July 25, 2021

NASA Rocket, Satellite Tag-Team to View the Giant Electric Current in the Sky

By NASA  //  July 4, 2021

nasa & space news

Some 50 miles up, where Earth’s atmosphere blends into space, the air itself hums with an electric current. Scientists call it the atmospheric dynamo, an Earth-sized electric generator. (NASA image)

(NASA) – Some 50 miles up, where Earth’s atmosphere blends into space, the air itself hums with an electric current. Scientists call it the atmospheric dynamo, an Earth-sized electric generator.

It’s taken hundreds of years for scientists to lay the groundwork to understand it, but the principles that keep it running are only just now being revealed in detail.

Following up on its predecessor’s 2013 flight, the Dynamos, Winds, and Electric Fields in the Daytime Lower Ionosphere-2, or Dynamo-2, sounding rocket mission will soon pierce the atmospheric winds thought to keep the dynamo churning.

With the sounding rocket’s launch timed as NASA’s Ionospheric Connection Explorer satellite passes nearby, these two space missions will combine their perspectives to advance our understanding of the giant electric circuit in the sky.

See below for information on how to stream the launch and where it will be visible in person.

The Dynamo mission

The atmospheric dynamo is a pattern of electrical current swirling in continent-sized circuits high above our heads. Driven by the Sun, it migrates across the planet, centered wherever the Sun is directly overhead.

It comes alive in Earth’s ionosphere, a layer of the atmosphere where the Sun’s intense radiation separates electrons from their atoms, allowing electricity to flow.

A map of the ionospheric currents at the time of Dynamo 1’s launch on July 4, 2013. Currents – whose intensity is marked by red and blue coloring – travel in opposite directions on either side of the magnetic equator, marked with a pink line. The yellow dots are magnetometer readings from the ground. (NASA image)

Graph showing current strength and direction in the ionosphere: A map of the ionospheric currents at the time of Dynamo 1’s launch on July 4, 2013. Currents – whose intensity is marked by red and blue coloring – travel in opposite directions on either side of the magnetic equator, marked with a pink line.

The yellow dots are magnetometer readings from the ground.

Most measurements of the dynamo come from magnetometers on the ground, which monitor how that current disturbs Earth’s magnetic field (think of them as souped-up compasses).

Ground-based measurements have their advantages – they can monitor one location for long periods of time, for instance. But to really see what’s going on in detail, you have to take measurements from inside the ionosphere, right where the electric current flows.

“It’s a really tricky part of space to get measurements, because the air is much too thin for an aircraft, and yet it’s still too dense to fly most spacecraft,” said Scott England, a space physicist at Virginia Tech in Blacksburg and collaborator for the upcoming Dynamo-2 campaign.

“So one way of making these measurements is to fly a rocket through it.”

Sounding rockets, named for the nautical term “to sound,” meaning to measure, launch to make brief measurements in space before falling back to Earth a few minutes later.

They excel at reaching hard-to-access regions of space that are too low for satellites to measure and too high to reach with scientific balloons – and they’re ideal for comparing wind speeds at different altitudes since they slice through the atmosphere near-vertically.

“While ground-based methods can provide large-scale, integrated measurements, sounding rockets give us local, fine-scale data on the ionospheric current,” said Takumi Abe, a space physicist at the Japan Aerospace Exploration Agency, or JAXA, and collaborator for the Dynamo missions. “That’s when we use sounding rockets – when we’d like to see the small-scale physics.”

The first Dynamo mission – comprising scientists from NASA, JAXA, and several U.S. universities – launched their rockets on the 4th of July, 2013, from NASA’s Wallops Flight Facility on Wallops Island, Virginia.

The team divided their instruments between two rockets, the first measuring electric fields while the second, launched just 15 seconds later, traced the winds, leaving behind a cloudy plume that glistened red in the sunlight similar to those observed in firework shows.

Observing from the ground and from a NASA aircraft, the team watched the crimson clouds morph in the wind as simultaneous electric field measurements were beamed back to the ground.

The vapor trail teased about in the wind, twisting and curling into a spiraling zig-zag. The telltale shape meant the winds were changing direction along the rocket’s flight path.

“They moved first to the east, and then a few miles above, they’re all moving to the west, and a few miles above, they’re all moving back to the east,” England said.

The zig-zag confirmed one aspect of the theory of atmospheric tides, which create high-altitude winds thought to drive the atmospheric dynamo. The heat from the ground below radiates up in waves, forcing parts of the atmosphere to move back and forth like the ebb and flow of ocean waves as they hit the beach.

“The zig-zag is the signature of this huge wave moving through this region,” England added.

Though the winds were expected by theory, their strength was not.

Based on magnetometer readings from the ground at the time, the team expected a weak current and mild winds above. Indeed, things were calm below the ionosphere’s base. But right where the reddish cloud trail pierced the lower parts of the ionosphere, where the dynamo is strongest, it was rapidly smeared across the sky.

“Just in the dynamo region, the wind suddenly takes off and gets very fast, over 150 meters per second (335 miles per hour),” said Rob Pfaff, a space physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and principal investigator for both Dynamo missions.

“It’s much stronger than what’s predicted.”

These oppositely directed, high-speed winds were too fine-grained to be detected from ground-based measurements.

“It might look from the ground like the wind is going east at a very low speed,” said England. “But it turns out that’s a very high speed to the east and a slightly lower speed to the west averaged together.”

