Solar Flare Pulses At Sun And Earth Detected

When our Sun erupts with giant explosions — such as bursts of radiation called solar flares — we know they can affect space throughout the solar system as well as near Earth. But monitoring their effects requires having observatories in many places with many perspectives, much the way weather sensors all over Earth can help us monitor what’s happening with a terrestrial storm.

By using multiple observatories, two recent studies show how solar flares exhibit pulses or oscillations in the amount of energy being sent out. Such research provides new insights on the origins of these massive solar flares as well as the space weather they produce, which is key information as humans and robotic missions venture out into the solar system, farther and farther from home.

The first study spotted oscillations during a flare — unexpectedly — in measurements of the Sun’s total output of extreme ultraviolet energy, a type of light invisible to human eyes. On Feb. 15, 2011, the Sun emitted an X-class solar flare, the most powerful kind of these intense bursts of radiation. Because scientists had multiple instruments observing the event, they were able to track oscillations in the flare’s radiation, happening simultaneously in several different sets of observations.

“Any type of oscillation on the Sun can tell us a lot about the environment the oscillations are taking place in, or about the physical mechanism responsible for driving changes in emission,” said Ryan Milligan, lead author of this first study and solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Glasgow in Scotland. In this case, the regular pulses of extreme ultraviolet light indicated disturbances — akin to earthquakes — were rippling through the chromosphere, the base of the Sun’s outer atmosphere, during the flare.

What surprised Milligan about the oscillations was the fact that they were first observed in extreme ultraviolet data from NOAA’s GOES — short for Geostationary Operation Environmental Satellite, which resides in near-Earth space. The mission studies the Sun from Earth’s perspective, collecting X-ray and extreme ultraviolet irradiance data — the total amount of the Sun’s energy that reaches Earth’s atmosphere over time.

This wasn’t a typical data set for Milligan. While GOES helps monitor the effects of solar eruptions in Earth’s space environment — known collectively as space weather — the satellite wasn’t initially designed to detect fine details like these oscillations.

When studying solar flares, Milligan more commonly uses high-resolution data on a specific active region in the Sun’s atmosphere to study the physical processes underlying flares. This is often necessary in order to zoom in on events in a particular area — otherwise they can easily be lost against the backdrop of the Sun’s constant, intense radiation.

“Flares themselves are very localized, so for the oscillations to be detected above the background noise of the Sun’s regular emissions and show up in the irradiance data was very striking,” Milligan said.

There have been previous reports of oscillations in GOES X-ray data coming from the Sun’s upper atmosphere, called the corona, during solar flares. What’s unique in this case is that the pulses were observed in extreme ultraviolet emission at frequencies that show they originated lower, in the chromosphere, providing more information about how a flare’s energy travels throughout through the Sun’s atmosphere.

To be sure the oscillations were real, Milligan and his colleagues checked corresponding data from other Sun-observing instruments on board NASA’s Solar Dynamics Observatory or SDO, for short: one that also collects extreme ultraviolet irradiance data and another that images the corona in different wavelengths of light. They found the exact same pulses in those data sets, confirming they were a phenomenon with its source at the Sun. Their findings are summarized in a paper published in The Astrophysical Journal Letters on Oct. 9, 2017.

These oscillations interest the scientists because they may be the result of a mechanism by which flares emit energy into space — a process we don’t yet fully understand. Additionally, the fact that the oscillations appeared in data sets typically used to monitor larger space patterns suggests they could play a role in driving space weather effects.

In the second study, scientists investigated a connection between solar flares and activity in Earth’s atmosphere. The team discovered that pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a July 24, 2016, C-class flare. C-class flares are of mid-to-low intensity, and about 100 times weaker than X-flares.

Stretching from roughly 30 to 600 miles above Earth’s surface, the ionosphere is an ever-changing region of the atmosphere that reacts to changes from both Earth below and space above. It swells in response to incoming solar radiation, which ionizes atmospheric gases, and relaxes at night as the charged particles gradually recombine.

In particular, the team of scientists — led by Laura Hayes, a solar physicist who splits her time between NASA Goddard and Trinity College in Dublin, Ireland, and her thesis adviser Peter Gallagher — looked at how the lowest layer of the ionosphere, called the D-region, responded to pulsations in a solar flare.

“This is the region of the ionosphere that affects high-frequency communications and navigation signals,” Hayes said. “Signals travel through the D-region, and changes in the electron density affect whether the signal is absorbed, or degraded.”

