Geomagnetic Storm Headed For Earth Could Mean Auroras Will Be Visible Over Parts Of U.S.

A geomagnetic storm warning has been issued following three coronal mass ejections (CME) from a giant sunspot. The National Oceanic and Atmospheric Administration’s Space Weather Prediction Center said that a minor geomagnetic storm watch is in effect for May 15 and May 16.

As a result of the storm, northern parts of the U.S. may be able to see auroras over the next few nights. A forecast map showing where the auroras may be visible can be seen below.

CMEs come from our sun’s outer atmosphere. This is a region that has extremely strong magnetic fields. When these fields close, they can suddenly eject matter in a huge explosion—a CME. This matter—sometimes a billion tons of it—is ejected into space, impacting any object it comes across.

When a CME explodes in the direction of Earth, the solar material interacts with atoms and molecules in our atmosphere. The collisions produce auroras.

The three CMEs responsible for the latest geomagnetic storm came from the sunspot group Region 2741. The series started on May 10 and material from the first two is expected to arrive on May 15. The third will likely reach Earth on May 16.

“The source location for the CMEs has been associated with disappearing solar filaments (DSF) along areas of the magnetic neutral line in the vicinity of the unipolar sunspot group, Region 2741,” an NOAA statement said.

A solar filament is a long line of colder material that hovers above the sun’s corona. NASA notes that these filaments can float along like this for days before they disappear. “Sometimes they also erupt out into space, releasing solar material in a shower that either rains back down or escapes out into space, becoming a moving cloud known as a coronal mass ejection, or CME,” the space agency noted.

Sunspots are temporary regions on the surface of the sun that are darker and colder than the surrounding area—around 4,500 degrees Celsius cooler.

According to SpaceWeather, the sunspot that the latest three CMEs came from appears to be disintegrating and is no longer able to produce huge CMEs that pose a greater risk to Earth. When the sun does produce large explosions, a strong geomagnetic storm has the potential to cause disruption to GPS systems, satellites and power grids.

At the moment, the sun is in a period of quiet known as the solar minimum. The sun’s activity increases and decreases on an 11-year cycle. The solar maximum, when activity peaks, sees an increase in the number of sunspots. The next solar maximum is expected to peak around 2024.

What A Dying Star’s Ashes Tell Us About The Birth Of Our Solar System

A grain of dust forged in the death throes of a long-gone star was discovered by a team of researchers led by the University of Arizona.

The discovery challenges some of the current theories about how dying stars seed the universe with raw materials for the formation of planets and, ultimately, the precursor molecules of life.

Tucked inside a chondritic meteorite collected in Antarctica, the tiny speck represents actual stardust, most likely hurled into space by an exploding star before our own sun existed. Although such grains are believed to provide important raw materials contributing to the mix from which the sun and our planets formed, they rarely survive the turmoil that goes with the birth of a solar system.

“As actual dust from stars, such presolar grains give us insight into the building blocks from which our solar system formed,” said Pierre Haenecour, lead author of the paper, which is scheduled for advance online publication on Nature Astronomy’s website on Apr. 29. “They also provide us with a direct snapshot of the conditions in a star at the time when this grain was formed.”

Dubbed LAP-149, the dust grain represents the only known assemblage of graphite and silicate grains that can be traced to a specific type of stellar explosion called a nova. Remarkably, it survived the journey through interstellar space and traveled to the region that would become our solar system some 4.5 billion years ago, perhaps earlier, where it became embedded in a primitive meteorite.

Novae are binary star systems in which a core remnant of a star, called a white dwarf, is on its way to fading out of the universe, while its companion is either a low-mass main sequence star or a red giant. The white dwarf then begins syphoning material off its bloated companion. Once it accretes enough new stellar material, the white dwarf re-ignites in periodic outbursts violent enough to forge new chemical elements from the stellar fuel and spew them deep into space, where they can travel to new stellar systems and become incorporated in their raw materials.

Since shortly after the Big Bang, when the universe consisted of only hydrogen, helium and traces of lithium, stellar explosions have contributed to the chemical enrichment of the cosmos, resulting in the plethora of elements we see today.

