Posted on by Nancy Atkinson

New Results from GOCE: Earth is a Rotating Potato

In this GOCE image, gravity is strongest in yellow areas; it is weakest in blue ones. Credit: ESA

Although they aren’t particularly fond of the comparison, scientists from the GOCE satellite team had to admit that new data showing Earth’s gravity field – or geoid — makes our planet look like a rotating potato. After just two years in orbit, ESA’s sleek and sexy GOCE satellite (Gravity Field and Steady-State Ocean Circulation Explorer) has gathered sufficient data to map Earth’s gravity with unrivalled precision. While our world certainly doesn’t look like a spinning tuber, this exaggerated view shows the most accurate model of how gravity varies across the planet.

The geoid is nothing more than how the oceans would vary if there were no other forces besides gravity acting on our planet.

“If we had an homogeneous sphere, it would be a boring sphere,” said GOCE scientist Roland Pail from Technical University in Munich, speaking at the press briefing today. “But due to rotation, you get a flattening of the Earth, and we have topography such as mountains, and irregular mass distribution in Earth’s interior. What we are showing you here, in principle, is the gravity field by any deviations due to inhomogeneous mass distributions on the Earth and the Earth’s interior.”

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While a previous gravity satellite, the Gravity Recovery And Climate Experiment (GRACE) operated for 8 years, most of the new data from GOCE was gathered in about 14 months, and provides data where there was none before.

GOCE is able to sense tiny variations in the pull of gravity over Earth, and the data is used to construct an idealized surface, which traces gravity lumps and bumps, and is the shape the oceans would take without winds, currents, Earth’s rotation and other forces.

By comparing sea level and geoid data, GOCE is revealing data on ocean currents and circulation, sea-level change, ice dynamics, said Rory Bingham, from the University of Newcastle, which helps understand heat transport and the changing climate.

But also of interest is how GOCE data reveals shifting tectonic plates in earthquakes and magma movements under volcanoes. Following the earthquakes in Japan, scientists are looking closely, as the data should reveal a three-dimensional view of what was going on inside the Earth. Even though the motion cannot be observed directly from space, earthquakes create signatures in gravity data, which could be used to understand the processes leading to these natural disasters and ultimately help to predict them.

“Even though these quakes resulted from big movements in the Earth, at the altitude of the satellite the signals are very small. But we should still seem them in the data,” said Dr. Johannes Bouman from the German Geodetic Research Institute.

GOCE in orbit. Credit: ESA

“GOCE will give us dynamic topography and circulation patterns of the oceans with unprecedented quality and resolution,” said professor Reiner Rummel, former Head of the Institute for Astronomical and Physical Geodesy at the Technische Universität München. “I am confident that these results will help improve our understanding of the dynamics of world oceans.”

“You could say that, at its early conception, GOCE was more like science fiction,” said Volker Liebig, Director of ESA’s Earth Observation Program. “GOCE has now clearly demonstrated that it is a state-of-the-art mission.”

Sources: GOCE press briefing, ESA press release

Posted on by Nancy Atkinson

From the Earth and Moon (and Russia) With Love

Russia's Elektro-L spacecraft captured this view of the Moon over the Red Sea region of the Earth. Credit: NPO Lavochkin

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This stunning picture of the Moon and Earth was taken by Russia’s new Elektro-L spacecraft, a weather-forecasting satellite that launched in January 2011. This is the first major spacecraft developed in post-Soviet Russia, and it is designed to give Russian meteorologists the ability to watch the entire disk of the planet, thanks to the satellite’s position in the geostationary orbit 36,000 kilometers above the equator. The clarity of the images is fantastic, as you can see in another image of just the Earth, below. The Elektro-L is designed to last at least a decade, and will enable local and global weather forecasting, analysis of oceanic conditions, as well as space weather monitoring, such as measurements of solar radiation, properties of Earth’s ionosphere and magnetic field.

