.S. Air Force Research Laboratory (AFRL) and the University of Texas at Dallas, CINDI is revealing what happens during periods of low sunspot activity, when the upper atmosphere cools off.
The ionosphere plays a particularly important role in satellite communication and any type of technology that uses space-based communications. GPS systems used by ships, trucking companies, and airplanes depend on reliable, uninterrupted streams of information from satellites, which must punch a signal cleanly through the ionosphere.
“Any radio or location system signal that utilizes space-based communication has to go through the ionosphere,” said CINDI Principal Investigator Rod Heelis, director of the Hanson Center for Space Sciences at UT Dallas. “On its best day, the ionosphere just bends that signal rather like water bends light. On its worst day it can completely distort that signal so that it doesn’t make it out the other side.”
Predicting when these disturbances might occur is a key goal of the CINDI project and its satellite, the Communication/Navigation Outage Forecast System (C/NOFS).

CINDI reveals for the first time:

• A view of the ionosphere never seen before, during solar “quiet” times.
• A map showing the size and shape of the Earth’s ionosphere.
• That the ionosphere is up to 100 degrees cooler than previously thought.
• That the effective thickness of the ionospheric shell is less than expected.
• A link between the extent of the ionosphere and solar activity levels observed at solar minimum.
• A view of the daily expansion and contraction of the ionosphere around the equator.
  

“The ionosphere is extremely cold at night, leading to a much thinner altitude and less dense layer than we expected,” Heelis said. “We have found that it is up to 100 degrees cooler than we expected and the effective thickness of the ionospheric shell is smaller than we expected.”
Heelis said CINDI revealed that the ionosphere expands during the day, when the upper surface rises, but not as high as the team thought it might. Further, the daily expansion and contraction of the ionosphere has been observed continuously around the equator for the first time. Had sunspot activity not dropped off—with associated cooling of the ionosphere—scientists would not have been able to watch the ionosphere expand and contract.
The so-called “quiet time” view of the ionosphere, when sunspot activity is low, allows Heelis and Greg Earle, another UT Dallas physics professor and CINIDI team member, to study the region of the ionosphere that is hazardous to radio communications.

Heelis and Earle built the two instruments that comprise CINDI:

The Ion Velocity Meter, which measures the direction and speed of ions as well as their density, temperature and chemical composition.

The Neutral Wind Meter, which measures the speed and direction of the neutral atoms and molecules in the near vacuum of space.

The 20-pound package of sensors and electronic equipment was fabricated in Heelis’ UT Dallas laboratory with Earle’s assistance and in collaboration with Paul Mahaffey of NASA’s Goddard Space Flight Center.

CINDI was carried on the C/NOFS satellite that was launched on April 16, 2008 on a Pegasus XL rocket aboard Orbital Science Corporation’s L-1011 “Stargazer” jet. The C/NOFS mission was launched to explore ways to forecast disturbances in the Earth’s ionosphere that can result in a disruption of navigation and communication signals.
“Years ago, my basic question began as, ‘How does our space environment interact with the sun?’” Heelis said. “I was intellectually curious about that. But now, as we become more dependent on assets in space, answering that question has real importance to everyday commerce, to military and commercial communications and navigation. NASA and the Air Force want to know the answers, and it’s enlightening to see major agencies working with us at UT Dallas to share resources and work on these problems together.”
Heelis and representatives from NASA and the Air Force presented the recent results from CINDI at the 2008 fall meeting of the American Geophysical Union.

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."