Taking advantage of sophisticated ion and electron microscopy facilities at the UA’s Lunar and Planetary Laboratory, a research team led by Haenecour analyzed the microbe-sized dust grain down to the atomic level. The tiny messenger from outer space turned out to be truly alien — highly enriched in a carbon isotope called 13C.

“The carbon isotopic compositions in anything we have ever sampled that came from any planet or body in our solar system varies typically by a factor on the order of 50,” said Haenecour, who will join the Lunar and Planetary Laboratory as an assistant professor in the fall. “The 13C we found in LAP-149 is enriched more than 50,000-fold. These results provide further laboratory evidence that both carbon- and oxygen-rich grains from novae contributed to the building blocks of our solar system.”

Although their parent stars no longer exist, the isotopic and chemical compositions and microstructure of individual stardust grains identified in meteorites provide unique constraints on dust formation and thermodynamic conditions in stellar outflows, the authors wrote.

Detailed analysis revealed even more unexpected secrets: Unlike similar dust grains thought to have been forged in dying stars, LAP-149 is the first known grain consisting of graphite that contains an oxygen-rich silicate inclusion.

“Our find provides us with a glimpse into a process we could never witness on Earth,” Haenecour added. “It tells us about how dust grains form and move around inside as they are expelled by the nova. We now know that carbonaceous and silicate dust grains can form in the same nova ejecta, and they get transported across chemically distinct clumps of dust within the ejecta, something that was predicted by models of novae but never found in a specimen.”

Unfortunately, LAP-149 does not contain enough atoms to determine its exact age, so researchers hope to find similar, larger specimens in the future.

“If we could date these objects someday, we could get a better idea of what our galaxy looked like in our region and what triggered the formation of the solar system,” said Tom Zega, scientific director of the UA’s Kuiper Materials Imaging and Characterization Facility and associate professor in the Lunar and Planetary Laboratory and UA Department of Materials Science and Engineering. “Perhaps we owe our existence to a nearby supernova explosion, compressing clouds of gas and dust with its shockwave, igniting stars and creating stellar nurseries, similar to what we see in Hubble’s famous ‘Pillars of Creation’ picture.”

The meteorite containing the speck of stardust is one of the most pristine meteorites in the Lunar and Planetary Laboratory’s collection. Classified as a carbonaceous chondrite, it is believed to be analogous to the material on Bennu, the target asteroid of the UA-led OSIRIS-REx mission. By taking a sample of Bennu and bringing it back to Earth, the OSIRIS-REx mission team hopes to provide scientists with material that has seen little, if any, alteration since the formation of our solar system.

Until then, researchers depend on rare finds like LAP-149, which survived being blasted from an exploding star, caught in a collapsing cloud of gas and dust that would become our solar system and baked into an asteroid before falling to the earth.

“It’s remarkable when you think about all the ways along the way that should have killed this grain,” Zega said.

Scientists Predict Sun’s Activity Will Be Weak During Next Solar Cycle

Scientists charged with predicting the sun’s activity for the next 11-year solar cycle say that it’s likely to be weak, much like the current one. The current solar cycle, Cycle 24, is declining and predicted to reach solar minimum—the period when the sun is least active—late in 2019 or 2020.

Solar Cycle 25 Prediction Panel experts said Solar Cycle 25 may have a slow start, but is anticipated to peak with solar maximum occurring between 2023 and 2026, and a sunspot range of 95 to 130. This is well below the average number of sunspots, which typically ranges from 140 to 220 sunspots per solar cycle. The panel has high confidence that the coming cycle should break the trend of weakening solar activity seen over the past four cycles.

“We expect Solar Cycle 25 will be very similar to Cycle 24: another fairly weak cycle, preceded by a long, deep minimum,” said panel co-chair Lisa Upton, Ph.D., solar physicist with Space Systems Research Corp. “The expectation that Cycle 25 will be comparable in size to Cycle 24 means that the steady decline in solar cycle amplitude, seen from cycles 21-24, has come to an end and that there is no indication that we are currently approaching a Maunder-type minimum in solar activity.”

