iii. South Atlantic Anomaly

delete UPSC Sample Notes [English]

iii. South Atlantic Anomaly

The vast, developing phenomenon, called the South Atlantic Anomaly, has intrigued and concerned scientists for years. In simple words, it is an unusually weak spot in the earth’s magnetic field.

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 (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 scientists want to track and study the anomaly.

South Atlantic Anomaly (SAA)	The South Atlantic Anomaly is a weak spot in Earth’s magnetic field, which protects the planet from high doses of solar wind and cosmic radiation. This anomaly exists because the Earth’s inner Van Allen radiation belt comes closest to the planet’s surface, causing an increased flux of energetic particles. In turn, this anomaly also causes technical disturbances in satellites and spacecraft orbiting Earth. 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. The recent data shows the anomaly’s valley, or region of minimum field strength, has split into two lobes, creating additional challenges for satellite missions.
Van Allen belt	A Van Allen radiation belt is a zone of energetic charged particles, most of which originate from the solar wind. These particles are captured by and held around a planet by that planet’s magnetosphere. It surrounds Earth, containing a nearly impenetrable barrier that prevents the fastest, most energetic electrons from reaching Earth. The outer belt is made up of billions of high-energy particles that originate from the Sun and become trapped in Earth’s magnetic field, an area known as the magnetosphere. The inner belt results from interactions of cosmic rays with Earth’s atmosphere. The Van Allen radiation belts were discovered in 1958 by James A. Van Allen, the American physicist who designed the instruments on board Explorer 1, the first spacecraft launched by the United States. Although images of the Van Allen radiation belts make them look visible and colorful, this is actually just a representation. The radiation belts themselves are so dilute that astronauts don’t even see or feel them when they are outside in their spacesuits. In fact, scientists only detect them using sensitive instruments inside satellites and spacecraft. Courtesy: NASA
Mechanism of SAA	The South Atlantic Anomaly arises from two features of Earth’s core: The tilt of its magnetic axis 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. The magnetic field fluctuates in both space and time along with the core motion as a result of intricate geodynamic conditions both inside the core and at the boundary with the solid mantle above. These dynamic processes in the core bounce outward to the magnetic field around the globe, creating the SAA and other characteristics in the near-Earth environment including the tilt and drift of the magnetic poles, which are shifting 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 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.
Consequences of South Atlantic anomaly	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 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 region can be hazardous for low-Earth orbit satellites that travel through it. The International Space Station, which is in low-Earth orbit, also passes through the SAA. NASA has reported that modern laptops have crashed when Space Shuttle flights passed through the anomaly. It may also affect the navigation-mapping, telecommunication, and satellite systems which depend on the geomagnetic field. Earth’s magnetic field changes in strength and direction over time. It is believed that these fluctuations may eventually trigger a reversal of the Earth’s magnetic field. The effect of the south Atlantic anomaly may also contribute to this reversal.
Conclusion	Scientists are evaluating the status of the magnetic field using data from the European Space Agency’s Swarm constellation to comprehend how the SAA is changing and to prepare for upcoming hazards to satellites and sensors. Researchers now have new possibilities to comprehend Earth’s core dynamics and how they affect other facets of the Earth system. Researchers can better understand how our planet is changing by monitoring this slowly shifting “dent” in the magnetic field. This will also help us make satellites safer in the future.