Explanation:

Shape of magnetosphere of Earth is determined by the Earth’s internal magnetic field, the solar wind plasma, and the interplanetary magnetic field (IMF). This shape is not static but is dynamic.

Van Allen belts
In the inner region of the Earth’s magnetosphere, there are two distinct rings of electrically charged particles that encircle our planet. These are called Van Allen belts after their discover. The particles in these belts originate from different sources; some come from the solar wind, some from the Earth’s upper atmosphere, some from cosmic rays originating in the distant Universe. The belts are shaped like fat doughnuts, widest above Earth’s equator and curving downward toward Earth’s surface near the Polar
Regions.