The solar cycle prediction gives a rough idea of the frequency of space weather storms of all types, from radio blackouts to geomagnetic storms and solar radiation storms. It is used by many industries to gauge the potential impact of space weather in the coming years. Space weather can affect power grids, critical military, airline, and shipping communications, satellites and Global Positioning System (GPS) signals, and can even threaten astronauts by exposure to harmful radiation doses.

Solar Cycle 24 reached its maximum—the period when the sun is most active—in April 2014 with a peak average of 82 sunspots. The sun’s Northern Hemisphere led the sunspot cycle, peaking over two years ahead of the Southern Hemisphere sunspot peak.

Solar cycle forecasting is a new science

While daily weather forecasts are the most widely used type of scientific information in the U.S., solar forecasting is relatively new. Given that the sun takes 11 years to complete one solar cycle, this is only the fourth time a solar cycle prediction has been issued by U.S. scientists. The first panel convened in 1989 for Cycle 22.

For Solar Cycle 25, the panel hopes for the first time to predict the presence, amplitude, and timing of any differences between the northern and southern hemispheres on the sun, known as Hemispheric Asymmetry. Later this year, the Panel will release an official sunspot Number curve which shows the predicted number of sunspots during any given year and any expected asymmetry. The panel will also look into the possibility of providing a Solar Flare Probability Forecast.

“While we are not predicting a particularly active Solar Cycle 25, violent eruptions from the sun can occur at any time,” said Doug Biesecker, Ph.D., panel co-chair and a solar physicist at NOAA’s Space Weather Prediction Center.

An example of this occurred on July 23, 2012 when a powerful coronal mass ejection (CME) eruption missed the Earth but enveloped NASA’s STEREO-A satellite. A 2013 study estimated that the U.S. would have suffered between $600 billion and $2.6 trillion in damages, particularly to electrical infrastructure, such as power grid, if this CME had been directed toward Earth. The strength of the 2012 eruption was comparable to the famous 1859 Carrington event that caused widespread damage to telegraph stations around the world and produced aurora displays as far south as the Caribbean.

The Solar Cycle Prediction Panel forecasts the number of sunspots expected for solar maximum, along with the timing of the peak and minimum solar activity levels for the cycle. It is comprised of scientists representing NOAA, NASA, the International Space Environment Services, and other U.S. and international scientists. The outlook was presented on April 5 at the 2019 NOAA Space Weather Workshop in Boulder, Colo.

Solar Wind: And The Blobs Just Keep On Coming

When Simone Di Matteo first saw the patterns in his data, it seemed too good to be true. “It’s too perfect!” Di Matteo, a space physics Ph.D. student at the University of L’Aquila in Italy, recalled thinking. “It can’t be real.” And it wasn’t, he’d soon find out.

Di Matteo was looking for long trains of massive blobs — like a lava lamp’s otherworldly bubbles, but anywhere from 50 to 500 times the size of Earth — in the solar wind. The solar wind, whose origins aren’t yet fully understood, is the stream of charged particles that blows constantly from the Sun. Earth’s magnetic field, called the magnetosphere, shields our planet from the brunt of its radiation. But when giant blobs of solar wind collide with the magnetosphere, they can trigger disturbances there that interfere with satellites and everyday communications signals.

In his search, Di Matteo was re-examining archival data from the two German-NASA Helios spacecraft, which launched in 1974 and 1976 to study the Sun. But this was 45-year-old data he’d never worked with before. The flawless, wave-like patterns he initially found hinted that something was leading him astray.

It wasn’t until uncovering and removing those false patterns that Di Matteo found exactly what he was looking for: dotted trails of blobs that oozed from the Sun every 90 minutes or so. The scientists published their findings in JGR Space Physics on Feb. 21, 2019. They think the blobs could shed light on the solar wind’s beginnings. Whatever process sends the solar wind out from the Sun must leave signatures on the blobs themselves.

