METEO SEISMES INONDATIONS CATASTROPHES MONDIALES

 

AT 01:06 UT

Speed: 270 Km/s

Density: 4.20 p/cm3

http://www.meteo-reunion.com/

FIN DE L'ALERTE

TSUNAMI SOLAIRE ?

UPSIDE-DOWN RAINBOWS: 'tis the season for upside-down rainbows. Just yesterday, one appeared over Dothan, Alabama:

"I've never seen anything like it before," says photographer Maria Doty. "It was a very unusual sight and the colors were bright."

The technical name for this phenomenon is circumzenithal arc or "CZA" for short--and it's no rainbow. CZAs are formed by sunlight shining through plate-shaped ice crystals in high clouds. Atmospheric optics expert Les Cowley calls it "the most beautiful of all ice haloes." First timers often describe the CZA as an 'upside down rainbow' and "someone has also likened it to 'a grin in the sky,'" he adds.

Circumzenithal arcs typically appear in late autumn and early winter when the air is icy and the sun is low. "The CZA forms only when sun is less than 32.3° high," notes Cowley. As winter solstice approaches, "upside down rainbows" will become increasingly common. Look for them!

Gigantisches Ufo über der Schweiz?

Riesige, dunkelblaue Kreise zeigen die Radarbilder von Meteo Schweiz heute morgen über unserem Land. Droht uns ein mächtiger Wirbelsturm oder haben sich Ausserirdische die Schweiz als Landeplatz ausgesucht? Ein Meteorologe klärt auf.

 

November 24, 2009: Sometimes you really can believe your eyes. That's what NASA's STEREO (Solar Terrestrial Relations Observatory) spacecraft are telling researchers about a controversial phenomenon on the sun known as the "solar tsunami."

Years ago, when solar physicists first witnessed a towering wave of hot plasma racing along the sun's surface, they doubted their senses. The scale of the thing was staggering. It rose up higher than Earth itself and rippled out from a central point in a circular pattern millions of kilometers in circumference. Skeptical observers suggested it might be a shadow of some kind—a trick of the eye—but surely not a real wave.

"Now we know," says Joe Gurman of the Solar Physics Lab at the Goddard Space Flight Center. "Solar tsunamis are real."

The twin STEREO spacecraft confirmed their reality in February 2009 when sunspot 11012 unexpectedly erupted. The blast hurled a billion-ton cloud of gas (a "CME") into space and sent a tsunami racing along the sun's surface. STEREO recorded the wave from two positions separated by 90^o, giving researchers an unprecedented view of the event:

Above: A solar tsunami seen by the STEREO spacecraft from orthogonal points of view. The gray part of the animation has been contrast-enhanced by subtracting successive pairs of images, resulting in a "difference movie." [larger movie] [more information]

"It was definitely a wave," says Spiros Patsourakos of George Mason University, lead author of a paper reporting the finding in the Astrophysical Journal Letters. "Not a wave of water," he adds, "but a giant wave of hot plasma and magnetism."

The technical name is "fast-mode magnetohydrodynamical wave"—or "MHD wave" for short. The one STEREO saw reared up about 100,000 km high, and raced outward at 250 km/s (560,000 mph) packing as much energy as 2400 megatons of TNT (10²⁹ ergs).

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Solar tsunamis were discovered back in 1997 by the Solar and Heliospheric Observatory (SOHO). In May of that year, a CME came blasting up from an active region on the sun's surface, and SOHO recorded a tsunami rippling away from the blast site.

"We wondered," recalls Gurman, "is that a wave—or just a shadow of the CME overhead?"

SOHO's single point of view was not enough to answer the question—neither for that first wave nor for many similar events recorded by SOHO in years that followed.

The question remained open until after the launch of STEREO in 2006. At the time of the February 2009 eruption, STEREO-B was directly over the blast site while STEREO-A was stationed at right angles —"perfect geometry for cracking the mystery," says co-author Angelos Vourlidas of the Naval Research Lab in Washington DC. (diagram)

The physical reality of the waves has been further confirmed by movies of the waves crashing into things. "We've seen the waves reflected by coronal holes (magnetic holes in the sun's atmosphere)," says Vourlidas. "And there is a wonderful movie of a solar prominence oscillating after it gets hit by a wave. We call it the 'dancing prominence.'"

Right: The dancing prominence (circled). Watch it bounce up and down after getting hit by a faint but powerful solar tsunami: 4 MB gif animation, 54 MB Quicktime movie.

Solar tsunamis pose no direct threat to Earth. Nevertheless, they are important to study. "We can use them to diagnose conditions on the sun," notes Gurman. "By watching how the waves propagate and bounce off things, we can gather information about the sun's lower atmosphere available in no other way."

"Tsunami waves can also improve our forecasting of space weather," adds Vourlidas, "Like a bull-eye, they 'mark the spot' where an eruption takes place. Pinpointing the blast site can help us anticipate when a CME or radiation storm will reach Earth."

And they're pretty entertaining, too. "The movies," he says, "are out of this world."