On Feb. 26, 2011, at 14:30 Moscow Time, the Elektro-L satellite produced its first breathtaking image of the home planet. Credit: NPO Lavochkin

Learn more about the Elektro-L mission at their website.

h/t: SDO Facebook page.

Posted on by Tammy Plotner

Saturday, March 26, 2011 – Lights Out for Earth Hour!

At 8:30 PM on Saturday 26th March 2011, lights will switch off around the globe for Earth Hour and people will commit to actions that go beyond the hour. We need you…

Earth Hour started in 2007 in Sydney, Australia when 2.2 million individuals and more than 2,000 businesses turned their lights off for one hour to take a stand against climate change. Only a year later and Earth Hour had become a global sustainability movement with more than 50 million people across 35 countries/territories participating. Global landmarks such as the Sydney Harbour Bridge, CN Tower in Toronto, Golden Gate Bridge in San Francisco, and Rome’s Colosseum, all stood in darkness, as symbols of hope for a cause that grows more urgent by the hour.

In March 2009, hundreds of millions of people took part in the third Earth Hour. Over 4000 cities in 88 countries/territories officially switched off to pledge their support for the planet, making Earth Hour 2009 the world’s largest global climate change initiative.

On Saturday, March 27th, Earth Hour 2010 became the biggest Earth Hour ever. A record 128 countries and territories joined the global display of climate action. Iconic buildings and landmarks from Asia Pacific to Europe and Africa to the Americas switched off. People across the world from all walks of life turned off their lights and came together in celebration and contemplation of the one thing we all have in common – our planet.

Earth Hour 2011 will take place on Saturday 26 March at 8.30PM (local time). This Earth Hour we want you to go beyond the hour, so after the lights go back on think about what else you can do to make a difference. Together our actions add up.

“All over the world individuals, communities, businesses and governments are creating new examples for our common future – new visions for sustainable living and new technologies to realize it,” said UN Secretary General Ban Ki-moon. “Tomorrow, let us join together to celebrate this shared quest to protect the planet and ensure human well-being. Let us use 60 minutes of darkness to help the world see the light.”

Won’t you join us for one shining hour?

To learn more, visit the Earth Hour website!

Posted on by Nancy Atkinson

Scientists Predict Arctic Could Be Ice-Free Within Decades

Sea ice data through mid- March 2011. Credit: National Snow and Ice Data Center

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Bad news for what is now the beginning of the “melt season” in the Arctic. Right now, the sea ice extent maximum appears to be tied for the lowest ever measured by satellites as the spring begins, according to scientists at the University of Colorado Boulder’s National Snow and Ice Data Center. And because of the trend of how the amount of Arctic sea ice has been spiraling downward in the last decade, some scientists are predicting the Arctic Ocean may be ice free in the summers within the next several decades.

“I’m not surprised by the new data because we’ve seen a downward trend in winter sea ice extent for some time now,” said Walt Meier, a research scienitist with the NSIDC.

The seven lowest maximum Arctic sea ice extents measured by satellites all have occurred in the last seven years, and the from the latest data, the NSIDC research team believes the lowest annual maximum ice extent of 5,650,000 square miles occurred on March 7 of this year.

The maximum ice extent was 463,000 square miles below the 1979-2000 average, an area slightly larger than the states of Texas and California combined. The 2011 measurements were tied with those from 2006 as the lowest maximum sea ice extents measured since satellite record keeping began in 1979.

Virtually all climate scientists believe shrinking Arctic sea ice is tied to warming temperatures in the region caused by an increase in human-produced greenhouse gases being pumped into Earth’s atmosphere.

Meier said the Arctic sea ice functions like an air conditioner for the global climate system by naturally cooling air and water masses, playing a key role in ocean circulation and reflecting solar radiation back into space. In the Arctic summer months, sunlight is absorbed by the growing amounts of open water, raising surface temperatures and causing more ice to melt.

