Severe Geomagnetic Storm: March 23-24, 2023

March 24, 2023: Forecasters did not see this one coming. On March 23-24, auroras spread into the United States as far south as New Mexico (+32.8N) during a severe (category G4) geomagnetic storm–the most intense in nearly 6 years. The cause of the storm is still unclear; it may have been the ripple effect of a near-miss CME on March 23rd.

“Aurora pillars were visible from Shenandoah National Park in Central Virginia,” says Peter Forister, who photographed the light show at latitude +38.7 degrees:

“Beautiful red and green colors were visible to the naked eye around 11 pm local time,” he says. Other notable low-latitude sightings were made in Colorado (+38.7N), Missouri (+40.2N), Colorado again (+38.3N), Nebraska (+41N) and North Carolina (+36.2N). More than half of all US states were in range of the display.

Not every light in the sky was the aurora borealis, however. There was also STEVE:

Joseph Shaw photographed the luminous ribbon over Bozeman, Montana. It also appeared over South Dakota, Washington State, Idaho, Montana again, and Scotland.

STEVE (Strong Thermal Emission Velocity Enhancement) looks like an aurora, but it is not. The phenomenon is caused by hot (3000°C) ribbons of gas flowing through Earth’s magnetosphere at speeds exceeding 6 km/s (13,000 mph). These ribbons appear during strong geomagnetic storms, revealing themselves by their soft purple glow.

This remarkable and surprising storm began on March 23rd when magnetic fields in the space around Earth suddenly shifted. In the jargon of space weather forecasting “BsubZ tipped south.” South-pointing magnetic fields can open a crack in Earth’s magnetosphere and, indeed, that’s what happened. Earth’s “shields were down” for almost 24 hours, allowing solar wind to penetrate and the storm to build to category G4.

These developments may have been caused the close passage of an unexpected CME. The storm cloud could have left the sun on March 20-21 when SOHO coronagraph data were unusually sparse. We didn’t know it was coming. For aurora watchers, it was a welcome surprise. Aurora alerts: SMS Text.

A Solar Radio Burst at Night

March 23, 2023:

Something rare and strange happened last month. On Feb. 23rd, growing sunspot AR3234 produced an M-class solar flare. It was nearly midnight in Florida when the explosion occurred, so you’d expect no one there to notice. On the contrary, in the community of High Springs, FL, amateur radio astronomer Dave Typinski recorded a strong shortwave radio burst.

“You CAN see the sun at midnight in Florida… sometimes,” says Typinski. This is what his instruments recorded while the flare was underway:

A double wave of static washed over Florida, filling the radio spectrum with noise at all frequencies below 25 MHz. “The Sun was 69° below the horizon when this happened,” he marvels.

How is this possible? The entire body of our planet was blocking the event from Typinski’s antenna. It’s called “antipodal focusing.” First postulated by Marconi more than 100 years ago, antipodal focusing is a mode of radio propagation in which a signal starts out on one side of the planet, gets trapped between Earth’s surface and the ionosphere, and travels to the opposite hemisphere. Waves converging at the antipode can create a surprisingly strong signal.

Right: This diagram from a declassified US shows the basic geometry of antipodal focusing.

“This is the second or maybe third midnight solar radio burst I’ve seen in ten years, but it’s by far the strongest,” says Typinski. “The previous events happened at the height of Solar Cycle 24. They’re quite rare.”

Pause: Yes, solar flares can produce radio signals. Typinski’s midnight burst was a “Type V,” caused by streams of electrons shooting through the sun’s atmosphere in the aftermath of the flare. Plasma waves rippling away from the streams emited intense bursts of natural radio static. The burst was first observed in broad daylight at the Learmonth Solar Observatory in Australia, then it curved around Earth to reach Typinski.

Above: An example of antipodal focusing of seismic waves caused by the Chicxulub asteroid impact. The geometry is the same as for radio waves. [more].

“This propagation mode was used during the Cold War,” notes Typinski. “The U.S. would park a SIGINT ship in the south Pacific to grab signals from the Eastern Bloc. The Soviets probably did the same thing, parking in the southern Indian ocean.”