Making Way for New Science

Di Matteo’s research was the start of a project NASA scientists undertook in anticipation of the first data from NASA’s Parker Solar Probe mission, which launched in 2018. Over the next seven years, Parker will fly through unexplored territory, soaring as close as 4 million miles from the Sun. Before Parker, the Helios 2 satellite held the record for the closest approach to the Sun at 27 million miles, and scientists thought it might give them an idea of what to expect. “When a mission like Parker is going to see things no one has seen before, just a hint of what could be observed is really helpful,” Di Matteo said.

The problem with studying the solar wind from Earth is distance. In the time it takes the solar wind to race across the 93 million miles between us and the Sun, important clues to the wind’s origins — like temperature and density — fade. “You’re constantly asking yourself, ‘How much of what I’m seeing here is because of evolution over four days in transit, and how much came straight from the Sun?'” said solar scientist Nicholeen Viall, who advised Di Matteo during his research at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Helios data — some of which was collected at just one-third the distance between the Sun and Earth — could help them begin to answer these questions.

Modeling Blobs

The first step was tracing Helios’ measurements of the blobs to their source on the Sun. “You can look at spacecraft data all you want, but if you can connect it back to where it came from on the Sun, it tells a more complete story,” said Samantha Wallace, one of the study collaborators and a physics Ph.D. student at the University of New Mexico in Albuquerque.

Wallace used an advanced solar wind model to link magnetic maps of the solar surface to Helios’ observations, a tricky task since computer languages and data conventions have changed greatly since Helios’ days. Now, the researchers could see what sorts of regions on the Sun were likely to bud into blobs of solar wind.

Sifting the Evidence

Then, Di Matteo searched the data for specific wave patterns. They expected conditions to alternate — hot and dense, then cold and tenuous — as individual blobs engulfed the spacecraft and moved on, in a long line.

The picture-perfect patterns Di Matteo first found worried him. “That was a red flag,” Viall said. “The actual solar wind doesn’t have such precise, clean periodicities. Usually when you get such a precise frequency, it means some instrument effect is going on.” Maybe there was some element of the instrument design they weren’t considering, and it was imparting effects that had to be separated from true solar wind patterns.

Di Matteo needed more information on the Helios instruments. But most researchers who worked on the mission have long since retired. He did what anyone else would do, and turned to the internet.

Many Google searches and a weekend of online translators later, Di Matteo unearthed a German instruction manual that describes the instruments dedicated to the mission’s solar wind experiment. Decades ago, when Helios was merely a blueprint and before anyone ever launched a spacecraft to the Sun, scientists didn’t know how best to measure the solar wind. To prepare themselves for different scenarios, Di Matteo learned, they equipped the probes with two different instruments that would each measure certain solar wind properties in their own way. This was the culprit responsible for Di Matteo’s perfect waves: the spacecraft itself, as it alternated between two instruments.

After they removed segments of data taken during routine instrument-switching, the researchers looked again for the blobs. This time, they found them. The team describes five instances that Helios happened to catch trains of blobs. While scientists have spotted these blobs from Earth before, this is the first time they’ve studied them this close to the Sun, and with this level of detail. They outline the first conclusive evidence that the blobs are hotter and denser than the typical solar wind.

The Return of the Blobs

Whether blob trains bubble in 90-minute intervals continuously or in spurts, and how much they vary between themselves, is still a mystery. “This is one of those studies that brought up more questions than we answered, but that’s perfect for Parker Solar Probe,” Viall said.

Parker Solar Probe aims to study the Sun up close, seeking answers to basic questions about the solar wind. “This is going to be very helpful,” said Aleida Higginson, the mission’s deputy project scientist at Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “If you want to even begin to understand things you’ve never seen before, you need to know what we’ve measured before and have a solid scientific interpretation for it.”

Parker Solar Probe performs its second solar flyby on April 4, which brings it 15 million miles from the Sun — already cutting Helios 2’s record distance in half. The researchers are eager to see if blobs show up in Parker’s observations. Eventually, the spacecraft will get so close it could catch blobs right after they’ve formed, fresh out of the Sun.

Unexpected Coronal Rain On Sun Links Two Solar Mysteries

For five months in mid 2017, Emily Mason did the same thing every day. Arriving to her office at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, she sat at her desk, opened up her computer, and stared at images of the Sun — all day, every day. “I probably looked through three or five years’ worth of data,” Mason estimated. Then, in October 2017, she stopped. She realized she had been looking at the wrong thing all along.

