Satellite Hinobe, un sole a quattro poli?

Diversi siti Web cospirazionisti hanno fatto eco in questi giorni a un lancio dell'Asahi Shinbun, il quotidiano giapponese, che riportava a sua volta il comunicato stampa del team di scienziati che analizzano i dati del satellite Hinode (Sunrise, nome assegnato dopo che nel pre-lancio, risalente al 2006, il satellite si era chiamato Solar-B), una missione congiunta JAXA, NASA e ESA che esplora in dettaglio l'attività magnetica del sole. La notizia riguarda un evento che a una lettura superficiale suona abbasanza inquietante. Il sole si sta trasformando in un gigantesco quadrupolo magnetico.

Il livello di risoluzione raggiunto da Hinode ha consentito in questi anni di rafforzare la nostra conoscenza sul fenomeno della "dinamo solare", l'effetto allla base della produzione delle celebri macchie, nonché degli eventi a esse correlati, come le eiezioni di massa coronale. Alla base della dinamo solare c'è il campo magnetico dell'astro: secondo la teoria le linee che congiungono i due poli del sole subiscono all'altezza dell'equatore una progressiva distorsione causata dalla diversa velocità angolare del sole alla latitudine bassa. Le linee tendono a spezzarsi, a richiudersi in maniera indipendente e a formare quindi delle "zone di interdizione" al calore che a loro volta si traducono in macchie solari (poi anche le linee del campo locale associate alle macchie si ricongiungono con le linee del campo magnetico totale dando vita agli effetti eiettivi, ma questo è un altro discorso).

In un comunicato rilasciato il 19 aprile (questa la versione originale in giapponese, ve la fornisco perché la traduzione con Google è abbastanza chiara e c'è un sacco di materiale aggiuntivo, molto meno rispetto alla traduzione inglese pubblicata nella versione del sito Hinode in questa lingua). In questi 4 anni, dice il comunicato, Hinode ha osservato in dettaglio il fenomeno dell'inversione di polarità che caratterizza, tra i tanti, il famoso ciclo solare. Ogni 11 anni circa, in corrispondenza del massimo solare, il picco di intensità raggiunto dal flusso e dal numero di macchie, i poli magnetici del sole si invertono rapidamente, il polo nord prende il posto del sud e viceversa. In base alle previsioni, questa inversione avrebbe dovuto verificarsi intorno al 2013, data appunto prevista per il nuovo massimo. Ma come forse sapete se leggete questo blog regolarmente, stiamo attraversando un periodo di intensità solare molto bassa, con un minimo di macchie che è stato prolungatissimo. Per quasi un anno anzi, il sole non ne ha praticamente avute, di macchie.

Che qualcosa stia succedendo (gli esperti ipotizzano un effetto di Dalton, o addirittura Maunder, due osservatori che nel '600 e alla fine del '700 hanno descritto periodi estremamente lunghi di minimo solare) sembrano ora testimoniarlo le osservazioni di Hinode. Quali sono le conclusioni degli astrofisici giapponesi? In quest'ultimo anno di rilevamento del flusso magnetico in corrispondenza delle regioni polari del sole si è rafforzato un fenomeno che va avanti dal 2008: il polo nord geografico del sole sta cambiando rapidamente la polarità magnetica. Normale, direte voi, con l'approssimarsi del massimo.

E invece no: il cambiamento di polarità sta accelerando, passando dal meno al più (la polarità dovrebbe cambiare già quest'anno) mentre non sta accadendo la stessa cosa al polo sud geografico, dove il segno più magnetico è assolutamente stabile. Le immagini che potete vedere, allegate a una recente testi di astrofisica e distribuite dai responsabili della missione Hinobe a corredo dei loro comunicati, sono molto evidenti. Al colore arancione corrisponde una polarità negativa, all'azzurro una positiva. Nell'immagine che riguarda le latitudini nord (coppia di immagini in alto) le chiazze arancione si diradano, cedono il posto all'azzurro (il confronto è 2008-2011 e 2009-2012), mentre alle estreme latitudini meridionali le chiazze azzurre dominano senza flessioni. Insomma, tra poco tempo rischiamo di avere un sole con quattro poli magnetici, due, positivi entrambi, in corrispondenza dei poli geografici; più verosimilmente altri due, ma col segno meno, in regioni equatoriali opposte tra loro. Un quadrupolo magnetico al posto di un dipolo.
Seguendo tale ragionamento, ci si potrebbe chiedere quali potrebbero essere le conseguenze di tale anomalia sulla dinamo solare. La quadrupla polarità potrebbe influire sul "motore" delle macchie solari, riducendone, come per una sorta di messa a terra, l'output complessivo e trascinando il sistema terra-sole verso le condizioni climatiche pre-glaciali che duecento e trecentocinquanta anni fa furono il "segno" più evidente dei minimi profondi. Nonché verso un probabile letargo delle onde corte sulle frequenze più alte.

Intanto, anche la NASA conferma, con la sua ultima stima sull'andamento del ciclo 24, che il prossimo massimo solare si raggiungerà nella primavera del 2o13 e sarà il meno intenso degli ultimi 100 anni, con un numero normalizzato di macchie pari a 60,2, contro i 118,4 del settembre 2000, in corrispondenza con il massimo del ciclo 23.

Sole "senza macchie", colpa della corrente meridionale?

