Researchers track slowly splitting 'dent' in Earth's magnetic field


Date:
August 17, 2020
Source:
NASA/Goddard Space Flight Center
Summary:
Scientists in geomagnetic, geophysics, and heliophysics research
groups observe and model the SAA, to monitor and predict future
changes - and help prepare for future challenges to satellites
and humans in space.



FULL STORY ==========================================================================
A small but evolving dent in Earth's magnetic field can cause big
headaches for satellites.


========================================================================== Earth's magnetic field acts like a protective shield around the planet, repelling and trapping charged particles from the Sun. But over South
America and the southern Atlantic Ocean, an unusually weak spot in
the field -- called the South Atlantic Anomaly, or SAA -- allows these particles to dip closer to the surface than normal. Particle radiation
in this region can knock out onboard computers and interfere with the
data collection of satellites that pass through it -- a key reason why
NASA scientists want to track and study the anomaly.

The South Atlantic Anomaly is also of interest to NASA's Earth scientists
who monitor the changes in magnetic field strength there, both for how
such changes affect Earth's atmosphere and as an indicator of what's
happening to Earth's magnetic fields, deep inside the globe.

Currently, the SAA creates no visible impacts on daily life on the
surface.

However, recent observations and forecasts show that the region is
expanding westward and continuing to weaken in intensity. It is also
splitting -- recent data shows the anomaly's valley, or region of minimum
field strength, has split into two lobes, creating additional challenges
for satellite missions.

A host of NASA scientists in geomagnetic, geophysics, and heliophysics
research groups observe and model the SAA, to monitor and predict future changes -- and help prepare for future challenges to satellites and
humans in space.

It's what's inside that counts The South Atlantic Anomaly arises from
two features of Earth's core: The tilt of its magnetic axis, and the
flow of molten metals within its outer core.



========================================================================== Earth is a bit like a bar magnet, with north and south poles that
represent opposing magnetic polarities and invisible magnetic field
lines encircling the planet between them. But unlike a bar magnet, the
core magnetic field is not perfectly aligned through the globe, nor is
it perfectly stable. That's because the field originates from Earth's
outer core: molten, iron-rich and in vigorous motion 1800 miles below
the surface. These churning metals act like a massive generator, called
the geodynamo, creating electric currents that produce the magnetic field.

As the core motion changes over time, due to complex geodynamic conditions within the core and at the boundary with the solid mantle up above, the magnetic field fluctuates in space and time too. These dynamical processes
in the core ripple outward to the magnetic field surrounding the planet, generating the SAA and other features in the near-Earth environment - - including the tilt and drift of the magnetic poles, which are moving over
time. These evolutions in the field, which happen on a similar time scale
to the convection of metals in the outer core, provide scientists with
new clues to help them unravel the core dynamics that drive the geodynamo.

"The magnetic field is actually a superposition of fields from many
current sources," said Terry Sabaka, a geophysicist at NASA's Goddard
Space Flight Center in Greenbelt, Maryland. Regions outside of the solid
Earth also contribute to the observed magnetic field. However, he said,
the bulk of the field comes from the core.

The forces in the core and the tilt of the magnetic axis together produce
the anomaly, the area of weaker magnetism -- allowing charged particles
trapped in Earth's magnetic field to dip closer to the surface.

The Sun expels a constant outflow of particles and magnetic fields known
as the solar wind and vast clouds of hot plasma and radiation called
coronal mass ejections. When this solar material streams across space and strikes Earth's magnetosphere, the space occupied by Earth's magnetic
field, it can become trapped and held in two donut-shaped belts around
the planet called the Van Allen Belts. The belts restrain the particles
to travel along Earth's magnetic field lines, continually bouncing back
and forth from pole to pole. The innermost belt begins about 400 miles
from the surface of Earth, which keeps its particle radiation a healthy distance from Earth and its orbiting satellites.



========================================================================== However, when a particularly strong storm of particles from the Sun
reaches Earth, the Van Allen belts can become highly energized and
the magnetic field can be deformed, allowing the charged particles to
penetrate the atmosphere.

