The Thermosphere is Warming Up

March 23, 2022: Solar Cycle 25 is intensifying–and Earth’s upper atmosphere is responding.

“The Thermosphere Climate Index (TCI) is going up rapidly right now,” reports Linda Hunt of Science Systems and Applications, Inc. “It has nearly tripled in the past year.”

TCI is a number published daily by NASA, which tells us how hot Earth’s upper atmosphere is. The thermosphere, the very highest layer of our atmosphere, literally touches space and is a sort of “first responder” to solar activity. Hunt created this plot showing how TCI has unfolded during the last 7 solar cycles.  Solar Cycle 25 (shown in blue) is just getting started:

“So far Solar Cycle 25 is well ahead of the pace of Solar Cycle 24,” notes Hunt. If this trend continues, the thermosphere could soon hit a 20-year high in temperature.

Before we go any farther, a word of caution: This does not mean Earth itself is about to heat up. The thermosphere is hundreds of kilometers above our heads. Here on the planet’s surface we do not feel its heat; summer days are no warmer when TCI is “hot.” As Dr. Marty Mlynczak of NASA notes, “energy driving the climate system near Earth’s surface is hundreds of thousands of times greater than in the thermosphere.” As far as we know, cyclical warming and cooling of the thermosphere by the solar cycle does not affect climate.

Nevertheless, the thermosphere is important. When it heats up, as it is doing now, it also puffs up. Think of a marshmallow held over a campfire. The thermosphere can expand upward so much it actually touches Earth-orbiting satellites. Almost 40 Starlink satellites fell out of the sky earlier this year as a result of aerodynamic drag up there.

Above: Layers of the atmosphere. Credit: NASA

TCI might also have some predictive value. Hunt’s plot shows that the index is on an upward trajectory that most closely mimics Solar Cycle 20, which peaked back in the 1970s. Coincidentally, a new prediction for Solar Cycle 25 based on the arrival of the Termination Event suggests the same thing: It could look a lot like Solar Cycle 20–an above-average cycle with plenty of solar activity.

You can follow the progress of TCI as Solar Cycle 25 unfolds. It is published every day right here on

What is TCI?

TCI is the “Thermosphere Climate Index”, a number NASA publishes every day to keep track of the temperature at the top of Earth’s atmosphere–a layer of gas researchers call “the thermosphere.”


“The thermosphere always cools off during Solar Minimum–and it warms up again during Solar Maximum,” explains Martin Mlynczak of NASA’s Langley Research Center. “It’s one of the most important ways the solar cycle affects our planet.”

When the thermosphere warms, it expands, literally increasing the radius of Earth’s atmosphere. This expansion increases aerodynamic drag on satellites in low-Earth orbit, which can bring them down prematurely. When the thermosphere cools, it shrinks; satellites get a reprieve.

Mlynczak and colleagues recently introduced the “Thermosphere Climate Index” (TCI)–a number expressed in Watts that tells how much heat nitrogen oxide (NO) molecules in the thermosphere are dumping into space. During Solar Maximum, TCI is high (“Hot”); during Solar Minimum, it is low (“Cold”).


Above: An historical record of the Thermosphere Climate Index. Mlynczak and colleagues recently published a paper on the TCI showing that the state of the thermosphere can be discussed using a set of five plain language terms: Cold, Cool, Neutral, Warm, and Hot.

TCI is based on measurements from the SABER instrument onboard NASA’s TIMED satellite. SABER monitors infrared emissions from carbon dioxide (CO2) and nitric oxide (NO), two substances that play a key role in the energy balance of air 100 to 300 kilometers above our planet’s surface. By measuring the infrared glow of these molecules, SABER can assess the thermal state of gas up there.

Although SABER has been in orbit for only 17 years, Mlynczak and colleagues recently calculated TCI going all the way back to the 1940s. “SABER taught us to do this by revealing how TCI depends on other variables such as geomagnetic activity and the sun’s UV output–things that have been measured for decades,” he explains.

CME Wipes Out Cosmic Rays

March 17, 2022: The March 13th CME did more than spark bright auroras. It also wiped out a lot of cosmic rays. Neutron monitors at the Sodankyla Geophysical Observatory in Oulu, Finland, recorded a sharp drop in cosmic radiation just after the CME arrived:

This is called a “Forbush decrease,” named after American physicist Scott Forbush who studied cosmic rays in the early 20th century.  It happens when a coronal mass ejection (CME) sweeps past Earth and pushes galactic cosmic rays away from our planet. Radiation from deep space that would normally pepper Earth’s upper atmosphere is briefly wiped out.