In un articolo pubblicato ieri su Nature e annunciato da una conferenza stampa alla NASA, un team di scienziati di Calcutta, Bozeman nel Montana e Cambridge nel Massachusetts ha presentato i risultati di un lungo studio di modellazione della dinamica solare, affermando di aver trovato la possibile spiegazione del minimo solare prolungato che ha caratterizzato il biennio tra il 2008 e il 2009, ritardando l'avvento del ciclo solare 24 attualmente in corso. In quel periodo gli astrofisici solari hanno contato un elevato numero di giorni "spotless", privi di macchie solari, il più alto da un secolo a questa parte. I fisici dell'atmosfera hanno invece registrato un abbassamento della temperatura degli strati alti dell'atmosfera, che in molti punti ha collassato come una mela che avvizisce. Questa contrazione dell'atmosfera ha influito sui cosiddetti detriti spaziali, i resti dei satelliti artificiali che in condizioni normali entrano in contatto con l'atmosfera e finiscono distrutti. A causa dell'abbassamento di quota di quest'ultima, i detriti si sono accumulati e sul pianeta sono piovute per buona misura grandi quantità di raggi cosmici. Il raffreddamento causato dalla diminuzione della quantità di raggi UV provenienti dalle macchie potrebbe avere conseguenze climatiche sulla temperatura complessiva della terra. In occasione del celebre "minimo di Maunder" nel '600, i climatologi tendono ad associare la prolungata assenza di macchie alla "miniglaciazione", durata una settantina di anni, che si era verificata allora.

Il modello proposto dagli scienziati può essere equiparato a una fabbrica di macchie solari e agli effetti distorsivi della "corrente meridionale" che circola, come una corrente oceanica, dalle regioni polari del sole in direzione del suo equatore, un vero e proprio "nastro trasportatore di macchie", che trascina i resti delle macchie consumate per 300 mila chilometri nella profondità del sole e riporta verso la superficie le macchie rigenerate.

Nella prima parte del periodo spotless questo nastro ha subito una forte accelerazione, trascinando i resti magnetici delle macchie in modo troppo vorticoso, creando una sorta di tappo. A quel punto la corrente meridionale ha subito un rallentamento e il meccanismo di rigenerazione magnetica è andato in tilt. Solo adesso la situazione si sarebbe normalizzata ma intanto i ricercato stanno affinando i loro strumenti predittivi per l'analisi del prossimo minimo.

Le ultime previsioni pubblicate proprio pochi giorni fa dal Marshall Space Flight Center dicono che con un numero "normalizzato" pari a 58 macchie raggiunto a metà 2013, il massimo del ciclo 24 sarà il più basso in quasi 200 anni.

Researchers Crack the Mystery of the Spotless Sun

03.02.11

In 2008-2009, sunspots almost completely disappeared for two years. Solar activity dropped to hundred-year lows; Earth's upper atmosphere cooled and collapsed; the sun’s magnetic field weakened, allowing cosmic rays to penetrate the Solar System in record numbers. It was a big event, and solar physicists openly wondered, where have all the sunspots gone?

Now they know. An answer is being published in the March 3rd edition of Nature. "Plasma currents deep inside the sun interfered with the formation of sunspots and prolonged solar minimum," says lead author Dibyendu Nandi of the Indian Institute of Science Education and Research in Kolkata. "Our conclusions are based on a new computer model of the sun's interior."

For years, solar physicists have recognized the importance of the sun's "Great Conveyor Belt." A vast system of plasma currents called ‘meridional flows’ (akin to ocean currents on Earth) travel along the sun's surface, plunge inward around the poles, and pop up again near the sun's equator. These looping currents play a key role in the 11-year solar cycle. When sunspots begin to decay, surface currents sweep up their magnetic remains and pull them down inside the star; 300,000 km below the surface, the sun’s magnetic dynamo amplifies the decaying magnetic fields. Re-animated sunspots become buoyant and bob up to the surface like a cork in water—voila! A new solar cycle is born.

For the first time, Nandi’s team believes they have developed a computer model that gets the physics right for all three aspects of this process--the magnetic dynamo, the conveyor belt, and the buoyant evolution of sunspot magnetic fields.

"According to our model, the trouble with sunspots actually began in back in the late 1990s during the upswing of Solar Cycle 23," says co-author Andrés Muñoz-Jaramillo of the Harvard-Smithsonian Center for Astrophysics. "At that time, the conveyor belt sped up."

The fast-moving belt rapidly dragged sunspot corpses down to sun's inner dynamo for amplification. At first glance, this might seem to boost sunspot production, but no. When the remains of old sunspots reached the dynamo, they rode the belt through the amplification zone too hastily for full re-animation. Sunspot production was stunted.

Later, in the 2000s, according to the model, the Conveyor Belt slowed down again, allowing magnetic fields to spend more time in the amplification zone, but the damage was already done. New sunspots were in short supply. Adding insult to injury, the slow moving belt did little to assist re-animated sunspots on their journey back to the surface, delaying the onset of Solar Cycle 24. "The stage was set for the deepest solar minimum in a century," says co-author Petrus Martens of the Montana State University Department of Physics. Colleagues and supporters of the team are calling the new model a significant advance. "Understanding and predicting solar minimum is something we’ve never been able to do before---and it turns out to be very important," says Lika Guhathakurta of NASA’s Heliophysics Division in Washington, DC.

While Solar Max is relatively brief, lasting a few years punctuated by episodes of violent flaring, over and done in days, Solar Minimum can grind on for many years. The famous Maunder Minimum of the 17th century lasted 70 years and coincided with the deepest part of Europe's Little Ice Age. Researchers are still struggling to understand the connection.

One thing is clear: During long minima, strange things happen. In 2008-2009, the sun’s global magnetic field weakened and the solar wind subsided. Cosmic rays normally held at bay by the sun’s windy magnetism surged into the inner solar system. During the deepest solar minimum in a century, ironically, space became a more dangerous place to travel. At the same time, the heating action of UV rays normally provided by sunspots was absent, so Earth’s upper atmosphere began to cool and collapse. Space junk stopped decaying as rapidly as usual and started accumulating in Earth orbit. And so on….