La NASA alle origini del vento solare

Un volo di 8 minuti per cercare di carpire il segreto del vento solare. Il prossimo mese di aprile la NASA caricherà a bordo di un vettore Black Brant in partenza dalla base del Nuovo Messico uno speciale telescopio. Denominato Solar Ultraviolet Magnetograph Investigation, lo strumento servirà a osservare nell'ultravioletto la cosiddetta regione di transizione nell'atmosfera solare a 5mila metri dalla superficie dell'astro. E' in questa regione, dove il campo magnetico del sole esercita la sua azione di contenimento dei vorticosi gas al suo interno, che si verificano fenomeni come i brillamenti. E dove il vento solare viene inspiegabilmente accelerato fino alla velocità di quasi due milioni di chilometri all'ora. La regione di transizione è il punto di origine dello space weather, della meteorologia spaziale, studiata per cercare di prevedere l'andament o della propagazione radio qui sulla terra. Purtroppo, è anche una regione dove non è facile effettuare misurazioni magnetiche. Sulla superficie del sole le macchie vengono analizzate sfruttando un fenomeno definito per la prima volta dal fisico olandese Pieter Zeeman, che aveva scoperto che immergendo in un campo magnetico una bottiglia riempita di gas, le linee spettrali emesse da questo gas subiscono uno split, una fessura centrale: si spaccano in due longitudinalmente. Più forte è il campo, più ampia e profonda la spaccatura. Grazie allo split di Zeeman gli spettrogrammi delle macchie solari rivelano l'intensità magnetica del fenomeno e possono persino servire per determinane la direzione.
Tutto questo nella regione di transizione non è possibile farlo perché i gas in quella zona non producono linee spettrali nel visibile. Lo fanno nell'ultravioletto, ma qui a terra l'ultravioletto non è ben osservabile. Da cui la necessità di spedire un telescopio UV a una quota sufficientemente elevata: 300 chilometri. Sarà un volo morto corto, ma si spera indicativo. Servirà soprattutto a capire che cosa fare "dopo", quali strumenti utilizzare su quali tipi di sonde.

NASA to Explore "Secret Layer" of the Sun

Sept. 5, 2008: Next April, for a grand total of 8 minutes, NASA astronomers are going to glimpse a secret layer of the sun.

Researchers call it "the transition region." It is a place in the sun's atmosphere, about 5000 km above the stellar surface, where magnetic fields overwhelm the pressure of matter and seize control of the sun's gases. It's where solar flares explode, where coronal mass ejections begin their journey to Earth, where the solar wind is mysteriously accelerated to a million mph. It is, in short, the birthplace of space weather. Researchers hope it is about to yield its secrets.
"Early next year, we're going to launch an experimental telescope that can measure vector magnetic fields in the transition region," explains Jonathan Cirtain of the Marshall Space Flight Center (MSFC). Previous studies have measured these fields above and below the transition region—but never inside it. "We hope to be the first."
The name of the telescope is SUMI, short for Solar Ultraviolet Magnetograph Investigation. It was developed by astronomers and engineers at the MSFC and is currently scheduled for launch from White Sands, New Mexico, in April 2009.
SUMI works by means of "Zeeman splitting." Dutch physicist Pieter Zeeman discovered the effect in the 19th century. When a glass tube filled with incandescent gas is dipped into a magnetic field, spectral lines emitted by the gas get split into two slightly different colors—the stronger the field, the bigger the splitting. The same thing happens on the sun. Here, for instance, are some spectral lines from gaseous iron being split by the magnetic field of a sunspot:


Zeeman splitting of spectral lines from a strongly-magnetized sunspot








By measuring the gap, astronomers estimate the strength of the sunspot's magnetic field. Furthermore, by measuring the polarization of the split line, astronomers can figure out the direction of the magnetic field. Strength + direction = everything you ever wanted to know about a magnetic field!
This trick has been applied to thousands of sunspots on the solar surface, but never to the transition region just a short distance above.
Why not?
"Just bad luck, really," says Cirtain. "Gas in the transition region doesn't produce many strong spectral lines that we can see at visible wavelengths." It does, however, produce lines at UV wavelengths invisible from Earth's surface.
SUMI will blast off inside the nose cone of a Black Brant rocket on a sub-orbital flight that takes it to an altitude of 300 km. "We'll be above more than 99.99% of Earth's atmosphere," says Cirtain. About 68 seconds into the flight, payload doors will open, affording SUMI a crystal-clear view of the UV sun. "From that moment, we've only got 8 minutes to work with. We'll target an active region and start taking data."
SUMI's "vector magnetograph" is tuned to study a pair of spectral lines: one from triply-ionized carbon (CIV) at 155 nanometers and a second from singly-ionized magnesium (MgII) at 280 nanometers. "There's nothing special about those ions," notes Cirtain. "They just happen to produce the best and brightest lines at temperatures and densities typical of the transition region."
Cirtain anticipates how it will feel to have his precious instrument hurtling 300 km above Earth at 5,000 mph: "Eight minutes of terror." He'll start breathing again when the payload doors close and SUMI begins its descent back to Earth. Cirtain ticks off the stages: "Reentry into the atmosphere. Open parachutes. Landing back at White Sands. Recovery."
The short flight probably won't lead to immediate breakthroughs. "But it will demonstrate the SUMI concept and show us if it's going to work." A successful flight would lead to more flights and eventually to a SUMI-style magnetograph permanently installed on a space telescope.
"That's the dream," he says. Transition region, prepare to yield...

La polvere lunare interagisce col geomagnetismo

Per anni sono state formulate le più strampalate teorie sulla possibile influenza lunare sulla propagazione delle onde radio qui sulla terra. Come è possibile che una massa inerte interagisca con il campo magnetico e la nostra ionosfera? A parte qualche remota possibilità di una correlazione di tipo mareale, in cui il gioco gravitazionale del sistema terra-luna determini delle deformazioni della ionosfera (così come accade con le acque degli oceani) ci troviamo di fronte, appunto, a ipotesi strampalate.
Ora però gli scienziati della NASA hanno scoperto che una interazione c'è ed è quella tra la coda del nostro campo magnetico deformato dal vento solare. Investita dalle particelle ad alta energia durante il suo tragitto attraverso la "magnetocoda", la polvere sulla superficie lunare non illuminata si caricherebbe negativamente provocando esplosivi fenomeni di scariche elettrostatiche. I futuri esploratori lunari sono avvertiti. E chissà se le famose ipotesi...