The scientists used data from very low frequency, or VLF, radio signals to probe the flare’s effects on the D-region. These were standard communication signals transmitted from Maine and received in Ireland. The denser the ionosphere, the more likely these signals are to run into charged particles along their way from a signal transmitter to its receiver. By monitoring how the VLF signals propagate from one end to the other, scientists can map out changes in electron density.

Pooling together the VLF data and X-ray and extreme ultraviolet observations from GOES and SDO, the team found the D-region’s electron density was pulsing in concert with X-ray pulses on the Sun. They published their results in the Journal of Geophysical Research on Oct. 17, 2017.

“X-rays impinge on the ionosphere and because the amount of X-ray radiation coming in is changing, the amount of ionization in the ionosphere changes too,” said Jack Ireland, a co-author on both studies and Goddard solar physicist. “We’ve seen X-ray oscillations before, but the oscillating ionosphere response hasn’t been detected in the past.”

Hayes and her colleagues used a model to determine just how much the electron density changed during the flare. In response to incoming radiation, they found the density increased as much as 100 times in just 20 minutes during the pulses — an exciting observation for the scientists who didn’t expect oscillating signals in a flare would have such a noticeable effect in the ionosphere. With further study, the team hopes to understand how the ionosphere responds to X-ray oscillations at different timescales, and whether other solar flares induce this response.

“This is an exciting result, showing Earth’s atmosphere is more closely linked to solar X-ray variability than previously thought,” Hayes said. “Now we plan to further explore this dynamic relationship between the Sun and Earth’s atmosphere.”

Both of these studies took advantage of the fact that we are increasingly able to track solar activity and space weather from a number of vantage points. Understanding the space weather that affects us at Earth requires understanding a dynamic system that stretches from the Sun all the way to our upper atmosphere — a system that can only be understood by tapping into a wide range of missions scattered throughout space.

Oldest Recorded Solar Eclipse Helps Date The Egyptian Pharaohs

Researchers have pinpointed the date of what could be the oldest solar eclipse yet recorded. The event, which occurred on 30 October 1207 BC, is mentioned in the Bible, and could have consequences for the chronology of the ancient world.

Using a combination of the biblical text and an ancient Egyptian text, the researchers were then able to refine the dates of the Egyptian pharaohs, in particular the dates of the reign of Ramesses the Great. The results are published in the Royal Astronomical Society journal Astronomy & Geophysics.

The biblical text in question comes from the Old Testament book of Joshua and has puzzled biblical scholars for centuries. It records that after Joshua led the people of Israel into Canaan — a region of the ancient Near East that covered modern-day Israel and Palestine — he prayed: “Sun, stand still at Gibeon, and Moon, in the Valley of Aijalon. And the Sun stood still, and the Moon stopped, until the nation took vengeance on their enemies.”

“If these words are describing a real observation, then a major astronomical event was taking place — the question for us to figure out is what the text actually means,” said paper co-author Professor Sir Colin Humphreys from the University of Cambridge’s Department of Materials Science & Metallurgy, who is also interested in relating scientific knowledge to the Bible.

“Modern English translations, which follow the King James translation of 1611, usually interpret this text to mean that the sun and moon stopped moving,” said Humphreys, who is also a Fellow of Selwyn College. “But going back to the original Hebrew text, we determined that an alternative meaning could be that the sun and moon just stopped doing what they normally do: they stopped shining. In this context, the Hebrew words could be referring to a solar eclipse, when the moon passes between the earth and the sun, and the sun appears to stop shining. This interpretation is supported by the fact that the Hebrew word translated ‘stand still’ has the same root as a Babylonian word used in ancient astronomical texts to describe eclipses.”

Humphreys and his co-author, Graeme Waddington, are not the first to suggest that the biblical text may refer to an eclipse, however, earlier historians claimed that it was not possible to investigate this possibility further due to the laborious calculations that would have been required.

Independent evidence that the Israelites were in Canaan between 1500 and 1050 BC can be found in the Merneptah Stele, an Egyptian text dating from the reign of the Pharaoh Merneptah, son of the well-known Ramesses the Great. The large granite block, held in the Egyptian Museum in Cairo, says that it was carved in the fifth year of Merneptah’s reign and mentions a campaign in Canaan in which he defeated the people of Israel.

Earlier historians have used these two texts to try to date the possible eclipse, but were not successful as they were only looking at total eclipses, in which the disc of the sun appears to be completely covered by the moon as the moon passes directly between the earth and the sun. What the earlier historians failed to consider was that it was instead an annular eclipse, in which the moon passes directly in front of the sun, but is too far away to cover the disc completely, leading to the characteristic ‘ring of fire’ appearance. In the ancient world the same word was used for both total and annular eclipses.