"The observed SAA can be also interpreted as a consequence of weakening dominance of the dipole field in the region," said Weijia Kuang,
a geophysicist and mathematician in Goddard's Geodesy and Geophysics Laboratory. "More specifically, a localized field with reversed polarity
grows strongly in the SAA region, thus making the field intensity very
weak, weaker than that of the surrounding regions." A pothole in space Although the South Atlantic Anomaly arises from processes inside Earth,
it has effects that reach far beyond Earth's surface. The region can
be hazardous for low-Earth orbit satellites that travel through it. If
a satellite is hit by a high-energy proton, it can short-circuit and
cause an event called single event upset or SEU. This can cause the
satellite's function to glitch temporarily or can cause permanent damage
if a key component is hit. In order to avoid losing instruments or an
entire satellite, operators commonly shut down non-essential components
as they pass through the SAA. Indeed, NASA's Ionospheric Connection
Explorer regularly travels through the region and so the mission keeps
constant tabs on the SAA's position.

The International Space Station, which is in low-Earth orbit, also passes through the SAA. It is well protected, and astronauts are safe from
harm while inside. However, the ISS has other passengers affected by the
higher radiation levels: Instruments like the Global Ecosystem Dynamics Investigation mission, or GEDI, collect data from various positions on
the outside of the ISS. The SAA causes "blips" on GEDI's detectors and
resets the instrument's power boards about once a month, said Bryan Blair,
the mission's deputy principal investigator and instrument scientist,
and a lidar instrument scientist at Goddard.

"These events cause no harm to GEDI," Blair said. "The detector blips
are rare compared to the number of laser shots -- about one blip in
a million shots - - and the reset line event causes a couple of hours
of lost data, but it only happens every month or so." In addition to
measuring the SAA's magnetic field strength, NASA scientists have also
studied the particle radiation in the region with the Solar, Anomalous,
and Magnetospheric Particle Explorer, or SAMPEX -- the first of NASA's
Small Explorer missions, launched in 1992 and providing observations
until 2012. One study, led by NASA heliophysicist Ashley Greeley as part
of her doctoral thesis, used two decades of data from SAMPEX to show that
the SAA is slowly but steadily drifting in a northwesterly direction. The results helped confirm models created from geomagnetic measurements and
showed how the SAA's location changes as the geomagnetic field evolves.

"These particles are intimately associated with the magnetic field,
which guides their motions," said Shri Kanekal, a researcher in
the Heliospheric Physics Laboratory at NASA Goddard. "Therefore, any
knowledge of particles gives you information on the geomagnetic field
as well." Greeley's results, published in the journal Space Weather,
were also able to provide a clear picture of the type and amount of
particle radiation satellites receive when passing through the SAA,
which emphasized the need for continuing monitoring in the region.

The information Greeley and her collaborators garnered from SAMPEX's
in-situ measurements has also been useful for satellite design. Engineers
for the Low- Earth Orbit, or LEO, satellite used the results to design
systems that would prevent a latch-up event from causing failure or loss
of the spacecraft.

Modeling a safer future for satellites In order to understand how the
SAA is changing and to prepare for future threats to satellites and instruments, Sabaka, Kuang and their colleagues use observations and
physics to contribute to global models of Earth's magnetic field.

The team assesses the current state of the magnetic field using data from
the European Space Agency's Swarm constellation, previous missions from agencies around the world, and ground measurements. Sabaka's team teases
apart the observational data to separate out its source before passing
it on to Kuang's team. They combine the sorted data from Sabaka's team
with their core dynamics model to forecast geomagnetic secular variation
(rapid changes in the magnetic field) into the future.

The geodynamo models are unique in their ability to use core physics to
create near-future forecasts, said Andrew Tangborn, a mathematician in Goddard's Planetary Geodynamics Laboratory.

"This is similar to how weather forecasts are produced, but we are
working with much longer time scales," he said. "This is the fundamental difference between what we do at Goddard and most other research groups modeling changes in Earth's magnetic field." One such application that
Sabaka and Kuang have contributed to is the International Geomagnetic
Reference Field, or IGRF. Used for a variety of research from the core to
the boundaries of the atmosphere, the IGRF is a collection of candidate
models made by worldwide research teams that describe Earth's magnetic
field and track how it changes in time.

"Even though the SAA is slow-moving, it is going through some change in morphology, so it's also important that we keep observing it by having continued missions," Sabaka said. "Because that's what helps us make
models and predictions." The changing SAA provides researchers new opportunities to understand Earth's core, and how its dynamics influence
other aspects of the Earth system, said Kuang. By tracking this slowly
evolving "dent" in the magnetic field, researchers can better understand
the way our planet is changing and help prepare for a safer future
for satellites.


========================================================================== Story Source: Materials provided by
NASA/Goddard_Space_Flight_Center. Original written by Mara Johnson-Groh
and Jessica Merzdorf. Note: Content may be edited for style and length.


==========================================================================


Link to news story: https://www.sciencedaily.com/releases/2020/08/200817144121.htm

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