Auroras are the bright lights seen at Earth’s north and south poles.
Energy and particles from the Sun travel to Earth and interact with our planet’s magnetic field. This interaction causes the colorful lights seen in auroras.
Meet STEVE
People around the poles observe auroras in the night sky!
Through @TweetAurora, anyone can contribute to aurora science as a citizen scientist! Citizen scientists take photos and help track when and where auroras appear.
Sometimes they discover something entirely new. Like STEVE:
NASA scientists study a strange type of aurora in the Arctic. When these auroras shine, part of Earth’s atmosphere leaks into space!
Scientists launch rockets through these auroras to better understand the phenomenon.
Act fast!
Scientists study auroras because it can give us an insight on how our planet’s magnetosphere reacts to space weather.
We often launch rockets into the aurora because the dancing colors can be fleeting.
Caption: A NASA-funded GREECE sounding rocket launches into an aurora in the early morning of March 3, 2014, over Venetie, Alaska. The GREECE mission studies how certain structures – classic curls like swirls of cream in coffee – form in the aurora. Credit: NASA/Christopher Perry
Lucky for us, the Sun’s most harmful rays don’t reach the ground.
Instead they’re absorbed by Earth’s upper atmosphere. That extra energy breaks atoms into charged particles, creating the electrifying ionosphere.
Earth’s highest clouds
These wispy, high-flying clouds are a perfect blend of Earth and space: they form when water vapor from our air freezes around tiny grains of space dust.
Known as polar mesospheric clouds, NASA’s AIM satellite studies them for subtle clues about changes in our upper atmosphere.
Early this morning, there was a total solar eclipse across Antarctica!
During a total solar eclipse, the Moon blocks out the Sun, creating the illusion of night during the day and a breathtaking sight in our sky.
Join NASA Edge at 1:30 p.m. EST on NASA TV to see the eclipse and learn more: https://go.nasa.gov/3nTvrOA
Learning from eclipses
Eclipses have played a major role in scientific discoveries, from the Sun’s structure to the element helium. The corona – the Sun’s outer atmosphere – normally can’t be seen because of the bright solar surface, but during an eclipse, the corona emerges, offering unique science opportunities.
The corona up close
What we can see from the Sun’s corona during an eclipse can teach us a lot about our star. Imagine what we’d learn if we actually touched the corona? NASA has sent Parker Solar Probe to the Sun to do just that. ?
Eclipsing right along…
While today’s eclipse may be over, you still have opportunities to watch eclipses in person! An annular solar eclipse will cross the U.S. in 2023, and a total solar eclipse will cross the U.S. in 2024. For now, see what’s next in our #SolarTour by joining in tomorrow.
Our solar tour begins on Earth. From here, one star shines brighter than all the rest. It’s the closest star and the center of our solar system: our Sun. Earth is in the Goldilocks zone, just the right distance from the Sun to be habitable.
A mission to touch the Sun
We can answer some questions about the Sun from 93 million miles away on Earth, but to learn more, we knew we’d have to venture to our nearest star. In 2018, NASA launched Parker Solar Probe, our mission to touch the Sun.
Why won’t it melt?
Flying close to the Sun is risky business (just ask Icarus), but engineers were up to the task. Check out this video to learn how they built a spacecraft that won’t melt, even when it’s heated to temperatures up to 2500° F. Hint: don’t use wax!
Next stop…?
Now, we’re heading south to catch a special event where day becomes night and the Moon is the star of the show. Can you guess what we’ll see?
The Sun has an immense influence in space. It shapes and impacts our entire solar system in ways that we are still trying to understand.
To help unravel some of the Sun’s biggest mysteries, NASA launched Parker Solar Probe in 2018 to study the Sun up close. This year, the mission has big news!
Follow along on our Solar Tour: Starting tomorrow, Dec. 3, we will begin our 12-day journey from Earth to the Sun. Each day, we’ll make pit stops to learn how our Sun influences different places across the solar system. The grand tour will end with Parker Solar Probe’s big announcement on Dec. 14 at our final destination!