Nandi notes that their new computer model explained not only the absence of sunspots but also the sun’s weakened magnetic field in 08-09. "It's confirmation that we’re on the right track."

Next step: NASA’s Solar Dynamics Observatory (SDO) can measure the motions of the sun’s conveyor belt—not just on the surface but deep inside, too. The technique is called helioseismology; it reveals the sun’s interior in much the same way that an ultrasound works on a pregnant woman. By plugging SDO’s high-quality data into the computer model, the researchers might be able to predict how future solar minima will unfold. SDO is just getting started, however, so forecasts will have to wait.

Indeed, much work remains to be done, but, says Guhathakurta, "finally, we may be cracking the mystery of the spotless sun."

Sole e clima, le possibili conseguenze di Maunder

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

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

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

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

Termosfera e minimo solare: una contrazione di troppo

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

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

A Puzzling Collapse of Earth's Upper Atmosphere

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

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

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

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

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

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

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

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

One possible explanation is carbon dioxide (CO2).

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

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

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

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

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

Or not.

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

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

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

NASA SDO, dall'orbita tutti i segreti del Sole

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

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

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

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

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.

Minimo solare senza macchie, scoperta la causa?

Gli scienziati del National Solar Observatory di Tucson, Arizona, potrebbero aver individuato la ragione del prolungato minimo che caratterizza da parecchi mesi il ciclo di attività solare. Nella profondità dell'astro esiste una "corrente a getto" che si muove come le correnti oceaniche o analoghi fenomeni atmosferici. Come spiega Spaceweather.com sarebbe questa corrente a partecipare a "innescare" il ciclo delle macchie solari e dei fenomeni ad esse associate: quando la corrente raggiunge una determinata latitudine del globo solare, i 22 gradi, le macchie ripartono. Negli ultimi tre o quattro anni, dicono i ricercatori di Tucson che si sono serviti di avanzate tecniche di indagine "eliosismica", la corrente a getto interna si è mossa con inusistata lentezza. La scoperta sembra confermare anche che il lungo minimo è arrivato alla fine perché la corrente in quesione si sta di nuovo muovendo. Contrariamente alle previsioni di alcuni, le macchie torneranno a ricoprire il disco del sole.

Mystery of the Missing Sunspots, Solved?
06.17.2009


June 17, 2009: The sun is in the pits of a century-class solar minimum, and sunspots have been puzzlingly scarce for more than two years. Now, for the first time, solar physicists might understand why. At an American Astronomical Society press conference today in Boulder, Colorado, researchers announced that a jet stream deep inside the sun is migrating slower than usual through the star's interior, giving rise to the current lack of sunspots.
Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained to a room full of reporters and fellow scientists. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear.
Howe and Hill found that the stream associated with the next solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to only two years for the previous solar cycle.
The jet stream is now, finally, reaching the critical latitude, heralding a return of solar activity in the months and years ahead. "It is exciting to see", says Hill, "that just as this sluggish stream reaches the usual active latitude of 22 degrees, a year late, we finally begin to see new groups of sunspots emerging."
The current solar minimum has been so long and deep, it prompted some scientists to speculate that the sun might enter a long period with no sunspot activity at all, akin to the Maunder Minimum of the 17th century. This new result dispells those concerns. The sun's internal magnetic dynamo is still operating, and the sunspot cycle is not "broken."
Because it flows beneath the surface of the sun, the jet stream is not directly visible. Hill and Howe tracked its hidden motions via helioseismology. Shifting masses inside the sun send pressure waves rippling through the stellar interior. So-called "p modes" (p for pressure) bounce around the interior and cause the sun to ring like an enormous bell. By studying the vibrations of the sun's surface, it is possible to figure out what is happening inside. Similar techniques are used by geologists to map the interior of our planet.
In this case, researchers combined data from GONG and SOHO. GONG, short for "Global Oscillation Network Group," is an NSO-led network of telescopes that measures solar vibrations from various locations around Earth. SOHO, the Solar and Heliospheric Observatory, makes similar measurements from space.
"This is an important discovery," says Dean Pesnell of NASA's Goddard Space Flight Center. "It shows how flows inside the sun are tied to the creation of sunspots and how jet streams can affect the timing of the solar cycle. We still don't understand exactly how jet streams trigger sunspot production," says Pesnell. "Nor do we fully understand how the jet streams themselves are generated."
To solve these mysteries, and others, NASA plans to launch the Solar Dynamics Observatory (SDO) later this year. SDO is equipped with sophisticated helioseismology sensors that will allow it to probe the solar interior better than ever before. "The Helioseismic and Magnetic Imager (HMI) on SDO will improve our understanding of these jet streams and other internal flows by providing full disk images at ever-increasing depths in the sun," says Pesnell.

Macchie solari, un minimo prolungato

Teoricamente doveva essere passato. E invece sembra proprio che il minimo di questo ciclo, il 24, non arrivi mai. Il 2008 è stato caratterizzato da un record di 266 giorni senza macchie (solo il 1913 era stato più avaro di formazioni sul disco solare). Ma nei primi 90 giorni del 2009 quelli senza macchie sono stati ben 78. Secondo gli scienziati della NASA stiamo vivendo un minimo prolungato dopo cinque cicli undecennale molto intensi. Quanto durerà? Non si sa, ma intanto le conseguenze sono una riduzione dell'attività aurorale e molto altro. Le osservazioni dimostrano per esempio che anche fenomeni come il vento solare, le emissioni radio o la stessa radianza dell'astro, hanno subito una contrazione in questi ultimi anni.