Editor's note: Scroll down to the "more information" section for a selection of solar tsunami movies

FLORIDA SUN PILLAR:

PILIER DU SOLEIL DE LA FLORIDE : La nuit dernière, quand l'ensemble du soleil au-dessus du panhandle de la Floride, un lept rouge lumineux de colonne vers le haut de l'horizon occidental. " ; C'était le pilier I' du soleil le plus gentil ;

 le VE jamais vu, " ; Dr. Wayne Wooten de jours, qui envoie cette image du campus de l'université de Jr. de Pensacola :

Des piliers de Soleil sont provoqués par les cristaux de glace en forme de plaque hexagones flottant vers le bas des nuages froids comme des feuilles tombant des arbres.

La résistance de l'air cause le crystals' ; larges surfaces à la ligne dans la direction horizontale. La lumière du soleil se reflétant des cristaux correctement alignés crée l'effet de pilier. Cristaux de glace en Floride ? L'état de soleil est censé être chaud. Même en Floride, cependant, l'air 5 à 10 kilomètres de haut gèle le froid, et le that' ; s où ces cristaux de glace sont localisés. Les gens partout devraient être alertes pour des piliers du soleil au lever de soleil et au coucher du soleil.

Last night, when the sun set over the panhandle of Florida, a luminous red column lept up from the western horizon. "It was the nicest sun pillar I've ever seen," days Dr. Wayne Wooten, who sends this picture from the campus of Pensacola Jr. College:

Sun pillars are caused by six-sided plate-shaped ice crystals fluttering down from cold clouds like leaves falling from trees. Air resistance causes the crystals' broad surfaces to line up in the horizontal direction. Sunlight reflecting from properly aligned crystals creates the pillar effect.

Ice crystals in Florida? The Sunshine State is supposed to be warm. Even in Florida, however, the air 5 to 10 km high is freezing cold, and that's where these ice crystals are located. People everywhere should be alert for sun pillars at sunrise and sunset. [more images]

 

Classic CME Observed (November 25, 2009)

Hi-res TIF image (2.2M)

Quicktime Movie: Large ( 14M), Small (2.2M)
MPEG Movie (3.5M)

The STEREO Ahead spacecraft observed a "classically shaped", bulbous coronal mass ejection (CME) on Nov. 21, 2009. As the bright, outer edge of the CME expands outwards, it almost looks like the Sun is blowing up a balloon. The first CME is followed by smaller CME events that blow even more particles out to the left and the right. In this coronagraph, the Sun is represented by the white circle. The black occulting disk blocks out the Sun and part of its inner atmosphere or corona to reveal faint structures beyond the Sun.
 
SOHO began its Weekly Pick some time after sending a weekly image or video clip to the American Museum of Natural History (Rose Center) in New York City. There, the SOHO Weekly Pick is displayed with some annotations on a large plasma display.

If your institution would also like to receive the same Weekly Pick from us for display (usually in Photoshop or QuickTime format), please send your inquiry to steele.hill@gsfc.nasa.gov.

EXTRATERRESTRIAL AURORAS: Lately, NASA's Cassini spacecraft has been monitoring some lovely Northern Lights--on Saturn! Saturn's auroras tower 750 miles above the planet's atmosphere, forming a ring of shimmering light wider than Earth itself. Mission scientist Andy Ingersoll discusses the findings in a 40 MB video from NASA.

SPACESHIP SIGHTINGS: The double flybys are over. Space shuttle Atlantis landed in Florida on Friday morning, Nov. 27th, leaving the International Space Station (ISS) to impress observers all by itself. No problem:

"The ISS put on a great show Friday night," says photographer Michael Harrison of Plano, Texas. "It was easy to see even in the brightly moonlit sky."

The space station, solo but still sensational, will continue flying over North America and Europe for several nights to come. Check the Simple Satellite Tracker to find out when to look.

more images: from Mustafa Erol of Antalya/Turkey; from Keith Geary of Shercock, Co.Cavan, Ireland; from Doug Zubenel of De Soto, Kansas; from Ian Mercier of East Angus, Québec, Canada; from Sylvain Weiller of Saint Rémy lès Chevreuse, France; from Ben Huset of New Brighton, MN; from Bryan Tobias of San Antonio, TX; from Bill Arnold of Woolmarket, MS; from Thomas Faber of Marietta, GA;

CLEAR AIR RAINBOW: Two days ago, photographer Martin McKenna was driving down a country road near Maghera, Northern Ireland, when he saw a curious thing. "There was a faint rainbow arcing through the crystal-clear blue sky," he says. Rainbows usually require rain, so a clear air rainbow is a curious thing indeed. Where did it come from? The answer may be found below McKenna's picture of the phenomenon:

"There was some rain," explains McKenna. "Strong winds had blown some precipitation over from the northwest where showers where gathering in the distance, and this is what caused the 'bow. It looked most unusual."

Atmospheric optics expert Les Cowley says that there is another way to make clear air rainbows. The method requires conditions of high humidity: "A rainbow can be formed by droplets condensing in a layer of saturated and otherwise apparently clear air. Droplets formed in this way tend to be small, and the rainbows they make are relatively broad."

"Clear air rainbows are always a surprise," he adds, "and where the raindrops come from can be puzzling." Sky watchers should look for them any time the sky is blue.

