July 29, 2021: They called it “Starfish Prime.” On July 9, 1962, the US military exploded a thermonuclear warhead 250 miles above the Pacific Ocean. What happened next surprised everyone.

Witnesses from Hawaii to New Zealand reported auroras dancing overhead, magnificent midnight “rainbow stripes” that tropical sky watchers had never seen before. Radios fell silent, then suddenly became noisy. Burglar alarms sounded as local streetlights in Honolulu went black.

Starfish Prime essentially created an artificial solar storm complete with auroras, geomagnetic activity, and blackouts. Much of the chaos that night was caused by the electromagnetic pulse (EMP)–a ferocious burst of radiation that can ionize the atmosphere and pepper the ground below with secondary particles akin to cosmic rays. Government and industry researchers have been studying the Starfish Prime EMP for decades.

A new paper just published in the research journal Earth and Space Science suggests they might be overlooking something.

“Typical EMP simulations found in government and industry reports use over-simplified models of the Earth,” says lead author Jeffrey Love of the United States Geological Survey. “They do not provide accurate estimates of the hazard in complex geological settings.”

In their paper, Love et al describe how a high-altitude nuclear blast jerks Earth’s magnetic field. First, the EMP ionizes a layer of air underneath the bomb. This layer presses downward, pinning Earth’s magnetic field lines in their pre-blast locations. Next, as the ionization subsides, the magnetic field springs back. It’s a sort of heaving, lurching geomagnetic storm.

Geomagnetic storms are famous for causing power blackouts. Usually the sun is to blame, but EMPs can do it, too. Lurching magnetic fields cause electrical currents to flow through the ground. Literally, rocks beneath your feet begin to tingle with electricity. These currents, in turn, make their way into grounded electric-power grids, potentially damaging transformers and blacking out power supplies.

The crucial point of Love’s paper is this: Earth is not the same everywhere. In recent years, researchers have been sounding Earth’s crust to determine the 3D electrical properties of our planet. These magnetotelluric surveys reveal huge variations in conductivity from place to place, depending on the mix of underlying rock. 

Love has been one of the pioneers in applying this type of Earth data to space weather, predicting how global geomagnetic storms might affect local power lines. Now he and his colleagues are doing the same with EMPs.

The team focused their attention on the eastern midcontinental USA, a region bracketed by St. Louis, Missouri, and Memphis, Tennessee. Between 2016 and 2019, the USGS conducted a magnetotelluric survey of the area, so the data are fresh. The terrain is remarkable for its mix of rock types. Underneath it all is a layer of Precambrian basement rock, which is electrically resistive; this is overlain by differing depths of younger, electrically conductive sedimentary rock. Notable features include the Ozark Dome, where the sedimentary layer is thin, and the Reelfoot Rift, which is deeply filled with sedimentary rock.

Love’s team simulated a nuclear explosion about 300 km above this region. They found a huge range of geoelectric responses. Some power lines in the simulation had excess voltages near 2000 V, while others were closer to 0 V. Both were sharp departures from previous studies.

“Given the results of our analysis for the Eastern Midcontinent, it is reasonable to envision performing similar analyses for other places,” the authors conclude. A geophysicists’s work is never done…

Read the original research at https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021EA001792

July 21, 2021: Noctilucent cloud (NLC) season is now 8 weeks old. This animation from NASA’s AIM spacecraft shows everything that has happened since the first clouds appeared in late May:

The last frame says it all: Noctilucent clouds are still bright and abundant. In fact, at the highest latitudes they are setting records.

“We’re seeing more clouds at 80°N than in any other year since AIM was launched,” says Cora Randall of the University of Colorado’s Laboratory for Atmospheric and Space Research. “Cloud frequencies at 80°N are around 85%, whereas it’s more typical to see frequencies of about 75%.” (‘Frequencies’ are a measure of patchiness. 100% is complete coverage; 0% is no clouds at all.)

“This morning, I watched a fantastic display, the best of the year so far ,” reports Marek Nikodem, who photographed the clouds from Szubin, Poland (53°N) on July 21st:

“It’s not the end of the season yet,” he says. Indeed, it’s not.

NLCs are Earth’s highest clouds. They form when summertime wisps of water vapor rise up to the edge of space, about 83 km high, and crystalize around disintegrated meteoroids. When you see one, you’re literally seeing a cloud of frosted meteor smoke.

Earlier this summer, NLCs were seen in Europe as far south as the mediterranean coast of Spain (+37N). Given the current surge, another low-latitude excursion cannot be ruled out before the season ends in August. Watch for them!