By Miles Hatfield NASA’s Goddard Space Flight Center
New results from NASA satellite data show that space weather – the changing conditions in space driven by the Sun – can heat up Earth’s hottest and highest atmospheric layer.
The findings, published in July in Geophysical Research Letters, used data from NASA’s Global Observations of the Limb and Disk, or GOLD mission. Launched in 2018 aboard the SES-14 communications satellite, GOLD looks down on Earth’s upper atmosphere from what’s known as geosynchronous orbit, effectively “hovering” over the western hemisphere as Earth turns. GOLD’s unique position gives it a stable view of one entire face of the globe – called the disk – where it scans the temperature of Earth’s upper atmosphere every 30 minutes.
GOLD scans the thermosphere from a position in geostationary orbit, which stays over one particular spot on Earth as it orbits and the planet rotates. Credit: NASA’s Goddard Space Flight Center/Tom Bridgman
“We found results that were not previously possible because of the kind of data that we get from GOLD,” said Fazlul Laskar, who led the research. Dr. Laskar is a research associate at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.
From its perch some 22,000 miles (35,400 kilometers) above us, GOLD looks down on the thermosphere, a region of Earth’s atmosphere between about 53 and 373 miles (85 and 600 kilometers) high. The thermosphere is home to the aurora, the International Space Station, and the highest temperatures in Earth’s atmosphere, up to 2,700 °F (1,500 °C). It reaches such incredible temperatures by absorbing the Sun’s high-energy X-rays and extreme ultraviolet rays, heating the thermosphere and stopping these types of light from making it to the ground.
The thermosphere is the highest and hottest atmospheric layer, where the ISS flies and the aurora and airglow can be observed. Credits: NASA’s Goddard Space Flight Center/Genna Duberstein
But the new findings point to some heating not driven by sunlight, but instead by the solar wind – the particles and magnetic fields continuously escaping the Sun.
Animation of the solar wind blowing past Earth. Credit: NASA’s Goddard Space Flight Center/Scientific Visualization Studio/Greg Shirah
The solar wind is always blowing, but stronger gusts can disturb Earth’s magnetic field, inducing so-called geomagnetic activity. Laskar and his collaborators compared days with more geomagnetic activity to days with less, and found an increase of over 160 °F (90 °C) in thermospheric temperatures. Magnetic disturbances, driven by the Sun, were heating up Earth’s hottest atmospheric layer.
Some amount of heating was expected near Earth’s poles, where a weak point in our magnetic field allows some solar wind to pour into our upper atmosphere. But GOLD’s data showed temperature increases across the whole globe – even near the equator, far from any incoming solar wind.
Laskar and colleagues suggest it has to do with changing circulation patterns. There’s a swirling of air high above us — a global circulation that pushes air from the equator up to the poles and back around at lower altitudes. As the solar wind pours into the thermosphere near the poles, the added energy can alter this circulation pattern, driving winds and atmospheric compression that can raise temperatures even far away.
Changing circulation might also underlie another surprise finding. GOLD’s data showed the amount of heat added depended on the time of day. The team discovered a stronger effect in the morning hours compared to that in the afternoon. They suspect that geomagnetic activity might especially strengthen the circulation during the night and early morning hours, though this explanation awaits confirmation in further studies.
Laskar was most impressed with the subtlety of the changes they could detect in GOLD’s data.
“We used to believe that only prominent geomagnetic events could change the thermosphere,” Laskar said. “We are now seeing that even minor activity can have an impact.”
With its steady stream of temperature measurements, GOLD is painting a picture of an upper atmosphere much more sensitive to the magnetic conditions around Earth than previously thought.
NASA’s SunRISE mission — short for the Sun Radio Interferometer Space Experiment — passed a mission review on Sept. 8, 2021, moving the mission into its next phase.
“SunRISE will detect and study eruptions of radio waves from the Sun that often precede major solar events containing high energy particle radiation,” said Justin Kasper, SunRISE principal investigator at the University of Michigan in Ann Arbor. “Knowing when and how solar storms produce intense radiation will help us better prepare and protect our astronauts and technology.”