 

DOUBLE FLYBY ALERT: Yesterday, space shuttle Atlantis undocked from the International Space Station, setting the stage for some spectacular double flybys of towns and cities around the world. Johnny Perkins reports from Mechanicsville, Virginia: "I got home from work at 6:00 pm and saw on Spaceweather.com that the spaceships were coming my way at 6:19 pm. I hurried outside just in time to catch Atlantis and the ISS as they cleared the trees."

"I have seen a lot of passes, but I still enjoy catching one when I can," he says. "The image is a 20-second exposure with a Canon 350D."

The double flybys continue tonight. Atlantis and the ISS are still circling Earth together as Atlantis prepares to land in Florida on Friday morning, Nov. 27th. Check the Simple Satellite Tracker for viewing times.

more images: from Ernie Mross of Arches National Park, Moab, Utah; from Robert T. Smith of Stoneville, NC; from Olivier Staiger near Sion in the Swiss Alps.; from Mark A. Brown of Springfield, Virginia; from Daniel Owen of Monarch, Utah; from Ethan Tweedie of Pottsboro, Texas; from Christopher Calubaquib of El Sobrante,California; from Marco Vidovic of Stojnci, Slovenia; from Tamas Ladanyi of Veszpremfajsz, Hungary;

NORTHERN LIGHTS: This is a good week to be around the Arctic Circle. "Last night, the skies over the Pangnirtung Fjord were once again filled with dancing lights," reports Claus Vogel from Baffin Island in northern Canada. "We've had dazzling auroras all week." He took this picture using a Nikon D700:

"The half moon provides ideal lighting conditions for photographing Northern Lights. I'm keeping my fingers crossed for more in the days ahead," he says.

He may get his wish. The solar wind stream that fueled last night's display is still buffeting Earth's magnetic field. Polar sky watchers should remain alert for auroras.

DOUBLE FLYBY ALERT: Space shuttle Atlantis undocked from the International Space Station this morning at 4:53 am EST. The separation sets the stage for double flybys of North America on Wednesday evening, when Atlantis and the ISS will soar through the night sky side by side--a fantastic sight! Check the Simple Satellite Tracker for flybys.

Earlier this evening, astrophotographer Olivier Staiger caught the pair flying over the Swiss Alps:

 

"It was a little more than 7 hours after undocking," says Saiger. "A very nice flyby!"

more images: from Marco Vidovic of Stojnci, Slovenia; from Tamas Ladanyi of Veszpremfajsz, Hungary;

NIGHT LIGHTS: Last night, sky watchers around the world witnessed a beautiful conjunction of Jupiter and the Moon. Together, the two heavenly bodies were so bright they could be seen through clouds and city lights. In Hong Kong, astrophotographer Wah! opened the shutter of his Canon 450D and watched the pair blaze a trail above the tropical urban landscape:

 

"To make the picture, I combined more than two hundred 30-second exposures," he explains. "What a nice display!"

If you missed it, there is a second chance. Jupiter and the Moon will gather again on Dec. 20th and 21st for a conjunction even more beautiful than last night's. It's a solstice sky show that must not be missed. Mark your calendar and, meanwhile, browse the images below.

more images: from M. Raşid Tuğral of Ankara, Turkey; from Monika Landy-Gyebnar of Veszprem, Hungary; from Bryan Tobias at Ft. Sam Houston National Cemetary, San Antonio, Texas; from Mohamad Soltanolkottabi of Kashan, Esfajan, Iran; from Tamas Ladanyi of Veszprem, Hungary; from Wioleta Zarzycka of Iceland; from Valentin Grigore of Targoviste, Romania; from Frankie Lucena of Cabo Rojo, Puerto Rico; from Doug Zubenel of De Soto, Kansas.

NORTHERN LIGHTS: A solar wind stream is buffeting Earth's magnetic field and causing geomagnetic storms around the Arctic Circle. Last night in Lofoten, Norway, geoscientist Rob Stammes says the needle on his magnetograph spent the whole evening swinging wildly and he could see auroras beaming through the clouds. Not far away in Kvaløya, the sky was filled with green:

"The Northern Lights were everywhere--north, south, east and west," says photographer Fredrik Broms. "It was a magical sight."

Polar sky watchers should remain alert for auroras tonight as the solar wind continues to blow.

 

ICE HALO ENIGMA: Nov. 17th was a cold day in Silvercreek-Granby, Colorado. The air itself was filled with tiny ice crystals called "diamond dust," and when the morning sun rose over the eastern hills and rays of light mixed with the ice, luminous arcs filled the sky. A photographer named Jay photographed the display:

It was not only a beautiful sight, but also a mysterious one. Atmospheric optics expert Les Cowley explains:

"This diamond dust display contains an enigma. The 'V' shaped halo is a Moilanen arc named after its Finnish discoverer. We know it might be formed by sun rays passing between ice crystal faces sloping at an unusual angle of 34o to each other. But that is all we know. Experts in Finland have sampled ice crystals whenever they have seen the Moilanen arc, but so far they can find no traces of crystals with the required angles. How and what forms it is one of the halo world's biggest mysteries!"

"And that is not all," he adds. "Jay's display has two helic arcs. These are also very rare, but at least we know how they were made!"