“I think one of the reasons the Arctic sea ice maximum extent is declining is that the autumn ice growth is delayed by warmer temperatures and the ice extent is not able to ‘catch up’ through the winter,” said Meier. “In addition, the clock runs out on the annual ice growth season as temperatures start to rise along with the sun during the spring months.”

Since satellite record keeping began in 1979, the maximum Arctic sea ice extent has occurred as early as Feb. 18 and as late as March 31, with an average date of March 6. Since the researchers determine the maximum sea ice extent using a five-day running average, there is small chance the data could change.

As of March 22, ice extent declined for five straight days. But February and March tend to be quite variable, so there is still a chance that the ice extent could expand again. Ice near the edge is thin and is highly sensitive to weather, scientists say, moving or melting quickly in response to changing winds and temperatures, and it often oscillates near the maximum extent for several days or weeks, as it has done this year.

In early April the NSIDC will issue a formal announcement on the 2011 maximum sea ice extent with a full analysis of the winter ice growth season, including graphics comparing 2011 to the long-term record.

Source: NSIDC, University of Colorado-Boulder

Posted on by Anne Minard

Probing the Moho Boundary – Earth’s Own Unexplored Frontier

Chikyu. Credit: JAMSTEC-CDEX

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JOIDES Resolution. Credit: IODP

The boundary where Earth’s crust gives way to the unexplored mantle was first detected in 1909, because of a change in the travel of seismic waves. Named the Moho boundary for Andrija Mohorovicic, who listened to those seismic waves, the crust-mantle boundary is a frontier that remains elusive and compelling — harboring tantalizing clues as to the story of Earth’s formation — even as our technologies push into the outer reaches of the solar system and beyond.

The first serious attempts to probe the Moho boundary ran aground in the late 1950s. Now, technology already in use on a Japanese ship, combined with a United States digging program already under way, could finally yield success. Damon Teagle and Benoît Ildefonse have written about the ongoing efforts for an article in the journal Nature, released today.

Teagle is at the University of Southampton’s National Oceanography Centre in the UK, and Ildefonse is at Université Montpellier in France. They are co-chief scientists on an expedition called the IODP Expedition 335, “to obtain for the first time a section of the lower oceanic crust — the material lying just above the mantle,” they write.

The IODP is using the U.S. ship JOIDES Resolution, pictured above, which will drill from April to June this year off the coast of Costa Rica.

“This site is in ocean crust that formed superfast — at more than 20 centimetres a year, much faster than any present day crust formation,” the co-authors write. “That makes the upper crust there much thinner than elsewhere, so it is possible to reach the lower portions without having to drill very deep. Three previous expeditions to Hole 1256D have drilled down to more than 1.5 kilometres below the sea floor, into the transition zone between dikes and gabbros.”

This spring they hope to push it another 400 meters, and recover gabbros from the lower crust, “which will be the deepest types of rock ever extracted from beneath the sea floor,” even though the deepest hole reached 2,111 meters under the eastern Pacific off of Colombia, they write.

Microphotograph of a mantle xenolith, sampled on Rapa Island in French Polynesia. The colourful minerals (seen here under the microscope in cross-polarized light, each grain is about 1 to 5mm large) are olivine, the main constituent of the upper mantle. Credit : Andréa Tommasi (CNRS, Géosciences Montpellier)

Teagle and Ildefonse note that some pieces of the mantle have been thrust up to Earth’s surface during tectonic mountain building, and ejected from volcanoes and sea floor dikes. Those samples have provided clues to the mantle’s composition, but they don’t reveal the variability of the mantle — and all of the samples have been altered by the processes that revealed them.

They say the IODP mission should help to settle many debates, including how crust is formed at mid-ocean ridges, how magma from the mantle is intruded into the lower crust, the geometry and vigor of how sea water can pull heat from the lower oceanic crust and the contribution of the lower crust to marine magnetic anomalies. The project will also provide “further impetus for, and confidence in, deep ocean crust drilling,” write Teagle and Ildefonse — but it will reach a depth far less than what will be needed to actually get at the Moho boundary. It occurs at least 30 kilometers (18 miles) under the continents but just 6 kilometers (3.7 miles) under the seas.