There’s something odd about this Forbush decrease. It’s a double dip decrease. Cosmic rays dropped precipitously on March 13th–then they surged midday on March 14th–then they dropped precipitously again. The up-and-down may be a sign of structure inside the CME.

As Solar Cycle 25 intensifies, more and more CMEs will sweep past Earth. Forbush decreases will become increasingly common and may even begin to overlap. This will cause a persistent decline in cosmic rays around our planet.

A recent paper in the Astrophysical Journal looked at the last two solar cycles and compared the daily rate of CMEs to the strength of cosmic rays. The plot, above, shows the results. At the peak of Solar Cycle 24, the sun was spitting out more than 5 CMEs per day; at the same time, galactic cosmic rays (GCRs) dropped more than 60%.

Evidence is mounting that new Solar Cycle 25 will be stronger than Solar Cycle 24. If so, CMEs will be more abundant and cosmic rays even more depressed–a welcome reduction for astronauts, air travelers, and even some mountain climbers.

Meanwhile, the March 13th Forbush decrease is still underway. Cosmic rays remain depressed 4 full days after the CME arrived.

The Mystery of Orange Auroras

March 4, 2022: A recent display of auroras over Canada has experts scratching their heads. The mystery? They were orange. Pilot Matt Melnyk was flying 36,000 feet over Canada on Feb. 23rd when he saw the strangely-colored lights from the cockpit window:

“I have been chasing and photographing auroras for more than 13 years (often from airplanes) and this is the first time I have ever seen orange,” says Melnyk.

What’s so strange about orange? Joe Minow of NASA’s Marshall Space Flight Center explains: “Theoretically, nitrogen and oxygen (N2, N2+, and O2+) can produce emissions at orange wavelengths, but these are typically weak compared to stronger emissions from the same molecules at the red end of the spectrum. It is hard to understand how orange could dominate in an auroral display.”

Even so, Melnyk says “these appeared to be real auroras.” The orange fringe danced in sync with regular red and green auroras overhead. It did not appear to be an artifact of city lights or distant twilight. Moreover, Melnyk saw the orange color with his naked eye, and his camera recorded it, too.

Above: The red pushpin marks the approximate location of the plane on Feb. 23rd (22:48 EST) when the orange auroras appeared. Inset is the camera’s view.

Kjellmar Oksavik, a space physicist at the University Center in Svalbard (UNIS), has an idea: “Normally, auroras are produced by electrons with energies less than 10 keV. Raining down from space, they stop an an altitude of 100 km where the dominant color is green (caused by electrons hitting oxygen). During strong activity, however, electrons can reach energies of 20 keV and even higher. These electrons penetrate deeper, all the way down to 80-100 km. Here nitrogen molecules dominate, with multiple emission lines in blue, purple, orange, red and magenta.”

“I think this is what is happening in the picture,” says Oksavik. “On this particular day the precipitating electrons were so energized that they reached deeper into the atmosphere (probably 80-90 km) where nitrogen molecules emitted a wide range of colors, that combines into what looks like an orange glow.”

Oksavik’s colleague Fred Sigernes, chief of the UNIS Aurora Observatory, agrees with Oksavik, but also wonders “why have we never observed this up here with our cameras in Svalbard?” It’s a mystery, indeed.

Have you observed orange auroras? Submit your photos here.

The Termination Event has Arrived

Feb. 26, 2022: Something big just happened on the sun. Solar physicists Scott McIntosh (NCAR) and Bob Leamon (U. Maryland-Baltimore County) call it “The Termination Event.”

“Old Solar Cycle 24 has finally died–it was terminated!” says McIntosh. “Now the new solar cycle, Solar Cycle 25, can really take off.”

The “Termination Event” is a new idea in solar physics, outlined by McIntosh and Leamon in a December 2020 paper in the journal Solar Physics. Not everyone accepts it–yet. If Solar Cycle 25 unfolds as McIntosh and Leamon predict, the Termination Event will have to be taken seriously.

Above: Predictions for Solar Cycle 25. Blue is the “official” prediction of a weak cycle. Red is a new prediction based on the Termination Event.

The basic idea is this: Solar Cycle 25 (SC25) started in Dec. 2019. However, old Solar Cycle 24 (SC24) refused to go away. It hung on for two more years, producing occasional old-cycle sunspots and clogging the sun’s upper layers with its decaying magnetic field.  During this time, the two cycles coexisted, SC25 struggling to break free while old SC24 held it back.

“Solar Cycle 24 was cramping Solar Cycle 25’s style,” says Leamon.

Researchers have long known that solar cycles can overlap. The twist added by McIntosh and Leamon is the realization that overlapping cycles interact. This makes sense. In the early 20th century, George Ellery Hale discovered that the magnetic polarity of sunspot pairs reverses itself from one cycle to the next; indeed, the sun’s entire global magnetic field flips every ~11 years. When adjacent, opposite-polarity solar cycles overlap, they naturally interfere.

