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.
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.
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.
“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.