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.

Macchie solari osservate prima che diventino macchie

Da oggi la meteorologia del sole dispone di uno strumento in più per anticipare le macchie e le tempeste magnetiche che si verificano sul nostro astro. In uno spettacolare studio appena pubblicato su Science, i ricercatori di Stanford hanno applicato i principi dell'analisi acustica predittiva utilizzati sul nostro pianeta dai sismologi, per anticipare l'emergere delle macchie solari sulla superficie del sole. Le macchie sono gigantesche aree di intensa attività magnetica che si formano nelle profondità dell'astro ed emergono letteralmente, come sottomarini, per effetto della spinta di galleggiamento magnetico. Analizzando i dati della sonda SOHO e dell'osservatorio solare SDO, i dottorandi di Stanford sono riusciti ad "ascoltare graficamente" le onde acustiche generate nel sole dai mostruosi fenomeni di convezione e a individuare così, in profondità e con molto anticipo rispetto all'effettivo emergere in superficie, il magnetismo delle macchie.

Una volta emerse, alle macchie solari si associano fenomeni come brillamenti ed espulsioni di massa coronale, che possono determinare eventi dirompenti a terra: tempeste geomagnetiche, interferenze alle telecomunicazioni, blackout sulle reti di distribuzione dell'energia elettrica.

Sunspot Breakthrough

August 25, 2011: Imagine forecasting a hurricane in Miami weeks before the storm was even a swirl of clouds off the coast of Africa—or predicting a tornado in Kansas from the flutter of a butterfly's wing1 in Texas. These are the kind of forecasts meteorologists can only dream about.

Could the dream come true? A new study by Stanford researchers suggests that such forecasts may one day be possible—not on Earth, but on the sun.

"We have learned to detect sunspots before they are visible to the human eye," says Stathis Ilonidis, a PhD student at Stanford University. "This could lead to significant advances in space weather forecasting."

Sunspots are the "butterfly's wings" of solar storms. Visible to the human eye as dark blemishes on the solar disk, sunspots are the starting points of explosive flares and coronal mass ejections (CMEs) that sometimes hit our planet 93 million miles away. Consequences range from Northern Lights to radio blackouts to power outages.

Astronomers have been studying sunspots for more than 400 years, and they have pieced together their basic characteristics: Sunspots are planet-sized islands of magnetism that float in solar plasma. Although the details are still debated, researchers generally agree that sunspots are born deep inside the sun via the action of the sun’s inner magnetic dynamo. From there they bob to the top, carried upward by magnetic buoyancy; a sunspot emerging at the stellar surface is a bit like a submarine emerging from the ocean depths.

In the August 19th issue of Science, Ilonidis and co-workers Junwei Zhao and Alexander Kosovichev announced that they can see some sunspots while they are still submerged.

Their analysis technique is called "time-distance helioseismology2," and it is similar to an approach widely used in earthquake studies. Just as seismic waves traveling through the body of Earth reveal what is inside the planet, acoustic waves traveling through the body of the sun can reveal what is inside the star. Fortunately for helioseismologists, the sun has acoustic waves in abundance. The body of the sun is literally roaring with turbulent boiling motions. This sets the stage for early detection of sunspots.

"We can't actually hear these sounds across the gulf of space," explains Ilonidis, "but we can see the vibrations they make on the sun's surface." Instruments onboard two spacecraft, the venerable Solar and Heliospheric Observatory (SOHO) and the newer Solar Dynamics Observatory (SDO) constantly monitor the sun for acoustic activity.

Submerged sunspots have a detectable effect on the sun's inner acoustics—namely, sound waves travel faster through a sunspot than through the surrounding plasma. A big sunspot can leapfrog an acoustic wave by 12 to 16 seconds. "By measuring these time differences, we can find the hidden sunspot."

Ilonidis says the technique seems to be most sensitive to sunspots located about 60,000 km beneath the sun’s surface. The team isn't sure why that is "the magic distance," but it's a good distance because it gives them as much as two days advance notice that a spot is about to reach the surface.

"This is the first time anyone has been able to point to a blank patch of sun and say 'a sunspot is about to appear right there,'" says Ilonidis's thesis advisor Prof. Phil Scherrer of the Stanford Physics Department. "It's a big advance."

"There are limits to the technique," cautions Ilonidis. "We can say that a big sunspot is coming, but we cannot yet predict if a particular sunspot will produce an Earth-directed flare."

So far they have detected five emerging sunspots—four with SOHO and one with SDO. Of those five, two went on to produce X-class flares, the most powerful kind of solar explosion. This encourages the team to believe their technique can make a positive contribution to space weather forecasting. Because helioseismology is computationally intensive, regular monitoring of the whole sun is not yet possible—"we don’t have enough CPU cycles," says Ilonidis —but he believes it is just a matter of time before refinements in their algorithm allow routine detection of hidden sunspots.

