The Earth’s magnetic field protects the planet from these streams of charged particles like water around the bow of a ship. This veil extends tens of thousands of kilometres into space to protect us from harmful radiation of the Sun.
When these charged particles (often called solar wind) are trapped in this magnetic field, this zone of energetic particles is called the Van Allen radiation belt. There are two of such belts around the planet that extend from around 500 to 60,000 kilometres above the Earth's surface.
The south of the inner Van Allen radiation belt makes its closest approach to Earth over one particular region of the planet: primarily over the South Atlantic and also stretching into southern Africa and South America. This is caused by the small (around 11 degrees) offset of these belts from Earth's geometric center. In other words, Earth's magnet and magnetic field are at a different angle from which the Earth is rotating. This means the belt comes rather close - roughly 200 kilometres - to the planet over one region that we call the South Atlantic Anomaly.
This region is of particular importance for satellites orbiting the Earth that are located within this altitude range. Charged particles like protons that are trapped in the inner Van Allen belt can damage electronics if exposed to this harmful radiation for some time. For example, collected astronomical data can glitch, computers can age or shut down, and electronic systems can fail to perform properly.
Many of the objects orbiting the Earth have to account for the dangerous region. For example, the International Space Station needs extra shielding to deal with this problem and the Hubble Space Telescope does not observe or collect data while passing through the Anomaly to protect its valuable instruments. In fact, Hubble spends around 15% of its time orbiting the Earth in this anomaly. Computers onboard NASA Space Shuttle flights have crashed when passing through this region, requiring the design of new computer systems that are equipped not to crash or read any memory that may be altered by radiation.
The first generation of Globalstar satellites were also harmed by the South Atlantic Anomaly in 2007. This constellation of low-orbit satellites were designed for low-speed data communications and satellite phones, however their performance was diminished by exposure to this harmful area of radiation. Spare satellites and a second-generation of satellites has since corrected the problem.
Even astronauts can witness changes when in this region. There have been cases of astronauts seeing strange flashing lights or "shooting stars" in their visual fields while passing through the anomaly.
In 2016, Japan's innovative Hitomi satellite, designed to study supernovas, galaxy clusters and black holes by observing x-rays, was likely lost at the hands of the South Atlantic Anomaly. The $300 million spacecraft failed to align itself in the proper position for passing through this area. When the satellite attempted to correct this fault, it spun out of control. Ultimately, the satellite broke apart and communications were lost. The Japan Aerospace Exploration Agency (JAXA) have since announced another x-ray astronomy satellite called the X-Ray Astronomy Recovery Mission. The current launch date is set for 2021 and the project is regarded as an upgraded successor to the original Hitomi satellite.