Turns out, this method of spying works for radio astronomers, too. Would you like to record an event like this? NASA’s Radio JOVE program makes it easy. Off-the-shelf radio telescope kits allow even novices to monitor radio outbursts from the sun, which are becoming more frequent as Solar Cycle 25 intensifies.

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Extremely Rare CME

March 13, 2023: Something big just happened on the farside of the sun. During the early hours of March 13th, SOHO coronagraphs recorded a farside halo CME leaving the sun faster than 3000 km/s:

Because of its extreme speed, this CME is classified as “extremely rare,” a fast-mover that occurs only once every decade or so. A NASA model of the event shows the CME heading almost directly away from Earth. Good thing!

Although the CME was not Earth-directed, it has nevertheless touched our planet. See all the snowy dots and streaks in the coronagraph movie above? Those are energetic particles accelerated by shock waves in the CME. They create short-lived luminous speckles when they hit SOHO’s digital camera.

NOAA’s GOES-16 satellite has detected the particles reaching Earth–all from the CME’s backside. Imagine what a frontside blast would have been like. Earth’s magnetic field is funneling the particles toward the poles where a type of radio blackout is underway–a polar cap absorption (PCA) event:

Note the broad red areas. Airplanes flying over these regions may find that their shortwave radios won’t work due to the ionizing effect of infalling protons. This PCA could persist for a day or more. You can monitor its progress here. Solar flare alerts: SMS Text.

A “Chain Reaction” Explosion on the Sun

Feb. 25, 2023: A magnetic filament connected to sunspot AR3229 erupted on Feb. 24th, producing a chain reaction of events that could lead to a geomagnetic storm on Earth. The action began at 1949 UTC when the filament rose up and sliced through the sun’s atmosphere:

The violent liftoff destabilized sunspot AR3229, sparking a long duration M3-class solar flare (2030 UTC). Radiation from the flare, in turn, ionized the top of Earth’s atmosphere, blacking out shortwave radio transmissions around the Pacific Ocean: map. Mariners and ham radio operators may have noticed loss of signal at frequencies below 25 MHz for as much as an hour after the explosion.

Next, a CME emerged from the blast site. Coronagraph images from SOHO show a lopsided halo with an Earth-directed component:

Type II solar radio emissions from the leading edge of the CME suggest a departure speed of 1200 km/s (2.7 million mph). The flank of the fast-moving cloud could reach Earth on Feb. 27th. NOAA analysts are modeling the CME now, so stay tuned for a refined forecast.

There’s more: Shock waves inside the CME accelerated protons to nearly light speed, and they have already reached Earth. Our planet’s magnetic field is funneling the particles toward the poles where a second type of radio blackout is underway–a polar cap absorption (PCA) event. Airplanes flying over these regions may find that their shortwave radios won’t work due to the ionizing effect of infalling protons: map.

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Sunspot Counts Hit Their Highest Level in 9 Years

Feb. 1, 2023: In a continued sign of strength for Solar Cycle 25, sunspot counts just hit a 9-year high. This plot from NOAA shows how the monthly sunspot number skyrocketed in January 2023:

The monthly sunspot number of 144 in January 2023 was only percentage points away from topping the previous solar cycle, Solar Cycle 24, which peaked in Feb. 2014 with a monthly value of 146.

Originally, forecasters thought Solar Cycle 25 would be about the same as Solar Cycle 24, one of the weakest solar cycles in a century. Current trends suggest Solar Cycle 25 will surpass that low threshold, at least. Solar Maximum is not expected until 2024 or 2025, so it has plenty of time to strengthen further, perhaps far exceeding Solar Cycle 24. You can follow the progression here.

Extra: What made January 2023 so special? This picture says it all:

This is a composite image created by Patricio Leon of Santiago, Chile. Almost every day in January, Leon photographed the sun, and stacked the images to show the march of large sunspots across the solar disk.

