Sent in by Robert. An interesting story at https://earthobservatory.nasa.gov/images/144141/a-fire-in-the-middle-of-… … the Visible Infrared Imaging Radiometer- Suite on the Suomi NPP satellite captured thermal anomalies off the coast of Brazil (in the South Atlantic). The thermal anomaly means an area flagged by the satellite as unusually warm. Most such anomalies captured by the satellite are fires but obviously there is no fire burning in the middle of an ocean. Natural gas flares also trigger thermal anomalies but they are only found in shallow water locations. Volcanic activity can also light up the satellite but as far as is known there are no volcanoes near the anomaly. Instead, they are suggesting the anomaly is a weakness in Earth's magnetic field, centred over South America and the South Atlantic. This allows one of Earth's Van Allen radiation belts (zones of energetic particles trapped by the magnetic field) to dip closer to the atmosphere. Whilst the atmosphere blocks most high energy particles so they don't cause a problem at the surface there are enough of them in space close to Earth to cause issues for the electronics systems of spacecraft. Thewre are plenty of these zipping around in the atmosphere, apparently, that the sensitive radiometer detects them – but still, scientists were surprised at how often the particles showed up as fires when they first began to process the data. Each night the senso was detecting serveral dozen thermal anomalies over the Atlantic that simply did not make sense. Their response was to build a series of filters into their active fire algorithm and remove false signals in this region. All thermal anomalies that are especially weak, over the ocean, and are short lived, are removed by the algorithm – but occasionally a stray still slips through the filters.