Earth's magnetosphere and the Sun's magnetic field are constantly pressed against one another on the dayside of Earth. Approximately every eight minutes, these fields briefly merge, forming a temporary "portal" between the Earth and the Sun through which high-energy particles such as solar wind can flow. The portal takes the shape of a magnetic cylinder about the width of Earth.
Since Cluster and THEMIS have directly sampled FTEs, scientists can simulate FTEs on computers to predict how they might behave. Jimmy Raeder of the University of New Hampshire told his colleagues simulations show that the cylindrical portals tend to form above Earth's equator and then roll over Earth's winter pole. In December, FTEs roll over the north pole; in July they roll over the south pole.