Illustration of NASA’s Ionospheric Connection Explorer, or ICON. ICON explores Earth’s upper atmosphere and ionosphere, a region influenced by both terrestrial weather and changes in near-Earth space. (NASA image)

A Satellite and Rocket Tag-Team

Though the 2013 observations from the Dynamo rockets were surprising, they jibe with newer measurements from NASA’s Ionospheric Connection Explorer, or ICON, satellite.

ICON, a satellite mission launched in October 2019, flies at an altitude of about 360 miles, looking down on the same ionospheric winds that Dynamo rockets measured from within.

Lately, ICON had also observed much faster winds than expected by theory, and the team didn’t know what to make of them.

“Having the verification by these rocket results that what we’re seeing with ICON is real – it’s even sharper than what we can see,” said England, who is the project scientist for the ICON mission.

ICON’s wind measurements aren’t as high resolution as the Dynamo rockets’ were, but it can see much broader swaths of space and can repeat those observations on each orbit.

The Dynamo-2 mission campaign will combine its strengths.

“We are going to time it so that ICON is flying past around the same time that rocket is launching,” England said. “That way we can really combine all the amazing strengths in the data that’s highlighted in this paper with the larger picture view from ICON.”

The first Dynamo rockets launched together around noon when the current was flowing from east to west. This time, the Dynamo-2 rockets will likely launch at different times, in the morning and afternoon, to capture the current when it is flowing in different directions.

“We’re going to take measurements in the morning and in the afternoon to complete the circle, so to speak, and see how all this comes together in one big picture,” Pfaff said.

However, Pfaff may instead launch one rocket during geomagnetically “quiet” times and one during “disturbed” times, when the ionosphere’s activity is especially complex, which would provide equally valuable insight.

Which plan they follow will depend on how solar activity and the dynamo currents themselves are looking in real-time once the launch window opens.

The Dynamo-2 rockets will also use a novel instrument developed by co-investigator Jim Clemmons at the University of New Hampshire in Durham. The instrument measures wind by monitoring pressure gradients in the air around the rockets instead of releasing clouds that must be tracked from the ground or sky.

“And the beauty of that is we don’t have to rely on clear skies and we don’t have to get an airplane in the air – we can just do it,” Pfaff said.

Pfaff hopes the new results will help the team understand what’s driving the unduly fast winds, and what the consequences are for understanding the atmospheric dynamo.

Figure 1 from Appleton’s Nobel Prize lecture in 1947, demonstrating how a radio wave can travel long distances by reflecting off an ionized layer of the atmosphere. (NASA image)

Discovering the Dynamo in the Sky

The atmospheric dynamo is so named because it operates with the same principles as the electric dynamo, a kind of electric generator. The first dynamo was not found in nature but rather constructed in a lab.

In the early 1800s, on the cusp of the Victorian era in Britain, fascination with electricity was reaching a fever pitch as reports of fundamental discoveries arrived from across Europe.

The invention of the battery, the discovery of electrical current, and several puzzling effects relating electricity to magnetism were related on a nearly monthly basis.

Michael Faraday – a bookbinder’s apprentice turned self-taught experimentalist – was toiling in his London lab, working on a strange new device that, though he didn’t know it, would eventually change the world.

It consisted of a copper disc, mounted like a bicycle wheel so as to spin between two magnets. He connected the disc to an instrument that measured electric current, invented just 10 years earlier.

Faraday rotated the disc and the needle on his instrument wiggled – a small electric current was beginning to flow. Historians would later identify this moment – October 28, 1831, according to his diary – as the first time humans turned motion into electricity.

Faraday had discovered electrical induction, and as a bonus, built the first dynamo, or electric generator. It was the prototype of a technology that today keeps our lights on, our computers running, and the entire modern economy afloat.

What made Faraday’s device work were three key ingredients: a magnetic field (created by the two magnets), a conductor (the copper disc), and motion.

Combining those three, he had discovered that moving a conductive material within a stationary magnetic field – or moving a magnetic field around a stationary conductor – will start an electric current flowing.

Eventually, scientists discovered each of those three ingredients operating on Earth at a much larger scale.

First map of Earth’s magnetic field based on compass readings, by Edmond Halley, after sailing the Atlantic Ocean on the Paramore. Since we now know Earth’s magnetic pole shifts over time, these lines are not stable – scientists update the World Magnetic Model every five years. (NASA image)

The Atmospheric Dynamo, One Piece at a Time

Of the three components of the atmospheric dynamo – a magnetic field, a conductor, and motion – Earth’s magnetic field was discovered first.

By the early 1100s, Chinese seafarers were already using magnetic compasses to navigate on cloudy, starless nights, though the reason for their reliable alignment wasn’t known.

William Gilbert’s De Magnete, published in London in 1600, was the first to explain this behavior with the idea that the Earth itself was a giant magnet.

Astronomers began mapping Earth’s magnetic field, and by 1701, English astronomer Edmond Halley, charting the Atlantic with his compass, produced the first map of Earth’s magnetic field.

The Dynamo-2 rockets will launch from NASA’s Wallops Flight Facility on Wallops Island, Virginia between July 6-20. The two rockets will not be launched on the same day.

The launch window on July 6 runs from 12:15 p.m. to 2 p.m. EDT. On July 7-13, the launch window runs from 10 a.m. to 2 p.m. EDT and from 8 a.m. to noon EDT on July 14-20.

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