Deep Solar Minimum
04.01.2009

April 1, 2009: The sunspot cycle is behaving a little like the stock market. Just when you think it has hit bottom, it goes even lower.
2008 was a bear. There were no sunspots observed on 266 of the year's 366 days (73%). To find a year with more blank suns, you have to go all the way back to 1913, which had 311 spotless days: plot. Prompted by these numbers, some observers suggested that the solar cycle had hit bottom in 2008.
Maybe not. Sunspot counts for 2009 have dropped even lower. As of March 31st, there were no sunspots on 78 of the year's 90 days (87%).
It adds up to one inescapable conclusion: "We're experiencing a very deep solar minimum," says solar physicist Dean Pesnell of the Goddard Space Flight Center.
"This is the quietest sun we've seen in almost a century," agrees sunspot expert David Hathaway of the Marshall Space Flight Center.
Quiet suns come along every 11 years or so. It's a natural part of the sunspot cycle, discovered by German astronomer Heinrich Schwabe in the mid-1800s. Sunspots are planet-sized islands of magnetism on the surface of the sun; they are sources of solar flares, coronal mass ejections and intense UV radiation. Plotting sunspot counts, Schwabe saw that peaks of solar activity were always followed by valleys of relative calm—a clockwork pattern that has held true for more than 200 years: plot.
The current solar minimum is part of that pattern. In fact, it's right on time. "We're due for a bit of quiet—and here it is," says Pesnell.
But is it supposed to be this quiet? In 2008, the sun set the following records:

A 50-year low in solar wind pressure: Measurements by the Ulysses spacecraft reveal a 20% drop in solar wind pressure since the mid-1990s—the lowest point since such measurements began in the 1960s. The solar wind helps keep galactic cosmic rays out of the inner solar system. With the solar wind flagging, more cosmic rays are permitted to enter, resulting in increased health hazards for astronauts. Weaker solar wind also means fewer geomagnetic storms and auroras on Earth.

A 12-year low in solar "irradiance": Careful measurements by several NASA spacecraft show that the sun's brightness has dropped by 0.02% at visible wavelengths and a whopping 6% at extreme UV wavelengths since the solar minimum of 1996. These changes are not enough to reverse the course of global warming, but there are some other, noticeable side-effects: Earth's upper atmosphere is heated less by the sun and it is therefore less "puffed up." Satellites in low Earth orbit experience less atmospheric drag, extending their operational lifetimes. That's the good news. Unfortunately, space junk also remains longer in Earth orbit, increasing hazards to spacecraft and satellites.

A 55-year low in solar radio emissions: After World War II, astronomers began keeping records of the sun's brightness at radio wavelengths. Records of 10.7 cm flux extend back all the way to the early 1950s. Radio telescopes are now recording the dimmest "radio sun" since 1955: plot. Some researchers believe that the lessening of radio emissions is an indication of weakness in the sun's global magnetic field. No one is certain, however, because the source of these long-monitored radio emissions is not fully understood.

All these lows have sparked a debate about whether the ongoing minimum is "weird", "extreme" or just an overdue "market correction" following a string of unusually intense solar maxima.
"Since the Space Age began in the 1950s, solar activity has been generally high," notes Hathaway. "Five of the ten most intense solar cycles on record have occurred in the last 50 years. We're just not used to this kind of deep calm."
Deep calm was fairly common a hundred years ago. The solar minima of 1901 and 1913, for instance, were even longer than the one we're experiencing now. To match those minima in terms of depth and longevity, the current minimum will have to last at least another year.
see captionIn a way, the calm is exciting, says Pesnell. "For the first time in history, we're getting to see what a deep solar minimum is really like." A fleet of spacecraft including the Solar and Heliospheric Observatory (SOHO), the twin STEREO probes, the five THEMIS probes, ACE, Wind, TRACE, AIM, TIMED, Geotail and others are studying the sun and its effects on Earth 24/7 using technology that didn't exist 100 years ago. Their measurements of solar wind, cosmic rays, irradiance and magnetic fields show that solar minimum is much more interesting and profound than anyone expected.
Modern technology cannot, however, predict what comes next. Competing models by dozens of top solar physicists disagree, sometimes sharply, on when this solar minimum will end and how big the next solar maximum will be. Pesnell has surveyed the scientific literature and prepared a "piano plot" showing the range of predictions. The great uncertainty stems from one simple fact: No one fully understands the underlying physics of the sunspot cycle.
Pesnell believes sunspot counts will pick up again soon, "possibly by the end of the year," to be followed by a solar maximum of below-average intensity in 2012 or 2013.
But like other forecasters, he knows he could be wrong. Bull or bear? Stay tuned for updates.

Sole, primi sintomi del dopo minimo

Difficile ricordare di un periodo così favorevole alla ricezione delle stazioni nordamericane in onde medie oltre Atlantico. In Scozia sono arrivate due o tre stazioni delle Hawaii, qui in Italia si sentono stati ben oltre la linea di demarcazione che distingue le "W" dalle "K stations": il tortuoso confide del Mississipi (in realtà qualche stazione a est del fiume porta ancora la K nell'identificativo.
Eppure la Nasa pubblica in questo articolo un resoconto dei primi timidi segni di attività del Sole del dopo-minimo. Mancano ancora diversi anni alla vera rampa del prossimo anno e venti giorni di ottobre su trentuno sono stati "senza macchie", ma qualcosa si muove sul disco del nostro astro. Macchie che non solo non impediscono le eccezionali aperture di queste settimane (ci credo, non posso accendere la radio...) ma che con molta probabilità "stimolano" positivamente la ionosfera.