Finally, don't leave without viewing the full-sized photo, in which individual diamond dust crystals may be seen glinting in sunlight.

ÉNIGME DE HALO DE GLACE 

 Le 17 novembre était un jour froid dans Silvercreek-Granby, le Colorado. L'air lui-même a été rempli de cristaux de glace minuscules appelés  " ; la poussière de diamant, " ; et quand le soleil de matin s'est levé au-dessus des collines et des rayons de la lumière orientaux mélangés à de la glace, les arcs lumineux ont rempli ciel. Un photographe appelé Jay a photographié l'affichage : C' était non seulement une belle vue, mais également mystérieux. Le systeme optique atmosphérique Les expert Cowley expliquent : " ; Cet affichage de la poussière de diamant contient une énigme. Le ' ; V' ; le halo formé est un arc de Moilanen baptisé du nom de son découvreur finlandais. Nous savons qu'il pourrait être constitué par des rayons du soleil passant entre les visages en cristal de glace inclinant à un angle peu commun de 34o entre eux. Mais c'est tout que nous savons. Les experts en matière de la Finlande ont prélevé des cristaux de glace toutes les fois qu'ils ont vu l'arc de Moilanen, mais jusqu'ici ils peuvent ne trouver aucune trace des cristaux avec les angles priés. Comment et quelles formes il est un du halo world' ; les plus grands mystères de soleil ! " ; " ; Et ce n'est pas tout, " ; il ajoute. " ; Jay' ; l'affichage des  deux arcs helic. Ce sont également très rares, mais au moins nous savons elles ont été faites ! " ; En conclusion, donc ; congé de  sans regarder la photo normale, en laquelle les différents cristaux de la poussière de diamant peuvent être vu briller  au soleil .

WEEKEND AURORAS: Saturday night on Baffin Island near the Canadian Arctic Circle, "the skies finally opened up after weeks of cloudy weather to showcase the dance of the Northern Lights," reports Claus Vogel. "As luck would have it, a student of mine drove me by snow machine to the beach just in time to see the aurora explode over Pangnirtung Fjord." He recorded the display using a Nikon D700:

With the recent fall of polar night, "the season of the arctic lights has begun again!" says Vogel. High-latitude sky watchers should be alert for auroras.

SOLAR ACTIVITY: For a change, there is something to see on the sun. Two new-cycle active regions are putting on a show for astronomers with backyard solar telescopes. Alan Friedman sends this picture from Buffalo, New York:

"While I was hard at work taking pictures of the sun, my big golden retriever Harry was also hard at work--enjoying the sun on a warm November Sunday," says Friedman. "I guess that makes him a sundog."

Thousands of miles away in sunny California, astrophotographer Gary Palmer was attracted by the same active regions. He video-recorded an expanse of solar terrain 400,000 km wide--"about the same as the distance between Earth and the Moon," Palmer notes. "I call this movie Going with the Flow." An 'IMAX' version is also available.

more images: from Andy Yeung of Hong Kong; from David Leong of Hong Kong; from Michael Wilk of Augsburg, Germany

EXTRA SUN HALOS: Normally, when we see an ice halo around the sun, it is a single ring. But yesterday in Sumrall, Mississippi, sky watcher Barry Russell counted more. "There were [at least] 3 halos around the sun! I was really shocked to see 3 of them at once," he says. (continued below)

 

Where did the extra rings come from? Atmospheric optics expert Les Cowley explains: "Ice crystals with pyramid-shaped ends made these halos. Most of the halos we see are from six-sided plate-shaped and pencil-shaped crystals with flat ends. Put pyramids on their ends and the sun's rays can pass through them in several more ways to make odd-radius halos. Here, in addition to the familiar 22o circular halo we have ones of 9o, 18o, 23o and 24o radius."

" Pyramidal halos are often overlooked," Cowley notes. "Search for them whenever cirrus clouds drift in front og the sun."

SPACESHIP SIGHTINGS: Space shuttle Atlantis is docked to the International Space Station (ISS) and together the two spacecraft are putting on a good show in the night sky. On Nov. 19th, Tamas Ladanyi caught the pair arcing over Balatonaliga, Hungary:

"I took the picture using a Canon 450D and a fisheye lens," he says. "In the full-sized photo you can see Jupiter peeking through the branches of the tree and the Moon setting in the distance. It was a beautiful autumn night at Lake Balaton."

On Nov. 25th, Atlantis will undock from the ISS. At that time, the brilliant streak shown above will split in two and double flybys will commence for a couple of nights while Atlantis prepares to land on Earth. Monitor the Simple Satellite Tracker for sighting opportunities.

more images: from Nicolas Biver of Versailles, France; from Jiri Srba of Valasske Mezirici, Czech Republic; from Pawel Warchal of Cracow, Poland; from Dewey Vanderhoff of Cody Wyoming; from Michał Nyklewicz of Poland; from Janusz Krysiak of Koluszki, Poland

NORTHERN LIGHTS: A solar wind stream is buffeting Earth's magnetic field and causing bright auroras around the Arctic Circle. Last night in Tromsø, Norway, sky watcher Thomas Hagen looked up and saw this:

 

"It was stunning!" he says. "I photographed the display using a Canon 40D set at ISO 800 for 4 seconds."