The researchers developed a new eclipse code, which takes into account variations in the Earth’s rotation over time. From their calculations, they determined that the only annular eclipse visible from Canaan between 1500 and 1050 BC was on 30 October 1207 BC, in the afternoon. If their arguments are accepted, it would not only be the oldest solar eclipse yet recorded, it would also enable researchers to date the reigns of Ramesses the Great and his son Merneptah to within a year.

“Solar eclipses are often used as a fixed point to date events in the ancient world,” said Humphreys. Using these new calculations, the reign of Merneptah began in 1210 or 1209 BC. As it is known from Egyptian texts how long he and his father reigned for, it would mean that Ramesses the Great reigned from 1276-1210 BC, with a precision of plus or minus one year, the most accurate dates available. The precise dates of the pharaohs have been subject to some uncertainty among Egyptologists, but this new calculation, if accepted, could lead to an adjustment in the dates of several of their reigns and enable us to date them precisely.

Solar Research On The Sun’s Chromosphere

At any given moment, as many as 10 million wild snakes of solar material leap from the Sun’s surface. These are spicules, and despite their abundance, scientists didn’t understand how these jets of plasma form nor did they influence the heating of the outer layers of the Sun’s atmosphere or the solar wind. Now, for the first time, in a study partly funded by NASA, scientists have modeled spicule formation.

For the first time, a scientific team has revealed their nature by combining simulations and images taken with the NASA’s IRIS spectrograph and the Swedish Solar Telescope of the Roque de los Muchachos Observatory (Garafía, La Palma). The study, led by Dr. Juan Martinez-Sykora, researcher at Lockheed Martin’s Solar and Astrophysics Laboratory (California, USA) and astrophysicist at the University of La Laguna (ULL), is published today in the journal Science.

The observations were made with IRIS (NASA’s Interface Region Imaging Spectrograph), a 20 cm ultraviolet space telescope with a spectrograph able to observe details of about 240 km, and the Swedish Solar Telescope, located at the Roque de los Muchachos Observatory. This spacecraft and the ground-based telescope study the lower layers of the solar atmosphere, where the spicules form: chromosphere and the region of transition

In addition to the images, they used computer simulations whose code was developed for almost a decade. “In our research,” says Prof. Bart De Pontieu, also author of the study, “both go hand in hand. “We compare observations and models to figure out how well our models are performing, as well as how we should interpret our space-based observations.”

Their model is based in the dynamics of plasma – the hot gas of charged particles that streams along magnetic fields and constitutes the Sun. Earlier versions of the model treated the interface region as a uniform, or completely charged, plasma, but the scientists knew something was missing because they never saw spicules in the simulations.

The model they generated is based on plasma dynamics, a very hot partially ionized gas flowing along the magnetic fields. Previous versions considered the lower atmosphere to be a uniform or fully charged plasma, but they suspected something was missing since they never detected spikes in the simulations.

The key, the scientists realized, was neutral particles. They were inspired by Earth’s own ionosphere, a region of the upper atmosphere where interactions between neutral and charged particles are responsible for numerous dynamic processes. In cooler regions of the Sun, such as the interface region, plasma isn’t actually uniform. Some particles are still neutral, and neutral particles aren’t subject to magnetic fields like charged particles are. Scientists based previous models on a uniform plasma in order to simplify the problem – modeling is computationally expensive, and the final model took roughly a year to run with NASA’s supercomputing resources – but they realized neutral particles are a necessary piece of the puzzle.

“Usually magnetic fields are tightly coupled to charged particles,” said Juan Martínez-Sykora, lead author of the study and a solar physicist at Lockheed Martin. “With only charged particles in the model, the magnetic fields were stuck, and couldn’t rise to the surface. When we added neutrals, the magnetic fields could move more freely.”

Neutral particles facilitate the buoyancy the marled knots of magnetic energy need to rise through the boiling plasma and reach the surface. There, they snap producing spicules, releasing both plasma and energy. The simulations closely matched the observations; spicules occurred naturally and frequently.

“This result is a clear example of the breakthrough that can be achieved by combining powerful theoretical-numerical methods, state-of-the-art observations and supercomputing tools to better understand astrophysical phenomena,” explains Prof.Fernando Moreno-Insertis, solar physicist at IAC, Professor ar the ULL and supervisor of the work Diploma of Advanced Studies (DEA) of Juan Martínez-Sykora. “The great complexity of many of the phenomena that occur in the solar atmosphere forces us to consider at the same time the dynamics of partially ionized gas, the magnetic field and the radiation-matter interaction in order to be able to explain them satisfactorily.”