That’s where Chikyu comes in. Launched in 2002, “Chikyu is a giant ship, capable of carrying 10 kilometres of drilling pipes, and is equipped for riser drilling in 2.5 kilometres of water,” the authors write. Although Chikyu wouldn’t yet be able to go the full distance, its design is advanced enough to be the launching pad for such efforts:

“The vessel has a riser system: an outer pipe surrounds the drill string — the steel pipe through which cores are recovered,” the co-authors write. “The drilling mud and cuttings are returned up to the vessel in the space between the two pipes. This helps to recycle the drilling mud, control its physical properties and the pressure within the drill hole and helps to stabilize the borehole walls.”

Teagle and Ildefonse say the ideal drilling program to reach the mantle boundary will happen in one of three places — off the coasts of Hawaii, Baja California and Costa Rica — where the water is the most shallow, over the coldest possible crust. Wherever and however it happens, they write, it will be worth doing:

“Drilling to the mantle is the most challenging endeavour in the history of Earth science. It will provide a legacy of fundamental scientific knowledge, and inspiration and training for the next generation of geoscientists, engineers and technologists.”

Source: Nature. See also the websites for Chikyu and JOIDES.

Posted on by Anne Minard

NASA: Happy St. Paddy’s Day!

Collection of Ireland images, captured from the AIRS instrument onboard NASA's Aqua satellite on March 3. Credit: NASA JPL, Ed Olsen/ Henry Kline

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With the luck o’ the Irish, NASA’s Aqua satellite was fortunate to capture mostly clear views of the Emerald Isle in these near-infrared/visible, infrared and microwave light views acquired by Aqua’s Atmospheric Infrared Sounder (AIRS) instrument. And with holiday flair, the agency has arranged the images into a clover and released them as a St. Paddy’s Day treat.

From the press release:

Ireland, located in the Atlantic Ocean, is the third-largest island in Europe, and originated the St. Patrick’s Day holiday. Located west of Great Britain and separated from it by the Irish Sea, it is surrounded by hundreds of islands and islets. In March, Ireland’s average daytime high temperature is near 9.4 degrees Celsius (49 degrees Fahrenheit) and its average nighttime low temperature is near 3.3 degrees Celsius (38 degrees Fahrenheit).

The AIRS instrument measures temperatures of land, sea and air to provide a better understanding of what is happening in those environments. The March 3 images reveal temperatures near the surface that were near normal for this time of year.

NASA’s Aqua satellite circles Earth pole-to-pole 15 times a day in a sun-synchronous orbit to provide data and images to researchers in Earth, ocean and atmospheric sciences. When Aqua passed over Ireland on March 3, it captured visible, infrared and microwave images: a clover of images from one instrument.

The false-color near-infrared/visible image revealed a mostly cloud-free country, except for the northernmost area, as a cold front approached from the west. Also visible were some of the navigable rivers that extend inland.

The visible image also showed areas over the North Sea, Spain and the French-Italian border region where the clouds were heavy enough to confine AIRS infrared data to the higher regions of the atmosphere above the cloud tops. Over the Pyrenees at the Spanish-French border and the Alps at the French-Italian border, the clouds were heavy enough (and contained some precipitation) so that the surface is not visible even using the microwave wavelength.

The infrared image showed that the clouds approaching Ireland from the west were low clouds associated with the cold front moving east. There were no areas of high, cold clouds that would indicate convection and the possibility of thunderstorms. “The brightness temperature of the island is approximately 283 Kelvin, which amounts to 10 degrees Celsius or 50 degrees Fahrenheit,” said Ed Olsen of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Olsen provides images for the AIRS instrument. “This brightness temperature is a combination of the temperature of the near-surface air temperature and the (land) surface temperature. This is close to the ambient temperature that the population there experienced outdoors.”