The Sun Shows Signs of Life
10.07.2008

Nov. 7, 2008: After two-plus years of few sunspots, even fewer solar flares, and a generally eerie calm, the sun is finally showing signs of life.
"I think solar minimum is behind us," says sunspot forecaster David Hathaway of the NASA Marshall Space Flight Center.
His statement is prompted by an October flurry of sunspots. "Last month we counted five sunspot groups," he says. That may not sound like much, but in a year with record-low numbers of sunspots and long stretches of utter spotlessness, five is significant. "This represents a real increase in solar activity."
Even more significant is the fact that four of the five sunspot groups belonged to Solar Cycle 24, the long-awaited next installment of the sun's 11-year solar cycle. "October was the first time we've seen sunspots from new Solar Cycle 24 outnumbering spots from old Solar Cycle 23. It's a good sign that the new cycle is taking off."
Old Solar Cycle 23 peaked in 2000 and has since decayed to low levels. Meanwhile, new Solar Cycle 24 has struggled to get started. 2008 is a year of overlap with both cycles weakly active at the same time. From January to September, the sun produced a total of 22 sunspot groups; 82% of them belonged to old Cycle 23. October added five more; but this time 80% belonged to Cycle 24. The tables have turned.
At first glance, old- and new-cycle sunspots look the same, but they are not. To tell the difference, solar physicists check two things: a sunspot's heliographic latitude and its magnetic polarity. (1) New-cycle sunspots always appear at high latitude, while old-cycle spots cluster around the sun's equator. (2) The magnetic polarity of new-cycle spots is reversed compared to old-cycle spots. Four of October's five sunspot groups satisfied these two criteria for membership in Solar Cycle 24.
The biggest of the new-cycle spots emerged at the end of the month on Halloween. Numbered 1007, or "double-oh seven" for short, the sunspot had two dark cores each wider than Earth connected by active magnetic filaments thousands of kilometers long.
On Nov. 3rd and again on Nov. 4th, double-oh seven unleashed a series of B-class solar flares. Although B-flares are considered minor, the explosions made themselves felt on Earth. X-rays bathed the dayside of our planet and sent waves of ionization rippling through the atmosphere over Europe. Hams monitoring VLF radio beacons noticed strange "fades" and "surges" caused by the sudden ionospheric disturbances.
Hathaway tamps down the excitement: "We're still years away from solar maximum and, in the meantime, the sun is going to have some more quiet stretches." Even with its flurry of sunspots, the October sun was mostly blank, with zero sunspots on 20 of the month's 31 days.
But it's a start. Stay tuned for solar activity.

Minimo solare, più senza macchie non si può

Ormai è ufficiale, il disco solare del 2008 è quello con meno macchie di tutti degli ultimi 55 anni, la cosiddetta era spaziale. Ma per chi il sole cerca di studiarlo dentro, spiega la NASA, questo minimo prolungato potrebbe essere una panacea: le macchie rappresentano "rumore" e "perturbazione" per chi deve effettuare misure strumentali e modellamenti.
Intanto però le poche timide macchie che spuntano in questo inizio di ciclo 24 si sciolgono subito riuscendo comunque ad alimentare qualche perturbazione dellla attività geomagnetica.

Spotless Sun: Blankest Year of the Space Age

Sept. 30, 2008: Astronomers who count sunspots have announced that 2008 is now the "blankest year" of the Space Age.

As of Sept. 27, 2008, the sun had been blank, i.e., had no visible sunspots, on 200 days of the year. To find a year with more blank suns, you have to go back to 1954, three years before the launch of Sputnik, when the sun was blank 241 times.
"Sunspot counts are at a 50-year low," says solar physicist David Hathaway of the NASA Marshall Space Flight Center. "We're experiencing a deep minimum of the solar cycle."
The image, taken by the Solar and Heliospheric Observatory (SOHO) on Sept. 27, 2008, shows a solar disk completely unmarked by sunspots. For comparison, a SOHO image taken seven years earlier on Sept. 27, 2001, is peppered with colossal sunspots, all crackling with solar flares: image. The difference is the phase of the 11-year solar cycle. 2001 was a year of solar maximum, with lots of sunspots, solar flares and geomagnetic storms. 2008 is at the cycle's opposite extreme, solar minimum, a quiet time on the sun.
And it is a very quiet time. If solar activity continues as low as it has been, 2008 could rack up a whopping 290 spotless days by the end of December, making it a century-level year in terms of spotlessness.
Hathaway cautions that this development may sound more exciting than it actually is: "While the solar minimum of 2008 is shaping up to be the deepest of the Space Age, it is still unremarkable compared to the long and deep solar minima of the late 19th and early 20th centuries." Those earlier minima routinely racked up 200 to 300 spotless days per year.

Above: A histogram showing the blankest years of the last half-century. The vertical axis is a count of spotless days in each year. The bar for 2008, which was updated on Sept. 27th, is still growing.