Arctic people should take note of those settings. The solar wind is still blowing and the auroras could return tonight. NOAA forecasters estimate a 20%-30% chance of high-latitude geomagnetic activity.

November Northern Lights Gallery
[previous Novembers: 2008, 2007, 2006, 2004, 2003, 2002, 2001]

ASTEROID CLOUD: The electric-blue "mystery cloud" seen twisting over Colorado and Utah at daybreak on Nov. 18th is no longer a mystery. It was asteroid debris. Consider the following images:

 

On Oct. 7, 2008, asteroid 2008 TC3 hit the atmosphere and exploded over Sudan, creating the cloud pictured left. On Nov. 18, 2009, a similar-sized asteroid hit the atmosphere and exploded over Colorado and Utah in a flash of light that startled onlookers across at least eight states. Hours later, daybreak revealed the "mystery cloud" pictured right. It looks just like the debris from 2008 TC3.

Both clouds resemble icy noctilucent clouds that form naturally around Earth's poles during summer or in the aftermath of rocket launches. Researchers have long suspected that space dust can prompt the formation of noctilucent clouds by acting as nucleation points for high-altitude ice crystals. Dusty debris from exploded asteroids may serve this purpose quite nicely.

The explosion of 2008 TC3 in Oct. 2008 produced meteorites that were later recovered. The asteroid-blast of Nov. 2009 probably produced meteorites, too, although researchers aren't yet sure where they fell. Stay tuned for updates.

more images: from Lisa Cain of New Castle, Colorado; from Don Brown of Park City, Utah; from Daniel Owen of Monarch, Utah; from John Omohundro of Grand Junction, Colorado; from Jeff Kendrick of Salt Lake City, Utah; from Allan Jeffers of Denver, Colorado; from Scott Stringham of Salt Lake City, Utah; from Sean O'Leary of West Jordan, Utah;

http://spaceweather.com/

GREAT WESTERN FIREBALL: Yesterday, Nov. 18th, something exploded in the atmosphere above the western United States. Witnesses in Colorado, Utah, Wyoming and Idaho say the fireball "turned night into day" and issued shock waves that "shook the ground" when it exploded just after midnight Mountain Standard Time. The fireball was so bright it actually turned the sky noontime blue, as shown in this image from KSL TV in Utah:

Although the fireball appeared during the Leonid meteor shower, it was not a Leonid. Infrasound recordings of the blast suggest a small asteroid hitting Earth's atmosphere and exploding with an energy of 0.5 to 1 kiloton of TNT. Experts liken the event to the Park Forest fireball of 2003, which scattered dozens of meteorites across a suburb of Chicago. Meteorites are likely from this fireball as well. Stay tuned for developing information about the possible fall zone.

more fireball images: from KSL TV in Utah; from KTVB News in Idaho; from Thomas Ashcraft near Santa Fe, New Mexico; from Marsha Adams of Sedona, Arizona;

Approximately 6 hours after the fireball, people in Utah and Colorado got another surprise. As the sun rose over those states, a twisting electric-blue cloud appeared in the dawn sky:

"These curious clouds on the horizon caught my attention just before sunrise," says photographer Don Brown of Park City, Utah. "They were strangely bright relative to the rest of the sky."

The cloud strongly resembles artificial noctilucent clouds formed at high altitudes by rocket and shuttle launches. Yet there was no (officially reported) rocket launch at dawn on Nov. 18th. Could the cloud be associated with the fireball? The geographical coincidence is certainly striking. Debris from the fireball should have dissipated by sunrise, but the cloud remains unexplained and a connection to the fireball cannot yet be dismissed. Readers, if you have more information about this event, let us know.

more mystery cloud images: from Lisa Cain of New Castle, Colorado; from Daniel Owen of Monarch, Utah; from John Omohundro of Grand Junction, Colorado; from Jeff Kendrick of Salt Lake City, Utah; from Allan Jeffers of Denver, Colorado; from Scott Stringham of Salt Lake City, Utah; from Sean O'Leary of West Jordan, Utah;

ALERTE

GLANCING BLOW: Arctic sky watchers should be alert for Northern Lights on Nov. 5th. NOAA forecasters say there is a chance that a coronal mass ejection (CME) will hit Earth's magnetic field, and the impact could spark a high-latitude geomagnetic storm. The Solar and Heliospheric Observatory recorded this movie of the CME:

The billon-ton cloud was blown into space by departing sunspot 1029 on Oct. 31st. Normally, CMEs take only two or three days to reach Earth, but during the deep solar minimum of 2008-2009, the clouds have slowed to a veritable crawl (~350 km/s, down from 700 to 1000 km/s). Crossing the sun-Earth divide now requires about five days, so an Oct. 31st CME should arrive on Nov. 5th. Because the blast was not squarely Earth-directed, the sluggish CME will deliver at most a glancing blow. NOAA forecasters estimate a 5% chance of strong geomagnetic storms around Earth's poles.

