What happens on Earth doesn't stay on Earth.
Using observations from NASA's ICON mission, scientists presented the first
direct measurements of Earth's long-theorized dynamo on the edge of space: a
wind-driven electrical generator that spans the globe 60-plus miles above
our heads. The dynamo churns in the ionosphere, the electrically charged
boundary between Earth and space. It's powered by tidal winds in the upper
atmosphere that are faster than most hurricanes and rise from the lower
atmosphere, creating an electrical environment that can affect satellites
and technology on Earth.
The new work, published today in Nature Geoscience, improves our
understanding of the ionosphere, which helps scientists better predict space
weather and protect our technology from its effects.
Launched in 2019, ICON, short for Ionospheric Connection Explorer, is a
mission to untangle how Earth's weather interacts with the weather in space.
Radio and GPS signals zip through the ionosphere, which is home to auroras
and the International Space Station. Empty pockets or dense swells of
electrically charged particles can disrupt these signals.
Scientists who study the atmosphere and space weather have long included
Earth's dynamo in their models because they knew it had important effects.
But with little information, they had to make some assumptions about how it
works. Data from ICON is the first concrete observation of winds fueling the
dynamo, eventually influencing space weather, to feed into those models.
"ICON's first year in space has shown predicting these winds is key to
improving our ability to predict what happens in the ionosphere," said
Thomas Immel, ICON principal investigator at University of California,
Berkeley, and lead author of the new study.
Earth's sky-high generator
The ionosphere is like a sloshing sea of electrically charged particles,
created by the Sun and intermixed with the neutral upper atmosphere.
Sandwiched between Earth and space, the ionosphere responds to changes from
both the Sun above and Earth below. How much influence comes from each side
is what researchers are interested in figuring out. Studying a year of ICON
data, the researchers found much of the change they observed originated in
the lower atmosphere.
Generators work by repeatedly moving an electricity-carrying conductor—like
a copper wire—through a magnetic field. Filled with electrically charged
gases called plasma, the ionosphere acts like a wire, or rather, a tangled
mess of wires: Electricity flows right through. Like the dynamo in Earth's
core, the dynamo in the atmosphere produces electromagnetic fields from
motion.
Strong winds in the thermosphere, a layer of the upper atmosphere known for
its high temperatures, push current-carrying plasma in the ionosphere across
invisible magnetic field lines that arc around Earth like an onion. The wind
tends to push on chunky, positively charged particles more than small,
negatively charged electrons. "You get pluses moving differently than
minuses," said co-author Brian Harding, a physicist at University of
California, Berkeley. "That's an electric current."
In most generators, these components are bound tightly so they stay put and
act predictably. But the ionosphere is free to move however it likes. "The
current generates its own magnetic field, which fights Earth's magnetic
field as it's passing through," Immel said. "So you end up with a wire
trying to get away from you. It's a messy generator."
Following the whims of the ionosphere is key to predicting space weather's
potential impacts. Depending on which way the wind blows, plasma in the
ionosphere shoots out into space or plummets toward Earth. This behavior
results from the tug-of-war between the ionosphere and Earth's
electromagnetic fields.
The dynamo, which lies at the lower end of the ionosphere, has remained a
mystery for so long because it's difficult to observe. Too high for
scientific balloons and too low for satellites, it has eluded many of the
tools researchers have to study near-Earth space. ICON is uniquely equipped
to investigate this part of the ionosphere from above by taking advantage of
the upper atmosphere's natural glow to detect the motion of plasma.
ICON simultaneously observes powerful winds and migrating plasma. "This was
the first time we could tell how much the wind contributes to the
ionosphere's behavior, without any assumptions," said Astrid Maute, another
study co-author and ICON scientist at the National Center for Atmospheric
Research in Boulder, Colorado.
Only in the past decade or so, Immel said, have scientists realized just how
much those rising winds vary. "The upper atmosphere wasn't expected to
change rapidly," he said. "But it does, day to day. We're finding this is
all due to changes driven up from the lower atmosphere."
Wind power
Familiar are the winds that skim the surface of Earth, from gentle breezes
to bracing gusts that blow one way and then the other.
High-altitude winds are a different beast. From 60 to 95 miles above the
ground, in the lower thermosphere, winds can blast in the same direction at
the same speed—around 250 mph—for a few hours at a time before suddenly
reversing direction. (By comparison, winds in the strongest Category 5
hurricanes tear at 157 mph or more.)
These dramatic shifts are the result of waves of air, called tides, born at
Earth's surface when the lower atmosphere heats up during the day then cools
down at night. They surge through the sky daily, carrying changes from
below.
The farther the atmosphere stretches away from the surface, the thinner it
becomes and the less turbulence there is to disrupt these motions. That
means small tides generated near the surface can grow much larger when they
reach the upper atmosphere. "Changes in the winds up there are mostly
controlled by what happens below," Harding said.
ICON's new wind measurements help scientists understand these tidal patterns
that span the globe and their effects.
Tides ripple up through the sky, building in strength and growing before
gusting through the ionosphere. The electric dynamo whirs in response.
The scientists analyzed the first year of ICON data, and found high-altitude
winds strongly influence the ionosphere. "We traced the pattern of how the
ionosphere moves, and there was a clear wave-like structure," Harding said.
Changes in the wind, he explained, directly corresponded to the dance of
plasma 370 miles above Earth's surface.
"Half of the motion of the plasma can be attributed to the winds that we
observe right there on that same magnetic field line," Immel said. "That
tells you it's an important observation to make if you want to predict what
plasma is doing."
ICON's first year of observations coincided with solar minimum, the quiet
phase of the Sun's 11-year activity cycle. During this time, the Sun's
behavior was a low, constant hum. "We know the Sun's not doing much, but we
saw a lot of variability from below, and then remarkable changes in the
ionosphere," Immel said. That told the researchers they could rule out the
Sun as the main influence.
As the Sun ramps up to its active phase, scientists will be able to study
more complex changes and interactions between space and Earth's atmosphere.
Immel said he is excited to have this confirmation of long-held ionosphere
theories. "We found half of what causes the ionosphere to behave as it does
right there in the data," he said. "This is what we wanted to know."
Still, Maute said, "This leaves room to explore what else is contributing to
the ionosphere's behavior."
Reference:
Thomas J. Immel et al, Regulation of ionospheric plasma velocities by
thermospheric winds, Nature Geoscience (2021).
DOI: 10.1038/s41561-021-00848-4
Tags:
Space & Astrophysics
This is something that is already known for years by those who are interested in alternative history and athmospheric energy topics.
ReplyDeleteBut.. well done anyway!