July 6, 2021: Dust storms on Mars are bigger than we thought; they even spill into space. According to a recent paper in JGR Planets, Mars appears to be leaking dust, filling a huge volume of the inner solar system with gritty debris. You can see it with your naked eye. The bright triangle in this image from the Haleakalā Observatory in Hawaii is marsdust:

“A friend described it as blazing,” says Rob Ratkowski, who took the picture on Feb. 10th. “It was bright and very obvious.”

It’s called Zodiacal Light, and astronomers have long wondered what causes it. The usually faint triangle is sunlight scattered by dust in the plane of our solar system. The dust, it turns out, comes from Mars.

NASA’s Juno spacecraft flew through the dust cloud en route to Jupiter between 2011 and 2016. Dust grains smashed into Juno at about 10,000 mph, chipping off submillimeter pieces of spacecraft. Juno’s oversized solar arrays turned out to be excellent dust detectors, registering as many as 200 hits per day.

Ironically, the sandblasting allowed researchers to map the cloud for the first time. One theory of Zodiacal Light held that asteroids were responsible. Yet, as Juno flew through the asteroid belt toward Jupiter, impact rates sharply dropped, sometimes to zero. Asteroids were not the answer. Instead, they realized, the dust must be coming from Mars. Orbital elements of the dust grains essentially match that of the Red Planet.

Mars is the dustiest place in the Solar System, with dust storms that envelop the entire planet for months. But how does this dust escape? During storms, dust is sometimes launched to very high altitudes in the Martian atmosphere; researchers call it ‘rocket dust‘. However, leaving Mars requires overcoming escape velocity (~5 km/s), and even rocket dust has trouble doing that. Dust grains would have an easier time launching from Phobos and Deimos; however, those small moons don’t produce enough dust to explain the Zodiacal Light.

So, there’s still a mystery here. Mars has the dust, but researchers haven’t yet figured out how Mars delivers it. Lead author John Leif Jørgensen (Technical University of Denmark) and colleagues hope other scientists will help them solve this final piece of the puzzle.

July 3, 2021: Now, Solar Cycle 25 has really begun. On July 3rd, new sunspot AR2838 produced the first X-class solar flare since Sept. 2017. NASA’s Solar Dynamics Observatory recorded the extreme ultraviolet flash:

A pulse of X-rays ionized the top of Earth’s atmosphere, causing a shortwave radio blackout over the Atlantic Ocean: blackout map. Mariners, aviators, and amateur radio operators may have noticed unusual propagation effects below 30 MHz just after 1429 UT.

X-flares are the strongest kind of solar flare. They are typically responsible for the deepest radio blackouts and the most intense geomagnetic storms. This is the first X-flare of young Solar Cycle 25. More are in the offing. During the previous solar cycle (Solar Cycle 24) the sun produced 49 of them. Forecasters believe that Solar Cycle 25 should be at least that active. We can therefore expect dozens more X-flares as the sun approaches Solar Maximum in the year ~2025. Solar flare alerts: SMS Text.

SOLAR FLARE CAUSES RARE ‘MAGNETIC CROCHET’: The X-flare of July 3rd did something rare. “It disturbed all of my instruments,” reports Rob Stammes, who operates a space weather observatory in Lofoten, Norway. The flare produced a radio burst, an ionospheric disturbance, a surge of electrical currents in the ground, and a deflection of the observatory’s local magnetic field. All of these are shown in the strip chart recording, below.

“This is a first in many years,” says Stammes. “The magnetic disturbance (circled in yellow) is especially rare.”

The phenomenon is called a ‘magnetic crochet.’ Radiation from the flare ionized the top of Earth’s atmosphere and caused currents to flow 60 km to 100 km above Earth’s surface. These currents, in turn, altered Earth’s polar magnetic field. Unlike geomagnetic disturbances that arrive with CMEs days after a flare, a magnetic crochet occurs while the flare is in progress. They tend to occur during fast impulsive flares like this one.

June 30, 2021: This was not in the forecast. A low-amplitude interplanetary shock wave (data) hit Earth’s magnetic field during the early hours of June 30th, sparking mid-summer auroras over Canada:

Catalin Tapardel photographed the display from the Municipal District of Opportunity (#17) in Alberta. “I caught the auroras hovering just above an expanse of noctilucent clouds,” says Tapardel.

We don’t know where this shock wave came from. It might be the early arrival of the June 27th CME, originally expected July 1st, or perhaps a different stealthy CME that “flew under the radar” when it left the sun. If it’s the latter, another jolt could occur in the next 24 hours.

Update: Philip Granrud also saw the auroras from Kalispell, Montana. “…and a patch of noctilucent clouds, too!” he says. “It was a beautiful night in Montana.”