Mason, a graduate student at The Catholic University of America in Washington, D.C., was searching for coronal rain: giant globs of plasma, or electrified gas, that drip from the Sun’s outer atmosphere back to its surface. But she expected to find it in helmet streamers, the million-mile tall magnetic loops — named for their resemblance to a knight’s pointy helmet — that can be seen protruding from the Sun during a solar eclipse. Computer simulations predicted the coronal rain could be found there. Observations of the solar wind, the gas escaping from the Sun and out into space, hinted that the rain might be happening. And if she could just find it, the underlying rain-making physics would have major implications for the 70-year-old mystery of why the Sun’s outer atmosphere, known as the corona, is so much hotter than its surface. But after nearly half a year of searching, Mason just couldn’t find it. “It was a lot of looking,” Mason said, “for something that never ultimately happened.”

The problem, it turned out, wasn’t what she was looking for, but where. In a paper published today in the Astrophysical Journal Letters, Mason and her coauthors describe the first observations of coronal rain in a smaller, previously overlooked kind of magnetic loop on the Sun. After a long, winding search in the wrong direction, the findings forge a new link between the anomalous heating of the corona and the source of the slow solar wind — two of the biggest mysteries facing solar science today.

How It Rains on the Sun

Observed through the high-resolution telescopes mounted on NASA’s SDO spacecraft, the Sun — a hot ball of plasma, teeming with magnetic field lines traced by giant, fiery loops — seems to have few physical similarities with Earth. But our home planet provides a few useful guides in parsing the Sun’s chaotic tumult: among them, rain.

On Earth, rain is just one part of the larger water cycle, an endless tug-of-war between the push of heat and pull of gravity. It begins when liquid water, pooled on the planet’s surface in oceans, lakes, or streams, is heated by the Sun. Some of it evaporates and rises into the atmosphere, where it cools and condenses into clouds. Eventually, those clouds become heavy enough that gravity’s pull becomes irresistible and the water falls back to Earth as rain, before the process starts anew.

On the Sun, Mason said, coronal rain works similarly, “but instead of 60-degree water you’re dealing with a million-degree plasma.” Plasma, an electrically-charged gas, doesn’t pool like water, but instead traces the magnetic loops that emerge from the Sun’s surface like a rollercoaster on tracks. At the loop’s foot points, where it attaches to the Sun’s surface, the plasma is superheated from a few thousand to over 1.8 million degrees Fahrenheit. It then expands up the loop and gathers at its peak, far from the heat source. As the plasma cools, it condenses and gravity lures it down the loop’s legs as coronal rain.

Mason was looking for coronal rain in helmet streamers, but her motivation for looking there had more to do with this underlying heating and cooling cycle than the rain itself. Since at least the mid-1990s, scientists have known that helmet streamers are one source of the slow solar wind, a comparatively slow, dense stream of gas that escapes the Sun separately from its fast-moving counterpart. But measurements of the slow solar wind gas revealed that it had once been heated to an extreme degree before cooling and escaping the Sun. The cyclical process of heating and cooling behind coronal rain, if it was happening inside the helmet streamers, would be one piece of the puzzle.

The other reason connects to the coronal heating problem — the mystery of how and why the Sun’s outer atmosphere is some 300 times hotter than its surface. Strikingly, simulations have shown that coronal rain only forms when heat is applied to the very bottom of the loop. “If a loop has coronal rain on it, that means that the bottom 10% of it, or less, is where coronal heating is happening,” said Mason. Raining loops provide a measuring rod, a cutoff point to determine where the corona gets heated. Starting their search in the largest loops they could find — giant helmet streamers — seemed like a modest goal, and one that would maximize their chances of success.

She had the best data for the job: Images taken by NASA’s Solar Dynamics Observatory, or SDO, a spacecraft that has photographed the Sun every twelve seconds since its launch in 2010. But nearly half a year into the search, Mason still hadn’t observed a single drop of rain in a helmet streamer. She had, however, noticed a slew of tiny magnetic structures, ones she wasn’t familiar with. “They were really bright and they kept drawing my eye,” said Mason. “When I finally took a look at them, sure enough they had tens of hours of rain at a time.”

