Solar wind
The geomagnetic field will be symmetrical around earth, but the charged particles from the sun, streaming outward constantly through the solar system, distort the lines of flux.
This solar wind blows the geomagnetic field out of shape, as shown in the figure. At and near the earth's surface, the lines of flux are not affected very much, and the geomagnetic field is which are symmetrical.
Figure-- The geomagnetic field is distorted by the solar wind.