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Significant Farside Explosion

Jan. 4, 2023: Something just exploded on the farside of the sun. SOHO watched the debris–a very bright and fast CME–billow away from the sun’s southeastern limb on Jan. 3rd:

It won’t hit Earth. NOAA analysts have modeled the CME and determined that the edge of the storm cloud will narrowly miss our planet a few days from now.

NASA’s Solar Dynamics Observatory detected shock waves from the blast wrapping around both of the sun’s poles. This suggests a very powerful explosion–possibly an X-flare. Radiation from the flare was eclipsed by the edge of the sun, reducing its intensity by one to two orders of magnitude, so that Earth-orbiting satellites detected only a C4-class event.

Whatever exploded will soon turn to face Earth. Helioseismic echoes pinpoint its location no more than 2 days behind the sun’s eastern limb:

This might be old sunspot AR3163, which spent the last two weeks transiting the farside of the sun. It was big the last time we saw it in December and may have grown even bigger since. Stay tuned! Solar flare alerts: SMS Text.

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Sunspot Counts Hit a 7-Year High

Jan. 2, 2022: December was a busy month on the sun. How busy? Senol Sanli of Bursa, Turkey, answered the question by stacking 26 days of sun photos (Dec. 2nd – 27th) from NASA’s Solar Dynamics Observatory:

“There were more than 24 sunspot groups, some of them quite large, congested in two bands on opposite sides of the sun’s equator,” says Sanli.

The congestion of dark cores catapulted the monthly sunspot number to its highest value in 7 years:

This plot from NOAA shows the ascending progression of Solar Cycle 25. It has outperformed the official forecast for 35 months in a row. If the trend continues, Solar Maximum will either happen sooner or be stronger than originally expected–possibly both. Stay tuned for lots more sunspots.

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Cosmic Rays Sink to a 6-Year Low

Dec. 30, 2022: Cosmic rays reaching Earth just hit a six-year low. Neutron counters in Oulu, Finland, registered the sudden decrease on Dec. 26th when a coronal mass ejection (CME) hit Earth’s magnetic field:

The CME swept aside galactic cosmic rays near our planet, abruptly reducing radiation levels. Researchers call this a “Forbush Decrease,” after American physicist Scott Forbush, who studied cosmic rays in the early 20th century.

The Dec. 26th event continues a trend that began in 2020. Since then, cosmic ray fluxes have been fitfully decreasing as one CME after another hit Earth. The reason is Solar Cycle 25, which began around that time and has been gaining strength. The Forbush Decreases are adding up.

Scott Forbush was the first to notice the yin-yang relationship between solar activity and cosmic rays. When one goes up, the other goes down. CMEs play a big role in this relationship. The solar storm clouds contain tangled magnetic fields that do a good job scattering cosmic rays away from 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 near Earth. This plot shows the results:

At the peak of Solar Cycle 24, the sun was producing more than 5 CMEs per day. At the same time, galactic cosmic rays (GCRs) dropped more than 60%.

Neutron counts are now at their lowest level since 2016. If current trends continue, cosmic ray levels will plunge even further in the years ahead, perhaps even lower than Solar Cycle 24. This is good news for astronauts and polar air travelers who will benefit from less radiation.

FAQ: Why neutrons? When cosmic rays strike Earth’s atmosphere, they produce a spray of secondary particles that rain down on Earth. Among these particles are neutrons, which can make it all the way down to Earth’s surface. Researchers at the Sodankyla Geophysical Observatory in Oulu, Finland, have been counting neutrons every day since 1964, providing an unparalleled record of cosmic rays for almost 60 years.

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HAARP Pings a Near-Earth Asteroid

Dec. 26, 2022: Researchers from NASA and the University of Alaska are about to perform an unusual radar experiment. They’re going to ping a near-Earth asteroid using shortwave radio. The target is a 500-ft-wide space rock named “2010 XC15.” When it passes by Earth on Tuesday, Dec. 27th, the HAARP array in Alaska will hit it with a pulse of 9.6 MHz radio waves.