“This result is a clear example of the breakthroughs that can be achieved by combining powerful theoretical-numerical methods, state-of-the-art observations and supercomputing tools to better understand astrophysical phenomena,” explains Fernando Moreno-Insertis, solar physicist at IAC, Professor at the ULL and supervisor of the DEA thesis (equivalent to a master´s thesis) of Juan Martínez-Sykora. “The great complexity of many of the phenomena that occur in the solar atmosphere forces us to consider at the same time the dynamics of partially ionized gas, the magnetic field and the radiation-matter interaction in order to be able to explain them satisfactorily.”

The scientists’ updated model revealed something about solar energy transport as well. It turns out the energy in this whip-like process is high enough to generate Alfvén waves, a strong kind of wave scientists suspect is key to heating the Sun’s atmosphere and propelling the solar wind, which constantly bathes the solar system with charged particles from the Sun.

The National Academy of Sciences awarded Prof. Mats Carlsson and Prof. Viggo H. Hansteen, both developers of the model and authors of the study, with the 2017 Arctowski Medal in recognition of their contributions to the study of solar physics and the Sun-Earth connection. Juan Martínez-Sykora included the effects produced by the presence of the neutral particles.

NASA’s SDO Spots a Lunar Transit

On Oct. 19, 2017, the Moon photobombed NASA’s Solar Dynamics Observatory, or SDO, when it crossed the spacecraft’s view of the Sun, treating us to these shadowy images. The lunar transit lasted about 45 minutes, between 3:41 and 4:25 p.m. EDT, with the Moon covering about 26 percent of the Sun at the peak of its journey. The Moon’s shadow obstructs SDO’s otherwise constant view of the Sun, and the shadow’s edge is sharp and distinct, since the Moon has no atmosphere which would distort sunlight.

SDO captured these images in a wavelength of extreme ultraviolet light that shows solar material heated to more than 10 million degrees Fahrenheit. This kind of light is invisible to human eyes, but colorized here in green.

NASA Sounding Rocket Instrument Spots Signatures of Long-Sought Small Solar Flares

Like most solar sounding rockets, the second flight of the FOXSI instrument – short for Focusing Optics X-ray Solar Imager – lasted 15 minutes, with just six minutes of data collection. But in that short time, the cutting-edge instrument found the best evidence to date of a phenomenon scientists have been seeking for years: signatures of tiny solar flares that could help explain the mysterious extreme heating of the Sun’s outer atmosphere.

FOXSI detected a type of light called hard X-rays – whose wavelengths are much shorter than the light humans can see – which is a signature of extremely hot solar material, around 18 million degrees Fahrenheit. These kinds of temperatures are generally produced in solar flares, powerful bursts of energy. But in this case, there was no observable solar flare, meaning the hot material was most likely produced by a series of solar flares so small that they were undetectable from Earth: nanoflares. The results were published Oct. 9, 2017, in Nature Astronomy.

“The key to this result is the sensitivity in hard X-ray measurements,” said Shin-nosuke Ishikawa, a solar physicist at the Japan Aerospace Exploration Agency, or JAXA, and lead author on the study. “Past hard X-ray instruments could not detect quiet active regions, and combination of new technologies enables us to investigate quiet active regions by hard X-rays for the first time.”

These observations are a step toward understanding the coronal heating problem, which is how scientists refer to the extraordinarily – and unexpectedly – high temperatures in the Sun’s outer atmosphere, the corona. The corona is hundreds to thousands of times hotter than the Sun’s visible surface, the photosphere. Because the Sun produces heat at its core, this runs counter to what one would initially expect: normally the layer closest to a source of heat, the Sun’s surface, in this case, would have a higher temperature than the more distant atmosphere.

“If you’ve got a stove and you take your hand farther away, you don’t expect to feel hotter than when you were close,” said Lindsay Glesener, project manager for FOXSI-2 at the University of Minnesota and an author on the study.

The cause of these counterintuitively high temperatures is an outstanding question in solar physics. One possible solution to the coronal heating problem is the constant eruption of tiny solar flares in the solar atmosphere, so small that they can’t be directly detected. In aggregate, these nanoflares could produce enough heat to raise the temperature of the corona to the millions of degrees that we observe.

One of the consequences of nanoflares would be pockets of superheated plasma. Plasma at these temperatures emits light in hard X-rays, which are notoriously difficult to detect. For instance, NASA’s RHESSI satellite – short for Reuven Ramaty High Energy Solar Spectroscopic Imager – launched in 2002, uses an indirect technique to measure hard X-rays, limiting how precisely we can pinpoint the location of superheated plasma. But with the cutting-edge optics available now, FOXSI was able to use a technique called direct focusing that can keep track of where the hard X-rays originate on the Sun.