SOLAR PROMINENCE: Yesterday, Alan Friedman of Buffalo, New York, trained his telescope on the sun and waited for sunspot 1029 to reappear. But that wasn't going to happen. It was shaping up to be a dull observing session when something completely different popped into view:

"This magnificent looping prominence stole the show from the corpse of sunspot 1029," says Friedman. "It was the most dramatic prominence I have seen in many months."

The same prominence was putting on a show this morning, Nov. 15th, when the sun rose over the Philippines. "I was elated when I was able to see it clearly visible in the field of my eyepiece!" reports James Kevin Ty from Manila. "I quickly set up my PST (Personal Solar Telescope) and was able to monitor the prominence for more than 2 hours."

November 10, 2009: This year's Leonid meteor shower peaks on Tuesday, Nov. 17th. If forecasters are correct, the shower should produce a mild but pretty sprinkling of meteors over North America followed by a more intense outburst over Asia. The phase of the Moon will be new, setting the stage for what could be one of the best Leonid showers in years.

"We're predicting 20 to 30 meteors per hour over the Americas, and as many as 200 to 300 per hour over Asia," says Bill Cooke of NASA's Meteoroid Environment Office. "Our forecast is in good accord with independent theoretical work by other astronomers."¹

Right: A Leonid meteor at dawn, photographed in 2002 by Simon Filiatrault of Quebec, Canada. [larger image]

Leonids are bits of debris from Comet Tempel-Tuttle. Every 33 years the comet visits the inner solar system and leaves a stream of dusty debris in its wake. Many of these streams have drifted across the November portion of Earth's orbit. Whenever we hit one, meteors come flying out of the constellation Leo.

"We can predict when Earth will cross a debris stream with pretty good accuracy," says Cooke. "The intensity of the display is less certain, though, because we don't know how much debris is in each stream." Caveat observer!

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The first stream crossing on Nov. 17th comes around 0900 UT (4 a.m. EST, 1 a.m. PST). The debris is a diffuse mix of particles from several old streams that should produce a gentle display of two to three dozen meteors per hour over North America. Dark skies are recommended for full effect.

"A remarkable feature of this year's shower is that Leonids will appear to be shooting almost directly out of the planet Mars," notes Cooke.

It's just a coincidence. This year, Mars happens to be passing by the Leonid radiant at the time of the shower. The Red Planet is almost twice as bright as a first magnitude star, so it makes an eye-catching companion for the Leonids: sky map.

The next stream crossing straddles the hour 2100-2200 UT, shortly before dawn in Indonesia and China. At that time, Earth will pass through a pair of streams laid down by Comet Tempel-Tuttle in 1466 and 1533 AD. The double crossing could yield as many as 300 Leonids per hour.

Above: This side of Earth will be facing the Leonid debris stream at the time of the Nov. 17th outburst. Observers in India, China and Indonesia are favored with dark, pre-dawn skies. Image credit: Danielle Moser of the NASA Meteoroid Environment Office.

"Even if rates are only half that number, it would still be one of the best showers of the year," says Cooke.

The Leonids are famous for storming, most recently in 1999-2002 when deep crossings of Tempel-Tuttle's debris streams produced outbursts of more than 1000 meteors per hour. The Leonids of 2009 won't be like that, but it only takes one bright Leonid streaking past Mars to make the night worthwhile.

Enjoy the show.

AURORAS AHOY! "Who says one can't photograph the aurora from a moving ship? Digital photography has made things possible of which film shooters can only dream!" says traveling photographer Dennis Mammana. To prove it, he snapped this picture from the deck of the MS Midnatsol off the coast of Tromsø, Norway, on Nov. 12th:

When the auroras appeared, "I pulled out a 24mm f/1.4L lens, opened it up all the way, kicked up the camera's ISO to 3200 and shot 2 second exposures for the faintest lights, 1 second exposures for the brightest," Mammana explains. "I also made a panorama of four 1 second exposures at ISO 1600."

"Digital noise is, of course, present in all images at such high ISO settings, but thermal noise was minimized by the cold ambient temperatures and could be reduced easily by software."

So, readers, if you find yourself on a ship after dark off the coast of Norway, now you know what to do.

Une découverte scientifique

A LA REUNION

Ce mercredi 28 octobre 2009, les chercheurs partis à la conquête d'un canyon inexploré du Piton des neiges ont déclaré avoir fait une belle découverte. L'intérêt scientifique de cette aventure est désormais avéré, mais il va falloir attendre le retour de l'équipe pour en savoir plus. Retour prévu samedi a priori. Ce jeudi 29 octobre au matin, les 10 hommes sont coincés dans leur bivouac par le mauvais temps.

L'équipe communique avec l'extérieur, quelques minutes par jour, via un téléphone portable et des radios VHF prêtées par des parapentistes.

Ce groupe est formé deux géologues, dont Vincent Famin, chercheur au laboratoire géoscience de l'université de La Réunion à l'origine de ce projet et membre de l'Institut physique du globe de Paris. Ils sont suivis par un cinéaste accompagné de son assistant ainsi que par un photographe, un instituteur et un spécialiste du canyoning chargé de l'ouverture du chemin, de sa sécurisation et de l'encadrement des scientifiques.