Some solar physicists are welcoming the lull.
"This gives us a chance to study the sun without the complications of sunspots," says Dean Pesnell of the Goddard Space Flight Center. "Right now we have the best instrumentation in history looking at the sun. There is a whole fleet of spacecraft devoted to solar physics--SOHO, Hinode, ACE, STEREO and others. We're bound to learn new things during this long solar minimum."
As an example he offers helioseismology: "By monitoring the sun's vibrating surface, helioseismologists can probe the stellar interior in much the same way geologists use earthquakes to probe inside Earth. With sunspots out of the way, we gain a better view of the sun's subsurface winds and inner magnetic dynamo."
"There is also the matter of solar irradiance," adds Pesnell. "Researchers are now seeing the dimmest sun in their records. The change is small, just a fraction of a percent, but significant. Questions about effects on climate are natural if the sun continues to dim."
Pesnell is NASA's project scientist for the Solar Dynamics Observatory (SDO), a new spacecraft equipped to study both solar irradiance and helioseismic waves. Construction of SDO is complete, he says, and it has passed pre-launch vibration and thermal testing. "We are ready to launch! Solar minimum is a great time to go."
Coinciding with the string of blank suns is a 50-year record low in solar wind pressure, a recent discovery of the Ulysses spacecraft. (See the Science@NASA story Solar Wind Loses Pressure.) The pressure drop began years before the current minimum, so it is unclear how the two phenomena are connected, if at all. This is another mystery for SDO and the others.
Who knew the blank sun could be so interesting? More to come...

Aiuto, il sole ha esaurito le macchie? (No)

I DXer dell'FM lamentano una stagione deludente per la propagazione E sporadica, anche se le correlazioni tra macchie solari ed E sporadico sono piuttosto labili: se nello strato F della ionosfera la correlazione tra MUF e flusso solare è forte, nella formazione delle nuvole Es concorrono fenomeni e meccanismi non ancora chiari.
In ogni caso c'è un certo livello di preoccupazione per un minimo solare che sembra prolungarsi oltre il dovuto. Si è rotto qualcosa nel meccanismo delle macchie? David Hathaway, fisico della NASA, è andato a controllare e non ha riscontrato particolari anomalie. E' normale che in periodo di minimo il sole indugi anche molto a lungo nella sua "vacanza". Hathaway è andato a confrontare il numero di "giorni senza macchia" nei cicli solari precedenti e ha scoperto che nel 1933...

What's Wrong with the Sun? (Nothing)

07.11.2008

July 11, 2008: Stop the presses! The sun is behaving normally.

So says NASA solar physicist David Hathaway. "There have been some reports lately that Solar Minimum is lasting longer than it should. That's not true. The ongoing lull in sunspot number is well within historic norms for the solar cycle."
This report, that there's nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise.
But first, a status report: "The sun is now near the low point of its 11-year activity cycle," says Hathaway. "We call this 'Solar Minimum.' It is the period of quiet that separates one Solar Max from another."
During Solar Max, huge sunspots and intense solar flares are a daily occurance. Auroras appear in Florida. Radiation storms knock out satellites. Radio blackouts frustrate hams. The last such episode took place in the years around 2000-2001.
During Solar Minimum, the opposite occurs. Solar flares are almost non-existant while whole weeks go by without a single, tiny sunspot to break the monotony of the blank sun. This is what we are experiencing now.
Although minima are a normal aspect of the solar cycle, some observers are questioning the length of the ongoing minimum, now slogging through its 3rd year.
"It does seem like it's taking a long time," allows Hathaway, "but I think we're just forgetting how long a solar minimum can last." In the early 20th century there were periods of quiet lasting almost twice as long as the current spell. (See the end notes for an example.) Most researchers weren't even born then.
Hathaway has studied international sunspot counts stretching all the way back to 1749 and he offers these statistics: "The average period of a solar cycle is 131 months with a standard deviation of 14 months. Decaying solar cycle 23 (the one we are experiencing now) has so far lasted 142 months--well within the first standard deviation and thus not at all abnormal. The last available 13-month smoothed sunspot number was 5.70. This is bigger than 12 of the last 23 solar minimum values."
In summary, "the current minimum is not abnormally low or long."
The longest minimum on record, the Maunder Minimum of 1645-1715, lasted an incredible 70 years. Sunspots were rarely observed and the solar cycle seemed to have broken down completely. The period of quiet coincided with the Little Ice Age, a series of extraordinarily bitter winters in Earth's northern hemisphere. Many researchers are convinced that low solar activity, acting in concert with increased volcanism and possible changes in ocean current patterns, played a role in that 17th century cooling.
For reasons no one understands, the sunspot cycle revived itself in the early 18th century and has carried on since with the familiar 11-year period. Because solar physicists do not understand what triggered the Maunder Minimum or exactly how it influenced Earth's climate, they are always on the look-out for signs that it might be happening again.
The quiet of 2008 is not the second coming of the Maunder Minimum, believes Hathaway. "We have already observed a few sunspots from the next solar cycle," he says. (See Solar Cycle 24 Begins.) "This suggests the solar cycle is progressing normally."
What's next? Hathaway anticipates more spotless days1, maybe even hundreds, followed by a return to Solar Max conditions in the years around 2012.

Sole: nuovo ciclo iniziato?

Forse ci siamo. L'11 dicembre a una latitudine piuttosto elevata sul disco solare, in prossimità del bordo, è apparso un primo nodo di magnetismo a polarità invertita rispetto all'orientamento delle macchie negli ultimi 11 anni del ciclo 23. Secondo gli esperti della NASA le immagini trasmesse dal Solar and Heliospheric Observatory (SOHO) potrebbero segnalare l'inizio del nuovo ciclo. E a quanto dicono alcune prime stime potrebbe trattarsi di un ciclo molto intenso, ancora più intenso rispetto al duplice picco raggiunto tra il 2000 e il 2003 dal ciclo che si sta comunque concludendo. Il prossimo massimo è atteso a partire dal 2011 e potrebbe rivelarsi molto avverso per alcuni fondamentali servizi di telecomunicazione e radiolocalizzazione, oltre che per le infrastrutture elettriche ad alta tensione.