A coronal mass ejection erupts from the Sun and sends Type II radio bursts ahead of it. Credit: NASA
The review, Key Decision Point C, evaluated the mission’s preliminary design and project plan to achieve launch by its target launch readiness date. With the successful review, SunRISE now moves into Phase C, which includes the final design of the mission and fabrication of the spacecraft and instruments. The six spacecraft will then go through final assembly and testing before their launch readiness date of April 2024.
Consisting of six miniature solar-powered spacecraft known as CubeSats, the SunRISE constellation will operate together as one large telescope — forming the first space-based imaging low radio frequency interferometer — to create 3D maps pinpointing how giant bursts of energetic particles originate from the Sun and evolve as they expand outward into space. The mission will also map, for the first time, how the Sun’s magnetic field extends into interplanetary space — a key factor that drives where and how storms move throughout the solar system. Data from SunRISE will be collected and transmitted to Earth via NASA’s Deep Space Network. The six CubeSats will span roughly six miles across and fly slightly above geosynchronous orbit at 22,000 miles from Earth’s surface.
SunRISE measures radio bursts from solar events and transmits the data to NASA’s Deep Space Network. Credit: NASA
“The unique formation of the CubeSats gives us a detailed view of the Sun that will help us figure out how high energy particle radiation is initiated and accelerated near the Sun and how it affects interplanetary space,” said Joseph Lazio, SunRISE project scientist at NASA’s Jet Propulsion Laboratory. “Studying the radio waves that precede solar particle storms could potentially help us create an early warning system.”
SunRISE is a Mission of Opportunity under the Heliophysics Division of NASA’s Explorers Program Office. Missions of Opportunity are part of the Explorers Program, which is the oldest continuous NASA program designed to provide frequent, low-cost access to space using principal investigator-led space science investigations relevant to the Science Mission Directorate’s (SMD) astrophysics and heliophysics programs. The program is managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, for SMD, which conducts a wide variety of research and scientific exploration programs for Earth studies, space weather, the solar system and universe.
SunRISE will be built by the Space Dynamics Laboratory at Utah State University and be a hosted payload on a commercial spacecraft provided by Maxar of Westminster, Colorado. Once in orbit, the host spacecraft will deploy the six SunRISE spacecraft, place the CubeSats into their orbits, and then continue its prime mission. SunRISE will launch no earlier than April 2024 and no later than September 2025 depending on the schedule of the commercial host spacecraft.
SunRISE is led by the University of Michigan in Ann Arbor and managed by NASA’s Jet Propulsion Laboratory in Southern California.
By Joy Ng NASA’s Goddard Space Flight Center, Greenbelt, Md.
From its vantage point in geostationary orbit, NASA’s GOLD mission – short for Global-scale Observations of the Limb and Disk – has given scientists a new view of dynamics in Earth’s upper atmosphere. Together, three research papers show different ways the upper atmosphere changes unexpectedly, even during relatively mild conditions that aren’t typically thought to trigger such events.
Extra electrons
GOLD studies both neutral particles and those that have electric charge – collectively called the ionosphere – which, unlike neutral particles, are guided by electric and magnetic fields. At night, the ionosphere typically features twin bands of dense charged particles. But GOLD’s data revealed previously unseen structures in the nighttime ionosphere’s electrons, described in research published in the Journal of Geophysical Research: Space Physics on Aug. 24, 2020.
Data from NASA’s Global-scale Observations of the Limb and Disk, or GOLD, mission reveals the twin bands of charged particles that persist near the equator at night. Credit: NASA/GOLD/NASA’s Scientific Visualization Studio
While comparing GOLD’s data to maps created with ground-based sensors, scientists spotted a third dense pocket of electrons, in addition to the typical two electron bands near the magnetic equator. Reviewing GOLD data from throughout the mission, they found that the peak appeared several times in October and November of multiple years, suggesting that it might be a seasonal feature.