The original research reported in this story may be found in Science magazine: "Detection of Emerging Sunspot Regions in the Solar Interior" by Ilonidis, Zhao and Kosovichev, 333 (6045): 993-996.

Ciclo 24, un massimo davvero al minimo

Un ciclo solare, il numero 24 attualmente in corso, che dovrebbe raggiungere un massimo poco prominente, tra circa due anni e mezzo. Queste sono le prime previsioni formulate dagli esperti di fisica solare del Marshall Space Flight Center della NASA, disponibili qui. Allo stato le previsioni dicono che il massimo raggiungerà un numero di macchie normalizzato pari a 64 (davvero poco) verso il luglio 2013. Proseguendo il suo cammino, il ciclo che è da poco iniziato fornirà ulteriori indizi. Ecco un riassunto delle tre tecniche utilizzate dagli scienziati per questo tipo di proiezioni.

(...)

Among the most reliable techniques are those that use the measurements of changes in the Earth's magnetic field at, and before, sunspot minimum. These changes in the Earth's magnetic field are known to be caused by solar storms but the precise connections between them and future solar activity levels is still uncertain.

Of these "geomagnetic precursor" techniques three stand out. The earliest is from Ohl and Ohl [Solar-Terrestrial Predictions Proceedings, Vol. II. 258 (1979)] They found that the value of the geomagnetic aa index at its minimum was related to the sunspot number during the ensuing maximum. The primary disadvantage of this technique is that the minimum in the geomagnetic aa index often occurs slightly after sunspot minimum so the prediction isn't available until the sunspot cycle has started.

An alternative method is due to a process suggested by Joan Feynman. She separates the geomagnetic aa index into two components: one in phase with and proportional to the sunspot number, the other component is then the remaining signal. This remaining signal has, in the past, given good estimates of the sunspot numbers several years in advance. The maximum in this signal occurs near sunspot minimum and is proportional to the sunspot number during the following maximum. This method does allow for a prediction of the next sunspot maximum at the time of sunspot minimum.

A third method is due to Richard Thompson [Solar Physics 148, 383 (1993)]. He found a relationship between the number of days during a sunspot cycle in which the geomagnetic field was "disturbed" and the amplitude of the next sunspot maximum. His method has the advantage of giving a prediction for the size of the next sunspot maximum well before sunspot minimum.

(...)

Tempeste solari, quanto ci costano

Il potente (e da oggi murdochiano) Wall Street Journal si occupa delle conseguenze economiche delle tempeste solari (100 mila dollari per il rerouting di una tratta aerea) interrogandosi in un lungo articolo sull'opportunità di spendere qualcosa in più per le previsioni. Il giornale finanziario dice che il rpossimo ciclo solare partirà nel marzo 2008, raggiungerà il massimo nel 2012 e sarà particolarmente intenso. A proposito: DXLD comunica che lo Space Environment Center del NOAA si chiamerà, a partire dal 1 ottobre, Space Weather Prediction Center. Non so quanto il cambiamento inciderà sulla URL.

Space Environment Center Changing Name to Space Weather Prediction Center

The NOAA Space Environment Center has been approved to officially change its name to the Space Weather Prediction Center (SWPC). The center is one of the nine National Centers for Environmental Prediction (NCEP)within NOAA's National Weather Service. The new name aligns the space weather center with the other NCEP centers and more clearly conveys its operational nature. The date for the name change is Monday, October 1,2007.
Our new name will begin appearing in web pages and product headers on October 1. Some web pages will have an updated "look and feel" and use NOAA web page standards, but the data displays and content will not change. Text and graphical products will have Space Weather Prediction Center (or SWPC) in headers, but there will be no changes to the file formats or content.

Digital Age Means We Must Care More About Space Weather
September 28, 2007; Page B1
By ROBERT LEE HOTZ