Termination Events mark the end of interference, when a new cycle can break free of the old.

Above: Bands of coronal bright points (hot spots in the sun’s atmosphere) linked to old Solar Cycle 24 vanished in Dec. 2021, signalling a Termination Event. A Twitter thread from Scott McIntosh explains this in greater detail.

The timing of the Termination Event can predict the intensity of the new cycle. In their Solar Physics paper, McIntosh and Leamon looked back over 270 years of sunspot data and found that Termination Events happen every 10 to 15 years.

“We found that the longer the time between terminators, the weaker the next cycle would be,” explains Leamon. “Conversely, the shorter the time between terminators, the stronger the next solar cycle would be.”

So when did the latest Termination Event happen? Dec. 2021. This yields a specific, testable prediction for Solar Cycle 25.

“We have finalized our forecast of SC25’s amplitude,” says McIntosh. “It will be just above the historical average with a monthly smoothed sunspot number of 190 ± 20.”

“Above average” may not sound exciting, but this is in fact a sharp departure from NOAA’s official forecast of a weak solar cycle. It could be just enough to catapult Terminators into the forefront of solar cycle prediction techniques.

Stay tuned. We’ll be back.

Huge Explosion on the Farside of the Sun

Feb. 17, 2022: New images from the Solar and Heliospheric Observatory (SOHO) are giving us a better look at yesterday’s farside explosion. SOHO coronagraphs recorded the most dramatic CME in years:

No, there won’t be a geomagnetic storm. The explosion happened on the farside of the sun, so the CME is heading away from Earth. We dodged a bullet.

Some readers have asked “How strong was the underlying solar flare?” We don’t know. Solar flares are classified by their X-ray output, but there are no spacecraft on the farside of the sun with X-ray sensors. Best guess: It was an X-flare.

You might suppose that the farside of the sun is hidden from view. However, researchers using a technique called “helioseismology” can make crude maps of the sun’s hidden hemisphere. Their latest map reveals a huge farside active region:

The black blob is a sunspot group–a big one–and it is the likely source of the explosion. According to Junwei Zhao of Stanford University’s helioseismology group, active regions this large are rare. “This is only the second farside active region of this size since September 2017,” he says.

Lucas Guliano, a solar scientist at the Harvard-Smithsonian Center for Astrophysics, believes the active region might be an old friend: AR2936, a sunspot that was on the Earthside of the sun in early February.

“If so, it is the same sunspot responsible for the geomagnetic storm that downed the SpaceX satellites on Feb. 4th,” he says.

Apparently it has grown since then. Based on its current location, the sunspot could emerge into view over the sun’s northeastern limb about 4 days from now. It could be quite a sight, so stay tuned. Solar flare alerts: SMS Text.

The Starlink Incident

Feb. 9, 2022: As many as 40 Starlink satellites are currently falling out of the sky–the surprising result of a minor geomagnetic storm. SpaceX made the announcement yesterday:

“On Thursday, Feb. 3rd at 1:13 p.m. EST, Falcon 9 launched 49 Starlink satellites to low Earth orbit from Launch Complex 39A (LC-39A) at Kennedy Space Center in Florida. … Unfortunately, the satellites deployed on Thursday were significantly impacted by a geomagnetic storm on Friday, [Feb. 4th].”

Two days before launch a CME hit Earth’s magnetic field. It was not a major space weather event. In fact, the weak impact did not at first spark any remarkable geomagnetic activity. However, as Earth passed through the CME’s wake, some sputtering G1-class geomagnetic storms developed. It was one of these minor storms that caught the Starlink satellites on Feb. 4th.

Geomagnetic storms heat Earth’s upper atmosphere. Diaphanous tendrils of warming air literally reached up and grabbed the Starlink satellites. According to SpaceX, onboard GPS devices detected atmospheric drag increasing “up to 50 percent higher than during previous launches.”

“The Starlink team commanded the satellites into a safe-mode where they would fly edge-on (like a sheet of paper) to minimize drag,” says SpaceX. “Preliminary analysis show the increased drag at the low altitudes prevented the satellites from leaving safe-mode to begin orbit raising maneuvers, and up to 40 of the satellites will reenter or already have reentered the Earth’s atmosphere.”

The Sociedad de Astronomia del Caribe apparently caught one of the reentries over Puerto Rico on Feb. 7th:

SpaceX says that the deorbiting satellites “pose zero collision risk with other satellites and by design demise upon atmospheric reentry—meaning no orbital debris is created and no satellite parts hit the ground.”