The microwave brightness temperature is a bit colder than the infrared temperature data, approximately 273 Kelvin, which is just at the freezing point for water (0 degrees Celsius/32 degrees Fahrenheit). Olsen noted, “The major component of the 89 gigahertz radiances is due to emissions from the surface to about a centimeter below the surface.” He said the temperature of the ground just below the (land surface) that is warmed by the sun is colder–after all, it is still winter in Ireland.

AIRS infrared data can measure cold, high cloud tops in thunderstorms and tropical cyclones, warm or cold ocean waters and land surfaces. Cloud top temperatures, for example, provide clues to scientists about the power of the thunderstorms. The colder the clouds are, the higher they are, and the more powerful the thunderstorms. When AIRS measures cloud temperatures as cold as or colder than minus 52 degrees Celsius (minus 63 degrees Fahrenheit), that indicates high cloud tops, strong convection and the likelihood of powerful thunderstorms.

Data from the Advanced Microwave Sounding Unit (AMSU), another of the AIRS suite of instruments on Aqua, are used to create microwave images. Cold areas in AMSU images can indicate where there is precipitation or ice in cloud tops.

Every day, NASA’s Aqua satellite looks at conditions around the globe, just like looking over a clover (in this case, a three-leafed or imaged one) that it looked at before.

Source: NASA release, via Eurekalert

Posted on by Ken Kremer

Japan Quake May Have Shortened Earth Days, Moved Axis

TerraSAR-X Change Analysis of Sendai Area, Japan. Map show coastal area of Sendai effected by 9,0 magnitude Earthquake that triggered ensuing destructive Tsunami. Credit: Deutsches Zentrum fur Luft- und Raumfahrt (DLR) - German Aerospace Center

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The terribly destructive magnitude 9.0 earthquake which struck Japan on March 11, may have had another effect – Shortening the length of each Earth day and shifting its axis. Did you notice any change ?

Well according to NASA, the changes are so small that you won’t notice the difference.

Based on initial calculations conducted by Richard Gross, a research scientist at NASA’s Jet Propulsion Laboratory, the earthquake should have caused Earth to rotate just slightly faster, shortening the length of the day by about 1.8 microseconds (a microsecond is one millionth of a second), according to a statement released by NASA.

A reader posted this link to before and after photos

Gross used complex modeling and estimates of fault slippage to perform a preliminary theoretical calculation of how the earth’s rotation may have been affected.

Calculations by Gross also indicate that the position of Earth’s figure axis could have shifted by about 17 centimeters (6.5 inches), towards 133 degrees east longitude. The figure axis is the axis about which Earth’s mass is balanced.
Earth’s figure axis is therefore different and offset from the north-south axis by about 10 meters.

“This shift in Earth’s figure axis will cause Earth to wobble a bit differently as it rotates, but it will not cause a shift of Earth’s axis in space-only external forces such as the gravitational attraction of the sun, moon and planets can do that,” according to the NASA statement.

The estimates for both the shortening in the Earth’s rotation and shift in the figure axis are preliminary and will very likely change as more data is collected and the calculations are refined.

The March 11 earthquake was the fifth largest since 1900. So far, over 4000 people are confirmed dead and the overall death total may exceed 10,000.

Several heavily damaged nuclear reactors at the Fukushima plant are in danger of meltdown as hero workers inside put their lives on the line to avoid a catastrophic failure and try to prevent the spread of lethal radiation.

This view of Earth comes from NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite

Previously, Gross had calculated the affects of the magnitude 8.8 Chilean quake in 2010 and found them to be slightly smaller compared to the Japanese quake. He calculated a shortening in the length of day of about 1.26 microseconds and shifting of Earth’s figure axis of about 8 centimeters (3 inches). These affects are dependent on the magnitude of the quake, exactly where it is located as well as how the particulars of how the fault slips.