At first, Mason was so focused on her helmet streamer quest that she made nothing of the observations. “She came to group meeting and said, ‘I never found it — I see it all the time in these other structures, but they’re not helmet streamers,'” said Nicholeen Viall, a solar scientist at Goddard, and a coauthor of the paper. “And I said, ‘Wait…hold on. Where do you see it? I don’t think anybody’s ever seen that before!'”

A Measuring Rod for Heating

These structures differed from helmet streamers in several ways. But the most striking thing about them was their size.

“These loops were much smaller than what we were looking for,” said Spiro Antiochos, who is also a solar physicist at Goddard and a coauthor of the paper. “So that tells you that the heating of the corona is much more localized than we were thinking.”

While the findings don’t say exactly how the corona is heated, “they do push down the floor of where coronal heating could happen,” said Mason. She had found raining loops that were some 30,000 miles high, a mere two percent the height of some of the helmet streamers she was originally looking for. And the rain condenses the region where the key coronal heating can be happening. “We still don’t know exactly what’s heating the corona, but we know it has to happen in this layer,” said Mason.

A New Source for the Slow Solar Wind

But one part of the observations didn’t jibe with previous theories. According to the current understanding, coronal rain only forms on closed loops, where the plasma can gather and cool without any means of escape. But as Mason sifted through the data, she found cases where rain was forming on open magnetic field lines. Anchored to the Sun at only one end, the other end of these open field lines fed out into space, and plasma there could escape into the solar wind. To explain the anomaly, Mason and the team developed an alternative explanation — one that connected rain on these tiny magnetic structures to the origins of the slow solar wind.

In the new explanation, the raining plasma begins its journey on a closed loop, but switches — through a process known as magnetic reconnection — to an open one. The phenomenon happens frequently on the Sun, when a closed loop bumps into an open field line and the system rewires itself. Suddenly, the superheated plasma on the closed loop finds itself on an open field line, like a train that has switched tracks. Some of that plasma will rapidly expand, cool down, and fall back to the Sun as coronal rain. But other parts of it will escape — forming, they suspect, one part of the slow solar wind.

Mason is currently working on a computer simulation of the new explanation, but she also hopes that soon-to-come observational evidence may confirm it. Now that Parker Solar Probe, launched in 2018, is traveling closer to the Sun than any spacecraft before it, it can fly through bursts of slow solar wind that can be traced back to the Sun — potentially, to one of Mason’s coronal rain events. After observing coronal rain on an open field line, the outgoing plasma, escaping to the solar wind, would normally be lost to posterity. But no longer. “Potentially we can make that connection with Parker Solar Probe and say, that was it,” said Viall.

Digging Through the Data

As for finding coronal rain in helmet streamers? The search continues. The simulations are clear: the rain should be there. “Maybe it’s so small you can’t see it?” said Antiochos. “We really don’t know.”

But then again, if Mason had found what she was looking for she might not have made the discovery — or have spent all that time learning the ins and outs of solar data.

“It sounds like a slog, but honestly it’s my favorite thing,” said Mason. “I mean that’s why we built something that takes that many images of the Sun: So we can look at them and figure it out.”

‘Strange Blue Lights’ Spotted Over Arctic Circle Explained By NASA

Those observing the Northern Lights in Norway over the weekend were treated not only to the spectacular aurora, but also reported strange configurations of colourful lights moving through the sky.

While those who witnessed it could be forgiven for preparing to pledge allegiance to some new extra-terrestrial conquistadors, Nasa has owned up and explained it was in fact a pair of their rockets which created the unusual phenomenon.

The stunning geometric lights, made up of dark blue clouds, turquoise dots and pale orange vapour trails, lit up the sky over the Norwegian Sea on April 5.

They were the result of an experiment designed to study the processes inside the Earth’s “polar cusp”, where the planet’s magnetic field lines bend down through the atmosphere.

It is here that the charged particles from solar wind cause aurora – the colourful natural light displays which appear over the poles during periods of solar activity.