Rappelons que cette expédition scientifique au coeur du Piton des neiges est inédite. Son objectif est de retracer l'histoire de la formation de ce volcan, qui permettra notamment de mieux comprendre le processus du Piton de la Fournaise, toujours en activité, mais dont la formation est équivalente à celle du Piton des Neiges. « Je ne pourrais pas dire quand le piton de la fournaise entrera en éruption. Mais notre connaissance de son processus sera bien meilleure puisqu'on aura pu observer sa composition en profondeur. Pour l'heure, l'injection des magmas s'observe avec un sismomètre alors qu'on pourra le toucher du doigt au Piton de neiges », explique Vincent Famin. Un Piton qui s'est éteint il y a 12.000 ans, « à peine », précise le chercheur. Une caractéristique qui lui confère l'avantage d'offrir un spectacle particulièrement riche. L'érosion du volcan est importante, suffisamment pour observer la roche, mais pas excessive contrairement aux autres volcans éteints de part le monde, dont les roches, particulièrement érodées, ne révèlent plus suffisamment d'informations.



www.ipreunion.com

 

l' ILE DE LA REUNION

Volcan

La  Fournaise en éruption

Le volcan est entré ce soir (un peu avant 21 heures 30) en éruption. Une coulée s'échappe sur le flanc extérieur est sud-est du cratère Dolomieu. L'éruption se situe dans l'enclos et en constitue aucune menace pour le moment.

Malédiction sur la route des Laves ?
CLICANOO.COM | Publié le 22 novembre 2009
Confirmant le dossier que nous avions consacré à la dangerosité de la portion de RN2 située entre Sainte-Rose et Saint-Philippe et tout particulièrement durant la traversée du Grand-Brûlé du volcan (notre édition du 7 novembre), plusieurs sorties de routes se sont succédé ces derniers jours sur cet axe situé au pied du massif du Piton de la Fournaise.

19 réactions de lecteurs

Mercredi après-midi, première sortie de route spectaculaire (notre photo) : celle d'une conductrice originaire de Toulouse, vers 15h. Alors qu'elle traverse la coulée 2007 - abondamment arrosée ce jour-là - pour une raison inexpliquée la conductrice perd le contrôle de son véhicule qui se retrouve quelques mètres en contrebas de la route, à proximité d'un bras du lit de la ravine Criais, au milieu des gratons. Les traces d'impact sur le toit et les côtés laissent imaginer des tonneaux. On imagine le fracas et la frayeur pour la dame, âgée d'une quarantaine d'années ! Les pompiers de Sainte-Rose interviendront rapidement et prendront la conductrice en charge. Plus choquée que blessée, elle a été conduite à la clinique de Saint-Benoît pour examen.

Il ne faut pas oublier que la vitesse est limitée à 50 km/h sur cette portion de la RN 2, sur environ 1,5 km, longueur sur laquelle a été retracée la chaussée après l'éruption d'avril 2007, avec un revêtement toujours provisoire en attendant la stabilisation du sol.

Jeudi, rebelote pour les pompiers, cette fois entre Piton Sainte-Rose et Bois-Blanc. Heureusement, pas de blessés graves, de la tôle froissée seulement.

Jeudi, vers 17h30, le dernier dérapage en date s'est déroulé sur la route du Tremblet, alors particulièrement glissante. Le conducteur s'en est tiré avec des blessures légères.

Trois accidents plus matériels que corporels et qui ne figureront donc pas dans les statistiques de la Sécurité routière… Pour rappel, à trafic égal, cette portion de RN2 serait la plus accidentogène de l'île. Une dangerosité contrebalancée par un trafic parmi les plus faibles. Heureusement… Levez donc le pied, surtout par temps humide.

P.M.

La situation au Piton de la Fournaise

L'alerte 1 ("éruption probable ou imminente") est toujours en vigueur et l'accès à l'enclos est interdit. La sismicité était considérée, hier matin, comme "modérée" par l'observatoire volcanologique, qui a enregistré 56 séismes pour la journée de vendredi. Les scientifiques ont tout de même enregistré un séisme de magnitude 2 au cours de la nuit de vendredi à samedi, d'une intensité non négligeable pour le Piton de la Fournaise.

Volcan

 

Au lendemain de l'éruption éclair de la nuit de jeudi à vendredi, le calme régnait hier au Piton de la Fournaise. Les coulées issues des deux fissures éruptives qui se sont ouvertes en dessous du sommet, sur son flanc est-sud-est (altitude : 2530 m environ), ne sont pas descendues plus bas que 1 970 m d'altitude, soit au pied du cône terminal du volcan, malgré leur aspect spectaculaire, vues de la route nationale 2 dans le Grand-Brûlé. Cette éruption, qui a mis en jeu la faible quantité de laves montées à quelques centaines de mètres seulement sous la surface lors de la crise sismique du 19 octobre, n'a pas puisé dans le stock principal (la "chambre magmatique") localisé un peu au-dessus du niveau de la mer. Le sommet du volcan n'ayant pas dégonflé suite à cette éruption, tout porte à croire, selon les scientifiques de l'observatoire volcanologique, que cet épisode n'a rien changé à l'état du volcan : il est toujours sous pression et une nouvelle éruption est possible. Avec les pluies du week-end, il sera d'ailleurs intéressant de savoir si l'infiltration de masses d'eau tombées dans les entrailles surchauffées du sommet du Piton de la Fournaise (de l'ordre de 120 mm en 24 heures) a une quelconque influence sur l'activité. Il est déjà arrivé que des événements météorologiques de ce type servent de déclencheur, l'entrée en contact de l'eau de pluie avec le magma à près 1 200° provoquant sa vaporisation et des surpressions avec effet "cocotte-minute"... L'alerte 2 du plan de secours spécialisé volcan ("éruption en cours") a été levée dès vendredi soir, le niveau étant ramené à 1 ("éruption probable ou imminente"). L'accès à l'enclos du volcan reste interdit. Information sur l'activité au 02 62 27 54 61 (répondeur de l'observatoire volcanologique) ou sur internet : http://volcano.ipgp.fr rubrique > La Réunion > 

