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Thread: About STEVE and Celestial Phenomena

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    Default About STEVE and Celestial Phenomena


    The phenomenon STEVE is not an Aurora after all

    Monica Young Sky&Telescope
    Wed, 01 May 2019 02:51 UTC

    STEVE's mauve ribbon and green "picket fence." © Rocky Raybell

    A few years ago aurora chasers kept finding a mauve arc crossing the sky, sometimes accompanied by green stripes. The phenomenon lacked both an explanation and a name, so they dubbed it Steve. But even as their discovery went viral, its origin continued to stump amateurs and professionals alike.

    As scientists began to investigate the pinkish celestial ribbon from within, using satellite data, they managed to turn the name into a scientific description: Strong Thermal Emission Velocity Enhancement (STEVE). They soon found that the ribbon itself isn't an aurora after all but rather the warm glow from fast-flowing plasma above Earth's atmosphere. These regions appear following frequent space weather squalls called substorms, but still STEVE's origin remained unclear.

    Now, Toshi Nishimura (Boston University) and colleagues report on the energy source that fuels STEVE in the Geophysical Research Letters, following an in-depth probe of the regions just outside of Earth's atmosphere.

    Gathering Information from Space to Ground
    Nishimura's team worked with data from three satellite constellations orbiting Earth at different levels above the atmosphere. The three Swarm satellites returned data from 400 to 500 kilometers (250 to 310 miles) above Earth's surface, probing the middle part of the ionosphere. This region is where the Sun's radiation breaks apart atmospheric molecules into charged particles. Meanwhile the Defense Meteorological Satellite Program (DMSP) examines the sparser ionosphere up at 800 km. And far above the ionosphere, the Time History of Events and Macroscale Interactions (THEMIS) satellites explore the magnetosphere, where Earth's magnetic field dominates particles' behavior. The THEMIS probes travel as far as 80,000 km from Earth in their elliptical orbits.

    But Nishimura's team needed more than satellite data; the researchers also needed to know what was happening on the ground. The continued involvement of amateur astronomers was essential to the project, Nishimura explains:
    "There is no scientific camera in the Seattle area because that's not the place to do auroral research, but [astrophotographer's] beautiful photographs acted as mobile sensors for scientists to spot STEVE."
    Aurora chasers, such as study coauthor Rocky Raybell, notified researchers when they spotted (and photographed) STEVE. Then the researchers used satellite data to measure the electric and magnetic fields associated with the phenomenon, as well as particle energies and densities in the ionosphere and farther out in the magnetosphere.

    The Story of STEVE
    From this full spectrum of data, Nishimura's team has pieced together STEVE's story: First, a magnetic disturbance in the tail of Earth's magnetosphere pinched off a pocket of energetic electrons and pushed it inward toward Earth. THEMIS noted the substorm in this study from an altitude of 22,000 km.

    Generally, when electrons rain down on Earth, they crash into the ionosphere to produce nighttime auroras, and this is exactly what happened to make the green stripes, or "picket fence," associated with STEVE. So the green picket fence is aurora. But somehow the electrons that create it are finding a unique pathway, making the picket fence visible at more southern latitudes than ordinary aurora.

    STEVE is visible to the left in this image, while real aurorae glow toward the right. © Thomas J. Spence

    The team also confirms that, unlike the green picket fence, STEVE's pink ribbon is not aurora - that is, it doesn't come from the electrons that are raining down into the ionosphere. It does have the same energy source, though. The same substorm that pushes electrons toward Earth is the source of an energetic electric field, which propagates inward along with the electrons and accelerates charged particles along the way. These heated particles glow, creating STEVE's pink ribbon.

    That glow is a handy thing, as it associates STEVE with fast-flowing plasma streams that create low-density "holes" in the ionosphere. These holes delay and disrupt space-ground communications, such as GPS signals. "Those holes are difficult to spot because we can't see them," Nishimura explains, "but STEVE allows us to visualize where the holes are and how they evolve dynamically."