Scientists want to study exactly what happens during an aurora in the electrically charged and turbulent layer of the outer atmosphere which Nasa describes as a “tumultuous particle soup”.

Their pair of rockets were carrying scientific instruments for studying the energy exchange during the phenomenon, and also deployed what they called “visible gas tracers”, between 71 and 150 miles altitude.

The mixture of substances are similar to those found in fireworks, with chemicals which ionize when exposed to sunlight.

The multi-coloured vapours produced “allow researchers to track the flow of neutral and charged particles with the auroral wind,” Nasa said.

The project is called AZURE, which stands for Auroral Zone Upwelling Rocket Experiment, and was carried out by two black Brant I-A sounding rockets, which were launched from the Andøya Space Centre in north-west Norway.

Michael Theusner who captured a stunning time lapse of the kaleidoscopic illuminations, said: “While we were watching the after-effects of a beautiful northern lights display, the rockets were launched from the Andøya Space Centre only about 180 km away to the north.

“We saw two orange dots rise into the sky and disappear. A short while later strange lights and colourful, expanding clouds appeared I first did not have an explanation for. It looked like an alien attack.”

Solar Variability Weakens The Walker Cell

An international team of researchers from United Kingdom, Denmark, and Germany has found robust evidence for signatures of the 11-year sunspot cycle in the tropical Pacific. They analyzed historical time series of pressure, surface winds and precipitation with specific focus on the Walker Circulation—a vast system of atmospheric flow in the tropical Pacific region that affects patterns of tropical rainfall. They have revealed that during periods of increased solar irradiance, the trade winds weaken and the Walker circulation shifts eastward.

Stergios Misios, a postdoctoral researcher at the University of Oxford, said, “We deal with a very short record of observations in the tropical Pacific, and we must be very careful with how we filter out other interannual fluctuations. After a careful treatment of the data covering the last 60 years, we detected a robust slowdown of the Walker cell during years associated with solar-cycle maxima.” The analysis shows that in tandem with changes in the wind anomalies, the dominant patterns of tropical precipitation shift to the central Pacific during solar-cycle maxima. As a result, rainfall decreases over Indonesia and in the western Pacific, and increases over the central Pacific Ocean.

Simple mechanisms amplify the solar signal

The issue of solar influences on climate is long and controversial, as there have been numerous claims that did not survive proper statistical scrutiny in most cases. But besides statistical verification lies an even more challenging problem: How could miniscule changes in incoming solar radiation produce significant climate signatures?

“Soon enough, we realized that the magnitude of the wind anomalies that we detected in observations simply could not be explained by radiative considerations alone. We thought that if it comes from the sun, there must be another mechanism that amplifies the weakening of the Walker circulation,” said Prof. Lesley Gray of University of Oxford. With the aid of a global climate model, this mechanism was found in the dynamical coupling between the atmosphere and ocean circulation in the tropical Pacific.

Averaged over the globe, the surface temperature imprint of the solar cycle barely reaches 0.1 K in a solar maximum—almost eight times weaker than the global warming trends observed in the 20th century. Yet, even such a weak surface warming influences the Walker circulation through changes in global hydrology. As the surface warms, water vapor in the atmosphere increases at a higher rate than is lost by precipitation, necessitating a weakening of the Walker cell. This is a well-tested mechanism in model simulations of increased CO2 concentrations but it turns out that is operating under the 11-year solar cycle, too.

S. Misios said, “Our model showed westerly wind anomalies in the Pacific region even when we considered only changes in global hydrology, but the magnitude was far too weak. We hypothesized that atmosphere-ocean coupling, essentially the Bjerknes feedback, can amplify the solar signal.”

Using a climate model forced by the 11-year solar cycle alone, researchers found the evidence to support their hypothesis. Their model showed much stronger wind anomalies in the Pacific. They proposed that changes in global hydrology and the Bjerknes feedback mediate solar cycle influences on the Tropical Pacific. The researchers now hope that if the interplay between those mechanisms is properly represented by other climate models, it could give potential to improve the accuracy of decadal predictions in that region.