The Moon and the Magnetotail
04.17.2008

April 17, 2008: Behold the full Moon. Ancient craters and frozen lava seas lie motionless under an airless sky of profound quiet. It's a slow-motion world where even a human footprint may last millions of years. Nothing ever seems to happen there.
Right?
Wrong. NASA-supported scientists have realized that something does happen every month when the Moon gets a lashing from Earth's magnetic tail.
"Earth's magnetotail extends well beyond the orbit of the Moon and, once a month, the Moon orbits through it," says Tim Stubbs, a University of Maryland scientist working at the Goddard Space Flight Center. "This can have consequences ranging from lunar 'dust storms' to electrostatic discharges."
Yes, Earth does have a magnetic tail. It is an extension of the same familiar magnetic field we experience when using a Boy Scout compass. Our entire planet is enveloped in a bubble of magnetism, which springs from a molten dynamo in Earth's core. Out in space, the solar wind presses against this bubble and stretches it, creating a long "magnetotail" in the downwind direction.
Anyone can tell when the Moon is inside the magnetotail. Just look: "If the Moon is full, it is inside the magnetotail," says Stubbs. "The Moon enters the magnetotail three days before it is full and takes about six days to cross and exit on the other side."
It is during those six days that strange things can happen.
During the crossing, the Moon comes in contact with a gigantic "plasma sheet" of hot charged particles trapped in the tail. The lightest and most mobile of these particles, electrons, pepper the Moon's surface and give the Moon a negative charge.
On the Moon's dayside this effect is counteracted to a degree by sunlight: UV photons knock electrons back off the surface, keeping the build-up of charge at relatively low levels. But on the nightside, in the cold lunar dark, electrons accumulate and voltages can climb to hundreds or thousands of volts.
Walking across the dusty charged-up lunar terrain, astronauts may find themselves crackling with electricity like a sock pulled out of a hot dryer. Touching another astronaut, a doorknob, a piece of sensitive electronics—any of these simple actions could produce an unwelcome zap. "Proper grounding is strongly recommended," advises Stubbs.
The ground, meanwhile, may leap into the sky. There is compelling evidence that fine particles of moondust, when sufficiently charged-up, actually float above the lunar surface. This could create a temporary nighttime atmosphere of dust ready to blacken spacesuits, clog machinery, scratch faceplates (moondust is very abrasive) and generally make life difficult for astronauts.
Stranger still, moondust might gather itself into a sort of diaphanous wind. Drawn by differences in global charge accumulation, floating dust would naturally fly from the strongly-negative nightside to the weakly-negative dayside. This "dust storm" effect would be strongest at the Moon's terminator, the dividing line between day and night.
Much of this is pure speculation, Stubbs cautions. No one can say for sure what happens on the Moon when the magnetotail hits, because no one has been there at the crucial time. "Apollo astronauts never landed on a full Moon and they never experienced the magnetotail."
The best direct evidence comes from NASA's Lunar Prospector spacecraft, which orbited the Moon in 1998-99 and monitored many magnetotail crossings. During some crossings, the spacecraft sensed big changes in the lunar nightside voltage, jumping "typically from -200 V to -1000 V," says Jasper Halekas of UC Berkeley who has been studying the decade-old data.
"It is important to note," says Halekas, "that the plasma sheet (where all the electrons come from) is a very dynamic structure. The plasma sheet is in a constant state of motion, flapping up and down all the time. So as the Moon orbits through the magnetotail, the plasma sheet can sweep across it over and over again. Depending on how dynamic things are, we can encounter the plasma sheet many times during a single pass through the magnetotail with encounters lasting anywhere from minutes to hours or even days."
"As a result, you can imagine how dynamic the charging environment on the Moon is. The Moon can be just sitting there in a quiet region of the magnetotail and then suddenly all this hot plasma goes sweeping by causing the nightside potential to spike to a kilovolt. Then it drops back again just as quickly."
The roller coaster of charge would be at its most dizzying during solar and geomagnetic storms. "That is a very dynamic time for the plasma sheet and we need to study what happens then," he says.
What happens then? Next-generation astronauts are going to find out. NASA is returning to the Moon in the decades ahead and plans to establish an outpost for long-term lunar exploration. It turns out they'll be exploring the magnetotail, too.

L'aggiornamento dei satelliti guardiani del sole

Sì, c'è ancora un po' di tempo, i primi lanci sono previsti per il 2014. Il progetto GOES, i satelliti geostazionari NASA che sorvegliano le perturbazioni solari va avanti e sta prerando la serie R, cui si riferisce il contratto annunciato oggi dall'ente spaziale americano. Il dubbio è: che cosa resterà da ascoltare nel 2014 per noi?
NASA AWARDS NOAA GOES-R INSTRUMENT CONTRACT

WASHINGTON - NASA, in coordination with the National Oceanic and Atmospheric Administration's Geostationary Operational Environmental Satellites (GOES-R) Program, has awarded a contract to the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. The total estimated value is $92 million, including options.
The laboratory will build the Extreme Ultra Violet and X-Ray Irradiance Sensors that will fly on the next series of GOES-R. These instruments will help forecast solar disturbances that can affect communications and navigational operations. This satellite series will upgrade existing weather and environmental monitoring capabilities. The first launch of the series is scheduled for December 2014.
The design and development of the instruments will be performed at the contractor's facility in Boulder, Colo. The contractor also will provide post-delivery support for GOES-R.
The National Oceanic and Atmospheric Administration (NOAA) funds, operates and manages the GOES program. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the acquisition of GOES-R instruments for NOAA. For more information about the GOES-R program, visit: http://osd.goes.noaa.gov.