In fact, Earth’s rotation is changing all the time as a result of continual changes in atmospheric winds and oceanic currents and these effects are about 550 times larger than the Japanese earthquake.

“Over the course of a year, the length of the day increases and decreases by about a millisecond,” says Gross. Indeed, the effects of earthquakes on changing rotation are so tiny that they are smaller than the margin of error in the measurements themselves.

By comparison, measurements of the figure axis are much more reliable and meaningful. Changes to the figure axis can be accurately measured to within about 5 centimeters. This means that the estimated 17 centimeter shift from the Japanese quake may be real after accounting for the effects of the atmospheric winds and ocean currents. Further research is needed as more data are collected and analyzed.

“These changes in Earth’s rotation are perfectly natural and happen all the time. People shouldn’t worry about them,” said Gross.

Source: NASA Press Release:

Posted on by Nancy Atkinson

Massive 8.9 Earthquake Hits Japan; Tsunamis Predicted for Pacific Basin

Seismology
Earthquake map from the USGS of recent quake activity around Japan. Credit: USGS

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An 8.9-magnitude earthquake struck off the coast of northern Japan on March 11, one of the strongest to ever hit Japan. The massive quake has triggered tsunamis not only in Japan, but around the Pacific Basin. Walls of water and debris have inundated coastal areas of Japan, and tsunami warnings were issued for at least 20 countries and numerous Pacific islands, including coastal Russia, the western coast of Canada and the US, the Marcus Islands, Taiwan, Guam and the Hawaiian Islands, where a full coastal evactuation has been taking place throughout early Friday morning. Strong aftershocks, as strong as 6.5-magnitude continue to shake the region, (the latest U.S. Geological Survey map, above, shows 95 recent quakes in the area) and at least one nuclear power plant in Japan may be encountering problems. Images coming from Japan show widespread damage from both the quakes and the tsunamis.

The USGS reported that the epicenter of the earthquake was 373 kilometers (231 miles) northeast of Tokyo and 130 km (80 miles) east of Sendai, Honshu. Police reports from Sendai say that so 200-300 bodies have been recovered, but the total death toll will likely be much, much higher. Reports say this is the 6th largest earthquake ever monitored, and the largest in Japan in over 140 years.

Tokyo did not suffer much damage, but in northern Japan, many areas were devastated. Compounding the damage was a wall of water that rushed inland of the island nation, leveling houses and washing away boats, cars and other debris. Click here to see some shocking images from the New York Times.

Reports says Japan is evacuating thousands of people from nearby a nuclear power plant, but the current condition of the reactor core is unknown at this time. Four reactors are located near the Earthquake area. The reactors were shut down, and no leaks have been found so far, but the cooling system for the reactors may not be working correctly.

Reports via Twitter say the roof may have collapsed at JAXA Tsukuba Space Center.

Tsunami waves have now begun to wash ashore in the Hawaiian Islands. The first waves are not necessarily the strongest; waves are predicted to be 2-3 meters (6-8 ft.) in Hawaii. Tsunamis are very hard to predict, and the USGS says wave heights can vary widely.

Get the latest on the tsunami predictions from NOAA’s Pacific Tsunami Warning Center.

See this Google Map, overlaid with NOAA-predicted tsunami times.

Callan Bentley at the AGU Blogosphere has a good overview of earthquake and tsunami dynamics.

Predicted tusnami map from the March 11 earthquake. Credit: CNN
Posted on by Anne Minard

‘Climate Change Satellite’ Fails to Reach Orbit, Crashes in Ocean

Credit: NASA

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NASA’s Glory mission launched from Vandenberg Air Force Base in California Friday at 5:09:45 a.m. EST failed to reach orbit. Telemetry indicated the fairing, the protective shell atop the Taurus XL rocket, did not separate as expected about three minutes after launch. The failure represents a $420 million loss for NASA, and the loss of two important investigations related to climate change: ongoing data collection to monitor the sun’s energy reaching Earth, and a study of how aerosols move through Earth’s atmosphere and may influence climate.

