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Processes in Earth’s upper atmosphere create bands of vivid colors known as the air glow, as seen here in an image taken from the International Space Station. Credit: NASA
New research using data from NasaThe Global-scale Observations of the Limb and Disk, or GOLD, mission revealed unexpected behavior in the bands of charged particles that line the Earth’s equator – made possible by GOLD’s long-term global vision, the first of its kind for this type of measure.
OR is in geostationary orbit, which means that it orbits the Earth at the same rate as the planet spins and “hovers” over the same place above its head. This allows GOLD to monitor the same area for changes over time across longitude and latitude, which most satellites that study the upper atmosphere cannot.
“Since GOLD is on a geostationary satellite, we can capture the 2D temporal evolution of these dynamics,” said Dr. Xuguang Cai, a researcher at the High Altitude Observatory in Boulder, Colorado, and lead author of a new paper. of research.
GOLD focuses on parts of Earth’s upper atmosphere stretching from about 50 to 400 miles above sea level, including a neutral layer called the thermosphere and the electrically charged particles that make up the ionosphere. Unlike neutral particles in most of the Earth’s atmosphere, charged particles in the ionosphere respond to electric and magnetic fields that pass through the atmosphere and near-Earth space. But because charged and neutral particles are mixed together, something that influences one population can also impact the other.
NASA’s GOLD mission – short for Global-scale Observations of the Limb and Disk – saw surprising asymmetric motion in one of the twin bands of charged particles that form at night in Earth’s atmosphere. GOLD’s unique perspective (right) made this observation possible, as other types of measurements made from ground instruments (left) cannot see the changes that occur over open water. The red dots show the peak of the electron band measured by ground sensors that measure total electron content, while the black dots show the peak of the electron band measured by GOLD. Towards the end of the visualization, the measured peaks appear in different places. Credit: NASA Science Visualization Studio
This means that the ionosphere and the upper atmosphere are shaped by a multitude of complex factors, including space weather conditions – such as geomagnetic storms, brought on by the Sun – and terrestrial meteorology. These areas also serve as a highway for many of our communication and navigation signals. Changes in the density and composition of the ionosphere can scramble signals passing through it, such as radio and GPS.
From its vantage point on a commercial communications satellite in geostationary orbit, GOLD performs hemispheric-scale observations of the ionosphere approximately every 30 minutes. This unprecedented bird’s eye view gives scientists new insights into the evolution of this region.
Mysterious movement
One of the most distinctive features of the nocturnal ionosphere are the twin bands of dense charged particles on either side of the Earth’s magnetic equator. These bands, called equatorial ionization anomaly, or EIA, can change in size, shape, and intensity, depending on conditions in the ionosphere.
The bands can also change position. So far, scientists have relied on data captured by satellites passing through the region, averaging measurements over months to see how the bands might change over the long term. But short-term changes were more difficult to follow.
Before GOLD, scientists suspected that any rapid change that occurred in the bands would be symmetrical. If the north band moves north, the south band mirrors south. One night in November 2018, however, GOLD saw something that challenged that idea: the southern band of particles drifted south, while the northern band remained stable – all in less than two hours.
The shape of Earth’s magnetic field (represented by orange lines in this data visualization) near the equator pulls charged (blue) particles away from the equator, creating two dense bands just north and south of the known equator under the name of equatorial ionization anomaly. Credit: NASA Science Visualization Studio
This isn’t the first time scientists have seen bands move like this, but this shorter event – only around two hours, compared to the more typical six to eight hours seen before – was first seen, and n ‘could have been observed by GOLD. The observations are described in an article published on December 29, 2020 in the Journal of Geophysical Research: physics of space.
The symmetrical drift of these bands is caused by the rising air which carries charged particles with it. As night falls and temperatures cool, pockets of warmer air rise. The charged particles carried in these hotter air pockets are linked by magnetic field lines, and for those pockets near the Earth’s magnetic equator, the shape of the Earth’s magnetic field means that the upward motion also pushes the charged particles horizontally. . This creates the symmetrical north and south drift of the two charged particle bands.
The exact cause of the asymmetric drift observed by GOLD is still a mystery – although Cai suspects that the answer lies in a combination of the many factors that shape the movement of electrons in the ionosphere: ongoing chemical reactions, electric fields, and winds at high altitude. blows over the region.
While surprising, these findings may help scientists look behind the curtain of the ionosphere and better understand what drives its changes. Because every process cannot be observed with a satellite or a ground sensor, scientists rely heavily on computer models to study the ionosphere, much like models that help meteorologists predict the weather in the sky. ground. To create these simulations, scientists code in what they suspect is the underlying physics at work and compare the model’s prediction to the observed data.
Before GOLD, scientists obtained this data from occasional satellites and limited observations on the ground. Now, GOLD offers scientists a bird’s-eye view.
Reference: “Observation of Postsunset OI 135.6 nm Radiance Enhancement Over South America by the GOLD Mission” by Xuguang Cai, Alan G. Burns, Wenbin Wang, Liying Qian, Jing Liu, Stanley C. Solomon, Richard W. Eastes, Robert E. Daniell, Carlos R. Martinis, William E. McClintock and Inez S. Batista, December 29, 202, Journal of Geophysical Research: physics of space.
DOI: 10.1029 / 2020JA028108
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