It is important to realize that the position of the North Magnetic Pole given for a particular year is an average position. The Magnetic Pole wanders daily around this average position and, on days when the magnetic field is disturbed, may be displaced by 80 km or more. Although the North Magnetic Pole's motion on any given day is irregular, the average path forms a well-defined oval. The diagram shows the average path on disturbed days.
The cause of the North Magnetic Pole's diurnal motion is quite different than that of its secular motion. If we measure the Earth's magnetic field continually, such as is done at a magnetic observatory, we will see that it changes during the course of a day - sometimes slowly, sometimes rapidly. The ultimate cause of these fluctuations is the Sun. The Sun constantly emits charged particles that, on encountering the Earth's magnetic field, cause electric currents to flow in the ionosphere and magnetosphere. These electric currents disturb the magnetic field, resulting in a temporary shift in the North Magnetic Pole's position. The size and direction of this shift varies with time, in step with the magnetic field fluctuations. Since such fluctuations occur constantly, the Magnetic Pole is seldom to be found at its "official" position, which is the position in the absence of magnetic field fluctuations.