South Atlantic Anomaly

June 13, 2002


Provided by: Jim Heirtzler
Summary authors & editors: Jim Foster; Jim Heirtzler

The above map shows the total geomagnetic field contours as derived from NASA's Topography from Space Experiment satellite (TOPEX). Anomaly sites are represented by yellow dots, and the location of ground-based geomagnetic observations are the two dark squares. The South Atlantic Anomaly (SAA) is a roughly oval-shaped geographic region, centered off the east coast of Brazil, where the Earth's geomagnetic field is relatively weak at all altitudes. This permits Van Allen radiation to concentrate over this region, which can be problematic for satellites in low Earth orbit. Most all satellites orbiting over this region, below approximately 625 miles (1,000 km), have experienced some damage to computer components, cameras or other sensors as a result of the Van Allen radiation. For example, one year ago in June of 2001, the MODIS sensor on the Terra satellite was rendered temporarily inoperable while over the western flank of the SAA - red star on the map. The risk of damage to low orbit satellites is especially high during geomagnetic solar storms.

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