Is a New Solar Cycle Beginning?

Dec. 14, 2007: The solar physics community is abuzz this week. No, there haven't been any great eruptions or solar storms. The source of the excitement is a modest knot of magnetism that popped over the sun's eastern limb on Dec. 11th, pictured below in a pair of images from the orbiting Solar and Heliospheric Observatory (SOHO).
It may not look like much, but "this patch of magnetism could be a sign of the next solar cycle," says solar physicist David Hathaway of the Marshall Space Flight Center.
For more than a year, the sun has been experiencing a lull in activity, marking the end of Solar Cycle 23, which peaked with many furious storms in 2000--2003. "Solar minimum is upon us," he says.
The big question now is, when will the next solar cycle begin?
It could be starting now.
"New solar cycles always begin with a high-latitude, reversed polarity sunspot," explains Hathaway. "Reversed polarity " means a sunspot with opposite magnetic polarity compared to sunspots from the previous solar cycle. "High-latitude" refers to the sun's grid of latitude and longitude. Old cycle spots congregate near the sun's equator. New cycle spots appear higher, around 25 or 30 degrees latitude.
The region that appeared on Dec. 11th fits both these criteria. It is high latitude (24 degrees N) and magnetically reversed. Just one problem: There is no sunspot. So far the region is just a bright knot of magnetic fields. If, however, these fields coalesce into a dark sunspot, scientists are ready to announce that Solar Cycle 24 has officially begun.
Many forecasters believe Solar Cycle 24 will be big and intense. Peaking in 2011 or 2012, the cycle to come could have significant impacts on telecommunications, air traffic, power grids and GPS systems. (And don't forget the Northern Lights!) In this age of satellites and cell phones, the next solar cycle could make itself felt as never before.
The furious storms won't start right away, however. Solar cycles usually take a few years to build to a frenzy and Cycle 24 will be no exception. "We still have some quiet times ahead," says Hathaway.
Meanwhile, all eyes are on a promising little active region. Will it become the first sunspot of a new solar cycle?

DX e vini DOC, con il sole al minimo

Sulla costa est americana arrivano le stazioni in onde medie giapponesi e le transatlantiche arrivano sulla costa ovest. Il sole è tranquillissimo in questi giorni, anche se in Italia non ci sono segnalazioni particolari sulle onde medie. E io mi mangio le mani ogni volta che accendo una radio sotto gli 88 MHz per la quantità di rumori che ho qui a Milano. Solo Walter Mola qualche giorno fa, credo il 9 ottobre ha ascoltato un debole segnale quasi sicuramente emesso dall'isola del Pacifico Pohnpei su 4755,26 kHz (la religiosa Cross Radio); mentre Aldo Moroni sente i radiofari dal Canada alle 21.20 utc.
Secondo questo contributo appena apparso su Slashdot cominciano a circolare ipotesi di minimo solare prolungato, perché ancora non ci sono segni di inversione di polarità delle macchie e di ripartenza del ciclo 24.

"The phrase sounds like an oxymoron, and maybe it is, but the sun is extremely quiet right now, so much in fact that the Solar Influences Data Center in Belgium issued an unusual 'All quiet alert' on October 5th. Since then the sunspot number has remained at zero — solar cycle 24 has not yet started. There are signs that the sun's activity is slowing. The solar wind has been decreasing in speed, and this is yet another indicator of a slowing in the sun's magnetic dynamo. There is talk of an extended solar minimum occurring. There are a number of theories and a couple of dozen predictions about the intensity solar cycle 24 which has yet to start. One paper by Penn & Livingstonin in 2006 concludes: 'If [trends] continue to decrease at the current rate then the number of sunspots in the next solar cycle (cycle 24) would be reduced by roughly half, and there would be very few sunspots visible on the disk during cycle 25.' We'll know more in about six months what the sun decides to do for cycle 24."

A beneficiarne sono gli intrepidi norvegesi di Kongsfjord, la postazione dxistica più a nord d'Europa. Partita ufficialmente il 12 ottobre la DXpedition Kongs17 durerà fino al 24. Il 15 e il 16 pazzesca apertura verso il Pacifico con segnali locali per le stazioni australiane e neozelandesi. Leggersi il diario di bordo in real-time stilato da Arnstein Bue, Bjarne Mjelde, OJ Sagdahl e Tore Johnny Bråtveit fa semplicemente venire una amabile stizza. Non solo per i segnali da sogno, ma anche per il trattamento enograstronomico di questi quattro connoisseurs che abbinano il DX estremo a ottime bottiglie di vino di tutto il mondo e intriganti "King Crab carbonara".
Basta vedere il receiver summary di questa edizione e pensare alle antenne di 800 metri puntate dritto verso le Hawaii (che da quelle parti sono normalissime a mezzogiorno, figuriamoci):
Arnstein: 2 x Icom IC-R75, 1 x JRC NRD-525G, , 1 x Etón E1, 2 x SDR-IQ
Bjarne: 2 x Icom IC-746Pro, Icom IC-703, Etón E1, 2 x SDR-IQ
OJS: AOR AR7030+, R&S EK895, WJ HF-1000A, WJ-8712P, 4 x SDR-IQ
Tore Johnny: 3 x Icom IC-R75, 2 x SDR-IQ
La temperatura nell'artico norvegese è piacevolissima - 6 gradi diurni - e i nostri amici hanno un solo problema: digerire la carbonara di granchio bagnata (mi permetterei di dissentire sull'accostamento) da un Valpolicella Torre del Falasco metodo "ripasso" della Cantina Valpantena e mantenere la capacità di concentrazione per 18-20 ore al giorno, con la cuffia in testa e i ricevitori SDR che registrano contemporaneamente 20 canali da riascoltare per gli annunci. Che vitaccia, gente.