Though scientists don’t know what exactly creates this extra pocket of dense electrons, it appeared during a period of relatively mild space weather conditions. This was a surprise to scientists, given that big, unpredictable changes in the ionosphere are usually tied to higher levels of space weather activity.
Nitrogen drops
GOLD also saw large drops in the upper atmosphere’s oxygen-to-nitrogen ratio – a measurement typically linked to the electron changes that can cause GPS and radio signal disturbances.
This event was notable to scientists not for what happened, but when: The dips that GOLD saw happened during a relatively calm period in terms of space weather, even though scientists have long associated these events with intense space weather storms. The research was published on Sept. 9, 2020, in Geophysical Research Letters.
During a geomagnetic storm – space weather conditions that disturb Earth’s magnetosphere on a global scale – gases in the upper atmosphere at high latitudes can become heated. As a result, nitrogen-rich air from lower altitudes begins to rise and flow towards the poles. This also creates a wind towards the equator that carries this nitrogen-rich air down towards lower latitudes. Higher nitrogen in the upper atmosphere is linked to drops in electron density in the ionosphere, changing its electrical properties and potentially interfering with signals passing through the region. GOLD observed this effect several times during relatively calm space weather conditions during the day – outside of the disturbed conditions when scientists would normally expect this to happen.
These changes during seemingly calm conditions may point to a space weather system that’s more complicated than previously thought, responding to mild space environment conditions in bigger ways.
“The situation is more complex – the ionosphere is more structured and dynamic than we could have seen before,” said Dr. Sarah Jones, mission scientist for GOLD at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Improving models
Indeed, GOLD’s observations of changing atmospheric composition are already informing scientists’ computer models of these processes. A paper published in Geophysical Research Letters on May 20, 2021, uses GOLD’s data as a reference to show how changes near the poles can influence the ionosphere’s conditions in the mid-latitudes, even during periods of calm space weather activity. GOLD’s broad, two-dimensional view was critical to the finding.
“When you look in two dimensions, a lot of things that look mysterious from one data point become very clear,” said Dr. Alan Burns, a researcher at the High Altitude Observatory in Boulder, Colorado, who worked on the studies.
By Sarah Frazier NASA’s Goddard Space Flight Center, Greenbelt, Md.
By Mara Johnson-Groh NASA’s Goddard Space Flight Center
Plasma – a fourth state of matter after solid, liquid, and gas where particles have split into charged ions and electrons – is the most common form of matter in the universe. It’s somewhat rare on Earth, but it makes up 99% of the matter in the visible universe. Despite its prevalence, scientists haven’t been able to observationally verify a foundational theory describing how plasma moves in response to electric and magnetic forces. Until now.
With its ultraprecise measurements, NASA’s Magnetospheric Multiscale mission – MMS – has finally measured plasma’s movement on the small scales necessary to see if plasma collectively interacts with electromagnetic fields in the way the fundamental theory predicts, which is described mathematically by the so-called Vlasov equation.
Since the beginning of plasma physics research nearly 100 years ago, the Vlasov equation has often been assumed to be valid for many kinds of plasmas in space. But now the new MMS results, which were published in the journal Nature Physics on July 5, 2021, have allowed scientists to finally see the fundamental plasma variations described in the theory for the first time in nature.
Measuring the basic interactions of space plasmas with electric and magnetic fields helps scientists better understand different mechanisms that fuel energetic space weather events, from auroras to plasma ejections off the Sun, which can interfere with satellites and communications on Earth.
The thin boundary in Earth’s protective magnetic field, or magnetosphere, shown here between the blue and yellow regions, is where NASA’s Magnetospheric Multiscale mission measured terms of the Vlasov equation reported in a new study. The new measurements help scientists better understand how supersonic solar wind plasma particles penetrate the magnetosphere where they can produce auroras and damage communications satellites. Credits: NASA’s Goddard/ Space Flight Center/Mary Pat Hrybyk-Keith/Conceptual Image Lab/Josh Masters
A Century of Plasma Physics Progress
The basic theory of plasma motion originated out of a fundamental theory for gases from the nineteenth century. In the 1890s, an Austrian physicist by the name Ludwig Boltzmann came up with a way to describe the microscopic movement of gases and fluids using statistics. It’s known as the Boltzmann equation, and it’s still taught in physics courses today.