“It’s really a completely transformative way of making this type of measurement,” said Glesener. “Even just on a sounding rocket experiment looking at the Sun for about six minutes, we had much better sensitivity than a spacecraft with indirect imaging.”

FOXSI’s measurements – along with additional X-ray data from the JAXA and NASA Hinode solar observatory – allow the team to say with certainty that the hard X-rays came from a specific region on the Sun that did not have any detectable larger solar flares, leaving nanoflares as the only likely instigator.

“This is a proof of existence for these kinds of events,” said Steve Christe, the project scientist for FOXSI at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and an author on the study. “There’s basically no other way for these X-rays to be produced, except by plasma at around 10 million degrees Celsius [18 million degrees Fahrenheit]. This points to these small energy releases happening all the time, and if they exist, they should be contributing to coronal heating.”

There are still questions to be answered, like: How much heat do nanoflares actually release into the corona?

“This particular observation doesn’t tell us exactly how much it contributes to coronal heating,” said Christe. “To fully solve the coronal heating problem, they would need to be happening everywhere, even outside of the region observed here.”

Hoping to build up a more complete picture of nanoflares and their contribution to coronal heating, Glesener is leading a team to launch a third iteration of the FOXSI instrument on a sounding rocket in summer 2018. This version of FOXSI will use new hardware to eliminate much of the background noise that the instrument sees, allowing for even more precise measurements.

A team led by Christe was also selected to undertake a concept study developing the FOXSI instrument for a possible spaceflight as part of the NASA Small Explorers program.

FOXSI is a collaboration between the United States and JAXA. The second iteration of the FOXSI sounding rocket launched from the White Sands Missile Range in New Mexico on Dec. 11, 2014. FOXSI is supported through NASA’s Sounding Rocket Program at the Goddard Space Flight Center’s Wallops Flight Facility in Virginia. NASA’s Heliophysics Division manages the sounding rocket program.

Extreme Magnetic Storm: Red Aurora Over Kyoto In 1770

Auroras are lightshows that typically occur at high latitudes such as the Arctic and Antarctic; however, they expand equatorward under severe magnetic storms. Past observations of such unusual auroras can therefore allow us to determine the frequency and severity of magnetic storms. The more information that can be gathered about historic intense magnetic storms, the greater the opportunity to mitigate disruption of power grids in a future event.

Historical documents are becoming much more accessible for research as newly discovered records surface from private collections across the world. Researchers centered at Tokyo’s National Institute of Japanese Literature (NIJL) and National Institute for Polar Research (NIPR) examined a detailed painting from a Japanese manuscript Seikai (“understanding comets”) with associated commentary describes a red aurora occurring over Kyoto on 17 September 1770. Also investigated were detailed descriptions of the event from a newly discovered diary of the Higashi-Hakura family of Kyoto.

“The enthusiasm and dedication of amateur astronomers in the past provides us an exciting opportunity,” Kiyomi Iwahashi of NIJL says. “The diary was written by a kokugakusha [scholar of ancient Japanese culture], and provides a sophisticated description of the red aurora, including a description of the position of the aurora relative to the Milky Way.”

Using astrometric calculations of the elevations of the Milky Way as it would have been viewed from Kyoto on 17 September 1770, the researchers were able to calculate the geometry of the red aurora and check the results against the details from the Seikai painting and the diary. The success of the description of the aurora according to the historical documents allowed the researchers to estimate the strength of the magnetic storm that caused the September 1770 aurora.

“The magnetic storm on 17 September 1770 was comparable with or slightly larger than the September 1859 magnetic storm that occurred under the influence of the Carrington solar flare. The 1859 storm was the largest magnetic storm on record, in which technological effects were widely observed, “Ryuho Kataoka of NIPR says.” It was lucky for us that the 1770 storm predated our reliance on electricity.”

So how likely are such magnetic storms? ” We are currently within a period of decreasing solar activity, which may spell the end for severe magnetic storms in the near future,” Kataoka says. “However, we actually witnessed an extremely fast coronal mass ejection only several days ago [10 September 2017], which might be powerful enough to cause extreme storms. Fortunately, it just missed the Earth.”

Regardless of the specific likelihood of another perfect magnetic storm, interdisciplinary historical and scientific collaborations are invaluable in providing important physical details that could help us to understand the greatest magnetic storms in history and prepare for any potential future event.