This is the second time a Taurus XL rocket has failed to separate. NASA’s $273 million Orbiting Carbon Observatory crashed into the ocean in February 2009 due to a similar mishap. After that failure, Orbital Sciences redesigned the system. It has worked three times since on the company’s Minotaur rocket.

Source: NASA press release. Also see a previous story about the mission.

Posted on by Anne Minard

New Study: Sun’s Deep Physics Explain Sunspot-Free Days

Image credit: NASA/Goddard/SDO-AIA/JAXA/Hinode-XRT; Artistic rendering: Cygnus-Kolkata/William T. Bridgman; Conceptualization and simulation data: Dibyendu Nandy, Andres Munoz-Jaramillo and Petrus C.H. Martens.

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The long lull in sunspots at the end of Solar Cycle 23 wasn’t just fodder for global cooling predictions — it gave solar physicists plenty to study. And a new computer analysis may have come up with a fairly simple explanation for the sun’s odd quiet. Lead author Dibyendu Nandy, of the Indian Institute of Science Education and Research in Kolkata, and his colleagues report in Nature today that the long string of sunspot-free days between solar cycles 23 and 24 may directly correlate with the speed of north-south flow of plasma toward the sun’s equator. Their collage, above, shows magnetic fields in the interior of the Sun simulated using a solar dynamo model (center) and the observed solar corona at two different phases of solar activity: A quiescent phase during the recent, unusually long minimum, at right, and a comparatively active phase following the minimum, at left.

This visible-light photograph, taken in 2008 by NASA's Solar and Heliospheric Observatory (SOHO) spacecraft, shows the Sun's face free of sunspots. Credit: NASA/SOHO

The sun’s magnetic activity varies periodically, exhibiting an ~11-year cycle that can be monitored by observing the frequency and location of sunspots. Sunspots are strongly magnetized regions generated by the sun’s internal magnetic field and are the seats of solar storms that generate beautiful auroras but also pose hazards to satellites, navigation technologies like GPS and communications infrastructures.

Towards the end of solar cycle 23, which peaked in 2001 and wound down in 2008, the Sun’s activity entered a prolonged minimum, characterized by a very weak polar magnetic field and an unusually large number of days without sunspots: 780 days between 2008 and 2010. In a typical solar minimum, the sun goes spot-free for about 300 days, making the last minimum the longest since 1913.

The study authors conducted magnetic dynamo simulations of 210 sunspot cycles spanning some 2,000 years while varying the speed of the solar internal meridional (north-south) plasma flow. The sun’s plasma flows much like Earth’s ocean currents: rising at the equator, streaming toward the poles, then sinking and flowing back to the equator. At a typical speed of 40 miles per hour, it takes about 11 years to make one loop.

Nandy and his colleagues discovered that the Sun’s plasma rivers speed up and slow down like a malfunctioning conveyor belt, probably due to complicated feedback between the plasma flow and solar magnetic fields.

“It’s like a production line – a slowdown puts distance between the end of the last solar cycle and the start of the new one,” said study co-author Andres Munoz-Jaramillo, a visiting research fellow at the Harvard-Smithsonian Center for Astrophysics.

Specifically, the authors write, a fast meridional flow in the first half of a cycle, followed by a slower flow in the second half, leads to a deep sunspot minimum — and can reproduce the observed characteristics of the cycle 23 minimum.

Nandy and his colleagues say continued solar observations will be key to confirming and elaborating on the modeling results.

“We anticipate that NASA’s recently launched Solar Dynamics Observatory will provide more precise constraints on the structure of the plasma flows deep in the solar interior, which could be useful for complementing these simulations,” they write.

Source: Nature and the Harvard-Smithsonian Center for Astrophysics.