The High-frequency Active Auroral Research Program (HAARP) site in Gakona, Alaska

Radio astronomers ping asteroids all the time. What’s unusual about this experiment is the frequency: 9.6 MHz is hundreds of times lower than typical S-band and X-band frequencies used by other asteroid radars. The goal is to probe the asteroid’s interior.

Lead investigator Mark Haynes of the Jet Propulsion Laboratory (JPL) explains: “The low frequencies we are using can penetrate the asteroid, unlike S-band or X-band frequencies which reflect mostly off of the surface. Ultimately the idea is to use echoes to form tomographic images of asteroid interiors.”

Knowing the internal structure of an asteroid could come in handy — especially if you need to destroy it. 2010 XC15 poses no threat 770,000 km from Earth. Tomorrow’s experiment is proof-of-concept for a scarier object: Asteroid Apophis, which will buzz Earth closer than many satellites on April 13, 2029. If shortwave asteroid radar works for 2010 XC15, it should work for Apophis, too, giving planetary defense experts key data about the asteroid’s vulnerabilities.

Above: The OVRO Long Wavelength Array near Bishop, CA, will receive echoes from HAARP’s transmission

HAARP will transmit a continually chirping signal to asteroid 2010 XC15 at slightly above and below 9.6 MHz. The chirp will repeat at two-second intervals. The University of New Mexico Long Wavelength Array near Socorro, NM, and the Owens Valley Radio Observatory Long Wavelength Array near Bishop, CA, will receive the reflected signal.

“This will be the lowest frequency asteroid radar observation ever attempted,” notes Lance Benner, a co-investigator from JPL. If the experiment works it could mark a significant advance in asteroid radar. Stay tuned!

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A New Paradigm for Solar Activity: The Extended Solar Cycle

Dec. 12, 2022: So you thought you knew the solar cycle? Think again. A new paper published in Frontiers in Astronomy and Space Sciences confirms that there is more to solar activity than the well-known 11-year sunspot cycle. Data from Stanford University’s Wilcox Solar Observatory (WSO) reveal two solar cycles happening at the same time, and neither is 11 years long.

“We call it ‘the Extended Solar Cycle,'” says lead author Scott McIntosh of NCAR. “There are two overlapping patterns of activity on the sun, each lasting about 17 years.”

Solar physicists have long suspected this might be true. References to “overlapping solar cycles” can be found in research literature as far back as 1903.  A figure from the new Frontiers paper seems to clinch the case:

The top panel shows sunspot counts since 1976. The curve goes up and down every 11 years, which explains why everyone thinks the solar cycle is 11 years long. The bottom panel shows what’s really going on.

“The red and blue colors represent magnetic fields on the surface of the sun,” explains Phil Scherrer of Stanford University, a co-author of the paper who works closely with data from the Wilcox Solar Observatory. “We have been monitoring these fields since 1976, gathering a unique long-term record of the sun’s magnetism.”

Wilcox data show not one but two co-existing patterns of activity. They overlap in a way any music major will recognize: The sun is “singing rounds.” A round is a musical piece in which multiple voices sing the same melody, but start the song at different times. Imagine a group of children singing “Row, row, row your boat.” Half of the kids start first; the other half start 5 syllables later. The sun is doing the same thing with its magnetic fields, except instead of 5 syllables (“row, row, row your boat“) the gap is a little more than 5 years.

In the zoomed-in image, above, two representative cycles are labeled “1” and “2”. Most of the time both cycles are active, but not always. When one stops (….life is but a dream…), the other takes complete control of the sun and sunspot counts surge. This is when Solar Maximum happens. McIntosh calls the transition “the Terminator.”

11 years vs. 17 years. 1 cycle vs. 2 cycles. What difference does it make?

“The Extended Solar Cycle may be telling us something crucial about what’s happening deep inside the sun where sunspot magnetic fields are generated,” says McIntosh. “It poses significant challenges to prevalent dynamo theories of the solar cycle.”

Want to learn more? Milestone references in the development of the Extended Solar Cycle paradigm include Martin & Harvey (1979), Wilson et al (1988), Srivastava et al (2018).