In the 1930s, this work was extended to describe plasmas by Anatoly Vlasov, a Russian physicist. His work specifically described collisionless plasmas, which exist at such high temperatures and low densities that individual plasma particles almost never collide.
Collisionless plasma environments are common in space and can be found in the Sun’s outer atmosphere, solar wind, and in various regions throughout Earth’s magnetic environment, called the magnetosphere.
Unlike ordinary gases, plasmas are electrically charged, as they’re made of positively and negatively charged particles – namely atomic nuclei and their separated electrons. This makes plasmas behave very differently than gases since they are sensitive to electromagnetic forces, which influence their movements. Whereas individual particles in a gas constantly bounce off each other as they erratically travel along, collisionless plasma particles rarely interact and are instead controlled solely by electric and magnetic forces. Vlasov’s equation describes the interplay between plasma particles and electromagnetic fields in these unique collisionless plasma systems – and it has formed the foundation for many ideas about plasmas in the years since.
“The Vlasov equation governs all collisionless plasma phenomena that we know of,” said Jason Shuster, lead author on the new study, Assistant Research Scientist at the University of Maryland in College Park, and MMS scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Nevertheless, the terms in the Vlasov equation have never been directly measured because the observation requires seven different types of measurements to be made simultaneously at very small scales in a diffuse plasma – something which is only possible in space.
“In smaller experiments in labs we can’t probe the plasma without disturbing it,” said Barbara Giles, co-author on the new study, Project Scientist for MMS and research scientist at NASA’s Goddard Space Flight Center. “Only in space can we fully immerse instruments within the same phenomenon and accurately test these theories without disturbing the system.”
The MMS Tetrahedron
In 2015, the launch of the four MMS spacecraft changed the way physicists could study plasma in space. Flying in a tetrahedral – or pyramid-shaped – formation with high-resolution instruments, MMS can take measurements far beyond the capabilities of previous spacecraft missions. In their record-breaking tight flying formation, the four MMS spacecraft also fly close enough to measure small-scale properties of plasma, which enabled them to detect variations in terms of the Vlasov equation for the first time.
“With MMS, we can actually probe those minute details at higher resolution than ever before,” Shuster said.
To measure terms in the Vlasov equation, MMS used 64 particle spectrometers – instruments which measure particle energies and charges. The unprecedented spectrometers can simultaneously record multiple types of measurements in position, velocity, and time needed to resolve terms in Vlasov equation. Since each of the four spinning MMS spacecraft has 16 spectrometers sampling particles around its entire circumference, MMS is uniquely able to take these measurements at incredibly high speeds – every 0.03 seconds, which is nearly 100 times faster than previous missions.
“MMS takes advantage of the natural laboratory provided by Earth’s magnetic environment in outer space,” Shuster said. “In the lab, it is very difficult to create a vacuum with a pressure and density low enough to measure the types of electron-scale structures that we’re able to probe with MMS.”
Improving Global Predictions
Now that MMS has observationally confirmed fundamental predictions of the Vlasov equation, this data can be used to better understand phenomena in plasma environments in near-Earth space.
For example, applying small-scale knowledge of plasma to the global-scale magnetosphere can help scientists better understand different mechanisms that fuel energetic space weather events – such as magnetic reconnection, an explosive event unique to plasma that occurs when magnetic field lines sharply reverse direction.
Additionally, just as high- and low-pressure systems create winds and storms on Earth, electric currents and plasma flows drive weather systems in space. Fast moving jets of energetic plasma, such as those scientists observed in this study with MMS, can sustain strong electric currents and pressure gradients which drive space weather phenomena throughout Earth’s magnetic environment.