 

 

 

Les colères de la Terre épargneront-elles la Réunion

La Terre serait-elle en colère ? En Asie, ces deux dernières semaines furent meurtrières. Notamment en raison d'une série de secousses sismiques contre lesquelles l'homme est impuissant. La Réunion, pourtant, semble quelque peu épargnée par ce tumulte. Explications.

Les séismes survenus aux Samoa et Sumatra sont-ils exceptionnels ?

NON. Mais ils font partie des plus puissants enregistrés dans l'histoire récente. Jean-Louis Nédellec, directeur du bureau de recherches géologiques et minières de la Réunion qualifie de "monstrueuse" la magnitude du phénomène qui a causé le tsunami des îles Samoa le 29 septembre. "Elle était de 8,1 sur l'échelle de Richter. Pour mémoire, le séisme qui a provoqué le tsunami de Sumatra en 2004 était de 9,15. Or les plus importants séismes jamais enregistrés dépassaient tous 9. C'était dans les années 60, au Chili et en Alaska. Et c'est l'équivalent de centaines de bombes atomiques". Le 30 septembre dernier, à Sumatra, la magnitude était de 7,6, là encore une valeur énorme. Pour autant, ces mouvements n'ont rien d'anormaux. Les Samoa, comme Sumatra, se situent sur des lignes de jonction entre deux plaques tectoniques (Australienne et Pacifique pour les Samoa, Australienne et Eurasienne pour Sumatra). "Par un phénomène dit de "subduction", la plaque la plus lourde passe sous la plus légère, entraînant des frottements, une accumulation de contraintes jusqu'à ce que ça craque", poursuit Jean-Louis Nedellec. Ce mouvement des plaques tectoniques ne s'arrête jamais, dans l'histoire terrestre. Mais jamais les séismes n'ont été autant mesurés, leurs conséquences aussi médiatisées. Et comme la planète n'a jamais été aussi peuplée, les dégâts considérables donnent l'impression, factice, d'un dérèglement. Les sismologues estiment que les distances entre les épicentres sont trop grandes (10 000 km entre les Samoa et Sumatra) pour conclure que les événements sont liés.

Des séismes aussi graves peuvent-ils survenir à la Réunion ?

NON. "Très probablement, ça n'arrivera jamais", estime Jean-Louis Nédellec, car l'île ne se trouve pas à la jonction de deux plaques mais à l'intérieur de la plaque africaine. "Nous n'avons jamais eu de séisme important connu". Pourtant, depuis le 17ème siècle, 60 tremblements de terre ont été recensés à la Réunion, Maurice et Mayotte (voir ci-contre), qui sont classés selon une échelle d'intensité (basée sur le ressenti) et non sur l'échelle de Richter (qui mesure l'énergie). "Le niveau 6 se traduit par des lézardes sur les murs, le 7 par quelques dommages, le 8 par des maisons qui s'écroulent. A la Réunion, le 7 n'a jamais été dépassé". Ces secousses ne proviennent pas de mouvements tectoniques mais de deux phénomènes. D'abord le poids des îles elles-mêmes (Maurice et Réunion) : par simple gravité, elles exercent une pression sur la croûte océanique, d'où des tremblements de terre "d'ajustement". Ensuite, et plus fréquemment, l'intensité du magma dans la croûte terrestre. "La chambre magmatique se remplit, se fraye une place sous la terre et provoque des fissures. Nous les ressentons parce que ces mouvements sont situés très près de la surface". La nature de certains terrains a d'ailleurs tendance à amplifier les ondes, comme les plaines alluvionnaires du Port ou les bords de falaises.

La croissance démographique et le bétonnage de la Réunion aggravent-ils le risque ?

NON. "C'est absolument sans effet. Le poids qu'exercent les activités humaines n'est rien en comparaison avec la masse géologique de l'île", soutient le directeur du BRGM. La Réunion est-elle vraiment exposée aux tsunamis ? OUI. On l'a déjà constaté en décembre 2004, où l'onde venue d'Indonésie a provoqué des dégâts dans les ports de l'île. "Il suffit que le séisme ait lieu un peu plus au Sud et les conséquences seront beaucoup plus fortes", indique Jean-Louis Nédellec. D'où l'exercice d'alerte de mercredi prochain (voir page ci-contre). "L'

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