Van Allen Belts “Touch” The Earth In South Atlantic Anomaly

This night satellite image, taken on July 14, 2017, picks up the heat from dozens of fires but also an anomalous “hot spot” in the middle of the South Atlantic. NASA Earth Observatory image by Lauren Dauphin, using VIIRS data from the Suomi NPP satellite

What looks like a red rash on this image are “hot spots” caused by heat from fires sensed by the orbiting Suomi NPP satellite. But wait. What’s that odd dot off the coast of Brazil in the middle of the Atlantic Ocean? Can’t be a fire, and it’s not a volcano or a natural gas flare. Scientists working with the satellite think it’s almost certainly connected to SAMA.

SAMA or the South Atlantic Magnetic Anomaly is a weakness in Earth’s magnetic field centered over South America and the South Atlantic which allows the inner Van Allen radiation belt to dip down closer to the atmosphere. As a result, much of South America and part of the South Atlantic Ocean get an extra dose of radiation.

The Van Allen belts, located thousands of miles above the Earth’s surface, are laced with high speed subatomic particles. Their numbers and the extent of the belts wax and wane with solar activity. Wikipedia

Remember the Van Allen belts? Those are the two doughnut-shaped zones of energetic particles — mostly electrons and protons — trapped from the solar wind by the magnetic field. The inner belt starts around 620 miles (1,000 km) and extends to 3,700 miles (6,000 km) above the Earth. The outer belt (8,100 to 37,300 mi) contains high-energy electrons. While the atmosphere blocks most high-energy particles from reaching us ground-dwellers, the belts can be a danger for satellites, which have to be specially shielded if they spend much time there.

A cross-sectional view of the Van Allen radiation belts showing the location of the SAMA, where the inner belt comes within 120 miles (200 km) of the surface. Marko Markovich

SAMA can bring particles down to within 120 miles (200 km) of the surface. The International Space Station (ISS), which orbits 250 miles overhead, has extra shielding because of SAMA, and the Hubble Space Telescope powers down its science instruments when it passes through the region.

Suomi NPP is equipped with a sensitive radiometer (Visible Infrared Imaging Radiometer Suite or VIIRS), an instrument that can sense heat sources on and near the planet. It routinely detect some of the particles zipping above South America as “fires.” So many in fact that they had to create filters to remove the false signals caused by SAMA to better assess real fires.

In this illustration SAMA is the big red patch across part of South America and the South Atlantic. NASA, ESA, M. Kornmesser

“Each night, the sensor was detecting several dozen thermal anomalies over the Atlantic Ocean in places that didn’t make sense,” said Wilfrid Schroeder, the principal investigator for the VIIRS.


See a SAMA illustration in this short video that also shows how a satellite travels through the anomaly

Occasionally a stray SAMA pixel still slips through the filters like the red dot in the first photo and reminds us of an otherwise unseen whirlwind of particles constantly circulating above our heads.

4 Responses

  1. kevan hubbard

    Looks like it would sort of be over the area between St Helena and Tristan da chuna.very remote.st Helena now has a, badly designed,airport with,if cross winds will let the planes land,two flights a week from Johannesburg.tristain seven ships a year from cape Town,thats what I call remote!

      1. kevan hubbard

        Yes the airport was built at St Helena to save costs as previously it was served by a ship about 9 times a year from Southampton in England which went via asencion island and onwards to Tristan.sadly the shipping service is now withdrawn.however as you can imagine dangerous cross winds are a problem and I understand that the Johannesburg St Helena flight is often canncelled.of the 3 asencion is the easier to visit as the RAF run flights from brize Norton near Oxford to Port Stanley via asencion.ive looked at going but it has a host of silly rules.you need clearance from the military governor but you need to book the flights and accommodation before you can get clearance,however here’s the twist you can’t book the flights or hotel unless you have clearance!asencion is used by the English and American millitary and visitors are not really welcome.st Helena is a dark skies island,if you can get there!

Comments are closed.