Understanding the acceleration and energization of particles is a big challenge for the field of space physics. Scientists believe thin boundary layers, like the one depicted in this animation, are prime candidates for accelerating particles up to energies high enough that they can penetrate through Earth’s magnetic field and generate strong electric currents that can fuel space weather and geomagnetic storms inside Earth’s magnetosphere. Credit: NASA’s Scientific Visualization Studio/Tom Bridgman/Mara Johnson-Groh
Having direct observations of the terms in the Vlasov equation provides scientists with a deeper understanding of these basic plasma motions, which enables them to predict the triggers of these fundamental plasma processes more accurately.
“The measurements of terms in the Vlasov equation provide information we can use to constrain and increase the accuracy of our global space weather models, which currently rely on large-scale approximations,” Shuster said. “These discoveries improve our ability to predict space weather operating close to home in Earth’s magnetosphere and deepen our overall understanding of plasmas existing throughout the universe.”
By Miles Hatfield NASA’s Goddard Space Flight Center
About 50 miles up, Earth’s atmosphere undergoes a fundamental change. It starts at the atomic level, affecting only one out of every million atoms (but with about 91 billion crammed in a pinhead-sized pocket of air, that’s plenty). At that height, unfiltered sunlight begins cleaving atoms into parts. Where there once was an electrically neutral atom, a positively charged ion and negatively charged electron (sometimes several) remain.
The result? The air itself becomes electrified.
Scientists call this region the ionosphere. The ionosphere doesn’t form a physically separated atmospheric layer – the charged particles float amongst their neutral neighbors, like bits of cookie dough in a pint of cookie dough ice cream. Nonetheless, they follow a very different set of rules.
A layer of charged particles, called the ionosphere, surrounds Earth, extending from about 50 to 400 miles above the surface of the planet. Credits: NASA’s Goddard Space Flight Center/Genna Duberstein
Consider how the ionosphere moves. Charged particles are constrained by magnetism; like railroad cars, they trace Earth’s magnetic field lines back and forth unless something actively derails them. Neutral particles can cross those tracks unfazed – they’re more like passengers crisscrossing as they board and exit at the station.
The ionosphere also reflects radio signals, which pass right through the neutral atmosphere as if it was transparent. (In fact, radio is how the ionosphere was discovered.) Scientists still use ground-based radio waves to study the ionosphere from afar. Learning about the neutral atmosphere, however, usually requires going there – or looking down at it from above.
Despite their differences, the ionosphere and the neutral atmosphere are parts of a larger atmospheric system, where disturbances in one part have a way of spreading to the other. Their connection is explored in a new paper led by Scott England, space physicist at Virginia Tech in Blacksburg and co-investigator for NASA’s Global-scale Observations of the Limb and Disk, or GOLD mission, published in the Journal of Geophysical Research.
England and his coauthors combined ground-based radio signal measurements with special-purpose satellite observations to study whether Traveling Ionospheric Disturbances – waves regularly observed moving through the ionosphere – are at root the same event as Traveling Atmospheric Disturbances, pulses sometimes seen in the neutral atmosphere.
Traveling Ionospheric Disturbances, or TIDs, are giant undulations in the ionosphere, waves that stretch hundreds of miles from peak to peak. They’re are detected with ground-based radar beams, which bounce radars off the ionosphere to detect density enhancements move through.
Traveling Atmospheric Disturbances, or TADs, are gusts of wind that roll through the sky, pushing along neutral atoms as they go. TADs are harder to measure, best observed by flying within them – as somemissionshave – or by using indirect measures of airglow, the glimmer of oxygen and nitrogen in our atmosphere that brightens and dims as TADs move through it.
Earth’s limb at night, seen from the International Space Station, with an air glow visual composited into the image. Credit: NASA
TIDs and TADs are measured in quite different ways, and it can be hard to compare across them. Still, many scientists have assumed that if one is present, the other is too.
“There is this assumption that they’re just the same thing,” said England. “But how robust is that assumption? It may be extremely good – but let’s check.”
England designed 3-day campaign to look for TIDs and TADs at the same time and same place.