Pochi consensi sul ciclo solare numero 24

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

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

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

NEXT SOLAR STORM CYCLE WILL START LATE

Experts Split Over Intensity

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

Ciclo solare. Vado al minimo

Le stime di molti osservatori solari concordano sulla prossimità del minimo solare per questo ciclo. Sull'esatto momento sarà possibile esprimersi solo nei prossimi mesi, quando le macchie invertiranno la loro polarità (un sintomo preciso che segna l'avvento del nuovo ciclo) e sarà quindi possibile calcolare il numero di macchie in versione normalizzata. Per la NOAA il minimo si sta verificando proprio in questo mese. Per gli australiani dell'IPS sarà il prossimo settembre. L'ultimo reporto propagativo di K7RA dell'ARRL, la lega dei radioamatori americani (per riceverlo via mail potete andare a questo indirizzo) spiega tutto fornendo i link alle ultime tabelle.
Che cosa ci si deve attendere da un minimo solare in termini propagativi? Per prima cosa, il minimo dura in genere molto poco, un ciclo solare (il prossimo è il numero 24) in genere raggiunge il suo picco in pochi anni e poi impiega il resto degli undici in una più lenta discesa. La regola pratica è che molte macchie portano moltano attività solare e di conseguenza a un maggior numero di eventi geomagnetici intensi, come tempeste e così via. Attivo geomagnetismo significa a grandissime linee buona propagazione sulle frequenze elevate (aumento della MUF, la massima frequenza utlizzabile per un collegamento ionosferico). Viceversa, piccolo numero di macchie significa quiete geomagnetica, abbassamento della LUF (frequenza minima utilizzabile) e buona propagazione per le onde medie. Sono tutte regole non strettissime e soprattutto in quest'ultimo ciclo sono state contraddette da un forte geomagnetismo nella (teorica) fase calante del ciclo stesso. Fenomeni come l'E sporadico, invece, sembrano addirittura favoriti da una bassa attività solare. Con la ripresa del ciclo aumenteranno le chance di ascoltare meglio i programmi delle onde corte trasmessi a partire dai 25 metri, normalmente prodotti dalle emittenti internazionali. Le stazioni locali sono ormai quasi tutte concentrate nel segmento bande tropicali-31 metri, con qualche rara presenza più in alto. Difficile dire come andranno le cose tra i 2 e i 6 MHz, di solito le cose migliori si sentono quando la ionosfera sta subendo i primi effetti di una forte attività solare. I radioamatori invece attendono con buone aspettative i massimi solari, perché le due bande più frequentate, 15 e 20 metri, sono le più favorite.

On March 1 sunspot 944 was pointed straight at us. It was a small sunspot, followed a few days later by another small spot, 945. Sunspot 945 is visible in photos from March 5, just behind 944, but both spots seemed to disappear a day or two later, before they would have rotated off the visible solar disk. Now the Sun is blank, and the sunspot number is zero. The minimum non-zero sunspot number is 11, and lately sunspot numbers move from 0 to 11 to 23 or 24, and back to 11. No solar activity is expected for the next few days, so we will probably see at least several days with a zero sunspot number. Geomagnetic conditions are expected to remain quiet, at least until Monday or Tuesday, March 12-13. The USAF predicts a Planetary A index for March 9-15 of 5, 5, 7, 15, 20, 15 and 10. Geophysical Institute Prague predicts quiet conditions for March 9-10, quiet to unsettled March 11, active geomagnetic conditions for March 12, unsettled to active March 13, unsettled March 14 and quiet to unsettled March 15. A recurring solar wind stream is predicted for Monday, March 12, and should produce the expected geomagnetic instability. New predictions for the solar minimum are coming frequently of late. The monthly smoothed sunspot number forecast for the rest of 2007 from the NOAA Space Environment Center in the weekly Preliminary Report and Forecast has been adjusted again, the third time since the first of the year. The revised tables are on page 9 of issue 1635, and page 10 of issues 1640 and 1644 (the table in 1640 is mislabeled at the bottom of the page as 03 January when it is really 06 February). Currently they predict a solar minimum for right now, with a smoothed sunspot number of 6 for March and April 2007, then 7, 8, 10, 11, 13, 16, 18 and 21 for the remaining eight months of this year. As mentioned in past bulletins, these are smoothed sunspot numbers, averaged over a year. So the prediction of 6 for this month means that if the prediction is accurate, at the end of September 2007 you could take half the average of daily sunspot numbers for that month, add it to half the average of daily sunspot numbers for September 2006, add the total to the monthly averages for each month in between, divide by 12, and get 6 as the result. Currently we're seeing higher values, with an average daily sunspot number of 19 for last week, 19.6 the week before, 14.6 for the week prior to that, 6.3 for the previous week, and 28.7 for the week prior to that, which was February 1-7. You can see an explanation of the method for determining the 12 month smoothed sunspot number at, http://www.ngdc.noaa.gov/stp/IONO/sunspot.html. Jim Headrick, W3CP of Stanfield, Oregon sent in a different prediction from the Australian government. It has the solar minimum centered on September 2007, and you can see it at, http://tinyurl.com/2ymk92. Note that the NOAA version mentioned previously ends in December 2007, but the one Jim sent goes through 2008 and 2009 as well. By the way, I don't know how long Jim has been a ham, but he was born early in sunspot cycle 15, and I'm sure he hopes to see the new cycle 24 all the way through. See a page of all the 20th century sunspot cycles at, http://wm7d.net/hamradiosolar/historical.shtml.