    So, aurora chasers, keep chasing STEVE (and reporting your observations at Aurorasaurus) - you're catching a unique sky phenomenon that affects our understanding of space weather and satellite communications alike.
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    Default Re: About STEVE and Celestial Phenomena

    That's a little known one:

    Alaskan seismometers detect aurora activity

    Seismological Society of America
    Thu, 30 Jul 2020 19:56 UTC

    Auroras in the aftermath of a near-Earth magnetic explosion on Dec. 20, 2015. © Joseph Bradley of Whitehorse, Yukon, Canada

    Aaron Lojewski, who leads aurora sightseeing tours in Alaska, was lucky enough to photograph a "eruption" of brilliant pink light in the night skies one night in February.

    The same perturbations of the Earth's magnetic field that lit up the sky for Lojewski's camera were also captured by seismometers on the ground, a team of researchers reports in the journal Seismological Research Letters.

    By comparing data collected by all-sky cameras, magnetometers, and seismometers during three aurora events in 2019, University of Alaska Fairbanks seismologist Carl Tape and colleagues show that it's possible to match the striking display of lights with seismic signals, to observe the same phenomenon in different ways.

    Aurora near Poker Flats, Alaska. © Aaron Lojewski, Fairbanks Aurora Tours

    Researchers have known for a while that seismometers are sensitive to magnetic fluctuations — and have worked hard to find ways to shield their instruments against magnetic influence or to remove these unwanted signals from their seismic data. But the aurora study offers an example of how seismometers could be paired with other instruments to study these fluctuations.

    "It can be hard to be definitive that these seismometer recordings are originating from the same influence as what's going on 120 kilometers up in the sky," Tape said. "It helps to have a simultaneous view of the sky, to given you more confidence about what you're seeing from the signals at ground level."

    The aurora borealis, or northern lights, occurs when solar winds — plasma ejected from the Sun's surface — meet the protective magnetic field that surrounds the Earth. The collision of particles produces colorful lights in the sky and creates fluctuations in the magnetic field that are sometimes called solar or space "storms." Magnetometers deployed on the Earth's surface are the primary instrument used to detect these fluctuations, which can significantly impact electrical grids, GPS systems and other crucial infrastructure. The aurora is commonly visible in wintertime in high-latitude regions such as Alaska.

    The seismometers in the study are part of the USArray Transportable Array, a network of temporary seismometers placed across North America as part of the EarthScope project. The array in Alaska and western Canada was completed in the fall of 2017. The aurora paper is one of several included in an upcoming SRL focus section about EarthScope in Alaska and Canada.

    These temporary seismic stations are not shielded from magnetic fields, unlike more permanent stations that are often cloaked in mu-metal, a nickel-iron alloy that directs magnetic fields around the instrument's sensors. As a result, "I was blown away by how well you can record magnetic storms across the array," said U.S. Geological Survey seismologist Adam Ringler, a co-author on the SRL paper.

    Last month, Ringler and his colleagues published a paper demonstrating how the array's 200-plus seismometers in Alaska can be used to record space weather, potentially augmenting the 13 magnetometers in operation in the state.

    Along with the all-sky camera data, seismic array data can help make sense of the strong variations in the magnetic field that occur in a magnetic east-west direction, adding a second dimension to typical north-south directional studies of the aurora and other magnetic storms, Tape and colleagues suggest.

    The researchers noted in their paper that the link between the aurora borealis and magnetic perturbations was first discovered in Sweden in 1741, and that a seismometer in Germany detected an atmosphere-generated magnetic event for the first time during a strong solar storm in 1994.

    "People have been making these connections for 250 years," Tape said. "This shows that we can still make discoveries, in this case with seismometers, to understand the aurora."
    More information: Carl Tape et al, Recording the Aurora at Seismometers across Alaska, Seismological Research Letters (2020). DOI: 10.1785/0220200161 Journal information: Seismological Research Letters

    SOTT Comment: Could it be that, whilst auroras have been known to make audible sounds, as well as to disturb seismometers during intense storms, that it is only now, amidst solar minimum, with Earth's weakening magnetic field, that these effects are now much more pronounced? It's notable that various, previously rare, and even unknown, phenomena associated with our changing atmosphere is now becoming increasingly common: Rare red noctilucent clouds photographed over Sweden

    A meteor streaks overhead as a Strong Thermal Emission Velocity Enhancement (STEVE) dances near the aurora and Comet Neowise hangs over Manitoba, Canada, July 14, 2020. © Donna Lach

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