TIDs were tracked from below, using ground-based radio receivers from stations across the Eastern U.S. Meanwhile, NASA’s Global-scale Observations of the Limb and Disk, or GOLD satellite, was looking for TADs from above, measuring airglow variations to track movements of the neutral atmosphere. But it took a little re-jiggering to see them. GOLD typically scans the whole western hemisphere once every half hour, but that’s too quick a glance at any one location to see a TAD.
“GOLD was never designed to see these things,” said England. “So we devised a campaign where we have it not do what it normally does.”
Instead, England directed one of GOLD’s telescopes to stare to along a strip of sky, increasing its detection power 100-fold. That strip is shown below in purple – GOLD’s search space for TADs. The region measured by ground-based radio receivers, which looked for TIDs, is shown in light blue. The region where they overlapped was the focus of England’s study.
Location of the GOLD observations during the campaign (purple strip). The light blue region show the locations of the GPS radio data included in this study. Credit: NASA/England et al.
The radio receivers listened for changes in incoming signals, as these modulations could indicate a TID was passing by. The graph below shows the radar results from one of the three days in the campaign. The vertical axis represents latitude – higher up meaning more northern – and the horizontal axis represents time. The different colors show the strength of the signal modulation, dark red being the strongest.
Global Navigation Satellite System differential TEC (dTEC) for October 18, 2019 as a function of latitude and universal time. The range of longitudes included is shown along the vertical axis. Credit: NASA/England et al.
Over a span of 12 hours, three stripes formed in the data. These were TIDs: pulses or density enhancements in the ionosphere moving southward over time.
Meanwhile, GOLD was watching light from oxygen and nitrogen to discern the motion of the neutral atmosphere. The graph below shows the results. Note that the latitudes GOLD measured range farther than the radar measurements, from 60 degrees to 10 degrees, but over a slightly shorter period of time, about 8 hours.
Perturbations to the airglow observed on October 18, 2019. As oxygen and nitrogen signals were in counter-phase, this figure shows the perturbation in the oxygen minus twice the nitrogen airglow to highlight the difference. Credit: NASA/England et al.
It was a weak signal, just above the ambient environmental noise. Still, the faint outlines of TADs – diagonal stripes in the GOLD data – appeared at the same time.
“It’s really at the limit of what GOLD could see – if it was any smaller than this, we wouldn’t see it,” England said.
Aligning the two datasets and correlating them, England found that both sets of ripples moved at about the same rate. Then, with the help of some mathematical models, they tested out the idea that atmospheric gravity waves could be the underlying cause of both.
Gravity waves – not to be confused with gravitational waves, caused by distant supernova explosions and black hole mergers – form when buoyancy pushes air up, and gravity pulls it back down. They’re often created when winds blow against mountain faces, pushing plumes of air upward. Those plumes soon fall back down, but like a line of dominos, the initial “push” cascades all the way to the upper atmosphere.
England and his coauthors linked up a mathematical model of the atmosphere with an airglow simulator. They then mimicked a gravity wave by introducing an artificial sine wave to the models. The resulting simulated data produced similar “stripes,” both in the atmospheric model (TIDs) and the airglow simulator (TADs), indicating that gravity waves could indeed cause both.
So – are TIDs just TADs, as scientists assumed? While the pulses moved together, England’s team found that their amplitude, or size, were not as clearly related. Sometimes a large TID would be associated with a small TAD, and vice versa. Partly that’s because GOLD and the radio receivers don’t measure exact same altitudes – the radio receivers picked up a region about 40 miles above where GOLD could measure. But the largest contributor to that difference is probably the many other phenomena in the atmosphere that we don’t fully understand yet.
“And that makes what we’re looking at hard – but also interesting,” England added.
It will take more than three days of data to fully determine the relationship between TIDs and TADs. But England’s study provides something that virtually all scientists get excited about: a new tool for answering that question.
“We didn’t know if there would be a clear relationship between TIDs and TADs or not. And we certainly seem to have the ability to determine that now,” England said. “We just have to use the GOLD spacecraft instrument to do something we didn’t originally think of.”