A moody, middle-age star, our sun has an explosive temperament. Power surges that flare from its roiling magnetic fields send outbursts of charged particles, radio static and X-rays across the 93 million miles to Earth. With little warning, these cosmic tsunamis of energy periodically have disabled commercial satellites, overloaded power grid transformers, blacked out radio communications and sent space-station astronauts scrambling for radiation shelter.
At top, the eruption of a solar prominence, or a cloud of plasma suspended in the sun's corona. The hottest areas appear almost white, while redder areas are cooler. Middle, a widely-spreading solar mass ejection blasts more than a billion tons of matter into space. At bottom, a composite image reveals solar features unique to different wavelengths.
Space weather forecasters are bracing for a new season of intense sunspot activity that could begin by March and peak in 2012 -- and they worry that outages and damage could be even greater this time because the world has become increasingly dependent on wireless and cellular electronic networks. We are, therefore, even more susceptible to these sudden gales of solar wind.
"We are set up for a nasty surprise," said Thomas Bogdan, director of the federal Space Environment Center in Boulder, Colo., the largest of 13 international space weather warning centers. "There are going to be impacts on all these services in the next few years."
Worries about solar storms are as old as the telegraph. When 19th-century entrepreneurs first started stringing long-distance wires across the U.S., they discovered that the lines attracted so much electricity during peak solar activity that the system could run without batteries and telegraph operators risked electrocution.
In a world in which even temporary service outages can pose problems, commercial satellite operators are often reluctant to discuss the impact of solar storms on their global networks, but technical reports prepared for the U.S. Commerce Department after severe solar storms in 2003 reveal just how widespread such problems can become.
A barrage of 17 major solar flares -- each an interplanetary shotgun blast of charged electrons and protons -- briefly scrambled computer circuits on more than half of NASA's satellites and space probes. The charged particles disabled navigation systems, inserted spurious commands and disrupted computer memories. A few sensors were knocked completely out of commission, while others took days to recover.
The Defense Department lost control of three surveillance satellites over "high-interest areas" for 29 hours, while Japan permanently lost contact with a $640 million Earth observation satellite.
The geomagnetic storms also caused power outages in Northern Europe and a blackout in Sweden. They forced 13 U.S. nuclear power plants to take control-room precautions, so that the electrical surges wouldn't affect reactor operations.
Forecasters at the Boulder facility -- to be renamed the Space Weather Prediction Center next week -- can offer at best a few hours' or minutes' warning of solar disturbances to their 5,700 customers, often not enough time to protect vulnerable systems.
Consequences can be as minor as a sudden shower of dropped cellphone calls or as serious as the loss of an expensive satellite, said University of Colorado physicist Daniel Baker, chairman of a National Research Council panel evaluating space weather's economic impact. With more than 860 satellites in orbit, the losses during the most extreme solar storm could run up to $30 billion, NASA researchers reported this spring in the journal Space Weather.

Changing travel patterns also add risk.

To save time and fuel on flights between North America and Asia, 11 commercial airlines today routinely route planes over the high Arctic, where the aircraft are especially vulnerable to radio blackouts and radiation bursts. In 2005, 3,731 commercial flights took the shortcut over the North Pole -- 10 times the number at the height of the last sunspot season in 2000. As the next solar cycle reaches its peak in 2012, polar airline traffic is expected to grow to 1.7 million passengers a year.
At the height of the 2003 solar storms, polar flights had almost daily communications blackouts, which required that planes be rerouted. The Federal Aviation Administration for the first time also warned pilots on polar routes to stay at lower altitudes to avoid slightly higher radiation levels.
Every flight rerouted due to solar radiation or radio blackouts costs airlines up to $100,000 and, without sufficient warning, airlines must scramble at the last minute to take the necessary precautions. Passengers may be delayed or miss connections. The slightly increased radiation may also pose a health hazard to pregnant women and, over the long run, to flight crews who regular fly the Arctic.
"An airline passenger going over the Pole has to worry," said physicist Douglas Biesecker, chairman of the federal solar-cycle forecasting panel.
Until next spring, the sun is in a periodic lull. Even so, it can catch forecasters off-guard.
Last December, Cornell University researchers reported, the sun unleashed a burst of high-frequency radio waves 10 times as powerful as any previously measured -- strong enough to interfere with Global Positioning System signals world-wide.

RECOMMENDED READING

-- by Robert Lee Hotz

For the daily solar weather forecast, check the NOAA Space Environment Center, which offers free solar forecasts, warnings and alerts to 5,700 customers. It is the largest of 13 international solar weather warning centers.
* * *
The Space Weather Journal, published online by the American Geophysical Union, is a new journal devoted to the emerging field of space weather and its impact on technical systems, including telecommunications, electric power and satellite navigation.
* * *
NASA's Solar and Heliospheric Observatory is one of a growing number of satellites and observatories that keep a weather eye on the sun. The SOHO home page features images and movies of sunspots and solar activity, as well as animations of interactions between the sun and Earth.
* * *
Hinode (Sunrise) is a project to study the sun, led by the Japanese Aerospace Exploration Agency in collaboration with NASA, the Particle Physics and Astronomy Research Council, and the European Space Agency. Hinode's three-year mission is to explore the magnetic fields of the sun and improve our understanding of the mechanisms that power the solar atmosphere and drive solar eruptions.
* * *
Space Weather Resources is an online clearinghouse of sites and background information maintained by Rice University.

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