Keep an eye on the night sky this week. You might catch a Starlink satellite burning up overhead. Solar flare alerts: SMS Text.

Solar Cycle 25–A Different Point of View

Feb. 4, 2022: For much of the past year, the space weather community has been buzzing about the strong performance of young Solar Cycle 25 (SC25). Every month, sunspot numbers seem to blow past official predictions. This means we’re about to have a strong Solar Maximum, right?

“Not so fast,” cautions Dr. Ron Turner, an analyst at the ANSER research institute in Virginia. “It may be too early to anticipate a strong solar cycle.”

This graph shows why Turner is skeptical:

Solar Cycle 25 is doing something interesting. It is mimicking old Solar Cycle 24 (SC24). “I took sunspot numbers from the early years of SC24 (the red dashed line) and overlaid them on SC25,” says Turner. “They’re an almost perfect match.”

This is significant because Solar Cycle 24 went on to become the weakest solar cycle in a century. Its hot start did not lead to a strong maximum. Turner isn’t saying that Solar Cycle 25 will likewise be a dud. But, rather, “these early sunspot numbers are not enough to guarantee a strong cycle.”

Déjà vu, anyone?

An Outburst of Noctilucent Clouds

Jan. 25, 2022: On Jan 24th, skies above Argentina suddenly filled with noctilucent clouds (NLCs). A video camera in Rio Gallegos (Patagonia) captured the outburst:

“What a surprise!” says Gerd Baumgarten of Germany’s Leibniz Institute of Atmospheric Physics, who operates this remote camera to monitor southern skies for unusual events. “We haven’t seen NLCs all year. Now, suddenly, they are very bright.”

NLCs are Earth’s highest clouds. They form when wisps of water vapor rise up from the poles to the edge of space. Water crystallizing around specks of meteor dust create the electric-blue structures. NLCs are, literally, frosted meteor smoke.

Normally at this time of year, NLCs are confined inside the Antarctic Circle. So it is a surprise to see them bursting out to mid-southern latitudes; Rio Gallegos is at 51.6oS.

To confirm that these are truly NLCs, Natalie Kaifler of the German Aerospace Center (DLR) pinged the clouds using a laser radar (lidar) in Rio Grande. The echos returned from 85 km above Earth’s surface:

This is exactly where NLCs typically form. Reality confirmed.

Where did these clouds come from? Maybe Tonga. The eruption of the Hunga Tonga–Hunga Haʻapai volcano on Jan. 15th hurled a plume of ash, sulfur dioxide and (this is the important part) water vapor more than 55 km high. Baumgarten and others are investigating the possibility that water from the volcano has reached the mesosphere, creating an outburst of noctilucent clouds. Stay tuned for more information.

Solar Cycle 25 Update

Jan. 10, 2022: Solar Cycle 25 is heating up. New sunspot counts from NOAA confirm that the young solar cycle is outrunning the official forecast. You are here:

Actual sunspot counts have now exceeded predictions for 15 straight months. The monthly value at the end of December 2021 was more than twice the forecast, and the highest in more than 5 years.

The “official forecast” comes from the Solar Cycle Prediction Panel representing NOAA, NASA and International Space Environmental Services (ISES). Using a variety of leading indicators, the Panel predicted that Solar Cycle 25 would peak in July 2025 as a relatively weak cycle, similar in magnitude to its predecessor Solar Cycle 24. Instead, Solar Cycle 25 is shaping up to be stronger.

Sky watchers have already noticed the change. “We are definitely seeing the effects on the ground in the Arctic!” reports Chad Blakley of the Swedish tour guide service Lights over Lapland. “Auroras now are the best in years.”

Indeed, geomagnetic activity has nearly tripled since the new solar cycle began. In 2020, the first full year of Solar Cycle 25, there were 9 days with at least minor (G1-class) geomagnetic storms. That number skyrocketed to 25 days in 2021. One of those “storm days” (Nov. 4, 2021) was a borderline G4-class (severe) event with auroras sighted as far south as California and New Mexico. A similar progression may be expected in 2022.

Auroras over Deming, New Mexico, photographed by Allen Hwang on Nov. 4, 2021.

Another sign of increasing solar activity is the X-flare. X-flares are the most powerful type of solar flare. They can cause strong radio blackouts, pepper Earth’s atmosphere with energetic particles, and herald intense geomagnetic storms. The sun produced zero of these flares from late 2017 until mid-2021. Solar Cycle 25 busted the drought on July 3, 2021, with an X1.6 category explosion, followed by an X1-flare on Oct. 28, 2021.

Two down, 98 to go? Typical 11-year solar cycles produce more than 100 X-flares during the years around Solar Max. Stay tuned for updates as Solar Cycle 25 intensifies.